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Effects of histamine and pentagastrin on fasting equine gastric and duodenal contents

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Title:
Effects of histamine and pentagastrin on fasting equine gastric and duodenal contents
Creator:
Kitchen, Diane Lynn
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English
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xv, 214 leaves : ill. ; 29 cm.

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Subjects / Keywords:
Balloons ( jstor )
Catheterization ( jstor )
Catheters ( jstor )
Chlorides ( jstor )
Gastric juice ( jstor )
Histamines ( jstor )
Horses ( jstor )
Receptors ( jstor )
Secretion ( jstor )
Sodium ( jstor )
Department of Veterinary Medicine thesis Ph.D ( mesh )
Dissertations, Academic -- College of Veterinary Medicine -- Department of Veterinary Medicine -- UF ( mesh )
Fasting ( mesh )
Gastrointestinal Agents -- pharmacology ( mesh )
Gastrointestinal Contents -- drug effects ( mesh )
Histamine -- pharmacology ( mesh )
Horses ( mesh )
Pentagastrin -- pharmacology ( mesh )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Thesis:
Thesis (Ph. D.)--University of Florida, 1997.
Bibliography:
Includes bibliographical references (leaves 202-212).
Additional Physical Form:
Also available online.
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Diane Lynn Kitchen.

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University of Florida
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University of Florida
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51556783 ( OCLC )

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EFFECTS OF HISTAMINE
AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS













By

DIANE LYNN KITCHEN




















A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1997




























Copyright 1997

by

Diane Lynn Kitchen

























This dissertation is dedicated to my father, Hyram

Kitchen, D.V.M., Ph.D., who taught me the importance of the pursuit of excellence. I continuously strive to approach the high standards he spent a lifetime instilling in me. Even today, I look to his approval as the ultimate in reward. Thank you, Daddy, and I do wish you were here to share this with me.














ACKNOWLEDGMENTS


I acknowledge the help of many individuals and animals who have been instrumental in my pursuit of this degree and the completion of this dissertation. I wish to thank Dr. Alfred M. Merritt, my mentor and the head of the Island Whirl Equine Colic Research Laboratory, where these studies were conducted. I thank him for the collaboration throughout the multiple attempts to define this project and various sidelines along the way, and also for the constructive criticism in the preparation of this dissertation and associated papers'.

I thank James A. Burrow for all the technical assistance over the years. His computer skills and laboratory assistance have been invaluable. Through the many changes in this project, the committee has remained intact and I thank them for staying on the committee. I thank Christie Stieble for her work on the statistical analysis of data for the balloon study. I thank Dr. Philip



iv









Kosch for his role as Associate Dean for Research and Graduate Studies.

Dr. Martha Campbell-Thompson, who is one of the

pioneers in equine gastric secretion, provided a wealth of knowledge and was invaluable in the development of this project as did her chairman at the Health Sciences Center, Dr. J. McGuigan. I must also thank Dr. Dan Hogan and Mr. M. Koss who taught me not only the method for analyzing bicarbonate concentration, but who were instrumental in the construction of my specialized duodenal catheter.

For emotional support, I must thank several important people in my life. I am afraid that most have had to suffer me during one stage or another of this process and deserve accolades for this. I thank my mother, Yvonne H. Kitchen, R.N., for the shoulder. I know it has been a tough several years, but she were always there with unconditional love and I do love her for it. Michael S. Kitchen, M.D., my dearest brother keeps me humble. Dr. Jerry and Gayle Spears have had to "live" with me day by day and have always been there for me. I cannot thank them enough. Roger Reynolds gave me peace of mind and allowed me to focus on my own goals. Elmer and Harriet Heubeck, Cynthia McFarland, Gail



v









Leichliter and John R. Phillips have been loyal friends, providing me unending support throughout the course of this program. I also thank my private practice clients, who have had to deal with my erratic schedule and a goal they cannot comprehend.

A special acknowledgement and dedication must go to

Zero and One, two brave ponies who taught me so much in our brief acquaintance. The horses involved in these studies have each contributed not only data, but added to my life. I thank Adam, Buddy, Dick, Ethel, Harry, Iso, Jeff, Lucy, Mama, Spot, and Tom. Tejas, Clay, Blondie, and all my other four-legged family have provided my most ardent source of solace. A special thought for Valiant who did not make it to the end, but is still remembered fondly.





















vi
















TABLE OF CONTENTS





ACKNOWLEDGMENTS . . . . . . . . . . iv

LIST OF TABLES . . . . . . . . . . xi

LIST OF FIGURES . . . . . . . . . . xii

ABSTRACT . . . . . . . . . . . xiii

CHAPTERS

1 INTRODUCTION AND REVIEW OF LITERATURE . . . 1

Introduction . . . . . . . . . . 1
Historical Background . . . . . . . 2
Review of Literature . . . . . . . . 5
Development of Hypothesis . . . . . . 1. 26

2 EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID
SECRETION . . . . . . . . . 31

Introduction . . . . . . . . . . 31
Materials and Methods . . . . . . . 33
Results . . . . . . . . . . . 36
Basal Secretion . . . . . . . . 37
Pyrilamine Infusion . . . . . . . 39
Histamine dose-response . . . . . . 39
Volume . . . . . . . . . 39
Acid Concentration . . . . . . 40
Acid Output . . . . . . . 40
Sodium concentration . . . . . 41
Sodium Output . . . . . . . 42
Pentagastrin Outputs . . . . . . 42
Discussion . . . . . . . . . . 42



vii









3 THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON
PENTAGASTRIN- STIMULATED EQUINE GASTRIC
SECRETION....................52

Introduction.....................52
Materials and Methods.................54
Horses.....................54
Experimental preparation ............54
Experimental protocol. .............55
Sample analysis..................56
Analysis of data.................57
Results . . . . . . . . . . . 5
Basal Collections................58
Post-Pyrilamine Collections ...........58
Early Infusion Collections...........58
Late Infusion Collections ............59
Discussion......................60

4 PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL
CONTENTS IN HORSES WITH CHRONIC GASTRIC CANNIJLAS
AND ITS EFFECT ON GASTRIC SECRETION .. .....66

Introduction.....................66
Materials and Methods.................68
Horses.....................68
Experimental preparation............70
Catheter Design............. ....72
Experimental protocol. .............74
Sample analysis..................75
Analysis of data.................77
Results.......................78
Gastric Contents.................78
Volume....................78
Acid Concentration .............78
Acid Output.................80
Sodium Concentration ............80
Sodium Output ...............80
Duodenal Contents.................81
Discussion......................82








viii











5 THE EFFECT OF PYLORIC OBSTRUCTION ON EQUINE BASAL AND
STIMULATED GASTRIC SECRETION............86

Introduction.....................86
Materials and Methods.................87
Horses.....................87
Experimental protocol..............88
sample analysis.................92
Analysis of data.................94
Results........................95
Pre-infusion..................96
Gastric samples..............96
Post-infusion..................98
Gastric samples..............98
Pre-infusion..................209
Duodenal samples...............109
Post-infusion..................111
Duodenal samples..............111
Bile Acids...................115
Discussion.....................116

6 SUMMARY AND CONCLUSIONS...............130

Summary.......................130
Conclusions......................236

APPENDICES

A HISTAMINE DOSE-RESPONSE DATA.............138

B PYRILAMINE PRETREATMENT STUDY DATA..........144

C DATA FROM BALLOON/NO BALLOON STUDY..........147

D STATISTICAL ANALYSIS OF HISTAMINE DOSE RESPONSE
DATA.....................179

E STATISTICAL ANALYSIS OF PYRILAMINE MAIJEATE DATA .181

F STATISTICAL ANALYSIS OF CATHETER/NO CATHETER DATA 183

G STATISTICAL ANALYSIS OF BALLOON/NO BALLOON DATA .186



ix









LIST OF REFERENCES . . . . . . . . . 202

BIOGRAPHICAL SKETCH . . . . . . . . . 213















LIST OF TABLES


Table page

1 Acid and Sodium Concentration Histamine Infusion 29 2 Equine Gastric Contents . . . . . . . 38

3 Acid and Sodium: Histamine versus Pentagastrin . 48 4 Gastric Contents with and without Pretreatment . 59 5 Horses used in Gastric Collection Studies . . . 68 6 Descriptions and Abbreviations for Each Study . 69 7 Data from Study With and Without Duodenal Catheter 79 8 Electrolyte Composition of Duodenal Contents . . 81 9 Experimental Design . . . . . . . . 91

10 Volume and Ph of Gastric Contents . . . . 99 11 Potassium in Gastric Contents . . . . . 101 12 Chloride in Gastric Contents . . . . . 103

13 Acid in the Gastric Contents . . . . . 106

14 Sodium in Gastric Contents . . . . . . 108

15 Bicarbonate in Duodenal Contents . . . . ill 16 Sodium in Duodenal Contents . . . . . 112

17 Potassium in Duodenal Contents . . . . . 113 18 Chloride in Duodenal Contents . . . . . 113 19 Volume of Duodenal Contents . . . . . 115


xi















LIST OF FIGURES
Figure Page

1 Mean acid output/15 min. of each treatment. ... 45

2 Regression analysis of acid vs. sodium outputs during
pentagastrin and histamine infusion........49

3 Mean pentagastrin stimulated acid output with and
without pyrilamine pretreatment. ...........64

4 Cross sectional view of duodenal catheter passing
through the gastric cannula and to the duodenum . 71 5 Specialized catheter.................72

6 Specialized Balloon catheter............89

7 Cross sectional view showing balloon catheter
positioned in the proximal duodenum..........90 8 Acid concentration. A curvilinear line .......121 9 Acid output. A curvilinear line. ..........122

10 Sodium concentration. A curvilinear line . ..124 11 Sodium output. A curvilinear line. .........125

12 Collections from catheter or cannula. ........134












xii















Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy


EFFECTS OF HISTAMINE AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS By
Diane Lynn Kitchen

May 1997


Chairperson: Alfred M. Merritt, II Major Department: Veterinary Medicine

The composition of equine gastric contents has been

determined to differ markedly from that of other monogastric species. In the fasted animal, there is a voluminous sodium-rich fluid component which becomes greater during pentagastrin infusion, which is not eliminated by acid blockade. Potential pancreatic stimulation by pentagastrin was suggested by Alexander and Hickson. Histamine infusion, however, seemed to cause a classic parietal secretion, as opposed to the mixed parietal and nonparietal response to pentagastrin. These findings led to the formulation of the hypothesis for this dissertation: In the equine gastric



xiii









cannula model, the vigorous sodium-rich component of pentagastrin stimulated gastric contents is extragastric in origin.

The testing of this hypothesis was accomplished by a series of studies on horses with chronic gastric cannulae. A full histamine dose-response study was necessary to determine an optimal dose for the stimulation of maximal acid output. Since this required pretreatment of the horses with the H-1 receptor antagonist, pyrilamine maleate, a small study of the effect of this pretreatment on pentagastrin-stimulated secretion was designed. A technique was developed for the placement of an intraduodenal ballooned catheter via the gastric cannula to occlude the pylorus. A study was also performed to evaluate the effect of the presence of the intraduodenal catheter. Finally, the critical study involving a comparison of the gastric and duodenal contents during histamine and pentagastrin infusion, with and without obstruction of the pylorus, was done.

Gastric contents were analyzed in each of the studies for volume and electrolyte composition. The histamineinduced maximal acid ouput was equivalent to that previously



xiv









reported for horses stimulated with pentagastrin. Pyrilamine maleate dampened the gastric acid secretory response to pentagastrin infusion. The introduction of an intraduodenal catheter did not alter the maximal acid output to pentagstrin, although it may have enhanced the reflux of duodenal fluid into the gastric lumen. Most importantly, the obstruction of the pylorus with the balloon catheter significantly decreased the sodium output in gastric collections suggesting that the vigorous sodium-rich component of pentagastrin stimulated secretion is primarily of extragastric origin.



























xv













CHAPTER 1


INTRODUCTION AND REVIEW OF LITERATURE



Introduction



The regulation of gastric secretion has long interested scientists and clinicians due to the vital role gastric acid secretion plays in the normal gastrointestinal function and in certain pathologic conditions. The stomach, with both endocrine and exocrine function, is not a simple collection vat for food prior to digestion. A diverse group of cells with numerous capabilities are found within the highly

specialized gastric mucosa.1 Parietal cells secrete acid at the apical membranes containing the H+/K+ ATPase pump.2 Other cells are responsible for the production of mucus, zymogens, and other biologically active peptides and

amines.1 Numerous endocrine cells secrete substances that modulate various gastrointestinal functions.' The secretion of hydrochloric acid by the parietal cells is regulated by neural, hormonal, and paracrine mechanisms which interact to









2

control the rate of secretion.'1-3 Acetylcholine is the primary neurotransmitter involved in gastric acid secretion. Muscarinic nerve endings near the gastric glands release acetylcholine as part of the vagal reflex system.3 Enteric neurons in Meissner's plexus release GRP (gastrin releasing peptide) which acts on G cells in the gastric antrum. Gastrin is the peptide hormone released in response to specific substrates within the gastric lumen and distension of the antrum. Released by antral G cells, gastrin is an important hormone which is involved in all phases of gastric secretion and also exerts influence on DNA transcription and cellular replication.' Histamine acts directly on parietal cells, as a paracrine substance, to stimulate gastric acid secretion via H-2 receptors. Histamine originates from enterochromaff in-like (ECL) cells present within the mucosa, in response primarily to gastrin stimulation, with modulation by numerous other substances.'1



Historical Background



Understanding the mechanisms of gastric acid secretion and the regulation of these mechanisms has required decades









3

of research by many eminent scientists using a wide array of models and techniques. From the time of Pavlov and the fistulated dogs until the "in vitro" cellular studies of H~kanson et'al., debate has raged around the regulation of gastric acid secretion. Pavlov's work with fistulated models confirmed that subjective observations of a link between emotional status and digestive function were correct and introduced the role of a central neural component of

gastric secretory regulation.' Even today we use the term "Pavlovian" when referring to the brain's input into a function, such as the cephalic phase of gastric secretion.

Bayliss and Starling paved the way to investigation of hormonal substances involved in gastrointestinal secretion.5 In 1906, Edkins suggested that a hormone "gastrin"1 was released in the pyloric portion of the stomach and resulted

in the gastric phase of the acid secretory response.6 The presence of this distinct secretagogue was demonstrated by Komarov in 1938,7 and clarified in 1941 by Gregory and Ivy. B Gregory and Tracy were able to isolate the substance in two forms from pig antral mucosa and validate the hormonal regulation of gastric secretion by gastrin in the 1960s.9









4

Histamine was reported to stimulate the secretion of gastric acid in the early 1920s. Then, in the late 1930s, MacIntosh stated that vagal stimulation resulted in

histamine release within the gastric mucosa'0; however, controversy surrounded the role of histamine since known antihistamine agents were unable to prevent acid secretion."' The identification of different subtypes of histamine receptors by Black et al. in the 1970s and subsequent studies with H-2 receptor antagonist clearly demonstrated that histamine was an integral component in the normal gastric secretory response."," The complex interworking of each of these components confused investigators and resulted in conflicting studies. only in the 1970s, with studies focusing on "in vitro" cellular preparations and technical advances in immunology and histology, were scientists able to begin unravelling this complex regulatory process. The enterochromaff in-like (ECL) cell was the key to the combined action of acetylcholine,

gastrin, histamine and many other effectors.' Though ECL cells had been noticed in the early drawings and writings of Heidenhain, their role in the secretory response was not known.' The demonstration by HAkanson et al.'13 and Capella








5

et al.14 that the fundic ECL cells contained histamine, began the explosion of new concepts in gastric secretory regulation which has led to better understanding of the process.


Review of Literature



Today, it is apparent that gastric acid secretion by

parietal cells results from paracrine histamine released by nearby ECL cells. The release of histamine is mediated by many substances including gastrin, acetylcholine, somatostatin, vasoactive intestinal peptide (VIP), prostaglandins, calcitonin gene-related peptide, TGF-a, and even histamine.' Histamine acts on the basolateral membrane of parietal cells at H-2 receptors.23 Stimulation of these receptors activates the basolateral adenylate cyclase and leads to increased intracellular cAMP within the parietal cell."5 In contrast, parietal cell gastrin receptors and muscarinic M3 receptors result in increased intracellular Ca++ when stimulated.6 The increased cAMP and/or Ca++ may activate protein kinases involved in the phosphorylation of the apical H,K ATPase as occurs in Na,K ATPases.6 Several









6

cellular changes occur with activation of the secondary messenger system within the parietal cell. The proton pump, H,K ATPase, is present in the membrane of cytoplasmic membrane compartments during the resting or unstimulated state and, after stimulation within the membranes of extensive apical canaliculi. 16 The mechanics of this transformation are not clearly understood. It is possible that the cytoplasmic vesicles observed in the resting state are connected to the apical membrane and that tubules simply expand to expose the proton pump to the lumen of the gastric glands. An alternative explanation is that activation of the cell results in the fusion of cytoplasmic membranes with the apical membrane."'6

Another change occurring following stimulation of the parietal cell is the activation and transformation of parallel K and Cl channels, which provide the extracellular K+ needed for the proton pump.16 The pump requires oxygen as well as Mg+ The energy required by the proton pumps is supplied as ATP by the large mitochondrial content in the parietal cell.16 The proton pump transports H+into the gastric gland in exchange for K+. In order to maintain intracellular homeostasis, several membrane exchange









7

pathways are present within the membrane of the parietal

cell including Cl/HCO3 and Na/H exchangers.15 During stimulation, the parietal cell secretes H+ actively via the proton pump, Cl- passively via the Cl channel, and H,

passively into the gastric lumen.'5 Parietal secretion of HCl provides a high concentration (-140 mEq/L) of acid within the gastric glands that empty into the lumen of the stomach.

Gastric secretion is commonly described as either basal or stimulated. Basal secretion is also termed interdigestive secretion and occurs without external stimulation, such as ingestion of food, or conditioned response 2,1 In terms of volume and acid content, basal secretion varies greatly between species. '7 A circadian rhythm has been observed in human basal secretion with higher rates during the evening and low rates in the morning 2,3,17, 18 The rate of basal secretion is independent of serum gastrin concentration and is not abolished by vagotomy. 2.17

Stimulated gastric secretion is classically divided into three phases, with some overlap between them. These phases are commonly termed cephalic, gastric, and








8

intestinal.2,3, 118 The link between the brain and gastric function has been speculated about since the early 1800's.19 Sight, smell, taste, thought, and swallowing stimulate gastric acid secretion during the cephalic phase.2,39" The vagus nerve is the key link in the cephalic phase through its stimulation of gastrin release as well as direct innervation of the parietal cell.2,17"1 As mentioned, these effects may be mediated through ECL cells rather than directly through receptors on the parietal cell. Many neurotransmitters and certain peptides have been shown to act centrally on the regulation of acid secretion.9 Cholinergic agonists, prostaglandin inhibitors, GABAergic agonists, gastrin/CCK, TRH-related peptides, and somatostatin-related peptides administered into the CSF stimulate gastric acid secretion. Inhibition occurs following CSF injection of cholinergic antagonists, adrenergic agonists, prostaglandins, serotonin, bombesinlike peptides, opioid peptides, CRF-like peptides, and calcitonin-related peptides.19

The gastric phase of stimulated secretory response is a result of gastric distension or chemical stimulation of the gastric mucosa.2,3,17,18 This phase is mediated primarily









9

by gastrin. Distension of the stomach walls activates stretch receptors involved in release of gastrin. However, this release does not occur if the gastric contents are acidic due to a pH-sensitive, oxyntopyloric reflex with inhibition by somatostatin .217,118 Certain breakdown products of food are strong stimulants of gastric acid secretion, particularly peptides and amino acids, specifically, phenylalanine and tryptophan 2, "18 These stimulants induce the release of gastrin by action at the apical microvilli of G cells within the antral mucosa. 17

The intestinal phase of acid secretion is

responsible for only a small portion of the total acid secretory response *18 Stimulating -agents are the same as those involved in the gastric phase. The substances act directly at G cells in the upper small intestine as a gastrin-dependent mechanism and absorbed amino acids exert their effect by a gastrin-independent mechanism.' All phases of acid secretion are, in part, mediated by gastrin, through the release of histamine from ECL cells.'

The secretion of gastric acid follows the action of

histamine on H-2 receptors on the parietal cell. Inhibition of histamine release allows the parietal cell to return to a








10

resting state. Acidification of the gastric contents inhibits gastrin release by release of somatostatin from antral D cells."a The presence of acid, fat, or hyperosmolar solutions within the small intestine inhibits the acid secretory response through one or more of the peptides such as secretin, peptide YY, neurotensin, VIP (vasoactive intestinal peptide), GIP (gastric inhibitory peptide), and enteroglucagon released by cells within the small intestinal mucosa.1 011 These inhibitory substances have receptors on the ECL cell and have been shown to inhibit the release of histamine from these cells.' Histamine also exerts negative feedback on ECL cells via H-1 and H-3 receptors.' The rapid catabolism of histamine and its speedy removal from the extracellular space surrounding the parietal cell eliminates the stimulation of these cells and terminates the secretory process.20

Many drugs have demonstrated antisecretory actions that have been crucial in clarifying the mechanisms of acid secretion and in treatment of pathologic conditions related the secretion of gastric acid.21 Histamine H-2 receptor antagonists are able to prevent gastrin, food, and vagalinduced acid secretion. This finding was pivotal in the











determination of the central role of histamine in the secretory response.22 As a result, numerous H-2 blockers have become a mainstay in the treatment of peptic ulcers.21 Substituted benzimidazoles, such as omeprazole, have more recently joined the battery of antiulcer medication due to their inhibition of the H,K ATPase.' Certain prostaglandin E2 analogues also have an antisecretory effect, due to actions at CNS as well as ECL cell level."121 Gastrin receptor antagonists (ie. Proglumide) are also capable of inhibiting acid secretion.2' The target of some presently available drugs and many of the drugs of the future may not be parietal cells directly, but other cells within the gastric mucosa which act on the parietal cell.23 Accordingly, the increasing understanding of the role of the ECL cell is likely to make it the target of investigational agents for the regulation of acid secretion.

The gastric ECL cell is considered to be one of the amine precursor uptake decarboxylation (APUD) series of cells."24 Numerous endocrine cells are found scattered within the gastric mucosa and may represent from 0.5% to 2% of the cells present. The prevalence of ECL cells vary among species, as they are particularly common in the rat








12

and appear in lesser numbers in the dog and primates.1,24 Other endocrine cells observed in the gastric mucosa include enterochromaffin cells which produce 5-hydroxytryptamine (serotonin), D cells that secrete somatostatin, gastrinproducing G cells, and P and X cells which have unknown functions.' The ECL cells are found near parietal cells within the gastric glands and have prominent cytoplasmic extensions."24 They contain a large number of cytoplasmic vesicles and electron-dense granules, and take up aromatic amino acids and decarboxylate them. Histidine decarboxylase (HDC) and histamine are also found within these cells."124 Histamine is concentrated into cytoplasmic vesicles by a Vtype ATPase which acts as a H+/histamine antiporter.122,24 As indicated above, the production and storage of histamine by the ECL cell makes it the critical interface in the regulation of gastric acid secretion.124 The primary mediator of histamine release is gastrin acting through the CCK-B receptor to increase cytosolic Ca++.1.22,24 Histamine release can also be stimulated by acetylcholine at muscarinic M1 receptors, epinephrine through P adrenergic receptors, isoproterenol, forskolin, interleukin 18 and VIP,








13

and can be inhibited by somatostatin (subtype 2), TGF-, TGF-P, calcitonin gene-related peptide, and histamine via H1 and H-3 receptors.1222425 It appears that there is substantial neurotransmitter modulation of gastrin and its regulation of histamine release from ECL cells.25 Although, it is known that Ca++ acts as a secondary messenger within the ECL cell, cAMP is likely to also play a role in the release of histamine.12224

In addition to stimulating the release of histamine, gastrin regulates HDC activity and ECL cell proliferation."124 It stimulates DNA synthesis by a pathway distinct from that of histamine release, although both processes appears to begin with the binding of gastrin at the CCK-B receptors."124 Hypergastremia has been associated with increased numbers of ECL cells and may play a significant part in the development of gastric carcinoids."124 The chronic use of antiulcer medication with resultant hypergastremia have been shown to lead to ECL hyperplasia and gastric mucosal hypertrophy.122,24 The recent advances in the "in vitro" cellular techniques have expanded our knowledge of the regulation of the gastric secretory response; however, as history shows us, advances








14

just open the door to a multitude of additional questions. Although, much knowledge has been gained by isolated cell work such as that with the ECL cell, the wide array of species differences points to the continuing need for both "in vivo,, and "in vitro', studies.

Early classical studies were "in vivo," performed

primarily on animals with a variety of surgically prepared pouches or fistulas. Even human studies in the early 1900's, were performed on subjects with gastric fistulas.19 Historically, experimental preps commonly utilized dogs and cats with transplanted pouches or surgically isolated stomachs 8,26,27 over time, chronic gastric cannulas have been placed in the stomachs of dogs, rats, rabbits, pigs, cats, humans, and horses to allow studies to be performed on conscious animals 5.28-31 Amphibian mucosa was the first tissue used in the "in vitro" studies that provided the cardinal information about the acid transporting ATPase .32 Subsequent cellular studies have been performed on canine,

22,32-36
equine, rabbit, and rat gastric glands. Initially,

food and food extracts were selected to stimulate gastric secretion, later histamine and alcohol were used in many studies 8,26,27 Histamine continues to be a valuable











secretagogue for investigation of the acid secretory process and its regulation. 120,29,30 After Gregory and Tracy found that an extract of porcine antral mucosa was an effective stimulant of acid secretion9, gastrin became a popular investigational tool.28 A synthetic polypeptide analog to the C terminal tetrapeptide of gastrin is pentagastrin, or peptavlon, which has become the secretagogue most commonly used for stimulation of gastrin related secretion."'-,"1,30,31 Today, gastric secretory studies range from chronically implanted gastric cannulas in intact animal models to receptor immunochemical studies on ECL cells isolated from the gastric mucosa.

The hundreds of studies of gastric acid secretion have accumulated a vast amount of information with marked similarities in the process and its regulation. However, some striking differences have also been observed. The relative sensitivity to specific secretagogue, the rate of basal secretion, the response to inhibition, and ECL cell shape and prevalence are markedly different between species." In the rat, the gastric acid secretory process is highly sensitive to pentagastrin and very resistant to histamine .17,30 Histamine and gastrin are equally effective









16

on canine mucosa; 17,30 in rabbits histamine is much more effective than gastrin. 17,30 Basal secretion is minimal in dogs and cats and high in rats and rabbits, whereas humans, primates, pigs, and horses fall somewhere in between. 17,28-31 Maximal acid outputs on a normalized bodyweight basis induced by either histamine or pentagastrin, also differ between species. Maximal histamine-stimulated output is greater in rabbits than dogs, while in dogs it is greater than that of rats, pigs, and cats, which in turn, have rates of secretion markedly greater than that of primates and man. 1729'30 During pentagastrin-induced acid secretion, rabbit and dog have a comparable maximal response, but that of rats is significantly less 30 As with histamine, pig,' rat, and cat maximal acid secretory rates in response to pentagastrin are comparable .29337,38 Maximal acid output is used to determine the necessary dosage of either secretagogue for the purpose of most experimental work; however, the gastric contents collected during these studies consist of fluid containing many electrolytes, pepsin, mucus and other substances, as well as acid.

The electrolyte composition of gastric secretion other than H+ also changes with the secretory rate. The secretory








17

pattern has been examined with both histamine and pentagastrin in experimental models394 and in patients with gastroduodenal diseases.42 In man, the infusion of either histamine or pentagastrin results in similar changes in gastric electrolyte concentrations and outputs. Sodium concentration decreases and output remains constant, while potassium concentration increases slightly and output increases significantly. The concentration of calcium and phosphate decreases and outputs are unchanged.39 Acid and sodium concentrations have a strong inverse correlation under these stimulatory conditions.39 The histaminestimulated maximal acid output in dogs is greater than that of pentagastrin; however, peak acid output is reached more quickly with pentagastrin than with histamine.41 Sodium ion concentration is inverse to acid in the canine studies just as in human studies.

Thus, gastric secretions are a combination of parietal and nonparietal fluids. The parietal component is isotonic HCl that is secreted in response to specific secretagogues at a rate that increases significantly with simulation of the parietal cell.' The nonparietal component is believed to be a constantly secreted isotonic ultrafiltrate of









18

plasma."3 No change in nonparietal secretory rate is observed during stimulation with any of the known gastric secretagogues. Sodium ions are the predominate cation of this nonparietal component. The differences in response to secretagogues of these two components explains the inverse relationship of sodium and acid concentrations reported during increasing acid secretory rates.43

Various gastroduodenal diseases are characterized by alterations in the electrolyte composition of gastric contents.4 Patients with active duodenal ulcers have increased acid and chloride concentration and decreased sodium concentration, while gastric ulcer patients have increased sodium concentrations in-the gastric content without changes in the concentrations of acid, potassium, or chloride.4 Other changes in the composition of electrolytes are suggestive of trophic gastric ulcers, chronic gastritis, and Zollinger-Ellison syndrome."' The characteristic gastric secretory response to stimulated gastric secretion has been consistently observed in all species except the horse .4

Due to the relative difficulty in collecting the

contents, little was known about equine gastric secretion









19

until the 1980s. The apparent increase in gastric and duodenal ulcer disease in horses provoked a particular interest in'equ~ine gastric physiology.11'44 Gastric mucosal ulceration has been observed in horses as a sequela to the administration of nonsteroidal anti-inflammatory drugs, and as a spontaneously occurring problem of unknown etiology. 44-47 Intermittent aspiration of gastric contents via nasogastric tube, placement of indwelling pH probes nasogastrically, and chronic indwelling gastric cannulas to collect contents by drainage have been used in recent studies of equine gastric secretion.'485 Only the cannula allows complete collection of gastric contents, but these studies can only be performed on fasted animals. Intermittent aspiration also requires fasted horses, but may not collect gastric contents in their entirety. The indwelling pH probe makes it possible to monitor the intragastric environment for a long periods of time in either fed or fasted states.

Basal secretion in horses has been described as continuously variable, with periods of spontaneous alkalinization as has also been observed in humans, pigs, rodents, monkeys, and chickens.14'85 Thus, the hydrogen ion concentration and acid output range widely during









20

unstimulated gastric collection periods .31,4 The basal equine acid output of approximately 30% of maximal output is consistent with pigs and rats, and it is greater than that of humans.44 On a body weight basis, equine basal acid output over time is similar to that found in man.34

Up to now, pentagastrin has been the only

secretagogue used "in viva" to stimulate equine gastric acid secretion to characterize the species-specific responses and to study drugs designed to prevent or treat gastric ulcers. 48,49,51,53,54 Its administration to horses results in a significant increases in both gastric acid and sodium outputs.44 Acid concentration increases after stimulation, but not to the maximal magnitude observed in other species. In addition, the increased sodium output during stimulation is unique to horses. As the dose of pentagastrin is increased, the concentration of sodium decreases slowly and remains greater than the acid concentration, unlike in other species where the sodium concentration rapidly decreases in an inversely proportional relationship to the increasing acid concentration .44 This is a major species-specific difference in the equine secretory response to pentagastrin. Thus, it has been suggested pentagastrin stimulates both the








21

parietal and nonparietal components of gastric secretion in the horse.44 A variety of compounds have been shown to inhibit equine basal and pentagastrin-stimulated gastric acid secretion, such as histamine H-2 antagonist ranitidine, the proton pump blocking agent omeprazole, and the prostaglandin misoprostol,48495153,54 The profound sodium rich nonparietal secretion characteristic of the equine response to pentagastrin is evident even after omeprazole has effectively inhibited the acid secretory response.5' The origin of this voluminous nonparietal component of gastric contents has not been clearly defined.

The periods of high pH of gastric contents during basal secretion have raised much speculation about the equine gastric secretory capacity, gastric emptying rates, and the buffering capacity of the various secretory products.50 Potential buffering fluids include saliva, gastric nonparietal secretions, and duodenogastric reflux.44 Saliva is not a likely candidate since the production of saliva in the horse is minimal except during mastication.55 Fasting equine gastric contents are frequently dark green to yellow in color and viscous, suggesting possible contamination with bile.44 Duodenogastric reflux has been observed during








22

endoscopic examination of the stomach."1 The fluid refluxed could potentially contain a mixture of biliary, pancreatic and duodenal secretions, since the duodenal diverticulum, where the bile and minor pancreatic ducts enter, is in relatively close proximity to the pylorus.51 Furthermore, the absence of a gallbladder leads to continuous secretion of bile in horses and equine pancreatic secretion is reported to be profuse and continuous. ,56

Pancreatic secretion of the horse is distinct from that of other species. The resting secretion of approximately 25 l/g gland/min is increased by four to fivefold during eating, stimulation of the vagus nerve, or after the administration of secretin or pentagastrin.55,7 Neither resting nor vagal-induced pancreatic secretion is abolished by atropine.55,58 Vagotomy does not alter the basal secretion. Studies with ponies fitted with re-entrant cannula in the pancreatic duct found that they may secrete a volume equivalent to up to 10% of their own body weight daily.55 The concentration of amylase and the proteolytic activity of equine pancreatic juice is particularly low, and it has a very weak ability to emulsify fat, compared to other species.." Small increases in the concentration of









23

amylase are found during stimulation of the vagus, or during secretin or pentagastrin administration. The concentration of sodium and potassium are similar to respective plasma concentrations and chloride is the predominate anion at all levels of secretion. The bicarbonate concentration is low relative to other species and does not increase to the extent anticipated when the volume of secretion increases.55 That is, in most species, the concentration of bicarbonate is less than chloride concentration at rest, but increases to become the predominate anion during maximally stimulated secretion .55 The composition of the large non-parietal component of the fasting gastric contents is also similar to that of equine pancreatic fluid. Therefore, the observed species-specific particulars of equine pancreatic juice contents might explain the voluminous fluid response observed during pentagastrin-stimulated gastric collection.

The pancreas is a multifunctional organ which is

responsible for the secretion of fluid, electrolytes, and enzymes essential to the normal digestive process and the endocrine secretion of hormones critical to metabolic homeostasis .59 Just as with gastric secretion, pancreatic secretion has traditionally been divided into basal and








24

meal-induced patterns, with meal related secretion further divided into cephalic, gastric, and intestinal phases.60 In most species, basal enzyme secretion ranges from 10% to 30% of maximal secretion, whereas, basal bicarbonate secretion is only 1% to 2% of maximal.60 The regulation of basal enzyme secretion appears to vary between species, while basal bicarbonate secretion is dependent primarily on secretin augmented by cholinergic neural input.60 Basal enzyme secretion is almost entirely due to cholinergic stimulation in the rat, whereas, in man, both CCK and cholinergic stimulation mediate it. Brief bursts of pancreatic enzyme and bicarbonate secretion are associated with the migrating myoelectric complex and a circadian rhythm has also been reported.60 The normal pancreatic secretory response to a meal is increased enzymatic secretion to aid digestion and increased bicarbonate secretion to buffer the chyme and assure the optimum intraluminal pH for enzymatic activity. As with gastric secretion, "cephalic" pancreatic secretion seems to be stimulated either directly or indirectly by the vagus nerve.50 "Gastro-pancreatic reflexes" are initiated by food or gastric distension and mediated by cholinergic vagovagal








25

reflex.50 The two classical pancreatic regulatory hormones, cholecystokinin (CCK) and secretin, and vagal cholinergic reflexes are involved in the "intestinal" phase.0 Postganglionic cholinergic neurons are important in the regulation of enzyme and bicarbonate secretion by the release of acetylcholine at muscarinic receptors. Secretin is the most potent stimulant of the bicarbonate-rich fluid component of exocrine pancreatic secretion in dogs, cats, rats, and humans., while the primary hormonal stimulant of enzyme secretion is CCK.9,60 In the rat, rabbit, pig and guinea pig, CCK is responsible for a copious fluid and electrolyte secretion which may have a low concentration of bicarbonate and a high concentration of chloride.59 Enzyme secretion is stimulated by the action of CCK at CCK-A receptors on pancreatic acinar cells.61 Although CCKB/gastrin receptors have been identified on pancreatic acinar cells, their function remains unknown.61 Caerulein is even more potent than CCK, and both are significantly more potent than gastrin, at stimulating pancreatic enzyme and fluid secretion in dogs.62 A multitude of other receptors are present on pancreatic acinar cells, including those to bombesins, tachykinins, VIP, somatostatin, insulin,








26

endothelin, insulin-like growth factor and epidermal growth factor. Much of the electrolyte secretion by the pancreas is secreted by duct cells rather than acinar cells 63 The electrolyte composition of pancreatic secretions vary with the rate. Bicarbonate and chloride concentrations have a reciprocal relationship, but the cumulative anion

13
concentration remains constant. As the secretory rate increases, bicarbonate concentrations increase and chloride concentrations decrease .63 The volume of the secretion in response to secretin vary with species. Cats, dogs, pigs and man have greater secretory rates per gram of gland than

63
rats and rabbits. The specific differences observed in the limited studies on equine pancreatic secretion are unique to the horse and similar secretory patterns have not been reported in other species.




Development of Hypothesis


After reviewing the overwhelming information about

gastric secretory physiology in general, and equine gastric secretion specifically, it is apparent that equine gastric physiology requires still more investigation. The








27

development of a silastic indwelling gastric cannula by Campbell-Thompson and Merritt for the collection of equine gastric secretions was pivotal. The distinct composition of equine gastric contents, particularly the uncharacteristic "non-parietal" response to pentagastrin stimulation, is of special interest. Since pentagastrin has been the only exogenous secretagogue utilized to date in equine secretory studies, it would be of interest to see if the horse responded to other secretagogues in a similar way. Therefore, the initial project for this series of studies was to characterize the equine gastric secretory response to histamine. Pilot studies were performed with moderate trepidation due to the potential side effects of histamine administration to horses. These studies required pretreatment of the horses with a H-1 antagonist, pyrilamine maleate. The results of a small pilot study were the last key to the development of a hypothesis for this dissertation.

Histamine-stimulated equine gastric contents were markedly different than those following pentagastrin stimulation reported in previous studies. The mean acid and sodium concentrations from the pilot study are presented









28

in Table 1. It was apparent from these studies that the horse is capable of developing the "classical" parietal response to an acid secretagogue that is comparable to that of other monogastric species. During histamine stimulation, the maximal acid concentration values were much greater than those induced by pentagastrin, and sodium concentrations decreased in the classical reciprocal relationship to acid. The sodium output over various doses of histamine was constant, unlike the pentagastrin responses. Yet, the maximal acid output provoked by histamine was equivalent to that of pentagastrin stimulated secretion. These pilot findings made it evident that the stimulation of gastric acid secretion with histamine could be safely performed in horses, with certain precautions, and that well-designed dose response study was needed. This led to the study described in chapter 2. The predominant conclusion of early investigation of histamine stimulation was that, as opposed to pentagastrin, it induced a purely parietal gastric secretion in horses.









29

Table 1.
Acid and Sodium Concentration during Histamine Infusion (n=4 horses)


Histamine Mean [H+] Mean [Na+]
Dose mEq/L mEq/L
rg/kg-hr

Basal 26.5 101.3

15 73.9 57.8

30 95.1 55.5

45 97.5 52.4




In order to perform controlled comparisons between histamine and pentagastrin, without potential extraneous factors, it was necessary to evaluate the secretory response to pentagastrin following pyrilamine maleate pretreatment. Chapter 3 presents the unexpected results of that study.

Four crucial facets of equine gastric secretion were considered to develop the dissertation hypothesis. First, equine basal and pentagastrin-stimulated gastric secretion has an uncharacteristically low concentration of acid and high concentration and output of sodium. Second, acid blockade with numerous agents does not eliminate the profound sodium-rich nonparietal component of pentagastrinstimulated secretion. Third, Hickson and Alexander reported









30

that equine pancreatic water and electrolyte secretion is profuse and continuous and can be stimulated by pentagastrin. Finally, the stimulation of gastric secretion with histamine resulted in purely parietal secretion resembling that of other species. Therefore, the dissertation hypothesis is as follows. In the equine gastric cannula model, the vigorous sodium-rich component of pentagastrin stimulated gastric contents is extragastric in origin.

A technique of duodenal catheterization through the

chronic gastric cannula was developed to allow for occlusion of the pylorus during acid secretory studies. Chapter 4 discusses the technique for duodenal catheterization, the effect of the technique on gastric secretion, and the composition of duodenal contents. The primary study of this dissertation, describing results with and without the obstruction of the pylorus, is presented in chapter 5 and was designed to definitively determine if the sodium rich fluid found during pentagastrin stimulation and absent during histamine stimulation is secreted by the gastric glandular mucosa or by a extragastric source.













CHAPTER 2


EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID SECRETION



Introduction




Previous studies of equine gastric physiology have all utilized pentagastrin to stimulate gastric secretion. 44, 50,52 Increased recognition of clinical disease in horses due to gastric and duodenal ulceration has led to interest in the potential use of horses as a model for peptic ulcer disease in humans as well as a desire to increase our knowledge about horses, themselves. Gastric- ulceration has been shown to be a widespread phenomenon in horses and foals .64 Compared to other species, pentagastrin-stimulated gastric contents in horses differs by being relatively low in acid concentration and high in sodium concentration, even at maximal secretory responses .44 Nevertheless, the inhibition of pentagastrin-stimulated gastric acid secretion has been an important and effective means to evaluate therapeutic potential of various anti-ulcer agents in this specie S. 31,49 31








32

Histamine-2 receptor antagonists have been used successfully to treat horses with clinical signs related to gastric ulceration. 64

In order to better characterize equine gastric

physiology, investigation of the effects of a secretagogue other than pentagastrin is essential. Histamine seems the obvious choice, but its use in horses has been avoided due to the presumed equine respiratory and CNS hypersensitivity to this agent. Ideally, "Histalog", a specific H-2 agonist, might be used, but it is no longer available. In other species, the undesirable side-effects of histamine have been largely avoided by pretreatment with an H-1 antagonist29, and such a protocol was chosen for the studies described herein. Specific objectives of the study were to: 1) determine the dose of histamine needed to elicit a maximal acid secretory response in the horse and how equidae compare with other species, and; 2) see if the non-parietal component of the secretory response to histamine is similar to, or different from, that seen with pentagastrin stimulation.








33


Materials and Methods



Six adult horses, both mares and geldings, were used.

All studies were done with the approval of the University of Florida IACUC. The horses ranged from 2 to 20 years of age. The five Thoroughbreds, and one Arabian weighed an average of 484 kg (range 444-506 kg). All horses were free of clinical signs of gastrointestinal disease, were deformed every 2 months and were vaccinated for encephalitis and tetanus every 6 months. They were maintained on grass pasture with coastal hay ad liband 12% protein grain twice daily. Each horse was previously prepared with a chronic indwelling gastric cannula as described by Campbell-Thompson and Merritt .31

The horses were fasted with free choice water for 20

hours prior to each experiment. At least one week interval occurred between experiments on any given horse. Studies were performed while the horse was loosely restrained in the laboratory.

After placement of an indwelling jugular catheter, the gastric cannula was opened and drained by gravity for 30









34

minutes allowing emptying of residual gastric contents. During the experiments, gastric contents were collected in 15 minute aliquots. The volume was measured to the nearest

5 ml in a graduated cylinder. Samples were filtered through gauze to remove feed particles and foam. The pH was determined using a glass electrode (Radiometer, Copenhagen,

Denmark) calibrated at 200C using commercial buffer solutions of pH 2 and 7 (pH standard, Fisher Scientific). Hydrogen ion concentration was measured in duplicate by electrometric titration with O.1N NaOH to an endpoint of

7.4. (Radiometer, Copenhagen, Denmark) Sodium ion concentration was measured by flame photometry (Instrumentation Laboratories Inc., Lexington, MA) on samples diluted in an internal standard lithium solution (Dilumat, Fisher Scientific). The machine was calibrated

with known [Na+]/[K-1] standards (Instrumentation Laboratories Inc., Lexington, MA) prior to analysis and after every 5 samples. Acid and sodium outputs were calculated for each time period on a per kg body weight basis.

The first three 15-minute time periods were during basal (no treatment) gastric collections. At time t=45








35

minutes, pyrilamine maleate ("Histavet-P", Schering-Plough, NJ) was infused IV at 1 mg/kg over the entire 15 minute collection period. No treatment was given during the subsequent two collection periods (t=60-90 minutes). Histamine infusion (7.5 pg/kg-hr) was begun at time t=90 minutes and continued for 60 minutes. Two additional 60 minute infusions of histamine, of 15 jg/kg-hr and 30 pg/kg-hr respectively, followed. Therefore, the whole experiment lasted for 4.5 hours.

Crystalline histamine (Sigma Chemical Co., St. Louis Mo) was dissolved in 60 mls of 0.9% NaCl and filtered through a 0.22 pm cellulose nitrate filter (Corning, Corning NY) in preparation for infusion, given by infusion pump. (Harvard Apparatus, South Natick MA)

In a separate trial, the horses were maximally

stimulated with pentagastrin44 for collection of data for comparison. The horses were prepared as described for histamine trial. After two hours of basal collection, pentagastrin was infused at 6 jg/kg-hr for two hours. Gastric collections were analyzed as during the histamine trials.









36

Maximal acid output per histamine dose was calculated

from the last two 15-minute collections at each dose. Values were expressed as pEq/kg BW/15 min. Results are presented as mean and SEM for all parameters. Data were subjected to one-way analysis of variance for repeated measures. A significance value of p<0.05 was selected. Pairwise multiple comparison testing of significance was performed using Student-Newman-Keuls test. Acid output vs. sodium output data were subjected to linear regression for comparison to respective pentagastrin-stimulated outputs from the same horses.



ResultsThe horses used had been involved in gastric secretory studies for at least one year prior to these studies. They demonstrated no evidence of gastrointestinal disease or problems related to the gastric cannula. Endoscopic examination of the gastric and duodenal mucosa as a part of another project in the laboratory revealed an occasional Gastrophilus spp. larvae and healthy intact gastric squamous and glandular mucosas.








37

Two horses did not complete the entire experiment. In one experiment, the infusion had to be terminated after the 15 .g/kg-hr histamine infusion period because the horse developed marked muscle tremors and mild abdominal contractions. After the infusion was stopped, the gastric cannula closed and hand-feeding begun, the horse recovered rapidly. Thirty minutes into the 30 tg/kg-hr infusion into a second horse, it developed generalized muscle tremors and mild synchronous diaphragmatic flutter. It became clinically normal within 20 minutes of ending the experiment and being allowed to eat.


Basal Secretion


Contents collected under pretreatment (basal)

conditions were generally yellow-tinged, viscid, and cloudy. The 15-minute aliquots ranged in volume from 280 to 640 mls, with a mean of 428.3 + 34.1 mls/15 min. The mean acid concentration was 42.5 + 3.9 mEq/L, and mean acid output was 39.8 + 6.6 JLEq/kg BW/15 min with a range from 19.3 to 82.7 pEq/kg/15 min. The pH of the samples varied greatly between 1.38 and 2.01, with a mean of 1.67 + 0.036. The mean sodium concentration was 75.7 + 7.2 mEq/L, and mean sodium








38

output was 68.2 + 8.2 pEq/kg BW/15 min with a range from

17.7 to 101.7 iEq/kg/15 min.

TABLE 2.

Data from Equine Gastric Contents Collected Before and After Histamine Infusion.


BASAL POST- 7.5 15 30
PYRIL- (pg/kg- (pg/kg- (pg/kgAMINE hr) hr) hr)

Volume 428.3 + 356.7 + 591.7 + 591.7 + 508.9 +
(mls/ 34.1 37.3 41.4 28 54.8
15 min) a,b a,b a,b

pH 1.67 + 1.79 + 1.46 + 1.48 + 1.29 +
0.036 0.08 0.09 0.13 0.03

Peak 42.5 + 33.5 + 72.2 + 81,3 + 82.9 +
[Hi] 3.9 3.5 3.9 5.1 6.8
(mEq/1) a,b a,b,c a,b,c

PeakAcid 39.8 + 25.9 + 87.9 + 99.5 + 98.4 + Output 6.6 4.4 7.7 8.1 4.2
(pEq/kg/ a,b a,b,c a,b,c
15min)

Peak 75.7 + 79.5 + 48.8 + 46.7 + 39.1 +
[Na'] 7.2 7.5 5.8 6.2 9.0
(mEq/1) a,b a,b a,b

Peak Na 68.2 + 60.6 + 61.7 + 58.5 + 50.3 + Output 8.2 9.6 8.8 9.4 14.7
(gEq/kg/
15min)

Values expressed as Mean + SEM Pairwise Multiple Comparison procedure-Student-Newman-Keuls
a-significantly different (p<0.05) than basal
b-significantly different (p<0.05) than post-pyrilamine
c-significantly different (p<0.05) than 7.5 pg/kg-hr Peak values derived from the final 30 minutes of each treatment.








39

Pyrilamine Infusion


The volume of contents collected ranged from 70 to 550 mls, with a mean of 356.7 + 37.3 mls/15 min and was not significantly different than basal collections. The mean acid concentration was 33.5 + 3.5 mEq/L, mean sodium concentration was 79.5 + 7.5 mEq/L, and mean sodium output was 60.6 9.6 pEq/kg BW/15 min. Acid output ranged from

3 to 55 tEq/kg BW/15 min, with a mean of 25.9 + 4.4 pEq/kg BW/15 min. These results were not significantly different from the basal time periods.


Histamine dose-response


Gastric collections became progressively more clear as acid concentration increased. During maximal histamine stimulation, the contents were colorless and watery. Volume

Maximal secretory volumes ranged from 360 to 850

ml/15min. For each increasing dose of histamine, the mean volume was 591.7, 591.7, and 508.9 ml/15min, respectively. The volume collected during each dose of histamine infusion was significantly greater (p<0.0001) than basal volume;









40

however, the stimulated volumes did not differ significantly among doses.

Acid Concentration

The mean acid concentration during basal and increasing histamine infusion doses showed the expected vigorous response to the treatments. Maximal acid concentration (MAC) ranged from 51 to 110 mEq/L, and mean MAC was significantly greater (p<0.0001) than basal acid concentration at all doses. Acid concentration at all doses was also significantly greater (p<0.05) than during the

post-pyrilamine period. The [H+1 during the 7.5 jg/kg-hr infusion was significantly lower (p<~0.05) than during either the 15 or 30 jg/kg-hr infusion. The MAC during 15 and 30 jg/kg-hr infusions did not differ significantly. Acid Output

Acid output (AC) for each treatment was calculated as the mean of the final two 15 minute collections of each infusion period. The individual highest AC was 155 jEq/kg BW/15 min occurring at t=195 min during the 15 jg/kg-hr histamine infusion. The AC in response to all histamine doses was significantly greater (p<.0001) than basal








41

output, and was the greatest during the 15 pg/kg-hr infusion. However, there was no significant difference between the responses to 15 pg/kg-hr and 30 pg/kg-hr infusions, whereas both the 15 and 30 pg/kg-hr infusion resulted in an AO significantly greater (p<0.05) than that from the 7.5 pg/kg-hr infusion. Sodium concentration

The sodium concentration was inversely related to acid concentration and ranged from 48.8 mEq/L to 39.1 mEq/L. The mean sodium concentration was significantly less (p=0.000119) during the 15 and 30 pg/kg-hr histamine infusion than during the basal period. The 7.5 pg/kg-hr infusion resulted in (Na] significantly greater than either the 15 or 30 pg/kg-hr infusion and not significantly different from either basal or post-pyrilamine periods. The concentration of Na in collections during the 15 and 30 pg/kg-hr infusions did not differ significantly from one another.








42

Sodium Output

Mean maximal sodium outputs decreased from 61.7 +

8.8 jEq/kg/15 min to 50.3 + 14.7 pEq/kg/15 min as the histamine infusion rates increased from 7.5 Jtg/kg-hr to 30 pg/kg-hr. No significant differences were observed in the sodium output during basal, post-pyrilamine or histaminestimulated collection periods. Pentagastrin Outputs


The mean maximal acid output during pentagastrin

infusion was 91.8 + 3.5 gEq/kg/15 min. Corresponding mean peak sodium output during the pentagastrin trial was 100.8 +

5.0 pEq/kg/15 min.



Discussion



As in other species, intravenous administration of

histamine base stimulated gastric acid secretion in horses resulting in maximal acid outputs (MAO) comparable to those of pentagastrin-stimulated horses. Infusions were performed without serious complications. Pretreatment with pyrilamine








43

maleate, a selective H-i receptor blocking agent", presumably eliminated any potential respiratory or neurologic side-effects of histamine infusion. Histamine-induced dyspnea results from bronchoconstriction mediated by H-I receptors." Both H-i and H-2 receptors are located in the central nervous system and horses are more susceptible to pronounced excitation and anxiety than some other species. The histamine provocation test for studies of equine bronchial responsiveness requires sedation to prevent apprehension and anxiety.65

Two experiments were not completed because the horses

developed synchronous diaphragmatic flutter (SDF) and muscle twitches. It is our belief that this was due to metabolic alkalosis with hypocalcemia and hypochloremia following marked HCl secretion.6 Changes in the ionization potential during metabolic alkalosis alter the free to bound calcium ratio and results in SDF.66 Once stimulation of HCI secretion ceased and the cannula was occluded, fluid and electrolyte loss ended and the horses responded rapidly. These individual horses were apparently hyper-responsive to histamine, since the MAO was reached during the 7.5 [tg/kg-hr infusion in one horse and after the first 15








44

minutes of the 15 ptg/kg-hr infusion in the other. These horses did not exhibit long-term effects following these episodes, and subsequent histamine infusions were administered to them without incident.

Antihistaminic agents, such as pyrilamine maleate, specific to H-I receptors are not expected to have antisecretory effects and are routinely used as part of the histamine challenge of gastric secretion in humans." A post-pyrilamine decrease in acid concentration and output was consistently observed and could reflect receptor cross-reaction or changes in blood flow to the gastric mucosa, since both H-1 and H-2 receptors are involved in histamine effects on vasculature.11 H-1 receptor blockade may also affect the delivery of substances to the basolateral membrane of parietal cells, since H-i receptors are involved in the regulation of capillary permeability."

The results indicate that a histamine dose of 30

jLg/kg-hr can be considered as that which will induce a maximal gastric acid secretory response in the horse. (See fig.l) In pilot studies for this trial, horses were infused with 15, 30, and 45 gg/kg-hr of histamine. However, some of these horses exhibited signs of metabolic alkalosis









45











100
Er/



80
U,
~'60


S 40
0

~20



BASAL PYRILAMINE 7.5 15 30
TREATMENT


Figure 1. Mean acid output/15 min. during the last 30 minutes of each treatment. "Basal" indicates the status prior to any treatment. "Pyrilamine" indicates the output after treatment with pyrilamine maleate (1 mg/kg IV) and peak outputs during IV histamine infusion of 7.5, 15, and 30 pg/kg-hr are indicated accordingly. Data are expressed as mean + SEM.


during the 45 pg/kg-hr infusion; therefore, we elected not to utilize this higher dose in this trial. Four horses completed the pilot study and the MAO during the 45 g/kg-hr infusion was not significantly different from the MAO during








46

30 [tg/kg-hr infusion in these horses.(unpublished results) As with other species2941, some individual horses were maximally stimulated at lower doses, but there was no "supramaximal depression,40,67 of the mean response seen when the dose was increased from 15 to 30 gg/kg-hr. Thus, the horse is apparently slightly more sensitive to histamine than man, in which the infusion of 42 jg/kg-hr results in MAO(1); the pig and dog are more resistant, requiring 60 jg/kg-hr29 and 50 pg/kg-hr24, respectively. The peak secretory response to histamine in horses was more gradually attained than the response to pentagastrin infusion.44 This phenomenon has been previously reported in other species, as well.41

Mean maximal acid output in horses induced by histamine was similar to that seen in humans on mEq/kg basis. Furthermore, the maximal responses to histamine and pentagastrin are not significantly different in horses, as was anticipated. Species differences in maximal acid output and relative sensitivity to histamine and pentagastrin are numerous.17,8 The majority of "in vivo" gastric secretory studies have involved dogs, rats, and humans.69 Dogs have








47

minimal basal acid secretion, whereas humans and rats have active, though erratic, basal secretion, as do horses.44 The maximal acid secretory response to histamine and pentagastrin is equivalent in dogs and humans, while rats are much more sensitive to pentagastrin than histamine. 1 It appears that horses may be very comparable to humans "in vivo," since they are equally responsive to both secretagogues and have similar basal acid secretory activity.(Table 3) "In vitro" studies of isolated parietal cells have demonstrated species differences in sensitivity to specific secretagogues. Canine parietal cells can be stimulated by carbachol, gastrin, or histamine, with carbachol being the most potent. Conversely, human and rat parietal cells are strongly stimulated by histamine and only weakly stimulated by gastrin and carbachol. The horse appears to be more like the human and rat, since histamine is the most effective secretagogue of isolated equine parietal cells, followed by gastrin and carbachol.34








48

TABLE 3.
Acid and Sodium Concentrations Histamine versus Pentagastrin

PARAMETER EQUINE HUMAN EQUINE
Pentagastrin PG or HI** Histamine
(PG)* (HI)

Basal Max. Basal Max. Basal Max.
Stim. Stim. Stim.

[HI] mEq/L 21-45 35-57 10-40 70-120 28-45 75 120 [Na ]mEq/L 45-92 75-146 30-70 15-30 62-123 23-70

* from ref no.66
** from ref no.42

In this study, mean acid concentration during maximal histamine stimulation was markedly greater than that observed during maximal pentagastrin stimulation. Maximal acid concentrations in other species have ranged from 100-140 mEq/L17,39, irrespective of stimulant. Individual maximal acid concentrations in these horses ranged from 75-125 mEq/L during histamine infusion. In contrast, in pentagastrin stimulated horses, the maximal acid concentration rarely reached 75 mEq/L, which was reported44 to be a major difference between horses and other species. Apparently,a nonparietal sodium rich fluid component of gastric secretion was strongly stimulated by pentagastrin.









49

Sodium outputs increased coincident with acid outputs


during pentagastrin stimulation in horseS44; whereas, in the


studies described here, sodium concentration decreased as


acid concentrations increased during histamine stimulation,


and the sodium output was constant as the acid output


increased to a maximal level. (fig.2) Thus, in the horse as


in other species, histamine appears to stimulate a purely


parietal secretion, with acid concentrations rising to


expected levels and a reciprocal decrease in sodium


concentration.19,41













2000

0
O
150 00 0 O
00
000 PG
0
~100- 0~ 0t0 A;
1A A
AO AA A
0 o AA A AA HI
2 50 A A
OOA CPA

0 0

I I I I I I
0 30 60 90 120 150
ACID OUTPUT (pEq/kg/15min)


Figure 2. Regression analysis of acid vs. sodium outputs during pentagastrin (0) and histamine (A) infusion.








5o

The exact origin of the histamine which stimulates

parietal cells and the mechanisms involved in its release have not been clearly documented in most species24, but it is known to act via H-2 receptors on parietal cells as a paracrine mediator.2,20 In rats, enterochromaffinlike (ECL) cells are the major histamine source in the gastric mucosa and gastrin has been shown to stimulate its release from them. 22,24 Rabbit and human gastric mucosal preparations also release histamine in response to gastrin but the cells responsible have not been identified.22 Few ECL cells are found in the normal human and canine mucosa; however, many mast cells are observed and may serve as the histamine source.24 Human patients with hypergastrinemia appear to have increased numbers of ECL cells in their gastric mucosa.24 The density of ECL cells in equine gastric mucosa is greatest in the pyloric gland region.70 Fewer ECL cells have been identified in the fundic gland mucosa and in the proximal duodenum.

In this study, we determined that histamine can be used as a stimulant of gastric acid secretion in horses. Histamine stimulated mean maximal acid output was comparable to that previously reported with pentagastrin.44








51

In contrast, the mean maximal acid concentration in response to histamine was much greater than that observed during maximal pentagastrin stimulation. These findings suggest that in horses, histamine stimulates purely parietal secretion, while pentagastrin stimulates the production of gastric contents that appear to be both parietal and nonparietal in origin.














CHAPTER 3
THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON PENTAGASTRIN-STIMULATED EQUINE GASTRIC SECRETION



Introduction



The interaction between gastrin and histamine

receptors has long been controversial.1.3 The ability of histamine receptor antagonists to eliminate pentagastrinstimulated gastric acid secretion supports the indirect action of gastrin on parietal cells.21,3137,48,49,51.53,54 This inhibition of gastric secretion has been limited specifically to histamine H-2 receptor antagonists. The administration of antihistamines directed at H-i receptors has not been shown to suppress acid production during stimulation with various secretagogues, including pentagastrin. 11,29,71 Although differences in the relative sensitivity to various secretagogues have been observed between species, the characteristics of gastric contents during maximal stimulation with histamine or pentagastrin are similar, with the exception of the horse.

52









53

Equine gastric contents during maximal stimulation with histamine have a high concentration of acid and low concentration of sodium as is characteristic of parietal secretion in other species, (see Chap. 2) whereas, pentagastrin-stimulated equine gastric contents have a high concentration of sodium and a relatively low acidity.44 Histamine stimulation of gastric secretion induces a maximal acid outputs (MAO) equal to those of pentagastrin-stimulated horses. (See Chap. 2) In horses, as in other species, it is necessary to administer an H-1 antagonist prior to histamine infusion to prevent side-effects.1,29,65 During gastric secretory studies on horses stimulated with histamine, pretreatment with the H-1 antagonist, pyrilamine maleate, resulted in a short-lived decrease in basal volume, acid concentration and acid output. (See Chap.2) The effect of this pretreatment on pentagastrin-stimulated gastric secretion is thus far unknown. Since we planned to further investigate the species specific disparity in the histamine and pentagastrin-stimulated secretory responses, we designed this study to consider the effect of pyrilamine maleate pretreatment on pentagastrin-stimulated gastric secretion.









54


Materials and Methods



Horses


Two mixed breed, one Thoroughbred and one Arabian [2 mares, 2 geldings] ranging from 3 to 20 years were used in this study. The horses were all healthy and ranged in weight from 370 to 490 kg. They were maintained on grass pasture and provided coastal hay ad lib and 12% protein grain twice daily. All horses were deformed every 2 months, vaccinated for encephalomyelitis and tetanus every 6 months and were free of clinical signs of gastrointestinal disease. Chronic indwelling gastric cannulas as described by Campbell-Thompson and Merri tt3l had been prepared in these horses 1 to 24 months prior to this study. All studies were approved by the University of Florida IACUC.


Experimental preparation


Horses were fasted with free choice water for 20 hours prior to an experiment. Experiments were performed with no less than a one week interval between them. The horses were loosely restrained in the laboratory for the entire








55

experiment. The gastric cannula was opened and allowed to drain by gravity for 15 to 20 minutes, while a indwelling jugular catheter was emplaced. The gastric contents were collected into IL fluid bags suspended from a surcingle. Experimental protocol


Gastric contents were collected in 15 minute aliquots and were filtered through gauze prior to analysis. Collections were measured for volume and if available, a 50 ml sample was saved for further analyses. Analyses were performed either immediately or samples were frozen for later analysis. Each experiment lasted 3 hours. During the first 45 minutes [basal collection], no treatment was given. In the treatment experiments, pyrilamine maleate (Histavet-P, Schering-Plough NJ) was infused IV at 1 mg/kg over a 15 minute period, beginning at time t=45min. No additional treatments were given for 30 minutes. In the no treatment experiments, basal collection was continued during time t=45-90 min. At time t=90min, an IV infusion of pentagastrin [6 ptg/kg-hr] was administered by infusion pump









56

(Harvard Apparatus, South Natick MA) in all experiments and continued for the remainder of the experiment.

Each infusion was given in a volume of 60 mi/hr. Horses were weighed the morning of the experiment to determine the amount of pentagastrin needed. Pentagastrin was prepared by dissolving with 0.8 ml of DMSO and 90 mls of

0.9!k NaCl and filtered through a 0.22 grn cellulose nitrate filter (Corning, Corning NY) in preparation for infusion. Sample analysis


Volume was measured in a graduated cylinder. Aliquots of gastric contents were analyzed immediately for hydrogen ion concentration, using a automatic titrator (Radiometer, Copenhagen Denmark). Hydrogen ion concentration of each aliquot was measured in duplicate by titration with 0.1N NaOH to an endpoint of pH of 7.4. Output was calculated on a per kg body weight basis from the volume and hydrogen ion concentration and was expressed as gEq/kg/15 min.









57

Analysis of data


Statistical analysis was performed on volume, acid

concentration, and acid output data. The last 30 minutes of basal (t=30&45 min), post-pyrilamine (t=75&90 min), and two infusion-related collections (early: t=105,120&135 min; late: t=150,165&180 mmn) were compared between the studies with and without pyrilamine pretreatment. Since the same horses were used in each study, a paired t-test was performed for each of the four time periods. The time periods were not compared to each other. A p< 0.05 was considered significant.



Results



In both studies, the volume and acid output rapidly

increased after pentagastrin infusion began. The horses had no adverse reactions during or following the administration of pyrilamine maleate. Physical characteristics of the gastric collections from both studies were the same. The mean and SEMs for each time period of both studies are shown in Table 4.








58


Basal Collections


The volume, acid concentration, and acid output during the basal time period of both studies did not differ significantly.


Post-Pyrilamine Collections


In the pyrilamine study, the volume collected during the 30 minutes following the administration of pyrilamine was significantly less (p=0.0145) than when no pyrilamine was given. The acid concentration did not differ between studies. The acid output was significantly less (p=0.0008) in the pyrilamine study than when no pyrilamine was given. Early Infusion Collections


The volume and acid concentration did not differ

significantly between the studies, however, the acid output was significantly less (p=0.0274) in the pyrilamine studies than when no pyrilamine was given.









59

TABLE 4.
Mean and SEM Data from Gastric Contents Collected Before and After Pentagastrin Infusion with and without Pretreatment with Pyrilamine Maleate.



PYRIL- BASAL POST- EARLY LATE
AMINE PYRIL- INFUSION INFUSION
AMINE **

VOLUME NO 253.8 + 381.7 + 585.8 + 622.5 +
37.2 29.9 74.9 43.7
(ml)
YES 287.5 + 181.7 + 415 + 589.2 +
27.95 34.8 102.2 71.0

[H+] NO 31.14 + 39.7 + 31.2 + 48.0 +
9.54 11.0 5.5 5.6
(mEq/L)
YES 39.5 + 31.7 + 36.4 + 51.6 +

6.1 7.0 9.0 8.2

ACID NO 18.1 + 34.1 + 46.4 + 76.8 +
OUTPUT 5.2 7.5 5.8 5.6
(iEq/kg-15 YES 24.5 + 12.4 + 26.7 + 56.5 +
mi) 3.9 2.5* 6.0 4.0 *


First half of Pentagastrin Infusion (t=105,120,&135 min) * Last half of Pentagastrin Infusion (t=150,165,&180 min)
Significantly Less than during No Pyrilamine Study

Late Infusion Collections


As during early infusions, the volume and acid

concentration were not significantly different between the

two studies. Acid output was significantly greater

(p=0.0031) in the study with no pyrilamine pretreatment.









60

Discussion



Pentagastrin infusion resulted in secretion of gastric acid in both studies; however, the maximal acid output was affected by the administration of pyrilamine maleate. This finding was unexpected since pyrilamine pretreatment has been used as the pretreatment of choice when performing

histamine stimulation in other species;" where the use of an H-1 specific receptor antagonist does not affect the secretion of gastric acid during stimulation. In part, the confusion over whether or not histamine acts directly on gastric mucosa resulted from early classical studies in which antihistamines were found to-have no inhibitory effect

27
on histamine induced gastric secretion. Better understanding of histamine receptor classes has helped to clarify the role of histamine in gastric secretion and explain these earlier findings, 11,12 namely that parietal cells have H-2 receptors and histamine stimulated gastric acid secretion appears to be a H-2 specific response. 1,2,3,68,69

Histamine receptors are involved in other aspects of gastric function as well as acid secretion. Three specific receptor types, H-1, H-2, and H-3 have, to date, been









61

recognized. As well as regulation of acid secretion, these receptors also play a role in the regulation of gastric microcirculation and motility."' Mucosal circulation is affected by histamine primarily via H-i receptors, although H-2 and H-3 receptors may be involved. In the rat, for instance, it appears that both H-i and H-2 receptors are involved in histamine related vasodilation.72 Vasoconstriction occurs with H-I receptor stimulation in the rabbit.2'73 Pyrilamine has been shown to competitively inhibit histamine related vasodilation in the guinea pig.73 The changes, if any, in equine gastric circulation in response to histamine or histamine blocking agents are not known.

The importance of gastric mucosal circulation in the horse may be most clearly demonstrated by the relative sensitivity of the horse to gastric ulceration due to NSAID's, though no specific studies have quantified equine gastric mucosal blood flow or the regulation of flow. The administration of NSAID's results in gastric ulceration by inhibition of prostaglandins involved in mucosal blood flow and cytoprotection.47 Gastrointestinal injury can be seen endoscopically in horses with or without accompanying








62

clinical signs within a few days of initiation of administration of even the recommended dose of phenylbutazone or flunixin meglumine.47 Gastric microcirculation is a key component of gastric mucosal protection2 and can be rate-limiting for gastric secretion."

Secretagogues involved in stimulating gastric acid secretion result in increases in blood flow as well. Histamine, gastrin, and cholinergic agents produce vasodilator activity associated with the increasing secretory rate.7" Blood flow has been shown to be ratelimiting at high levels of stimulation and agents which decrease blood flow will also inhibit acid secretion.75 'A histamine H-2 antagonist, such cimetidine, has been shown to decrease blood flow and acid secretion during pentagastrin stimulation in cats, however, mucosal blood flow was not decreased under basal conditions.3772 Although secretion is increased by pentagastrin stimulation in this study, the secretory response may be restricted by limitations on blood flow.

Histamine H-i receptor antagonists may affect gastric microcirculation by action at histamine receptors or by








63

atropine-like activity at muscarinic receptors'' involved in vasodilation. In dogs, the cholinolytic properties of pipolphen, a H-1 blocker, have been shown to suppress gastric secretions.77 Agonist to H-3 receptors78-80 and antagonist of the H-2 receptor",12,31,78 result in decreased acid secretion. Pyrilamine has been utilized in numerous secretion studies and in most species does not elicit this antisecretory response.81 8283 In other equine studies pyrilamine maleate administration was followed by a decrease in basal secretion, but this decrease was not always significant.(See Chap. 4 & 5)

Histamine H-3 receptors are found in several locations including the brain, perivascular nerve terminals, pulmonary airways, and ECL cells in the gastric mucosa.3'84 These receptors appear to be involved in the autoregulation of histamine release from ECL cells during the stimulation of gastric acid secretion. ,243679,80 They may also be involved in the release of somatostatin which inhibits gastric acid secretion." Certain drugs have demonstrated simultaneous H-1 agonist/H-3 antagonist properties,85 however, it appears that pyrilamine has a low affinity for H-2 and H-3










64

receptors.86 The distribution of H-1, H-2, and H-3


receptors in the horse has not been documented.







90
j Without Pyrilamine
S* With Pyrilamine
80


70


60

S50


40
ub

30


20


10


0
0- I I
Basal Pretreatment Early Late Time Block



Figure 3 Mean pentagastrin stimulated acid output with and without pyrilamine pretreatment. "Basal" refers to acid output prior to any treatment.(t=30&45 min) "Pretreatment" indicates output after pretreatment with pyrilamine or from comparable period with no treatment.(t=75&90 min) "Early" represents the first half of pentagastrin infusion. (t=105,120&135 min) Output during the last half of pentagastrin infusion is labeled "late".(t=150,165&180 min)


In this study, maximal pentagastrin-stimulated acid


output was significantly decreased in horses that received









65

pyrilamine prior to stimulation. This finding is contrary to the results in other species where H-i receptor antagonist do not inhibit gastric acid secretion. Because the precise mechanism for this action is not clear, it is apparent that this may be yet another important equine specific finding that warrants further investigation.

Therefore, equine gastric secretion in response to pentagastrin differs not only in composition from the classical parietal response of other species and the histamine response in the horse (See Chap.2), but also by the ability of pyrilamine to inhibit a maximal acid response.














CHAPTER 4
PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL CONTENTS IN HORSES WITH CHRONIC GASTRIC CANNULAS AND ITS EFFECT ON GASTRIC SECRETION


Introduction



The contents of various parts of the gastrointestinal system differ in chemical and physical characteristics between location and species. Much of the normal gastrointestinal function of the individual species relates to the anatomy of their alimentary system and the type of diet which they consume. Increasing our understanding the normal function is often complicated by those same differences. Equine gastric secretion and the composition of the contents under various conditions have been studied by numerous investigators utilizing several techniques .31,44,48-54 The development of a chronic gastric cannula 31 for collection of gastric contents has added greatly to the knowledge regarding equine gastric physiology.


66









67

Study of the function of the equine proximal duodenum, biliary system, and pancreas has been even more difficult due to an anatomical location which strictly limits surgical exposure."8,8" Up to now, attempts to study the proximal duodenum and associated structures have met with serious difficulties and been basically unsuccessful in providing additional information on the physiology of this region.

The ref lux of duodenal contents into the empty equine stomach has been observed during endoscopic gastric examination even when there is no evidence of underlying pathology.051 The importance, frequency and volume of reflux have not been evaluated. Nor has the composition of the duodenal contents which are mixing with the gastric' contents been fully analyzed. Ref lux of large volumes of small intestinal contents into the stomach is reported during various disease conditions such as anterior enteritis and small intestinal obstruction. 8990

The presence of chronic indwelling gastric cannulas in research horses has made access to the duodenum much easier for investigator and animal. This study describes how, with the aid of an endoscope passed up through a gastric cannula, a catheter can be placed into the equine duodenum for the







68

collection of fluid. The two objectives of this study were to determine the composition of the duodenal fluid and whether the presence of the catheter passing into the duodenum had an effect on the gastric contents collected from the cannula before and during stimulation of secretion with pentagastrin.




Materials and Methods



Horses



Five Thoroughbreds(TB), two mixed breed (MB) horses, and one Arabian (AR) [3 mares, 5 geldings] between 3 and 20 years in age, were used in these studies. (TABLE 5) For TABLE 5.
Horses used in Gastric Collection Studies.


ID AGE BREED SEX B 5 y ARAB G

D 7 Y TB G

E 20 Y TB M

H 5 Y TB G

I 6 Y TB M

J 3 Y MIXED G M 7 Y MIXED M T 5 Y TB G








69

both catheter studies, six of the horses (5TB,1AR) were selected. The no catheter/pentagastrin study was performed on four (2MB,1AR,1TB) horses. Two horses (1TB,1AR) were involved in both studies.(TABLE 6) The horses were all healthy and ranged in weight from 430 to 510 kg. They were maintained on grass pasture and provided coastal hay ad lib and 12% protein grain twice daily. All horses were dewormed every 2 months, vaccinated for encephalomyelitis/tetanus every 6 months and were free of clinical signs of gastrointestinal disease. A chronic indwelling gastric cannula as described by Campbell-Thompson and Merritt3 1 had TABLE 6.
Descriptions and Abbreviations for Each Study.

EXPERIMENT INFUSION CATHETER HORSES USED
ABBREVIATION (secretagogue) (via cannula) PG/NOC Pentagastrin None B,E,J,M

PG/CATH Pentagastrin Intraduodenal B,D,E,H,I,T

been prepared in these horses 1 to 24 months prior to this study. All studies were approved by the University of Florida IACUC.








70

Experimental preparation


Experiments were performed with no less than a one week interval between them. The horses were fasted with free choice water for 20 hours prior to an experiment. They were loosely restrained in the laboratory for the entire experiment. The gastric cannula was opened and allowed to drain by gravity for 15 to 20 minutes while a indwelling jugular catheter was emplaced. For the catheter studies, a video endoscope (WelchAllyn, Skaneateles Fall, NY) was inserted through the gastric cannula into the stomach and steered into the duodenum to a point approximately 30 cm past the area of the duodenal diverticulum. A 4.5m long stylet was threaded through the biopsy port of the endoscope until it was seen passing from the distal end of the scope. The endoscope was slowly withdrawn as the stylet was threaded through the biopsy port, watching that it stayed in place as the scope was removed. The distance from the pylorus to the end of the gastric cannula was noted. The presence of the stylet passing through the pylorus was visually confirmed prior to removing the endoscope from the cannula. The stylet was marked at the end of the cannula, after which a specially modified stallion urinary catheter









71

(see below) was passed over it. The mark on the stylet was used to assure that it remained in position as the catheter was introduced through the cannula into the stomach, then through the pylorus and into the duodenum. The stylet was left in place until catheter placement was believed to be complete. The completed setup (fig. 4) resulted in the































Figure 4 Cross sectional view of duodenal catheter passing through the gastric cannula into the stomach and entering the proximal duodenum.









72

ability to collect gastric contents from the cannula and duodenal contents from the catheter into separate containers. The fluids were collected into IL fluid bags suspended from a surcingle. The cannula and catheter were both allowed to drain by gravity for 15 minutes after completion of catheter placement. In the studies where there was no intraduodenal catheter (NOC) in place, gastric contents only were collected by gravity into IL fluid bags.


Catheter Design


The specialized catheter was fashioned from a 137 cm stallion urinary catheter(Jorgensen Laboratories, Inc., Loveland, Co).(fig.5) It's end was opened to allow free passage of the stylet and several additional 5mm side holes were placed in the 15cm closest to the tip. It was distinctly marked at 20 cm from the tip and this mark was considered the "0cm" mark. Additional marks were made every 5cm markings from that point to the end. To fix the catheter in position, a 10cm section of silastic tubing [16mm I.D.] was placed over a 5cm section of the barrel of a 12ml syringe (Monoject, St. Louis, MO.) and the catheter









73

passed tightly through the wall of the silastic tubing into the lumen and out through the syringe barrel lumen.




























Figure 5 Specialized catheter for collection of duodenal contents. The bold mark is signified by and is located 20 cm from tip. Multiple fenestrations within that 20 cm region of the catheter.


One end of the syringe barrel locked into the end of the silastic gastric cannula and the other was attached to the short segment of silastic tubing which locked the catheter in a fixed position. The long stylet was made by joining together 3 stylets provided with stallion catheters. The








74

catheter was passed until the bold mark [0cm] was 5cm aborad to the pylorus.


Experimental protocol


Gastric (in all studies) and duodenal contents (only in the "catheter" studies [CATHI) were collected in 15 minute aliquots. Gastric samples were filtered through gauze prior to analysis. Volume of both gastric and duodenal collections was measured and, if available, a 50 ml sample was saved for sample analyses. Analyses were performed either immediately or samples were frozen for later analysis. Each experiment lasted 3 hours. During the first 45 minutes [basal collection], no treatment was given. Beginning at time t=45min, pyrilamine maleate (Histavet-P, Schering-Plough NJ) was infused IV at 1 mg/kg over a 15 minute period. No additional treatments were given for 30 minutes. At time t=90min, an IV infusion of pentagastrin [6 pg/kg-hr] was administered by infusion pump (Harvard Apparatus, South Natick MA) and continued for the remainder of the experiment. At the conclusion of the catheter









75

experiments, the catheter position was rechecked before the catheter was withdrawn, and the cannula closed.

Each infusion was given in a volume of 60 mis/hr.

Crystalline pentagastrin (Sigma Chemical Co., St. Louis MO) was prepared by dissolving with 0.8 ml of DMSO and 90 mis of

0.9% NaCi before filtering through a 0.22 I.In cellulose nitrate filter (Corning, Corning NY) in preparation f or infusion.


Sample analysis


Gastric and duodenal sample volume was measured in a graduated cylinder and then an aliquot was analyzed immediately for chloride ion concentration. Gastric samples were also analyzed immediately for hydrogen ion concentration. Duodenal samples were kept in an ice bath until they were analyzed for bicarbonate ion concentration. Both gastric and duodenal samples were frozen for later measurement of sodium and potassium ion concentration.

Using a automatic titrator (Radiometer, Copenhagen Denmark), hydrogen ion concentration was measured in duplicate by titration with 0.1N NaOH to an endpoint of 7.4.








76

Chloride ion concentration was measured in duplicate by a digital chloridometer (Buchler Instruments Div., Nuclear Chicago, Fort Lee NJ) with acid reagent (Labconco, Kansas City, Mo). Chloride standard (Labconco, Kansas City, Mo) was used to calibrate the machine prior to each experiment and after every 20 tests. Bicarbonate ion concentration was determined by back-titration method of Isenberg et al.91 with the automatic titrator (Radiometer, Copenhagen Denmark) using 0.1N NaOH to titrate to an endpoint of 8.4. Sample solutions were gassed with nitrogen washed in barium hydroxide to remove carbon dioxide prior to and during the titration and were analyzed in triplicate. Standard solutions prepared in laboratory were measured in quadruplicate prior to each experiment. Sodium and potassium ion concentration were measured by flame photometry (Instrumentation Laboratories Inc., Lexington MA) on samples which had been frozen at -200C. Samples were thawed to room temperature, and diluted in an internal standard lithium solution (Dilumat, Fisher Scientific). The machine was calibrated with known [Na ]/[K ] standards (Instrumentation Laboratories Inc., Lexington MA) prior to any analyses and after every 5 samples.









77


Analysis of data


For the purpose of this paper, duodenal contents were analyzed to determine electrolyte concentration ranges, but these data were not statistically evaluated. Statistical analysis was performed on volume, acid concentration, acid output, sodium concentration, and sodium output from the gastric samples. Output was calculated on a per kg body weight basis from the volume and hydrogen or sodium ion concentration and was expressed as pEq/kg-15min. The last 30 minutes of basal collections, post-pyrilamine collections, and the first and last 30 minutes of infusionrelated collections were compared between studies. A

two-way ANOVA was performed for factors of time (basal, post-pyrilamine, early infusion, and late infusion), and duodenal catheter (yes or no) and interactions of these factors. A p<0O.05 was considered significant and all pairwise multiple comparisons by Tukey test were performed.









78

Results



Gastric Contents


Volume. (Table 7) The volume of gastric collection

differed significantly (p<0.01) between the designated time blocks. The volume was significantly greater (p<0.05) during the late infusion block than during all other blocks. The early infusion volume was significantly greater (p<0.05) than the post-pyrilamine volume, but did not differ significantly from the basal volumes. The basal and postpyrilamine volumes did not differ significantly. The volumes collected during the CATH study were significantly (p<0.01) greater than during the NOC study. There was no significant interaction between time blocks and catheter status.

Acid Concentration. (Table 7) Acid concentration varied significantly (p=0.001) among the time blocks with a significantly higher (p<0.05) concentration during late infusion. The [H+] was not significantly different between basal, post-pyrilamine and early infusion blocks. The NOC study had a significantly (p=0.016) higher concentration of









79

acid than the CATH study. No significant interactions were

found between time blocks and catheter.

TABLE 7.
Data from Study With and Without Duodenal Catheter During Pentagastrin Stimulation (Mean and SEM's)


STUDY BASAL PYRILAMINE EARLY LATE
VOLUME NOC 287.5 + 171.3 + 405.0 + 568.8 +
(ml/15 28.0 27.0 125.4 83.4 *
min)
CATH* 541.7 + 396.6 + 653.3 + 885.8 + 29.7 32.1 66.0 26.7 *

[H] NOC** 39.5 + 32.3 + 5.2 31.9 + 52.4 +
(mEq/L) 6.1 10.0 9.4 *

CATH 26.5 + 28.9 + 3.3 20.4 + 42.4 +
4.1 3.7 2.2 *

ACID NOC 24.5 + 12.1 + 1.9 22.5 + 57.4 +
OUTPUT 3.9 6.5 3.8 *
(pEq/kg15rn CATH* 31.9 + 24.9 + 3.7 30.2 + 80.2 +
15m) 6.2 6.8 4.9 *

[Na] NOC 106.1 + 110.8 + 108.3 + 93.4 +
(mEq/L) 6.1 5.7 10.0 8.2

CATH 106.8 + 104.4 + 107.4 + 88.2 + 6.0 3.3 4.2 3.3

NA NOC 72.5 + 44.8 + 8.5 107.3 + 133.8 +
OUTPUT 10.0 40.0 29.2 *
(pEq/kg(Eq/kg- CATH* 122.1 + 88.0 + 8.0 146.4 + 167.5 + 15min)
15m) 8.4 13.6 9.9 *

* Significantly greater than NOC
** Significantly greater than CATH
* Significantly greater than all other time blocks Significantly greater than post-pyrilamine time block
* Significantly less than all other time blocks
* Significantly greater than basal & post-pyrilamine time
blocks









80


Acid Output. (Table 7) The output of acid decreased after the pyrilamine infusion and increased during pentagastrin infusion. These changes in acid output over time differed significantly (p<0.001). Acid output (AO) was significantly greater (p<0.05) during late infusion than during all other periods, however, the differences between outputs during each of the other times did not differ significantly. The AO was significantly greater (p=0.001) during the CATH study than the NOC study.

Sodium Concentration. (Table 7) The [Na ] was

relatively constant until the late infusion block during which time the concentration decreased significantly (p=0.01). There was no significant difference in the concentration between CATH and NOC studies.

Sodium Output.(Table 7) There was a significant (p<0.001) effect of time on sodium output. The output during late infusion was significantly greater (p<0.05) than during basal or post-pyrilamine periods, but not significantly greater than during the early infusion period. Early infusion sodium output was also significantly greater than post-pyrilamine, though it was not significantly








81

greater than the basal output. The output during the CATH study was significantly greater (p=0.001) than during the NOC study.


Duodenal Contents


Duodenal fluid was generally thick and mucoid and tended to be dark yellow to green, in color. The bicarbonate ion concentration ranged between 19-40 mEq/L; TABLE 8.
Electrolyte Composition of Fluid from Duodenal Catheter During Basal, Post-Pyrilamine, and Pentagastrin Infusion
Collection Periods. [Mean + SEMI

DUODENAL BASAL PYRILAMINE _INFUSION

[HCO3] 23.2 + 2.6 16.2 + 1.5 33.0 + 2.3
(mEq/L)

[Na'] 147.5 + 3.9 151.5 + 6.7 144.9 + 2.4
(mEq/L)

[K+] 4.5 + 0.2 4.4 + 0.3 3.6 + 0.1
(mEq/L)
[Cl-] 118.1 + 5.5 119.6 + 5.2 115.1 + 6.1
(mEq/L)

it decreased noticeably in the post-pyrilamine collections and was increased during pentagastrin infusion. The fluid had a high concentration of sodium (120-190 mEq/L) and low concentration of potassium (2.4-5.5 mEq/L) compared to that of gastric contents, in which the [Na'] ranged between 25-









82

125 mEq/L and [K+] between 6-20 mEq/L. Chloride ion concentrations were in the range of 95-160 mEq/L, whereas the gastric contents had [Cl]I ranging from 130 to 180 mEq/L. The mean concentrations of sodium, potassium, and chloride were consistent throughout the experiment.



Discussion



The placement of a duodenal catheter through the

gastric cannula required variable amounts of manipulation of the videoendoscope. The time required for introduction of the video endoscope into the duodenum and passage of the stylet and threading of the catheter ranged from 10 to 2+5 minutes. The differences related in position of the pylorus relative to the cannula and the dexterity of the investigator on that day. The horses did not appear to be bothered by the process nor by the presence of the catheter during the experiments. Catheter experiments proceeded as the no catheter experiments did. Gastric contents were easily collected from the cannula even with the catheter in place. During some time periods, no fluid was collected from the duodenal catheter. However, this did not indicate









83

blockage as fluid was collected during the next time period as patency was checked injection of air through the catheter.

In the catheter experiments, gastric contents had

significantly greater volume, acid output, and sodium output

as well as a significantly lower [Hi1 The presence of the catheter passing through the pylorus may have allowed additional fluid ref lux from the duodenum into the stomach. This may have occurred due to capillary action along the catheter or by preventing complete closure of the pylorus. The duodenal fluid had a high concentration of sodium and reflux: of this fluid may account for increased sodium output and volume of gastric contents in CATH experiments. The' acid response to pentagastrin with the duodenal catheter was similar to previous studies in the horse ;31,'44 however, during pentagastrin stimulation, the gastric contents [H+1. in the CATH study was less than in the NOC study. We suggest that this may have been due to dilution of the gastric secretions by the fluid refluxing from the duodenum around the catheter.

The increased acid output observed in the CATH study was not related to the ref lux of duodenal fluid. The post-









84

pyrilamine period decrease in acid output in the CATH study was not as dramatic in the NOC study. The increasing acid output during the early and late infusion periods of the CATH were closer to the normal pentagastrin response observed in horses without pyrilamine pretreatment(See Chap.3) than to an unusually profound response to pyrilamine in the NOC study. Decreased maximal acid output in horses stimulated with pentagastrin following the administration of pyrilamine maleate may be due to decreased mucosal blood flow. (See Chap. 3) The placement of the duodenal catheter may also potentiate gastric acid secretion by mechanical stimulation2,3811,18 in the gastric antrum resulting in the local release of gastrin or acetylcholine, thereby lessening the effect of the pyrilamine. In humans and dogs, distention of the antral region has been shown to augment histamine or gastrin- related secretion of acid.2'3"8 Although the catheter was not large and did not distend the antrum, it did contact the gastric mucosa and may have stimulated local intramural reflexes23"17,18 involved in the secretory response.

Sodium output increased dramatically during

pentagastrin infusion in both the CATH and NOC studies,








85

although, the output was significantly greater in the CATH studies. The infusion related increase in sodium output was consistent with the apparently equine specific response to pentagastrin. 11,44,51 Monitoring of sodium ions in the stomach has been used to assess duodenogastric ref lux in humans. 9293 The sodium rich fluid collected from the equine gastric cannulas is probably of duodenal origin5'5' and the ref lux of this sodium rich duodenal fluid around the duodenal catheter could explain the increased sodium output during the CATH study.

The equine gastric cannula model has been beneficial in the understanding of equine gastric physiology and the development pharmaceuticals for the treatment of gastric ulcers. 3149,53'54 It appears that this model may also allow further investigation of equine gastric and small intestinal physiology. The duodenal contents had a high concentration of sodium and chloride and low concentration of potassium and is most likely the fluid which dilutes parietal secretions during gastric collections. The passage of a duodenal catheter and collection of duodenal contents does not prevent normal acid stimulation in response to pentagastrin, but may enhance ref lux of duodenal contents into the stomach.




Full Text
203
11. Douglas WW. Histamine and 5-hydroxytryptamine
(Serotonin) and their Antagonists. In: Gilman AG, Goodman
LS, Gilman A, eds. The Pharmacological Basis of
Therapeutics, Sixth Edition. New York: Macmillan
Publishing Co.,Inc, 1980; 609-619.
12. Black JW, Duncan WAM, Durant CJ, Ganellin CR,
Parsons EM. Definition and Antagonism of Histamine H2-
receptors. Nature. 1972; 236:383-390.
13. Hkanson R, Owman CH, Sporong B, Sundler F.
Electron Microscopic Identification of the Histamine-storing
Argyrophil (enterochromaffin-like) Cells in the Rat Stomach.
Z Zellforsch. 1971; 122:460-466.
14. Capella C, Vassallo G, Solcia E. Light and
Electron Microscopic Identification of the Histamine-storing
Agyrophil (enterochromaffin-like) Cell in Murine Stomach and
its Equivalent in Other Mammals. Z Zellforsch. 1971;
118:68-84 .
15. Forte JG, Wolosin JM. HC1 Secretion by the
Gastric Oxyntic Cell. In: Johnson LR, ed. Physiology of
the Gastrointestinal Tract, Second Edition. New York: Raven
Press, 1987; 853-863.
16. Sachs G. The Gastric H,K ATPase. In: Johnson
LR, ed. Physiology of the Gastrointestinal Tract, Third
Edition. New York: Raven Press, 1994; 1119-1138.
17. Debas HT. Peripheral Regulation of Gastric Acid
Secretion. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Second Edition. New York: Raven
Press, 1987; 931-943.
18. Lloyd KCK, Debas HT. Peripheral Regulation of
Gastric Acid Secretion. In: Johnson LR, ed. Physiology of
the Gastrointestinal Tract, Third Edition. New York: Raven
Press, 1994; 1185-1210.


40
however, the stimulated volumes did not differ significantly
among doses.
Acid Concentration
The mean acid concentration during basal and increasing
histamine infusion doses showed the expected vigorous
response to the treatments. Maximal acid concentration
(MAC) ranged from 51 to 110 mEq/L, and mean MAC was
significantly greater (p<0.0001) than basal acid
concentration at all doses. Acid concentration at all doses
was also significantly greater (p<0.05) than during the
post-pyrilamine period. The [H+] during the 7.5 pg/kg-hr
infusion was significantly lower (p<0.05) than during either
the 15 or 30 pg/kg-hr infusion. The MAC during 15 and
30 (ig/kg-hr infusions did not differ significantly.
Acid Output
Acid output (AO) for each treatment was calculated as
the mean of the final two 15 minute collections of each
infusion period. The individual highest AO was 155 |aEq/kg
BW/15 min occurring at t = 195 min during the 15 p.g/kg-hr
histamine infusion. The AO in response to all histamine
doses was significantly greater (p<0.0001) than basal


37
Two horses did not complete the entire experiment. In
one experiment, the infusion had to be terminated after the
15 p.g/kg-hr histamine infusion period because the horse
developed marked muscle tremors and mild abdominal
contractions. After the infusion was stopped, the gastric
cannula closed and hand-feeding begun, the horse recovered
rapidly. Thirty minutes into the 30 pg/kg-hr infusion into
a second horse, it developed generalized muscle tremors and
mild synchronous diaphragmatic flutter. It became clinically
normal within 20 minutes of ending the experiment and being
allowed to eat.
Basal Secretion
Contents collected under pretreatment (basal)
conditions were generally yellow-tinged, viscid, and cloudy.
The 15-minute aliquots ranged in volume from 280 to 640 mis,
with a mean of 428.3 +34.1 mls/15 min. The mean acid
concentration was 42.5 + 3.9 mEq/L, and mean acid output was
3 9.8 + 6.6 p.Eq/kg BW/15 min with a range from 19.3 to
82.7 (.iEq/kg/15 min. The pH of the samples varied greatly
between 1.38 and 2.01, with a mean of 1.67 + 0.036. The mean
sodium concentration was 75.7 + 7.2 mEq/L, and mean sodium


121
histamine response, further implies a special pentagastrin
effect.
The finding that during the NB experiments the maximal
acid concentration induced by histamine was significantly
greater than that induced by pentagastrin, whereas, in the B
experiments, maximal histamine and pentagastrin related acid
concentrations were equivalent suggests that the equine
stomach per se, responds to these 2 secretagogues in a
Time (minutes)
Figure 8 Acid concentration. A curvilinear line derived
from mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials marks mean for NB trials.


14
just open the door to a multitude of additional questions.
Although, much knowledge has been gained by isolated cell
work such as that with the ECL cell, the wide array of
species differences points to the continuing need for both
"in vivo" and "in vitro" studies.
Early classical studies were "in vivo," performed
primarily on animals with a variety of surgically prepared
pouches or fistulas. Even human studies in the early
1900's, were performed on subjects with gastric fistulas.19
Historically, experimental preps commonly utilized dogs and
cats with transplanted pouches or surgically isolated
stomachs.8-26'27 Over time, chronic gastric cannulas have
been placed in the stomachs of dogs, rats, rabbits, pigs,
cats, humans, and horses to allow studies to be performed on
conscious animals.5,28'31 Amphibian mucosa was the first
tissue used in the "in vitro" studies that provided the
cardinal information about the acid transporting ATPase.32
Subsequent cellular studies have been performed on canine,
equine, rabbit, and rat gastric glands. 22,32'36 Initially,
food and food extracts were selected to stimulate gastric
secretion, later histamine and alcohol were used in many
studies.8'26,27 Histamine continues to be a valuable


I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
George A1 Gerencser
Professor of Physiology
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
(C3 VTuvK,
Robert J. MacKay
Associate Professor of
Veterinary Medicine
This dissertation was submitted to the Graduate Faculty
of the College of Veterinary Medicine and to the Graduate
School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
May, 1997


74
catheter was passed until the bold mark [Ocm] was 5cm aborad
to the pylorus.
Experimental protocol
Gastric (in all studies) and duodenal contents (only in
the "catheter" studies [CATH]) were collected in 15 minute
aliquots. Gastric samples were filtered through gauze prior
to analysis. Volume of both gastric and duodenal
collections was measured and, if available, a 50 ml sample
was saved for sample analyses. Analyses were performed
either immediately or samples were frozen for later
analysis. Each experiment lasted 3 hours. During the first
45 minutes [basal collection], no treatment was given.
Beginning at time t=45min, pyrilamine maleate (Histavet-P,
Schering-Plough NJ) was infused IV at 1 mg/kg over a 15
minute period. No additional treatments were given for 30
minutes. At time t=90min, an IV infusion of pentagastrin
[6 pg/kg-hr] was administered by infusion pump (Harvard
Apparatus, South Natick MA) and continued for the remainder
of the experiment. At the conclusion of the catheter


41
output, and was the greatest during the 15 pg/kg-hr
infusion. However, there was no significant difference
between the responses to 15 pg/kg-hr and 3 0 pg/kg-hr
infusions, whereas both the 15 and 30 pg/kg-hr infusion
resulted in an AO significantly greater (p<0.05) than that
from the 7.5 pg/kg-hr infusion.
Sodium concentration
The sodium concentration was inversely related to acid
concentration and ranged from 48.8 mEq/L to 39.1 mEq/L.
The mean sodium concentration was significantly less
(p=0.000119) during the 15 and 30 pg/kg-hr histamine
infusion than during the basal period. The 7.5 pg/kg-hr
infusion resulted in [Na+] significantly greater than either
the 15 or 30 pg/kg-hr infusion and not significantly
different from either basal or post-pyrilamine periods. The
concentration of Na* in collections during the 15 and
30 pg/kg-hr infusions did not differ significantly from one
another.


103
significant (p=0.04872). In SAL/NB experiments, the output
of chloride ion was significantly less than either HIST/NB
(p=0.00059) or PG/NB (p<0.00001), and during PG/NB, output
was significantly greater than during HIST/NB (p=0.00001).
Table 12.
CHLORIDE IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[C1-]
mEq/L
SAL
143.23.82
NB
143.4+5.6
143.16.32
HIST
144.9+3.62
PG
144.06.68
[ci-]
mEq/L
SAL
151.35.07
B4
151.15.2
153.35.57
HIST
156.93.53
PG
154.02.56
CL'
OUTPUT
iEq/kg/
15min
SAL *
143.38.82
NB
138.822.7
111.117.8
HIST*
207.320.45
+
PG *
272.919.47
CL'
OUTPUT
¡lEq/kg/
15min
SAL *
73.7+14.07
Bf
82.2+16.93
51.010.44
HIST*
14 9.2 + 19.53
+
PG *
172.0+19.07
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
+ Pyrilamine significantly different(p<0.05) from other
time
In the balloon experiments, pentagastrin stimulated outputs
that were significantly greater than histamine (p=0.04704)


APPENDIX B
PYRILAMINE PRETREATMENT STUDY DATA
VOLUME (ml)
TIME
TREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
247.50
51.21
180.00
29.44
30
BASAL
BASAL
275.00
55.75
210.00
35.36
45
BASAL
BASAL
300.00
20.82
297.50
62.77
60
HVP
BASAL
272.50
13.15
317.50
60.05
75
P-P
BASAL
155.00
22.17
287.50
75.54
90
P-P
BASAL
187.50
52.18
330.00
82.87
105
PENTAGASTRIN
352.50
198.80
295.00
90.60
120
PENTAGASTRIN
457.50
179.04
327.50
76.64
135
PENTAGASTRIN
435.00
203.20
432.50
110.63
150
PENTAGASTRIN
630.00
148.72
707.50
156.86
165
PENTAGASTRIN
535.00
120.45
617.50
108.35
180
PENTAGASTRIN
602.50
131.24
627.50
69.69
195
PENTAGASTRIN
ND
ND
590.00
72.23
210
PENTAGASTRIN
ND
ND
650.00
101.41
225
PENTAGASTRIN
ND
ND
667.50
102.26
240
PENTAGASTRIN
ND
ND
645.00
41.33
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine
144


99
interaction. Further comparison demonstrated the following
gastric volume differences: PG/NB was significantly
greater than HIST/NB (p<0.00001) or SAL/NB (p<0.00001),
HIST/NB was significantly greater than SAL/NB (p=0.00178),
PG/B was significantly greater than HIST/B (p=0.04694) or
SAL/B (p<0.00001), and HIST/B was significantly greater than
SAL/B (p=0.00154).
Table 10.
VOLUME AND pH OF GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
VOLUME
ml/15min
SAL *
472.93 0.5
NB
466.158.4
361.6+51.1
HIST *
664.251.5
+
PG *
885.83 9.5
VOLUME
ml/l5min
SAL *
226.942.5
B4
251.04 8.9
153.930.1
HIST *
445.556.0
+
PG *
523.8+52.4
pH
SAL
2.450.70
NB
2.100.48
2.430.64
HIST §
1.330.07
+
PG
1.590.05
PH
SAL
2.450.91
B
1.950.41
2.64+0.85
HIST §
1.21+0.04
+
PG
1.27+0.02
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
§ HIST significantly less (p<0.05) than other infusions
+ Pyrilamine significantly different than other time blocks


Copyright 1997
by
Diane Lynn Kitchen


117
those of previous equine secretory studies without any kind
of catheter in place.
The pretreatment of the horses with pyrilamine maleate
in all experiments was necessary to allow for comparison of
histamine and pentagastrin. The results of the pyrilamine
pretreatment were not significantly different between
groups, however, they were significantly different from
basal collections prior to treatment. These results are
consistent with previous findings suggesting that the equine
acid secretory response may be dampened by the
administration of an H-l receptor antagonist.(See Chap. 3)
In this study, as predicted, collection volume, acid
concentration, and acid, sodium, potassium and chloride
outputs decreased following infusion of pyrilamine maleate,
while the pH and sodium concentration of the gastric
contents increased.
The trends observed during the NB experiments were
consistent with the species specific equine response that
has been observed in earlier studies as distinct from the
results observed in other species during similar
stimulation.31-44 The infusion of both pentagastrin and
histamine resulted in the stimulation of increased acid


cannula model, the vigorous sodium-rich component of
pentagastrin stimulated gastric contents is extragastric in
origin.
The testing of this hypothesis was accomplished by a
series of studies on horses with chronic gastric cannulae.
A full histamine dose-response study was necessary to
determine an optimal dose for the stimulation of maximal
acid output. Since this required pretreatment of the horses
with the H-l receptor antagonist, pyrilamine maleate, a
small study of the effect of this pretreatment on
pentagastrin-stimulated secretion was designed. A technique
was developed for the placement of an intraduodenal
h
/
ballooned catheter via the gastric cannula to occlude the
pylorus. A study was also performed to evaluate the effect
of the presence of the intraduodenal catheter. Finally, the
critical study involving a comparison of the gastric and
duodenal contents during histamine and pentagastrin
infusion, with and without obstruction of the pylorus, was
done.
Gastric contents were analyzed in each of the studies
for volume and electrolyte composition. The histamine-
induced maximal acid ouput was equivalent to that previously
xiv


100
pH. (Table 10) The only significant effect on pH
(p=0.02600) was related to the drug of infusion. Histamine
infusion resulted in pH significantly lower than saline
(p=0.00866), but not significantly different from
pentagastrin.
Potassium ion concentration (Table 11) The
concentration of potassium ion increased significantly
(p=0.0001) after initiation of the infusions. The drug*time
interaction was also significant (p=0.0001). Histamine
infusion rapidly resulted in [K+] significantly greater than
pentagastrin (p=0.0029) or saline (p=0.0001). Time-related
changes in [K+] did not differ significantly between
pentagastrin and saline infusions. The [K+] was
significantly greater (p=0.00004) in experiments with the
balloon than in no balloon experiments. There was a
significant (p<0.00001) drug effect. The [K+] during
histamine infusion was significantly greater than during
pentagastrin (p=0.00007) or saline (p<0.00001) infusion, and
the pentagastrin induced [K+] was significantly greater than
that of saline (p=0.00168). The drug*balloon interaction
was significant (p=0.01112) with the following specific
concentration differences: HIST/NB was significantly


156
Chloride Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
151. l
3 08
148.8
4.56
149.5
6.68
30
BASAL
152.2
3.72
151.2
3 07
151.0
6.54
45
BASAL
150.9
3.22
152.3
7.46
149.0
7.34
60
HVP
151.2
4.80
155.4
7.89
145.8
4.11
75
148.5
4.72
160.9
6.01
146.7
5.79
90
149.1
4.84
167.6
5.10
147.4
6.99
105
INFUSION
149.7
4.78
162.0
4.15
147.8
3.70
120
INFUSION
148.8
5.79
165.4
3.68
156.5
4.60
135
INFUSION
150.3
4.43
159.4
5.31
149.0
3.04
150
INFUSION
151.0
6.58
153.6
5.87
151.7
3.69
165
INFUSION
151.8
4.77
156.4
2.70
153.6
2.64
180
INFUSION
150.7
5.37
157.5
4.37
154.5
2.47
HVP = Pyrilamine maleate infusion


LIST OF FIGURES
Figure Page
1 Mean acid output/15 min. of each treatment 45
2 Regression analysis of acid vs. sodium outputs during
pentagastrin and histamine infusion 49
3 Mean pentagastrin stimulated acid output with and
without pyrilamine pretreatment 64
4 Cross sectional view of duodenal catheter passing
through the gastric cannula and to the duodenum. . 71
5 Specialized catheter. 72
6 Specialized Balloon catheter. 89
7 Cross sectional view showing balloon catheter
positioned in the proximal duodenum 90
8 Acid concentration. A curvilinear line 121
9 Acid output. A curvilinear line 122
10 Sodium concentration. A curvilinear line .... 124
11 Sodium output. A curvilinear line 125
12 Collections from catheter or cannula 134
xii


87
between histamine and pentagastrin stimulation is the
relative sensitivity to each, rather than the composition of
the resultant secretions.17-28-30
Furthermore, when PG-induced gastric acid secretion of
horses is inhibited by either a histamine-2 receptor
antagonist or a proton pump blocking agent, a large volume
of basic, sodium-rich fluid can still be collected from the
stomach. 31- 49-51-53-54- This is also distinctly different from
the response in other monogastrics, where inhibition of acid
secretion results in coincident reduction in the volume of
gastric contents. 37-94 Whether the origin of this fluid is
primarily gastric or extragastric in origin has not been
identified. The objective of this study was to determine
more exactly the source of this large "nonparietal"
component of equine gastric contents that is seen in
response to PG stimulation.
Materials and Methods
Horses
Five Thoroughbreds and one Arabian [2 mares, 4
geldings] ranging from 3 to 20 years were used in this


3 THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON
PENTAGASTRIN-STIMULATED EQUINE GASTRIC
SECRETION 52
Introduction 52
Materials and Methods 54
Horses 54
Experimental preparation 54
Experimental protocol 55
Sample analysis 56
Analysis of data 57
Results 57
Basal Collections 58
Post-Pyrilamine Collections 58
Early Infusion Collections 58
Late Infusion Collections 59
Discussion 60
4 PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL
CONTENTS IN HORSES WITH CHRONIC GASTRIC CANNULAS
AND ITS EFFECT ON GASTRIC SECRETION 66
Introduction 66
Materials and Methods 68
Horses 68
Experimental preparation 70
Catheter Design . 72
Experimental protocol 74
Sample analysis 75
Analysis of data 77
Results 78
Gastric Contents 78
Volume 78
Acid Concentration 78
Acid Output 8 0
Sodium Concentration 80
Sodium Output 80
Duodenal Contents 81
Discussion 82
viii


57
Analysis of data
Statistical analysis was performed on volume, acid
concentration, and acid output data. The last 30 minutes
of basal (t=30&45 min), post-pyrilamine (t=75&90 min), and
two infusion-related collections (early: t=105,120&135 min;
late: t=150,165&180 min) were compared between the studies
with and without pyrilamine pretreatment. Since the same
horses were used in each study, a paired t-test was
performed for each of the four time periods. The time
periods were not compared to each other. A p< 0.05 was
considered significant.
Results
In both studies, the volume and acid output rapidly
increased after pentagastrin infusion began. The horses had
no adverse reactions during or following the administration
of pyrilamine maleate. Physical characteristics of the
gastric collections from both studies were the same. The
mean and SEMs for each time period of both studies are shown
in Table 4.


13
and can be inhibited by somatostatin (subtype 2), TGF-a,
TGF-p, calcitonin gene-related peptide, and histamine via H-
1 and H-3 receptors. 1-22-24-25 It appears that there is
i
substantial neurotransmitter modulation of gastrin and its
regulation of histamine release from ECL cells.25 Although,
it is known that Ca++ acts as a secondary messenger within
the ECL cell, cAMP is likely to also play a role in the
release of histamine.1-22-24
In addition to stimulating the release of histamine,
gastrin regulates HOC activity and ECL cell
proliferation.1-24 It stimulates DNA synthesis by a pathway
distinct from that of histamine release, although both
processes appears to begin with the binding of gastrin at
the CCK-B receptors.1-24 Hypergastremia has been associated
with increased numbers of ECL cells and may play a
significant part in the development of gastric
carcinoids.1-24 The chronic use of antiulcer medication with
resultant hypergastremia have been shown to lead to ECL
hyperplasia and gastric mucosal hypertrophy. 1-22-24 The
recent advances in the "in vitro" cellular techniques have
expanded our knowledge of the regulation of the gastric
secretory response; however, as history shows us, advances


Leichliter and John R. Phillips have been loyal friends,
providing me unending support throughout the course of this
program. I also thank my private practice clients, who have
had to deal with my erratic schedule and a goal they cannot
comprehend.
A special acknowledgement and dedication must go to
Zero and One, two brave ponies who taught me so much in our
brief acquaintance. The horses involved in these studies
have each contributed not only data, but added to my life.
I thank Adam, Buddy, Dick, Ethel, Harry, Iso, Jeff, Lucy,
Mama, Spot, and Tom. Tejas, Clay, Blondie, and all my other
four-legged family have provided my most ardent source of
solace. A special thought for Valiant who did not make it
to the end, but is still remembered fondly.
vi


2
control the rate of secretion.1'3 Acetylcholine is the
primary neurotransmitter involved in gastric acid secretion.
Muscarinic nerve endings near the gastric glands release
acetylcholine as part of the vagal reflex system.3 Enteric
neurons in Meissner's plexus release GRP (gastrin releasing
peptide) which acts on G cells in the gastric antrum.
Gastrin is the peptide hormone released in response to
specific substrates within the gastric lumen and distension
of the antrum. Released by antral G cells, gastrin is an
important hormone which is involved in all phases of gastric
secretion and also exerts influence on DNA transcription and
cellular replication.1 Histamine acts directly on parietal
cells, as a paracrine substance, to stimulate gastric acid
secretion via H-2 receptors. Histamine originates from
enterochromaffin-like (ECL) cells present within the
mucosa, in response primarily to gastrin stimulation, with
modulation by numerous other substances.1
Historical Background
Understanding the mechanisms of gastric acid secretion
and the regulation of these mechanisms has required decades


CHAPTER 1
INTRODUCTION AND REVIEW OF LITERATURE
Introduction
The regulation of gastric secretion has long interested
scientists and clinicians due to the vital role gastric acid
secretion plays in the normal gastrointestinal function and
in certain pathologic conditions. The stomach, with both
endocrine and exocrine function, is not a simple collection
vat for food prior to digestion. A diverse group of cells
with numerous capabilities are found within the highly
specialized gastric mucosa.1 Parietal cells secrete acid at
the apical membranes containing the H+/K+ ATPase pump.2
Other cells are responsible for the production of mucus,
zymogens, and other biologically active peptides and
amines.1 Numerous endocrine cells secrete substances that
modulate various gastrointestinal functions.1 The secretion
of hydrochloric acid by the parietal cells is regulated by
neural, hormonal, and paracrine mechanisms which interact to
1


128
Biliary secretion has an electrolyte composition
similar to that of the pancreas, and ductular secretion is
stimulated by secretin with a corresponding increased
bicarbonate concentration.97 Gastrin, but not pentagastrin,
has been shown to increase biliary flow in dogs.97 The
horse lacks a gallbladder and is reported to have continuous
biliary flow55, though which substances are involved in the
regulation of this flow, has not been reported. Increased
biliary secretion in response to pentagastrin is also a
possible source of some of the extragastric fluid in equine
gastric collections.
This study clearly demonstrates that pentagastrin
stimulates the secretion of an extragastric fluid which
dilutes the gastric contents during gastric collection from
the gastric cannula model. With separation of gastric and
extragastric secretions by obstruction of the pylorus, it
becomes apparent that pentagastrin does stimulate parietal
secretion comparable to that of histamine, similarly
comparable to that of other monogastric species. Although,
the exact origin of this extragastric fluid requires further
investigation, it is most likely of pancreatic and/or
biliary origin. The remarkable volume response to


56
(Harvard Apparatus, South Natick MA) in all experiments and
continued for the remainder of the experiment.
Each infusion was given in a volume of 60 ml/hr.
Horses were weighed the morning of the experiment to
determine the amount of pentagastrin needed. Pentagastrin
was prepared by dissolving with 0.8 ml of DMSO and 90 mis of
0.9% NaCl and filtered through a 0.22 pm cellulose nitrate
filter (Corning, Corning NY) in preparation for infusion.
Sample analysis
Volume was measured in a graduated cylinder. Aliquots
of gastric contents were analyzed immediately for hydrogen
ion concentration, using a automatic titrator (Radiometer,
Copenhagen Denmark). Hydrogen ion concentration of each
aliquot was measured in duplicate by titration with 0.IN
NaOH to an endpoint of pH of 7.4. Output was calculated on
a per kg body weight basis from the volume and hydrogen ion
concentration and was expressed as j.iEq/kg/15 min.


76
Chloride ion concentration was measured in duplicate by a
digital chloridometer (Buchler Instruments Div., Nuclear
Chicago, Fort Lee NJ) with acid reagent (Labconco, Kansas
City, Mo). Chloride standard (Labconco, Kansas City, Mo)
was used to calibrate the machine prior to each experiment
and after every 20 tests. Bicarbonate ion concentration was
determined by back-titration method of Isenberg et al.91
with the automatic titrator (Radiometer, Copenhagen Denmark)
using 0.IN NaOH to titrate to an endpoint of 8.4. Sample
solutions were gassed with nitrogen washed in barium
hydroxide to remove carbon dioxide prior to and during the
titration and were analyzed in triplicate. Standard
solutions prepared in laboratory were measured in
quadruplicate prior to each experiment. Sodium and
potassium ion concentration were measured by flame
photometry (Instrumentation Laboratories Inc., Lexington MA)
on samples which had been frozen at -20C. Samples were
thawed to room temperature, and diluted in an internal
standard lithium solution (Dilumat, Fisher Scientific). The
machine was calibrated with known [Na+] / [K+] standards
(Instrumentation Laboratories Inc., Lexington MA) prior to
any analyses and after every 5 samples.


191
Sodium Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
30181.87067
6036.37413
38.97
0.0001
BALLOON(B)
1
24969.04280
24969.04280
161.21
0.0001
DRUG
2
44132.80588
22066.40294
142.47
0.0001
B*DRUG
2
8922.09532
4461.04766
28.80
0.0001
HORSE*B*DRUG
25
46055.64502
1842.22580
11.89
0.0001
TIME
11
73160.32748
6650.93886
42.94
0.0001
B*TIME
11
7086.57970
644.23452
4.16
0.0001
DRUG*TIME
22
56593.70301
2572.44105
16.61
0.0001
B*DRUG*TIME
22
4775.21468
217.05521
1.40
0.1101
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
4954.00037
990.80007
6.40
0.0001
post,t effect
5
24135.98708
4827.19742
31.17
0.0001
pre, b*t
5
437.04981
87.40996
0.56
0.7273
post,b*t
5
1472.39968
294.47994
1.90
0.0936
pre,drug*t
10
1511.62991
151.16299
0.98
0.4641
post,drug*t
10
9416.88083
941.68808
6.08
0.0001
pre, b*drug*t
10
494.41269
49.44127
0.32
0.9759
post,b*drug*t
10
1359.65435
135.96544
0.88
0.5542
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
3703.48
3703.48
3.7088
0.06386
post,b effect
1
26442.69
26442.69
26.4810
0.00002
pre, d effect
2
250.42
125.21
0.1254
0.88262
post,d effect
2
89547.58
44773.79
44.8386
0.00000
pre, d*b
2
8239.65
4119.83
4.1258
0.02636
post, d*b
2
3603.59
1801.79
1.8044
0.18235


47
minimal basal acid secretion, whereas humans and rats have
active, though erratic, basal secretion, as do horses.44
The maximal acid secretory response to histamine and
pentagastrin is equivalent in dogs and humans, while rats
are much more sensitive to pentagastrin than histamine.17
It appears that horses may be very comparable to humans "in
vivo," since they are equally responsive to both
secretagogues and have similar basal acid secretory
activity.(Table 3) "In vitro" studies of isolated parietal
cells have demonstrated species differences in sensitivity
to specific secretagogues. Canine parietal cells can be
stimulated by carbachol, gastrin, or histamine, with
carbachol being the most potent. Conversely, human and rat
parietal cells are strongly stimulated by histamine and only
weakly stimulated by gastrin and carbachol. The horse
appears to be more like the human and rat, since histamine
is the most effective secretagogue of isolated equine
parietal cells, followed by gastrin and carbachol.34


APPENDIX A
HISTAMINE DOSE-RESPONSE DATA
Horses used in Histamine Study
NAME
BREED
SEX
AGE
WEIGHT
Buddy
Arabian
G
s y
445 kg
Dick
Thoroughbred
G
6 y
481 kg
Ethel
Thoroughbred
M
19 y
4 93 kg
Harry
Thoroughbred
G
4 y
495 kg
Lucy
Thoroughbred
M
9 y
5 06 kg
Tom
Thoroughbred
G
4 y
482 kg
138


83
blockage as fluid was collected during the next time period
as patency was checked injection of air through the
catheter.
In the catheter experiments, gastric contents had
significantly greater volume, acid output, and sodium output
as well as a significantly lower [H+] The presence of the
catheter passing through the pylorus may have allowed
additional fluid reflux from the duodenum into the stomach.
This may have occurred due to capillary action along the
catheter or by preventing complete closure of the pylorus.
The duodenal fluid had a high concentration of sodium and
reflux of this fluid may account for increased sodium output
and volume of gastric contents in CATH experiments. The
acid response to pentagastrin with the duodenal catheter was
similar to previous studies in the horse;31'44 however, during
pentagastrin stimulation, the gastric contents [H+] in the
CATH study was less than in the NOC study. We suggest that
this may have been due to dilution of the gastric
secretions by the fluid refluxing from the duodenum around
the catheter.
The increased acid output observed in the CATH study
was not related to the reflux of duodenal fluid. The post-


51
In contrast, the mean maximal acid concentration in response
to histamine was much greater than that observed during
maximal pentagastrin stimulation. These findings suggest
that in horses, histamine stimulates purely parietal
secretion, while pentagastrin stimulates the production of
gastric contents that appear to be both parietal and
nonparietal in origin.


123
Acid output in the B experiments was equal during
pentagastrin and histamine stimulation, however, in the NB
experiments, histamine related acid output was greater than
that of pentagastrin.(See fig. 9) Several factors seem to
be involved in this unexpected finding. The HIST/NB maximal
acid output was greater than HIST/B during some of the time
blocks, while the opposite relationship was noted for PG/B
and PG/NB. The lower maximal acid output in the PG/NB may
be the result of the loss of hydrogen ions through chemical
reaction with bicarbonate ions from the extragastric
component of NB collections.
Even more dramatic than the effects on acid were those
on sodium recorded in these experiments.(See fig. 10) As
with acid concentration, the pattern of the [Na+] response
to PG/B was that expected of the classic parietal secretory
response rather than the profound nonparietal response seen
in previous equine pentagastrin studies. The comparison of
sodium outputs under B vs. NB conditions was still more
spectacular.(See fig. 11) Sodium output was greater in all
NB experiments than those with the balloon, which is
consistent with the suggestion that the extragastric


151
Potassium Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
11.67
1.09
10.76
0.92
9.97
0.91
30
BASAL
10.88
1.05
9.73
0.77
9.76
0.76
45
BASAL
10.55
1.25
8.32
0.97
9.65
0.69
60
HVP
10.38
1.07
7.91
0.82
9.76
0.77
75
8.89
0.81
7.60
0.54
8.62
0.54
90
8.38
1.00
7.44
0.50
7.63
0.44
105
INFUSION
9.28
0.72
10.16
0.87
7.82
0.38
120
INFUSION
9.31
0.52
14.43
0.85
9.78
0.81
135
INFUSION
9.68
0.80
14.87
0.98
10.03
0.61
150
INFUSION
9.78
0.85
14.19
0.86
10.49
0.42
165
INFUSION
9.68
0.50
14.08
0.79
10.01
0.40
180
INFUSION
9.97
0.78
13.95
1.01
10.66
0.66
HVP = Pyrilamine maleate infusion


9
by gastrin. Distension of the stomach walls activates
stretch receptors involved in release of gastrin. However,
this release does not occur if the gastric contents are
i
acidic due to a pH-sensitive, oxyntopyloric reflex with
inhibition by somatostatin.2'17-18 Certain breakdown products
of food are strong stimulants of gastric acid secretion,
particularly peptides and amino acids, specifically,
phenylalanine and tryptophan.2-17'18 These stimulants induce
the release of gastrin by action at the apical microvilli of
G cells within the antral mucosa.17
The intestinal phase of acid secretion is
responsible for only a small portion of the total acid
secretory response.18 Stimulating agents are the same as
those involved in the gastric phase. The substances act
directly at G cells in the upper small intestine as a
gastrin-dependent mechanism and absorbed amino acids exert
their effect by a gastrin-independent mechanism.18 All
phases of acid secretion are, in part, mediated by gastrin,
through the release of histamine from ECL cells.1
The secretion of gastric acid follows the action of
histamine on H-2 receptors on the parietal cell. Inhibition
of histamine release allows the parietal cell to return to a


4
Histamine was reported to stimulate the secretion
of gastric acid in the early 1920s. Then, in the late
1930s, Macintosh stated that vagal stimulation resulted in
histamine release within the gastric mucosa10; however,
controversy surrounded the role of histamine since known
antihistamine agents were unable to prevent acid
secretion.11 The identification of different subtypes of
histamine receptors by Black et al. in the 1970s and
subsequent studies with H-2 receptor antagonist clearly
demonstrated that histamine was an integral component in the
normal gastric secretory response.11-12 The complex
interworking of each of these components confused
investigators and resulted in conflicting studies. Only in
the 1970s, with studies focusing on "in vitro" cellular
preparations and technical advances in immunology and
histology, were scientists able to begin unravelling this
complex regulatory process. The enterochromaffin-like (ECL)
cell was the key to the combined action of acetylcholine,
gastrin, histamine and many other effectors.1 Though ECL
cells had been noticed in the early drawings and writings of
Heidenhain, their role in the secretory response was not
known.1 The demonstration by Hkanson et al.13 and Capella


176
Potassium Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
3 86
0.29
4.17
0.15
3.96
0.29
30
BASAL
3.87
0.28
3 94
0.14
3.91
0.23
45
BASAL
3.72
0.39
3 83
0.11
4.14
0.30
60
HVP
3.95
0.37
3.79
0.18
3.88
0.20
75
3.71
0.36
3.82
0.18
3.95
0.24
90
3.68
0.30
3.96
0.07
3.95
0.29
105
INFUSION
4.19
0.50
3.85
0.12
3.77
0.18
120
INFUSION
3.58
0.35
3.78
0.06
3.50
0.28
135
INFUSION
3.66
0.44
3.67
0.12
3.73
0.34
150
INFUSION
3.87
0.28
3.63
0.10
3.62
0.34
165
INFUSION
3 83
0.30
3.71
0.11
3.57
0.31
180
INFUSION
3.61
0.28
3.68
0.12
3.49
0.39
HVP = Pyrilamine maleate infusion


62
clinical signs within a few days of initiation of
administration of even the recommended dose of
phenylbutazone or flunixin meglumine.47 Gastric
microcirculation is a key component of gastric mucosal
protection72 and can be rate-limiting for gastric
secretion.74
Secretagogues involved in stimulating gastric acid
secretion result in increases in blood flow as well.
Histamine, gastrin, and cholinergic agents produce
vasodilator activity associated with the increasing
secretory rate.75 Blood flow has been shown to be rate-
limiting at high levels of stimulation and agents which
decrease blood flow will also inhibit acid secretion.75 A
histamine H-2 antagonist, such cimetidine, has been shown to
decrease blood flow and acid secretion during pentagastrin
stimulation in cats, however, mucosal blood flow was not
decreased under basal conditions. 37,72 Although secretion is
increased by pentagastrin stimulation in this study, the
secretory response may be restricted by limitations on blood
flow.
Histamine H-l receptor antagonists may affect gastric
microcirculation by action at histamine receptors or by


12 9
pentagastrin when collecting gastric contents from the horse
via the cannula is related primarily to increased
duodenogastric reflux of sodium rich isotonic fluid.
Histamine infusion, on the other hand, stimulates the
parietal cells, but does not stimulate the secretion of the
extragastric secretion. Thus, the equine specific gastric
secretory response to pentagastrin is the result of
extragastric actions of pentagastrin rather than species
variation in the acid secretory response.


17
pattern has been examined with both histamine and
pentagastrin in experimental models39'41 and in patients with
gastroduodenal diseases.42 In man, the infusion of either
histamine or pentagastrin results in similar changes in
gastric electrolyte concentrations and outputs. Sodium
concentration decreases and output remains constant, while
potassium concentration increases slightly and output
increases significantly. The concentration of calcium and
phosphate decreases and outputs are unchanged.39 Acid and
sodium concentrations have a strong inverse correlation
under these stimulatory conditions.39 The histamine-
stimulated maximal acid output in dogs is greater than that
of pentagastrin; however, peak acid output is reached more
quickly with pentagastrin than with histamine.41 Sodium ion
concentration is inverse to acid in the canine studies just
as in human studies.
Thus, gastric secretions are a combination of parietal
and nonparietal fluids. The parietal component is isotonic
HC1 that is secreted in response to specific secretagogues
at a rate that increases significantly with simulation of
the parietal cell.4 The nonparietal component is believed
to be a constantly secreted isotonic ultrafiltrate of


ACKNOWLEDGMENTS
I acknowledge the help of many individuals and animals
who have been instrumental in my pursuit of this degree and
the completion of this dissertation. I wish to thank Dr.
Alfred M. Merritt, my mentor and the head of the Island
Whirl Equine Colic Research Laboratory, where these studies
were conducted. I thank him for the collaboration
throughout the multiple attempts to define this project and
various sidelines along the way, and also for the
constructive criticism in the preparation of this
dissertation and associated papers.
I thank James A. Burrow for all the technical
assistance over the years. His computer skills and
laboratory assistance have been invaluable. Through the
many changes in this project, the committee has remained
intact and I thank them for staying on the committee. I
thank Christie Stieble for her work on the statistical
analysis of data for the balloon study. I thank Dr. Philip
iv


174
Sodium Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
138.6
8.41
145.0
4.39
133.8
7.76
30
BASAL
138.2
6.98
136.4
5.29
136.9
5.98
45
BASAL
132.4
11.75
134.9
4.39
141.6
6.43
60
HVP
140.3
9.75
131.6
6.30
137.1
4.55
75
134.0
9.88
135.2
6.85
140.0
6.47
90
132.1
6.65
141.5
3.91
136.0
5.97
105
INFUSION
136.9
5.55
137.1
4.63
142.0
5.56
120
INFUSION
133.7
9.76
139.8
4.94
140.4
9.43
135
INFUSION
130.9
12.34
137.0
4.20
142.2
7.90
150
INFUSION
141.0
6.83
141.5
2.20
142.2
7.15
165
INFUSION
141.3
7.44
143.7
2.42
143.0
7.71
180
INFUSION
134.8
6.67
142.5
1.92
143.8
11.14
HVP = Pyrilamine maleate infusion


125
resulted in the accumulation of these secretions in the
proximal duodenum. The significantly greater volumes
observed during pentagastrin infusions were of particular
Figure 11 Sodium output. A curvilinear line derived from
mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials marks mean for NB trials.
interest. Furthermore, the fluid collected during these
experiments appeared to be less viscous than in experiments
with either histamine or saline infusion. The duodenal
contents collected during pentagastrin infusion also had a


3
of research by many eminent scientists using a wide array of
models and techniques. From the time of Pavlov and the
fistulated dogs until the "in vitro" cellular studies of
<
Hkanson et al., debate has raged around the regulation of
gastric acid secretion. Pavlov's work with fistulated
models confirmed that subjective observations of a link
between emotional status and digestive function were correct
and introduced the role of a central neural component of
gastric secretory regulation.4 Even today we use the term
"Pavlovian" when referring to the brain's input into a
function, such as the cephalic phase of gastric secretion.
Bayliss and Starling paved the way to investigation of
hormonal substances involved in gastrointestinal secretion.5
In 1906, Edkins suggested that a hormone "gastrin" was
released in the pyloric portion of the stomach and resulted
in the gastric phase of the acid secretory response.6 The
presence of this distinct secretagogue was demonstrated by
Komarov in 1938,7 and clarified in 1941 by Gregory and Ivy.8
Gregory and Tracy were able to isolate the substance in two
forms from pig antral mucosa and validate the hormonal
regulation of gastric secretion by gastrin in the 1960s.


114
significantly greater (p=0.00001) during saline infusion
than during either histamine or pentagastrin infusion.
Volume. (Table 19) The volume of fluid collected from
the duodenal catheter increased significantly (p=0.0378)
compared to pre-infusion during the first 30 minutes after
the infusions started and then gradually decreased
throughout the remaining 60 minutes of infusion to volumes
slightly greater than basal. The presence of pyloric
obstruction by the balloon significantly (p<0.00001)
increased the volume collected. The infusion composition
resulted in significant differences (p=0.00005), with
pentagastrin yielding volumes significantly greater than
either histamine (p=0.00008) or saline (p=0.00009), while
histamine and saline did not differ significantly from each
other. In the experiments without the balloon, there was no
significant difference between infusion volume; however,
with balloon, pentagastrin-induced volumes were
significantly greater than during either histamine
(p<0.00001) or saline (p<0.00001) infusion.


Ill
"Rl" and "R2" since there were no significant differences
between results of each infusion during this pre-infusion
time.
Post-infusion
Duodenal samples
Bicarbonate ion concentration. (Table 15) The
concentration of bicarbonate ion was significantly greater
(p=0.00397) in collections made while the balloon was in
place. There was also a significant (p=0.00002) drug effect
on [HC03'] Pentagastrin infusion resulted in [HC03']
Table 15.
BICARBONATE IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[HC03-]
mEq/L
SAL
23.6 2.7
NB
23.22.6
16.21.5
HIST
22.9 2.3
PG *
33.0 2.3
[HCO3-]
mEq/L
SAL
28.5 4.7
B
28.5+2.7
28.72.7
HIST
28.3 1.9
PG *
37.1 2.1
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB


116
Discussion
The placement of a duodenal catheter through the
indwelling gastric cannula has been used to analyze duodenal
contents and has been shown to allow simultaneous collection
of gastric and duodenal contents during both resting and
stimulated conditions.(See Chap. 4) This technique was
further modified in this study to provide a method to
occlude the pylorus to collect gastric contents that were
devoid of reflux from the duodenum. The previous studies
with the catheter suggest the reflux of duodenal fluid which
has been shown during endoscopic examination to occur
spontaneously in fasted animals50-51 may be enhanced by the
presence of the catheter passing through the pylorus.(See
Chap. 4) The absence of bile acids in the gastric contents
during the balloon experiments confirmed that reflux of
duodenal contents was eliminated. This technique allowed
us, therefore, to collect purely gastric or duodenal
contents during the balloon experiments, whereas, in the no
balloon experiments, the gastric contents were comparable to


177
Chloride Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
119.5
3.17
102.9
6.68
118.2
4.80
30
BASAL
123.4
3.98
102.7
4.00
126.6
6.12
45
BASAL
124.6
4.09
101.8
5.92
129.4
8.91
60
HVP
124.8
4.01
105.8
4.99
110.1
6.69
75
123.5
4.73
107.3
3.45
128.6
4.58
90
121.3
7.03
112.6
6.77
124.7
4.78
105
INFUSION
126.5
6.94
116.5
5.52
119.7
7.13
120
INFUSION
136.3
3.41
110.5
4.70
113.4
5.09
135
INFUSION
137.1
6.40
108.1
6.70
112.4
4.49
150
INFUSION
126.2
8.96
102.7
10.25
105.4
7.85
165
INFUSION
136.1
5.70
105.7
7.32
117.8
7.41
180
INFUSION
135.1
5.39
100.9
6.67
112.4
4.72
HVP = Pyrilamine maleate infusion


85
although, the output was significantly greater in the CATH
studies. The infusion related increase in sodium output was
consistent with the apparently equine specific response to
pentagastrin.31-44-51 Monitoring of sodium ions in the stomach
has been used to assess duodenogastric reflux in humans.92-93
The sodium rich fluid collected from the equine gastric
cannulas is probably of duodenal origin50-51 and the reflux of
this sodium rich duodenal fluid around the duodenal catheter
could explain the increased sodium output during the CATH
study.
The equine gastric cannula model has been beneficial in
the understanding of equine gastric physiology and the
development pharmaceuticals for the treatment of gastric
ulcers. 31-49-53-54 It appears that this model may also allow
further investigation of equine gastric and small intestinal
physiology. The duodenal contents had a high concentration
of sodium and chloride and low concentration of potassium
and is most likely the fluid which dilutes parietal
secretions during gastric collections. The passage of a
duodenal catheter and collection of duodenal contents does
not prevent normal acid stimulation in response to
pentagastrin, but may enhance reflux of duodenal contents
into the stomach.


EFFECTS OF HISTAMINE
AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS
By
DIANE LYNN KITCHEN
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1997

Copyright 1997
by
Diane Lynn Kitchen

This dissertation is dedicated to my father, Hyram
Kitchen, D.V.M., Ph.D., who taught me the importance of the
pursuit of excellence. I continuously strive to approach
the high standards he spent a lifetime instilling in me.
Even today, I look to his approval as the ultimate in
reward. Thank you, Daddy, and I do wish you were here to
share this with me.

ACKNOWLEDGMENTS
I acknowledge the help of many individuals and animals
who have been instrumental in my pursuit of this degree and
the completion of this dissertation. I wish to thank Dr.
Alfred M. Merritt, my mentor and the head of the Island
Whirl Equine Colic Research Laboratory, where these studies
were conducted. I thank him for the collaboration
throughout the multiple attempts to define this project and
various sidelines along the way, and also for the
constructive criticism in the preparation of this
dissertation and associated papers.
I thank James A. Burrow for all the technical
assistance over the years. His computer skills and
laboratory assistance have been invaluable. Through the
many changes in this project, the committee has remained
intact and I thank them for staying on the committee. I
thank Christie Stieble for her work on the statistical
analysis of data for the balloon study. I thank Dr. Philip
iv

Kosch for his role as Associate Dean for Research and
Graduate Studies.
Dr. Martha Campbell-Thompson, who is one of the
pioneers in equine gastric secretion, provided a wealth of
t
knowledge and was invaluable in the development of this
project as did her chairman at the Health Sciences Center,
Dr. J. McGuigan. I must also thank Dr. Dan Hogan and Mr. M.
Koss who taught me not only the method for analyzing
bicarbonate concentration, but who were instrumental in the
construction of my specialized duodenal catheter.
For emotional support, I must thank several important
people in my life. I am afraid that most have had to suffer
me during one stage or another of this process and deserve
accolades for this. I thank my mother, Yvonne H. Kitchen,
R.N., for the shoulder. I know it has been a tough several
years, but she were always there with unconditional love and
I do love her for it. Michael S. Kitchen, M.D., my dearest
brother keeps me humble. Dr. Jerry and Gayle Spears have
had to "live" with me day by day and have always been there
for me. I cannot thank them enough. Roger Reynolds gave
me peace of mind and allowed me to focus on my own goals.
Elmer and Harriet Heubeck, Cynthia McFarland, Gail
v

Leichliter and John R. Phillips have been loyal friends,
providing me unending support throughout the course of this
program. I also thank my private practice clients, who have
had to deal with my erratic schedule and a goal they cannot
comprehend.
A special acknowledgement and dedication must go to
Zero and One, two brave ponies who taught me so much in our
brief acquaintance. The horses involved in these studies
have each contributed not only data, but added to my life.
I thank Adam, Buddy, Dick, Ethel, Harry, Iso, Jeff, Lucy,
Mama, Spot, and Tom. Tejas, Clay, Blondie, and all my other
four-legged family have provided my most ardent source of
solace. A special thought for Valiant who did not make it
to the end, but is still remembered fondly.
vi

TABLE OF CONTENTS
ACKNOWLEDGMENTS iv
LIST OF TABLES xi
LIST OF FIGURES xii
ABSTRACT xiii
CHAPTERS
1 INTRODUCTION AND REVIEW OF LITERATURE 1
Introduction 1
Historical Background . 2
Review of Literature 5
Development of Hypothesis .26
2 EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID
SECRETION 31
Introduction 31
Materials and Methods 33
Results 36
Basal Secretion 37
Pyrilamine Infusion 39
Histamine dose-response 39
Volume 3 9
Acid Concentration 40
Acid Output 4 0
Sodium concentration 41
Sodium Output 42
Pentagastrin Outputs 42
Discussion 42
vii

3 THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON
PENTAGASTRIN-STIMULATED EQUINE GASTRIC
SECRETION 52
Introduction 52
Materials and Methods 54
Horses 54
Experimental preparation 54
Experimental protocol 55
Sample analysis 56
Analysis of data 57
Results 57
Basal Collections 58
Post-Pyrilamine Collections 58
Early Infusion Collections 58
Late Infusion Collections 59
Discussion 60
4 PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL
CONTENTS IN HORSES WITH CHRONIC GASTRIC CANNULAS
AND ITS EFFECT ON GASTRIC SECRETION 66
Introduction 66
Materials and Methods 68
Horses 68
Experimental preparation 70
Catheter Design . 72
Experimental protocol 74
Sample analysis 75
Analysis of data 77
Results 78
Gastric Contents 78
Volume 78
Acid Concentration 78
Acid Output 8 0
Sodium Concentration 80
Sodium Output 80
Duodenal Contents 81
Discussion 82
viii

5 THE EFFECT OF PYLORIC OBSTRUCTION ON EQUINE BASAL AND
STIMULATED GASTRIC SECRETION 86
Introduction 86
Materials and Methods 87
Horses 87
Experimental protocol 88
Sample analysis 92
Analysis of data 94
Results 95
Pre-infusion 96
Gastric samples 96
Post-infusion 98
Gastric samples 98
Pre-infusion 109
Duodenal samples 109
Post-infusion Ill
Duodenal samples Ill
Bile Acids 115
Discussion 116
6 SUMMARY AND CONCLUSIONS 130
Summary 130
Conclusions 13 6
APPENDICES
A HISTAMINE DOSE-RESPONSE DATA 138
B PYRILAMINE PRETREATMENT STUDY DATA 144
C DATA FROM BALLOON/NO BALLOON STUDY 147
D STATISTICAL ANALYSIS OF HISTAMINE DOSE RESPONSE
DATA 179
E STATISTICAL ANALYSIS OF PYRILAMINE MALEATE DATA 181
F STATISTICAL ANALYSIS OF CATHETER/NO CATHETER DATA 183
G STATISTICAL ANALYSIS OF BALLOON/NO BALLOON DATA 186
ix

LIST OF REFERENCES 2 02
BIOGRAPHICAL SKETCH 213
x

LIST OF TABLES
Table page
1 Acid and Sodium Concentration Histamine Infusion 2 9
2 Equine Gastric Contents 38
3 Acid and Sodium: Histamine versus Pentagastrin . 48
4 Gastric Contents with and without Pretreatment ... 59
5 Horses used in Gastric Collection Studies 68
6 Descriptions and Abbreviations for Each Study ... 69
7 Data from Study With and Without Duodenal Catheter 79
8 Electrolyte Composition of Duodenal Contents .... 81
9 Experimental Design 91
10 Volume and Ph of Gastric Contents 99
11 Potassium in Gastric Contents 101
12 Chloride in Gastric Contents 103
13 Acid in the Gastric Contents 106
14 Sodium in Gastric Contents 108
15 Bicarbonate in Duodenal Contents Ill
16 Sodium in Duodenal Contents 112
17 Potassium in Duodenal Contents 113
18 Chloride in Duodenal Contents 113
19 Volume of Duodenal Contents 115
xi

LIST OF FIGURES
Figure Page
1 Mean acid output/15 min. of each treatment 45
2 Regression analysis of acid vs. sodium outputs during
pentagastrin and histamine infusion 49
3 Mean pentagastrin stimulated acid output with and
without pyrilamine pretreatment 64
4 Cross sectional view of duodenal catheter passing
through the gastric cannula and to the duodenum. . 71
5 Specialized catheter. 72
6 Specialized Balloon catheter. 89
7 Cross sectional view showing balloon catheter
positioned in the proximal duodenum 90
8 Acid concentration. A curvilinear line 121
9 Acid output. A curvilinear line 122
10 Sodium concentration. A curvilinear line .... 124
11 Sodium output. A curvilinear line 125
12 Collections from catheter or cannula 134
xii

Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
EFFECTS OF HISTAMINE AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS
By
Diane Lynn Kitchen
May 1997
Chairperson: Alfred M. Merritt, II
Major Department: Veterinary Medicine
The composition of equine gastric contents has been
determined to differ markedly from that of other monogastric
species. In the fasted animal, there is a voluminous
sodium-rich fluid component which becomes greater during
pentagastrin infusion, which is not eliminated by acid
blockade. Potential pancreatic stimulation by pentagastrin
was suggested by Alexander and Hickson. Histamine infusion,
however, seemed to cause a classic parietal secretion, as
opposed to the mixed parietal and nonparietal response to
pentagastrin. These findings led to the formulation of the
hypothesis for this dissertation: In the equine gastric
xiii

cannula model, the vigorous sodium-rich component of
pentagastrin stimulated gastric contents is extragastric in
origin.
The testing of this hypothesis was accomplished by a
series of studies on horses with chronic gastric cannulae.
A full histamine dose-response study was necessary to
determine an optimal dose for the stimulation of maximal
acid output. Since this required pretreatment of the horses
with the H-l receptor antagonist, pyrilamine maleate, a
small study of the effect of this pretreatment on
pentagastrin-stimulated secretion was designed. A technique
was developed for the placement of an intraduodenal
h
/
ballooned catheter via the gastric cannula to occlude the
pylorus. A study was also performed to evaluate the effect
of the presence of the intraduodenal catheter. Finally, the
critical study involving a comparison of the gastric and
duodenal contents during histamine and pentagastrin
infusion, with and without obstruction of the pylorus, was
done.
Gastric contents were analyzed in each of the studies
for volume and electrolyte composition. The histamine-
induced maximal acid ouput was equivalent to that previously
xiv

reported for horses stimulated with pentagastrin.
Pyrilamine maleate dampened the gastric acid secretory-
response to pentagastrin infusion. The introduction of an
intraduodenal catheter did not alter the maximal acid output
to pentagstrin, although it may have enhanced the reflux of
duodenal fluid into the gastric lumen. Most importantly,
the obstruction of the pylorus with the balloon catheter
significantly decreased the sodium output in gastric
collections suggesting that the vigorous sodium-rich
component of pentagastrin stimulated secretion is primarily
of extragastric origin.
xv

CHAPTER 1
INTRODUCTION AND REVIEW OF LITERATURE
Introduction
The regulation of gastric secretion has long interested
scientists and clinicians due to the vital role gastric acid
secretion plays in the normal gastrointestinal function and
in certain pathologic conditions. The stomach, with both
endocrine and exocrine function, is not a simple collection
vat for food prior to digestion. A diverse group of cells
with numerous capabilities are found within the highly
specialized gastric mucosa.1 Parietal cells secrete acid at
the apical membranes containing the H+/K+ ATPase pump.2
Other cells are responsible for the production of mucus,
zymogens, and other biologically active peptides and
amines.1 Numerous endocrine cells secrete substances that
modulate various gastrointestinal functions.1 The secretion
of hydrochloric acid by the parietal cells is regulated by
neural, hormonal, and paracrine mechanisms which interact to
1

2
control the rate of secretion.1'3 Acetylcholine is the
primary neurotransmitter involved in gastric acid secretion.
Muscarinic nerve endings near the gastric glands release
acetylcholine as part of the vagal reflex system.3 Enteric
neurons in Meissner's plexus release GRP (gastrin releasing
peptide) which acts on G cells in the gastric antrum.
Gastrin is the peptide hormone released in response to
specific substrates within the gastric lumen and distension
of the antrum. Released by antral G cells, gastrin is an
important hormone which is involved in all phases of gastric
secretion and also exerts influence on DNA transcription and
cellular replication.1 Histamine acts directly on parietal
cells, as a paracrine substance, to stimulate gastric acid
secretion via H-2 receptors. Histamine originates from
enterochromaffin-like (ECL) cells present within the
mucosa, in response primarily to gastrin stimulation, with
modulation by numerous other substances.1
Historical Background
Understanding the mechanisms of gastric acid secretion
and the regulation of these mechanisms has required decades

3
of research by many eminent scientists using a wide array of
models and techniques. From the time of Pavlov and the
fistulated dogs until the "in vitro" cellular studies of
<
Hkanson et al., debate has raged around the regulation of
gastric acid secretion. Pavlov's work with fistulated
models confirmed that subjective observations of a link
between emotional status and digestive function were correct
and introduced the role of a central neural component of
gastric secretory regulation.4 Even today we use the term
"Pavlovian" when referring to the brain's input into a
function, such as the cephalic phase of gastric secretion.
Bayliss and Starling paved the way to investigation of
hormonal substances involved in gastrointestinal secretion.5
In 1906, Edkins suggested that a hormone "gastrin" was
released in the pyloric portion of the stomach and resulted
in the gastric phase of the acid secretory response.6 The
presence of this distinct secretagogue was demonstrated by
Komarov in 1938,7 and clarified in 1941 by Gregory and Ivy.8
Gregory and Tracy were able to isolate the substance in two
forms from pig antral mucosa and validate the hormonal
regulation of gastric secretion by gastrin in the 1960s.

4
Histamine was reported to stimulate the secretion
of gastric acid in the early 1920s. Then, in the late
1930s, Macintosh stated that vagal stimulation resulted in
histamine release within the gastric mucosa10; however,
controversy surrounded the role of histamine since known
antihistamine agents were unable to prevent acid
secretion.11 The identification of different subtypes of
histamine receptors by Black et al. in the 1970s and
subsequent studies with H-2 receptor antagonist clearly
demonstrated that histamine was an integral component in the
normal gastric secretory response.11-12 The complex
interworking of each of these components confused
investigators and resulted in conflicting studies. Only in
the 1970s, with studies focusing on "in vitro" cellular
preparations and technical advances in immunology and
histology, were scientists able to begin unravelling this
complex regulatory process. The enterochromaffin-like (ECL)
cell was the key to the combined action of acetylcholine,
gastrin, histamine and many other effectors.1 Though ECL
cells had been noticed in the early drawings and writings of
Heidenhain, their role in the secretory response was not
known.1 The demonstration by Hkanson et al.13 and Capella

5
et al.14 that the fundic ECL cells contained histamine,
began the explosion of new concepts in gastric secretory-
regulation which has led to better understanding of the
process.
Review of Literature
Today, it is apparent that gastric acid secretion by
parietal cells results from paracrine histamine released by
nearby ECL cells. The release of histamine is mediated by
many substances including gastrin, acetylcholine,
somatostatin, vasoactive intestinal peptide (VIP),
prostaglandins, calcitonin gene-related peptide, TGF-a, and
even histamine.1 Histamine acts on the basolateral membrane
of parietal cells at H-2 receptors.2,3 Stimulation of these
receptors activates the basolateral adenylate cyclase and
leads to increased intracellular cAMP within the parietal
cell.15 In contrast, parietal cell gastrin receptors and
muscarinic M3 receptors result in increased intracellular
Ca++ when stimulated.16 The increased cAMP and/or Ca++ may
activate protein kinases involved in the phosphorylation of
the apical H,K ATPase as occurs in Na,K ATPases.16
Several

6
cellular changes occur with activation of the secondary
messenger system within the parietal cell. The proton pump,
H,K ATPase, is present in the membrane of cytoplasmic
membrane compartments during the resting or unstimulated
state and, after stimulation within the membranes of
extensive apical canaliculi.16 The mechanics of this
transformation are not clearly understood. It is possible
that the cytoplasmic vesicles observed in the resting state
are connected to the apical membrane and that tubules simply
expand to expose the proton pump to the lumen of the gastric
glands. An alternative explanation is that activation of
the cell results in the fusion of cytoplasmic membranes with
the apical membrane.16
Another change occurring following stimulation of the
parietal cell is the activation and transformation of
parallel K and Cl channels, which provide the extracellular
K+ needed for the proton pump.16 The pump requires oxygen
as well as Mg++. The energy required by the proton pumps is
supplied as ATP by the large mitochondrial content in the
parietal cell.16 The proton pump transports H+into the
gastric gland in exchange for K+. In order to maintain
intracellular homeostasis, several membrane exchange

7
pathways are present within the membrane of the parietal
cell including C1/HC03 and Na/H exchangers.15 During
stimulation, the parietal cell secretes H+ actively via the
proton pump, Cl- passively via the Cl channel, and H20
passively into the gastric lumen.15 Parietal secretion of
HC1 provides a high concentration (-140 mEq/L) of acid
within the gastric glands that empty into the lumen of the
stomach.
Gastric secretion is commonly described as either basal
or stimulated. Basal secretion is also termed
interdigestive secretion and occurs without external
stimulation, such as ingestion of food, or conditioned
response.2-17 In terms of volume and acid content, basal
secretion varies greatly between species.17 A circadian
rhythm has been observed in human basal secretion with
higher rates during the evening and low rates in the
morning.2-3'17'18 The rate of basal secretion is independent
of serum gastrin concentration and is not abolished by
vagotomy.2'17
Stimulated gastric secretion is classically divided
into three phases, with some overlap between them. These
phases are commonly termed cephalic, gastric, and

8
intestinal.2-3'17'18 The link between the brain and gastric
function has been speculated about since the early 1800's.19
Sight, smell, taste, thought, and swallowing stimulate
gastric acid secretion during the cephalic phase.2-3'9'10 The
vagus nerve is the key link in the cephalic phase through
its stimulation of gastrin release as well as direct
innervation of the parietal cell.2'17'18 As mentioned, these
effects may be mediated through ECL cells rather than
directly through receptors on the parietal cell. Many
neurotransmitters and certain peptides have been shown to
act centrally on the regulation of acid secretion.19
Cholinergic agonists, prostaglandin inhibitors, GABAergic
agonists, gastrin/CCK, TRH-related peptides, and
somatostatin-related peptides administered into the CSF
stimulate gastric acid secretion. Inhibition occurs
following CSF injection of cholinergic antagonists,
adrenergic agonists, prostaglandins, serotonin, bombesin
like peptides, opioid peptides, CRF-like peptides, and
calcitonin-related peptides.19
The gastric phase of stimulated secretory response
is a result of gastric distension or chemical stimulation of
the gastric mucosa.2'3-17'18 This phase is mediated primarily

9
by gastrin. Distension of the stomach walls activates
stretch receptors involved in release of gastrin. However,
this release does not occur if the gastric contents are
i
acidic due to a pH-sensitive, oxyntopyloric reflex with
inhibition by somatostatin.2'17-18 Certain breakdown products
of food are strong stimulants of gastric acid secretion,
particularly peptides and amino acids, specifically,
phenylalanine and tryptophan.2-17'18 These stimulants induce
the release of gastrin by action at the apical microvilli of
G cells within the antral mucosa.17
The intestinal phase of acid secretion is
responsible for only a small portion of the total acid
secretory response.18 Stimulating agents are the same as
those involved in the gastric phase. The substances act
directly at G cells in the upper small intestine as a
gastrin-dependent mechanism and absorbed amino acids exert
their effect by a gastrin-independent mechanism.18 All
phases of acid secretion are, in part, mediated by gastrin,
through the release of histamine from ECL cells.1
The secretion of gastric acid follows the action of
histamine on H-2 receptors on the parietal cell. Inhibition
of histamine release allows the parietal cell to return to a

10
resting state. Acidification of the gastric contents
inhibits gastrin release by release of somatostatin from
antral D cells.18 The presence of acid, fat, or
i
hyperosmolar solutions within the small intestine inhibits
the acid secretory response through one or more of the
peptides such as secretin, peptide YY, neurotensin, VIP
(vasoactive intestinal peptide), GIP (gastric inhibitory
peptide), and enteroglucagon released by cells within the
small intestinal mucosa.17-18 These inhibitory substances
have receptors on the ECL cell and have been shown to
inhibit the release of histamine from these cells.1
Histamine also exerts negative feedback on ECL cells via H-l
and H-3 receptors.1 The rapid catabolism of histamine and
its speedy removal from the extracellular space surrounding
the parietal cell eliminates the stimulation of these cells
and terminates the secretory process.20
Many drugs have demonstrated antisecretory actions that
have been crucial in clarifying the mechanisms of acid
secretion and in treatment of pathologic conditions related
the secretion of gastric acid.21 Histamine H-2 receptor
antagonists are able to prevent gastrin, food, and vagal-
induced acid secretion. This finding was pivotal in the

11
determination of the central role of histamine in the
secretory response.22 As a result, numerous H-2 blockers
have become a mainstay in the treatment of peptic ulcers.21
Substituted benzimidazoles, such as omeprazole, have more
recently joined the battery of antiulcer medication due to
their inhibition of the H,K ATPase.21 Certain prostaglandin
E2 analogues also have an antisecretory effect, due to
actions at CNS as well as ECL cell level.1,21 Gastrin
receptor antagonists (ie. Proglumide) are also capable of
inhibiting acid secretion.21 The target of some presently
available drugs and many of the drugs of the future may not
be parietal cells directly, but other cells within the
gastric mucosa which act on the parietal cell.23
Accordingly, the increasing understanding of the role of the
ECL cell is likely to make it the target of investigational
agents for the regulation of acid secretion.
The gastric ECL cell is considered to be one of the
amine precursor uptake decarboxylation (APUD) series of
cells.1,24 Numerous endocrine cells are found scattered
within the gastric mucosa and may represent from 0.5% to 2%
of the cells present. The prevalence of ECL cells vary
among species, as they are particularly common in the rat

12
and appear in lesser numbers in the dog and primates.1-24
Other endocrine cells observed in the gastric mucosa include
enterochromaffin cells which produce 5-hydroxytryptamine
(serotonin), D cells that secrete somatostatin, gastrin-
producing G cells, and P and X cells which have unknown
functions.1 The ECL cells are found near parietal cells
within the gastric glands and have prominent cytoplasmic
extensions.1-24 They contain a large number of cytoplasmic
vesicles and electron-dense granules, and take up aromatic
amino acids and decarboxylate them. Histidine decarboxylase
(HDC) and histamine are also found within these cells.1,24
Histamine is concentrated into cytoplasmic vesicles by a V-
type ATPase which acts as a H+/histamine antiporter.1,22,24
As indicated above, the production and storage of histamine
by the ECL cell makes it the critical interface in the
regulation of gastric acid secretion.1,24 The primary
mediator of histamine release is gastrin acting through the
CCK-B receptor to increase cytosolic Ca++. 1,22,24 Histamine
release can also be stimulated by acetylcholine at
muscarinic Ml receptors, epinephrine through p adrenergic
receptors, isoproterenol, forskolin, interleukin ip and VIP,

13
and can be inhibited by somatostatin (subtype 2), TGF-a,
TGF-p, calcitonin gene-related peptide, and histamine via H-
1 and H-3 receptors. 1-22-24-25 It appears that there is
i
substantial neurotransmitter modulation of gastrin and its
regulation of histamine release from ECL cells.25 Although,
it is known that Ca++ acts as a secondary messenger within
the ECL cell, cAMP is likely to also play a role in the
release of histamine.1-22-24
In addition to stimulating the release of histamine,
gastrin regulates HOC activity and ECL cell
proliferation.1-24 It stimulates DNA synthesis by a pathway
distinct from that of histamine release, although both
processes appears to begin with the binding of gastrin at
the CCK-B receptors.1-24 Hypergastremia has been associated
with increased numbers of ECL cells and may play a
significant part in the development of gastric
carcinoids.1-24 The chronic use of antiulcer medication with
resultant hypergastremia have been shown to lead to ECL
hyperplasia and gastric mucosal hypertrophy. 1-22-24 The
recent advances in the "in vitro" cellular techniques have
expanded our knowledge of the regulation of the gastric
secretory response; however, as history shows us, advances

14
just open the door to a multitude of additional questions.
Although, much knowledge has been gained by isolated cell
work such as that with the ECL cell, the wide array of
species differences points to the continuing need for both
"in vivo" and "in vitro" studies.
Early classical studies were "in vivo," performed
primarily on animals with a variety of surgically prepared
pouches or fistulas. Even human studies in the early
1900's, were performed on subjects with gastric fistulas.19
Historically, experimental preps commonly utilized dogs and
cats with transplanted pouches or surgically isolated
stomachs.8-26'27 Over time, chronic gastric cannulas have
been placed in the stomachs of dogs, rats, rabbits, pigs,
cats, humans, and horses to allow studies to be performed on
conscious animals.5,28'31 Amphibian mucosa was the first
tissue used in the "in vitro" studies that provided the
cardinal information about the acid transporting ATPase.32
Subsequent cellular studies have been performed on canine,
equine, rabbit, and rat gastric glands. 22,32'36 Initially,
food and food extracts were selected to stimulate gastric
secretion, later histamine and alcohol were used in many
studies.8'26,27 Histamine continues to be a valuable

15
secretagogue for investigation of the acid secretory process
and its regulation.1'20'29'30 After Gregory and Tracy found
that an extract of porcine antral mucosa was an effective
stimulant of acid secretion9, gastrin became a popular
investigational tool.28 A synthetic polypeptide analog to
the C terminal tetrapeptide of gastrin is pentagastrin, or
peptavlon, which has become the secretagogue most commonly
used for stimulation of gastrin related secretion.17'19-21'30'31
Today, gastric secretory studies range from chronically
implanted gastric cannulas in intact animal models to
receptor immunochemical studies on ECL cells isolated from
the gastric mucosa.
The hundreds of studies of gastric acid secretion
have accumulated a vast amount of information with marked
similarities in the process and its regulation. However,
some striking differences have also been observed. The
relative sensitivity to specific secretagogue, the rate of
basal secretion, the response to inhibition, and ECL cell
shape and prevalence are markedly different between
species.17 In the rat, the gastric acid secretory process
is highly sensitive to pentagastrin and very resistant to
histamine.17-30 Histamine and gastrin are equally effective

16
on canine mucosa;1730 in rabbits histamine is much more
effective than gastrin.17-30 Basal secretion is minimal in
dogs and cats and high in rats and rabbits, whereas humans,
primates, pigs, and horses fall somewhere in between.17-28'31
Maximal acid outputs on a normalized bodyweight basis
induced by either histamine or pentagastrin, also differ
between species. Maximal histamine-stimulated output is
greater in rabbits than dogs, while in dogs it is greater
than that of rats, pigs, and cats, which in turn, have
rates of secretion markedly greater than that of primates
and man. 17-29-30 During pentagastrin-induced acid secretion,
rabbit and dog have a comparable maximal response, but that
of rats is significantly less.30 As with histamine, pig,
rat, and cat maximal acid secretory rates in response to
pentagastrin are comparable. 29-30-37-38 Maximal acid output is
used to determine the necessary dosage of either
secretagogue for the purpose of most experimental work;
however, the gastric contents collected during these studies
consist of fluid containing many electrolytes, pepsin, mucus
and other substances, as well as acid.
The electrolyte composition of gastric secretion other
than H+ also changes with the secretory rate. The secretory

17
pattern has been examined with both histamine and
pentagastrin in experimental models39'41 and in patients with
gastroduodenal diseases.42 In man, the infusion of either
histamine or pentagastrin results in similar changes in
gastric electrolyte concentrations and outputs. Sodium
concentration decreases and output remains constant, while
potassium concentration increases slightly and output
increases significantly. The concentration of calcium and
phosphate decreases and outputs are unchanged.39 Acid and
sodium concentrations have a strong inverse correlation
under these stimulatory conditions.39 The histamine-
stimulated maximal acid output in dogs is greater than that
of pentagastrin; however, peak acid output is reached more
quickly with pentagastrin than with histamine.41 Sodium ion
concentration is inverse to acid in the canine studies just
as in human studies.
Thus, gastric secretions are a combination of parietal
and nonparietal fluids. The parietal component is isotonic
HC1 that is secreted in response to specific secretagogues
at a rate that increases significantly with simulation of
the parietal cell.4 The nonparietal component is believed
to be a constantly secreted isotonic ultrafiltrate of

18
plasma.43 No change in nonparietal secretory rate is
observed during stimulation with any of the known gastric
secretagogues. Sodium ions are the predominate cation of
this nonparietal component. The differences in response to
secretagogues of these two components explains the inverse
relationship of sodium and acid concentrations reported
during increasing acid secretory rates.43
Various gastroduodenal diseases are characterized by
alterations in the electrolyte composition of gastric
contents.42 Patients with active duodenal ulcers have
increased acid and chloride concentration and decreased
sodium concentration, while gastric ulcer patients have
increased sodium concentrations in the gastric content
without changes in the concentrations of acid, potassium,
or chloride.42 Other changes in the composition of
electrolytes are suggestive of trophic gastric ulcers,
chronic gastritis, and Zollinger-Ellison syndrome.42 The
characteristic gastric secretory response to stimulated
gastric secretion has been consistently observed in all
species except the horse.44
Due to the relative difficulty in collecting the
contents, little was known about equine gastric secretion

19
until the 1980s. The apparent increase in gastric and
duodenal ulcer disease in horses provoked a particular
interest in equine gastric physiology.31-44 Gastric mucosal
4
ulceration has been observed in horses as a sequela to the
administration of nonsteroidal anti-inflammatory drugs, and
as a spontaneously occurring problem of unknown etiology.44'47
Intermittent aspiration of gastric contents via nasogastric
tube, placement of indwelling pH probes nasogastrically, and
chronic indwelling gastric cannulas to collect contents by
drainage have been used in recent studies of equine gastric
secretion. 31- 44-48'52 Only the cannula allows complete
collection of gastric contents, but these studies can only
be performed on fasted animals. Intermittent aspiration
also requires fasted horses, but may not collect gastric
contents in their entirety. The indwelling pH probe makes
it possible to monitor the intragastric environment for a
long periods of time in either fed or fasted states.
Basal secretion in horses has been described as
continuously variable, with periods of spontaneous
alkalinization as has also been observed in humans, pigs,
rodents, monkeys, and chickens. 31-44-48-50 Thus, the hydrogen
ion concentration and acid output range widely during

20
unstimulated gastric collection periods.31-44 The basal
equine acid output of approximately 30% of maximal output is
consistent with pigs and rats, and it is greater than that
of humans.44 On a body weight basis, equine basal acid
output over time is similar to that found in man.39-44
Up to now, pentagastrin has been the only
secretagogue used "in vivo" to stimulate equine gastric acid
secretion to characterize the species-specific responses and
to study drugs designed to prevent or treat gastric
ulcers. 48-49-51-S3-54 Its administration to horses results in a
significant increases in both gastric acid and sodium
outputs.44 Acid concentration increases after stimulation,
but not to the maximal magnitude observed in other species.
In addition, the increased sodium output during stimulation
is unique to horses. As the dose of pentagastrin is
increased, the concentration of sodium decreases slowly and
remains greater than the acid concentration, unlike in other
species where the sodium concentration rapidly decreases in
an inversely proportional relationship to the increasing
acid concentration.44 This is a major species-specific
difference in the equine secretory response to pentagastrin.
Thus, it has been suggested pentagastrin stimulates both the

21
parietal and nonparietal components of gastric secretion in
the horse.44 A variety of compounds have been shown to
inhibit equine basal and pentagastrin-stimulated gastric
acid secretion, such as histamine H-2 antagonist ranitidine,
the proton pump blocking agent omeprazole, and the
prostaglandin misoprostol.31'48'49'51'53,54 The profound sodium
rich nonparietal secretion characteristic of the equine
response to pentagastrin is evident even after omeprazole
has effectively inhibited the acid secretory response.51
The origin of this voluminous nonparietal component of
gastric contents has not been clearly defined.
The periods of high pH of gastric contents during basal
secretion have raised much speculation about the equine
gastric secretory capacity, gastric emptying rates, and the
buffering capacity of the various secretory products.50
Potential buffering fluids include saliva, gastric
nonparietal secretions, and duodenogastric reflux.44 Saliva
is not a likely candidate since the production of saliva in
the horse is minimal except during mastication.55 Fasting
equine gastric contents are frequently dark green to yellow
in color and viscous, suggesting possible contamination with
bile.44 Duodenogastric reflux has been observed during

22
endoscopic examination of the stomach.51 The fluid refluxed
could potentially contain a mixture of biliary, pancreatic
and duodenal secretions, since the duodenal diverticulum,
where the bile and minor pancreatic ducts enter, is in
relatively close proximity to the pylorus.51 Furthermore,
the absence of a gallbladder leads to continuous secretion
of bile in horses and equine pancreatic secretion is
reported to be profuse and continuous.55-56
Pancreatic secretion of the horse is distinct from that
of other species. The resting secretion of approximately 25
pl/g gland/min is increased by four to fivefold during
eating, stimulation of the vagus nerve, or after the
administration of secretin or pentagastrin.S5-57 Neither
resting nor vagal-induced pancreatic secretion is abolished
by atropine. 55-58 Vagotomy does not alter the basal
secretion. Studies with ponies fitted with re-entrant
cannula in the pancreatic duct found that they may secrete a
volume equivalent to up to 10% of their own body weight
daily.ss The concentration of amylase and the proteolytic
activity of equine pancreatic juice is particularly low, and
it has a very weak ability to emulsify fat, compared to
other species.55 Small increases in the concentration of

23
amylase are found during stimulation of the vagus, or during
secretin or pentagastrin administration. The concentration
of sodium and potassium are similar to respective plasma
concentrations and chloride is the predominate anion at all
levels of secretion. The bicarbonate concentration is low
relative to other species and does not increase to the
extent anticipated when the volume of secretion increases.55
That is, in most species, the concentration of bicarbonate
is less than chloride concentration at rest, but increases
to become the predominate anion during maximally stimulated
secretion.55 The composition of the large non-parietal
component of the fasting gastric contents is also similar to
that of equine pancreatic fluid. Therefore, the observed
species-specific particulars of equine pancreatic juice
contents might explain the voluminous fluid response
observed during pentagastrin-stimulated gastric collection.
The pancreas is a multifunctional organ which is
responsible for the secretion of fluid, electrolytes, and
enzymes essential to the normal digestive process and the
endocrine secretion of hormones critical to metabolic
homeostasis.59 Just as with gastric secretion, pancreatic
secretion has traditionally been divided into basal and

24
meal-induced patterns, with meal related secretion further
divided into cephalic, gastric, and intestinal phases.60 In
most species, basal enzyme secretion ranges from 10% to 30%
of maximal secretion, whereas, basal bicarbonate secretion
is only 1% to 2% of maximal.60 The regulation of basal
enzyme secretion appears to vary between species, while
basal bicarbonate secretion is dependent primarily on
secretin augmented by cholinergic neural input.60 Basal
enzyme secretion is almost entirely due to cholinergic
stimulation in the rat, whereas, in man, both CCK and
cholinergic stimulation mediate it. Brief bursts of
pancreatic enzyme and bicarbonate secretion are associated
with the migrating myoelectric complex and a circadian
rhythm has also been reported.60 The normal pancreatic
secretory response to a meal is increased enzymatic
secretion to aid digestion and increased bicarbonate
secretion to buffer the chyme and assure the optimum
intraluminal pH for enzymatic activity. As with gastric
secretion, "cephalic" pancreatic secretion seems to be
stimulated either directly or indirectly by the vagus
nerve.50 "Gastro-pancreatic reflexes" are initiated by food
or gastric distension and mediated by cholinergic vagovagal

25
reflex.50 The two classical pancreatic regulatory hormones,
cholecystokinin (CCK) and secretin, and vagal cholinergic
reflexes are involved in the "intestinal" phase.60
i
Postganglionic cholinergic neurons are important in the
regulation of enzyme and bicarbonate secretion by the
release of acetylcholine at muscarinic receptors. Secretin
is the most potent stimulant of the bicarbonate-rich fluid
component of exocrine pancreatic secretion in dogs, cats,
rats, and humans., while the primary hormonal stimulant of
enzyme secretion is CCK.59'60 In the rat, rabbit, pig and
guinea pig, CCK is responsible for a copious fluid and
electrolyte secretion which may have a low concentration of
bicarbonate and a high concentration of chloride.59 Enzyme
secretion is stimulated by the action of CCK at CCK-A
receptors on pancreatic acinar cells.61 Although CCK-
B/gastrin receptors have been identified on pancreatic
acinar cells, their function remains unknown.61 Caerulein
is even more potent than CCK, and both are significantly
more potent than gastrin, at stimulating pancreatic enzyme
and fluid secretion in dogs.62 A multitude of other
receptors are present on pancreatic acinar cells, including
those to bombesins, tachykinins, VIP, somatostatin, insulin,

26
endothelin, insulin-like growth factor and epidermal growth
factor.61 Much of the electrolyte secretion by the pancreas
is secreted by duct cells rather than acinar cells.63 The
electrolyte composition of pancreatic secretions vary with
the rate. Bicarbonate and chloride concentrations have a
reciprocal relationship, but the cumulative anion
concentration remains constant.63 As the secretory rate
increases, bicarbonate concentrations increase and chloride
concentrations decrease.63 The volume of the secretion in
response to secretin vary with species. Cats, dogs, pigs
and man have greater secretory rates per gram of gland than
rats and rabbits.63 The specific differences observed in
the limited studies on equine pancreatic secretion are
unique to the horse and similar secretory patterns have not
been reported in other species.
Development of Hypothesis
After reviewing the overwhelming information about
gastric secretory physiology in general, and equine gastric
secretion specifically, it is apparent that equine gastric
physiology requires still more investigation. The

27
development of a silastic indwelling gastric cannula by
Campbell-Thompson and Merritt for the collection of equine
gastric secretions was pivotal. The distinct composition of
equine gastric contents, particularly the uncharacteristic
"non-parietal" response to pentagastrin stimulation, is of
special interest. Since pentagastrin has been the only
exogenous secretagogue utilized to date in equine secretory
studies, it would be of interest to see if the horse
responded to other secretagogues in a similar way.
Therefore, the initial project for this series of studies
was to characterize the equine gastric secretory response to
histamine. Pilot studies were performed with moderate
trepidation due to the potential side effects of histamine
administration to horses. These studies required
pretreatment of the horses with a H-l antagonist, pyrilamine
maleate. The results of a small pilot study were the last
key to the development of a hypothesis for this
dissertation.
Histamine-stimulated equine gastric contents were
markedly different than those following pentagastrin
stimulation reported in previous studies. The mean acid
and sodium concentrations from the pilot study are presented

28
in Table 1. It was apparent from these studies that the
horse is capable of developing the "classical" parietal
response to an acid secretagogue that is comparable to that
of other monogastric species. During histamine stimulation,
the maximal acid concentration values were much greater than
those induced by pentagastrin, and sodium concentrations
decreased in the classical reciprocal relationship to acid.
The sodium output over various doses of histamine was
constant, unlike the pentagastrin responses. Yet, the
maximal acid output provoked by histamine was equivalent to
that of pentagastrin stimulated secretion. These pilot
findings made it evident that the stimulation of gastric
acid secretion with histamine could be safely performed in
horses, with certain precautions, and that well-designed
dose response study was needed. This led to the study
described in chapter 2. The predominant conclusion of early
investigation of histamine stimulation was that, as opposed
to pentagastrin, it induced a purely parietal gastric
secretion in horses.

Table 1.
Acid and Sodium Concentration during Histamine Infusion
(n=4 horses)
29
Histamine
Dose
pg/kg-hr
Mean [H+]
mEq/L
Mean [Na+]
mEq/L
Basal
26.5
101.3
15
73.9
57.8
30
95.1
55.5
45
97.5
52.4
In order to perform controlled comparisons between
histamine and pentagastrin, without potential extraneous
factors, it was necessary to evaluate the secretory response
to pentagastrin following pyrilamine maleate pretreatment.
Chapter 3 presents the unexpected results of that study.
Four crucial facets of equine gastric secretion were
considered to develop the dissertation hypothesis. First,
equine basal and pentagastrin-stimulated gastric secretion
has an uncharacteristically low concentration of acid and
high concentration and output of sodium. Second, acid
blockade with numerous agents does not eliminate the
profound sodium-rich nonparietal component of pentagastrin-
stimulated secretion. Third, Hickson and Alexander reported

30
that equine pancreatic water and electrolyte secretion is
profuse and continuous and can be stimulated by
pentagastrin. Finally, the stimulation of gastric secretion
with histamine resulted in purely parietal secretion
resembling that of other species. Therefore, the
dissertation hypothesis is as follows. In the equine
gastric cannula model, the vigorous sodium-rich component of
pentagastrin stimulated gastric contents is extragastric in
origin.
A technique of duodenal catheterization through the
chronic gastric cannula was developed to allow for occlusion
of the pylorus during acid secretory studies. Chapter 4
discusses the technique for duodenal catheterization, the
effect of the technique on gastric secretion, and the
composition of duodenal contents. The primary study of this
dissertation, describing results with and without the
obstruction of the pylorus, is presented in chapter 5 and
was designed to definitively determine if the sodium rich
fluid found during pentagastrin stimulation and absent
during histamine stimulation is secreted by the gastric
glandular mucosa or by a extragastric source.

CHAPTER 2
EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID SECRETION
Introduction
Previous studies of equine gastric physiology have all
utilized pentagastrin to stimulate gastric secretion.44'50'52
Increased recognition of clinical disease in horses due to
gastric and duodenal ulceration has led to interest in the
potential use of horses as a model for peptic ulcer disease
in humans as well as a desire to increase our knowledge
about horses, themselves. Gastric-ulceration has been shown
to be a widespread phenomenon in horses and foals.64
Compared to other species, pentagastrin-stimulated gastric
contents in horses differs by being relatively low in acid
concentration and high in sodium concentration, even at
maximal secretory responses.44 Nevertheless, the inhibition
of pentagastrin-stimulated gastric acid secretion has been
an important and effective means to evaluate therapeutic
potential of various anti-ulcer agents in this species.31-49
31

32
Histamine-2 receptor antagonists have been used successfully
to treat horses with clinical signs related to gastric
ulceration.64
In order to better characterize equine gastric
physiology, investigation of the effects of a secretagogue
other than pentagastrin is essential. Histamine seems the
obvious choice, but its use in horses has been avoided due
to the presumed equine respiratory and CNS hypersensitivity
to this agent. Ideally, "Histalog", a specific H-2 agonist,
might be used, but it is no longer available. In other
species, the undesirable side-effects of histamine have been
largely avoided by pretreatment with an H-l antagonist29,
and such a protocol was chosen for the studies described
herein. Specific objectives of the study were to: 1)
determine the dose of histamine needed to elicit a maximal
acid secretory response in the horse and how equidae compare
with other species, and; 2) see if the non-parietal
component of the secretory response to histamine is similar
to, or different from, that seen with pentagastrin
stimulation.

33
Materials and Methods
Six adult horses, both mares and geldings, were used.
All studies were done with the approval of the University of
Florida IACUC. The horses ranged from 2 to 20 years of age.
The five Thoroughbreds, and one Arabian weighed an average
of 484 kg (range 444-506 kg). All horses were free of
clinical signs of gastrointestinal disease, were dewormed
every 2 months and were vaccinated for encephalitis and
tetanus every 6 months. They were maintained on grass
pasture with coastal hay ad lib and 12% protein grain twice
daily. Each horse was previously prepared with a chronic
indwelling gastric cannula as described by Campbell-Thompson
and Merritt.31
The horses were fasted with free choice water for 20
hours prior to each experiment. At least one week interval
occurred between experiments on any given horse. Studies
were performed while the horse was loosely restrained in the
laboratory.
After placement of an indwelling jugular catheter, the
gastric cannula was opened and drained by gravity for 30

34
minutes allowing emptying of residual gastric contents.
During the experiments, gastric contents were collected in
15 minute aliquots. The volume was measured to the nearest
5 ml in a graduated cylinder. Samples were filtered through
gauze to remove feed particles and foam. The pH was
determined using a glass electrode (Radiometer, Copenhagen,
Denmark) calibrated at 20C using commercial buffer
solutions of pH 2 and 7 (pH standard, Fisher Scientific).
Hydrogen ion concentration was measured in duplicate by
electrometric titration with 0.IN NaOH to an endpoint of
7.4. (Radiometer, Copenhagen, Denmark) Sodium ion
concentration was measured by flame photometry
(Instrumentation Laboratories Inc.-, Lexington, MA) on
samples diluted in an internal standard lithium solution
(Dilumat, Fisher Scientific). The machine was calibrated
with known [Na*] / [K+] standards (Instrumentation
Laboratories Inc., Lexington, MA) prior to analysis and
after every 5 samples. Acid and sodium outputs were
calculated for each time period on a per kg body weight
basis.
The first three 15-minute time periods were during
basal (no treatment) gastric collections. At time t=45

35
minutes, pyrilamine malate ("Histavet-P", Schering-Plough,
NJ) was infused IV at 1 mg/kg over the entire 15 minute
collection period. No treatment was given during the
subsequent two collection periods (t=60-90 minutes).
Histamine infusion (7.5 |.ig/kg-hr) was begun at time t = 90
minutes and continued for 60 minutes. Two additional 60
minute infusions of histamine, of 15 ^g/kg-hr and 30
(ag/kg-hr respectively, followed. Therefore, the whole
experiment lasted for 4.5 hours.
Crystalline histamine (Sigma Chemical Co., St. Louis
Mo) was dissolved in 60 mis of 0.9% NaCl and filtered
through a 0.22 ^m cellulose nitrate filter (Corning, Corning
NY) in preparation for infusion, given by infusion pump.
(Harvard Apparatus, South Natick MA)
In a separate trial, the horses were maximally
stimulated with pentagastrin44 for collection of data for
comparison. The horses were prepared as described for
histamine trial. After two hours of basal collection,
pentagastrin was infused at 6 |^g/kg-hr for two hours.
Gastric collections were analyzed as during the histamine
trials.

36
Maximal acid output per histamine dose was calculated
from the last two 15-minute collections at each dose. Values
were expressed as f.iEq/kg BW/15 min. Results are presented
as mean and SEM for all parameters. Data were subjected to
one-way analysis of variance for repeated measures. A
significance value of p<_0.05 was selected. Pairwise multiple
comparison testing of significance was performed using
Student-Newman-Keuls test. Acid output vs. sodium output
data were subjected to linear regression for comparison to
respective pentagastrin-stimulated outputs from the same
horses.
Results
The horses used had been involved in gastric secretory
studies for at least one year prior to these studies. They
demonstrated no evidence of gastrointestinal disease or
problems related to the gastric cannula. Endoscopic
examination of the gastric and duodenal mucosa as a part of
another project in the laboratory revealed an occasional
Gastrophilus spp. larvae and healthy intact gastric squamous
and glandular mucosas.

37
Two horses did not complete the entire experiment. In
one experiment, the infusion had to be terminated after the
15 p.g/kg-hr histamine infusion period because the horse
developed marked muscle tremors and mild abdominal
contractions. After the infusion was stopped, the gastric
cannula closed and hand-feeding begun, the horse recovered
rapidly. Thirty minutes into the 30 pg/kg-hr infusion into
a second horse, it developed generalized muscle tremors and
mild synchronous diaphragmatic flutter. It became clinically
normal within 20 minutes of ending the experiment and being
allowed to eat.
Basal Secretion
Contents collected under pretreatment (basal)
conditions were generally yellow-tinged, viscid, and cloudy.
The 15-minute aliquots ranged in volume from 280 to 640 mis,
with a mean of 428.3 +34.1 mls/15 min. The mean acid
concentration was 42.5 + 3.9 mEq/L, and mean acid output was
3 9.8 + 6.6 p.Eq/kg BW/15 min with a range from 19.3 to
82.7 (.iEq/kg/15 min. The pH of the samples varied greatly
between 1.38 and 2.01, with a mean of 1.67 + 0.036. The mean
sodium concentration was 75.7 + 7.2 mEq/L, and mean sodium

38
output was 68.2 + 8.2 pEq/kg BW/15 min with a range from
17.7 to 101.7 jiEq/kg/15 min.
TABLE 2.
Data from Equine Gastric Contents Collected Before and After
Histamine Infusion.
BASAL
POST-
PYRIL
AMINE
7.5
(pg/kg-
hr)
15
(pg/kg-
hr)
30
(pg/kg-
hr)
Volume
(mis/
15 min)
428.3 +
34.1
356.7 +
37.3
591.7 +
41.4
a, b
591.7
28
a, b
508.9 +
54.8
a, b
PH
1.67
0.036
1.79 +
0.08
1.46
0.09
1.48 +
0.13
1.29 +
0.03
Peak
[H+]
(mEq/1)
42.5 +
3.9
33.5
3.5
72.2
3.9
a, b
81.3 +
5.1
a, b, c
82.9 +
6.8
a, b, c
PeakAcid
Output
(pEq/kg/
15min)
39.8 +
6.6
25.9
4.4
87.9
7.7
a, b
99.5 +
8.1
a, b, c
98.4 +
4.2
a, b, c
Peak
[Na+]
(mEq/1)
75.7 +
7.2
79.5
7.5
48.8
5.8
a, b
46.7
6.2
a, b
39.1 +
9.0
a, b
Peak Na
Output
(pEq/kg/
15min)
68.2 +
8.2
60.6 +
9.6
61.7
8.8
58.5 +
9.4
50.3
14.7
Values expressed as Mean + SEM
Pairwise Multiple Comparison procedure-Student-Newman-Keuls
a-significantly different (p<0.05) than basal
b-significantly different (p<0.05) than post-pyrilamine
c-significantly different (p<0.05) than 7.5 pg/kg-hr
Peak values derived from the final 30 minutes of each
treatment.

39
Pyrilamine Infusion
The volume of contents collected ranged from 70 to 550
mis, with a mean of 356.7 +37.3 mls/15 min and was not
significantly different than basal collections. The mean
acid concentration was 33.5 + 3.5 mEq/L, mean sodium
concentration was 79.5 + 7.5 mEq/L, and mean sodium output
was 60.6 + 9.6 ^Eq/kg BW/15 min. Acid output ranged from
3 to 55 j.iEq/kg BW/15 min, with a mean of
25.9 + 4.4 pEq/kg BW/15 min. These results were not
significantly different from the basal time periods.
Histamine dose-response
Gastric collections became progressively more clear as
acid concentration increased. During maximal histamine
stimulation, the contents were colorless and watery.
Volume
Maximal secretory volumes ranged from 360 to 850
ml/l5min. For each increasing dose of histamine, the mean
volume was 591.7, 591.7, and 508.9 ml/l5min, respectively.
The volume collected during each dose of histamine infusion
was significantly greater (pcO.0001) than basal volume;

40
however, the stimulated volumes did not differ significantly
among doses.
Acid Concentration
The mean acid concentration during basal and increasing
histamine infusion doses showed the expected vigorous
response to the treatments. Maximal acid concentration
(MAC) ranged from 51 to 110 mEq/L, and mean MAC was
significantly greater (p<0.0001) than basal acid
concentration at all doses. Acid concentration at all doses
was also significantly greater (p<0.05) than during the
post-pyrilamine period. The [H+] during the 7.5 pg/kg-hr
infusion was significantly lower (p<0.05) than during either
the 15 or 30 pg/kg-hr infusion. The MAC during 15 and
30 (ig/kg-hr infusions did not differ significantly.
Acid Output
Acid output (AO) for each treatment was calculated as
the mean of the final two 15 minute collections of each
infusion period. The individual highest AO was 155 |aEq/kg
BW/15 min occurring at t = 195 min during the 15 p.g/kg-hr
histamine infusion. The AO in response to all histamine
doses was significantly greater (p<0.0001) than basal

41
output, and was the greatest during the 15 pg/kg-hr
infusion. However, there was no significant difference
between the responses to 15 pg/kg-hr and 3 0 pg/kg-hr
infusions, whereas both the 15 and 30 pg/kg-hr infusion
resulted in an AO significantly greater (p<0.05) than that
from the 7.5 pg/kg-hr infusion.
Sodium concentration
The sodium concentration was inversely related to acid
concentration and ranged from 48.8 mEq/L to 39.1 mEq/L.
The mean sodium concentration was significantly less
(p=0.000119) during the 15 and 30 pg/kg-hr histamine
infusion than during the basal period. The 7.5 pg/kg-hr
infusion resulted in [Na+] significantly greater than either
the 15 or 30 pg/kg-hr infusion and not significantly
different from either basal or post-pyrilamine periods. The
concentration of Na* in collections during the 15 and
30 pg/kg-hr infusions did not differ significantly from one
another.

42
Sodium Output
Mean maximal sodium outputs decreased from 61.7 +
8.8 pEq/kg/15 min to 50.3 + 14.7 pEq/kg/15 min as the
histamine infusion rates increased from 7.5 (.ig/kg-hr to 30
pg/kg-hr. No significant differences were observed in the
sodium output during basal, post-pyrilamine or histamine-
stimulated collection periods.
Pentagastrin Outputs
The mean maximal acid output during pentagastrin
infusion was 91.8 + 3.5 pEq/kg/15 min. Corresponding mean
peak sodium output during the pentagastrin trial was 100.8 +
5.0 pEq/kg/15 min.
Discussion
As in other species, intravenous administration of
histamine base stimulated gastric acid secretion in horses
resulting in maximal acid outputs (MAO) comparable to those
of pentagastrin-stimulated horses. Infusions were performed
without serious complications. Pretreatment with pyrilamine

43
malate, a selective H-l receptor blocking agent11,
presumably eliminated any potential respiratory or
neurologic side-effects of histamine infusion.
Histamine-induced dyspnea results from bronchoconstriction
mediated by H-l receptors.11 Both H-l and H-2 receptors are
located in the central nervous system and horses are more
susceptible to pronounced excitation and anxiety than some
other species. The histamine provocation test for studies
of equine bronchial responsiveness requires sedation to
prevent apprehension and anxiety.65
Two experiments were not completed because the horses
developed synchronous diaphragmatic flutter (SDF) and muscle
twitches. It is our belief that this was due to metabolic
alkalosis with hypocalcemia and hypochloremia following
marked HC1 secretion.66 Changes in the ionization
potential during metabolic alkalosis alter the free to bound
calcium ratio and results in SDF.66 Once stimulation of
HC1 secretion ceased and the cannula was occluded, fluid and
electrolyte loss ended and the horses responded rapidly.
These individual horses were apparently hyper-responsive to
histamine, since the MAO was reached during the 7.5
M^j/kg-hr infusion in one horse and after the first 15

44
minutes of the 15 jxg/kg-hr infusion in the other. These
horses did not exhibit long-term effects following these
episodes, and subsequent histamine infusions were
administered to them without incident.
Antihistaminic agents, such as pyrilamine maleate,
specific to H-l receptors are not expected to have
antisecretory effects and are routinely used as part of the
histamine challenge of gastric secretion in humans.11 A
post-pyrilamine decrease in acid concentration and output
was consistently observed and could reflect receptor
cross-reaction or changes in blood flow to the gastric
mucosa, since both H-l and H-2 receptors are involved in
histamine effects on vasculature.11, H-l receptor blockade
may also affect the delivery of substances to the
basolateral membrane of parietal cells, since H-l receptors
are involved in the regulation of capillary permeability.11
The results indicate that a histamine dose of 30
|ig/kg-hr can be considered as that which will induce a
maximal gastric acid secretory response in the horse.(See
fig.l) In pilot studies for this trial, horses were infused
with 15, 30, and 45 }ig/kg-hr of histamine. However, some
of these horses exhibited signs of metabolic alkalosis

45
Figure 1. Mean acid output/15 min. during the last 30
minutes of each treatment. "Basal" indicates the status
prior to any treatment. "Pyrilamine" indicates the output
after treatment with pyrilamine malate (1 mg/kg IV) and
peak outputs during IV histamine infusion of 7.5, 15, and
30 (ag/kg-hr are indicated accordingly. Data are expressed
as mean + SEM.
during the 45 jag/kg-hr infusion; therefore, we elected not
to utilize this higher dose in this trial. Four horses
completed the pilot study and the MAO during the 4 5 |^g/kg-hr
infusion was not significantly different from the MAO during

46
30 ¡ig/kg-hr infusion in these horses. (unpublished results)
As with other species29-41, some individual horses were
maximally stimulated at lower doses, but there was no
"supramaximal depression"40-67 of the mean response seen when
the dose was increased from 15 to 3 0 jag/kg-hr. Thus, the
horse is apparently slightly more sensitive to histamine
than man, in which the infusion of 42 |ag/kg-hr results in
MAO(1); the pig and dog are more resistant, requiring
60 fig/kg-hr29 and 50 (ag/kg-hr24, respectively. The peak
secretory response to histamine in horses was more gradually
attained than the response to pentagastrin infusion.44 This
phenomenon has been previously reported in other species, as
well.41
Mean maximal acid output in horses induced by histamine
was similar to that seen in humans on mEq/kg basis.
Furthermore, the maximal responses to histamine and
pentagastrin are not significantly different in horses, as
was anticipated. Species differences in maximal acid output
and relative sensitivity to histamine and pentagastrin are
numerous.17-68 The majority of "in vivo" gastric secretory
studies have involved dogs, rats, and humans.69 Dogs have

47
minimal basal acid secretion, whereas humans and rats have
active, though erratic, basal secretion, as do horses.44
The maximal acid secretory response to histamine and
pentagastrin is equivalent in dogs and humans, while rats
are much more sensitive to pentagastrin than histamine.17
It appears that horses may be very comparable to humans "in
vivo," since they are equally responsive to both
secretagogues and have similar basal acid secretory
activity.(Table 3) "In vitro" studies of isolated parietal
cells have demonstrated species differences in sensitivity
to specific secretagogues. Canine parietal cells can be
stimulated by carbachol, gastrin, or histamine, with
carbachol being the most potent. Conversely, human and rat
parietal cells are strongly stimulated by histamine and only
weakly stimulated by gastrin and carbachol. The horse
appears to be more like the human and rat, since histamine
is the most effective secretagogue of isolated equine
parietal cells, followed by gastrin and carbachol.34

TABLE 3.
Acid and Sodium Concentrations
Histamine versus Pentagastrin
48
PARAMETER
EQUINE
Pentagastrin
(PG) *
HUMAN
PG or HI**
EQUINE
Histamine
(HI)
Basal
Max.
Stim.
Basal
Max.
Stim.
Basal
Max.
Stim.
[H+] mEq/L
21-45
35-57
10-40
70-120
28-45
75 120
[Na+] mEq/L
45-92
75-146
30-70
15-30
62-123
23-70
* from ref no.66
** from ref no.42
In this study, mean acid concentration during maximal
histamine stimulation was markedly greater than that
observed during maximal pentagastrin stimulation. Maximal
acid concentrations in other species have ranged from
100-140 mEq/L17-39, irrespective of stimulant. Individual
maximal acid concentrations in these horses ranged from
75-125 mEq/L during histamine infusion. In contrast, in
pentagastrin stimulated horses, the maximal acid
concentration rarely reached 75 mEq/L, which was reported44
to be a major difference between horses and other species.
Apparently,a nonparietal sodium rich fluid component of
gastric secretion was strongly stimulated by pentagastrin.

49
Sodium outputs increased coincident with acid outputs
during pentagastrin stimulation in horses44; whereas, in the
studies described here, sodium concentration decreased as
acid concentrations increased during histamine stimulation,
and the sodium output was constant as the acid output
increased to a maximal level.(fig.2) Thus, in the horse as
in other species, histamine appears to stimulate a purely
parietal secretion, with acid concentrations rising to
expected levels and a reciprocal decrease in sodium
concentration.39'41
Figure 2. Regression analysis of acid vs. sodium outputs
during pentagastrin (o) and histamine (A.) infusion.

50
The exact origin of the histamine which stimulates
parietal cells and the mechanisms involved in its release
have not been clearly documented in most species24, but it
<
is known to act via H-2 receptors on parietal cells as a
paracrine mediator.2-20 In rats, enterochromaffinlike (ECL)
cells are the major histamine source in the gastric mucosa
and gastrin has been shown to stimulate its release from
them. 22-24 Rabbit and human gastric mucosal preparations also
release histamine in response to gastrin but the cells
responsible have not been identified.22 Few ECL cells are
found in the normal human and canine mucosa; however, many
mast cells are observed and may serve as the histamine
source.24 Human patients with hypergastrinemia appear to
have increased numbers of ECL cells in their gastric
mucosa.24 The density of ECL cells in equine gastric mucosa
is greatest in the pyloric gland region.70 Fewer ECL cells
have been identified in the fundic gland mucosa and in the
proximal duodenum.
In this study, we determined that histamine can be used
as a stimulant of gastric acid secretion in horses.
Histamine stimulated mean maximal acid output was
comparable to that previously reported with pentagastrin.44

51
In contrast, the mean maximal acid concentration in response
to histamine was much greater than that observed during
maximal pentagastrin stimulation. These findings suggest
that in horses, histamine stimulates purely parietal
secretion, while pentagastrin stimulates the production of
gastric contents that appear to be both parietal and
nonparietal in origin.

CHAPTER 3
THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON
PENTAGASTRIN-STIMULATED EQUINE GASTRIC SECRETION
Introduction
The interaction between gastrin and histamine
receptors has long been controversial.1,2'3 The ability of
histamine receptor antagonists to eliminate pentagastrin-
stimulated gastric acid secretion supports the indirect
action of gastrin on parietal cells 21,31,37,48,49,51 53,54 This
inhibition of gastric secretion has been limited
specifically to histamine H-2 receptor antagonists. The
administration of antihistamines directed at H-l receptors
has not been shown to suppress acid production during
stimulation with various secretagogues, including
pentagastrin.11,29,71 Although differences in the relative
sensitivity to various secretagogues have been observed
between species, the characteristics of gastric contents
during maximal stimulation with histamine or pentagastrin
are similar, with the exception of the horse.
52

53
Equine gastric contents during maximal stimulation with
histamine have a high concentration of acid and low
concentration of sodium as is characteristic of parietal
secretion in other species,(see Chap. 2) whereas,
pentagastrin-stimulated equine gastric contents have a high
concentration of sodium and a relatively low acidity.44
Histamine stimulation of gastric secretion induces a maximal
acid outputs (MAO) equal to those of pentagastrin-stimulated
horses.(See Chap. 2) In horses, as in other species, it is
necessary to administer an H-l antagonist prior to
histamine infusion to prevent side-ef fects 11-29-6S During
gastric secretory studies on horses stimulated with
histamine, pretreatment with the H-l antagonist, pyrilamine
maleate, resulted in a short-lived decrease in basal
volume, acid concentration and acid output. (See Chap.2) The
effect of this pretreatment on pentagastrin-stimulated
gastric secretion is thus far unknown. Since we planned to
further investigate the species specific disparity in the
histamine and pentagastrin-stimulated secretory responses,
we designed this study to consider the effect of pyrilamine
maleate pretreatment on pentagastrin-stimulated gastric
secretion.

54
Materials and Methods
Horses
Two mixed breed, one Thoroughbred and one Arabian [2
mares, 2 geldings] ranging from 3 to 20 years were used in
this study. The horses were all healthy and ranged in
weight from 370 to 490 kg. They were maintained on grass
pasture and provided coastal hay ad lib and 12% protein
grain twice daily. All horses were dewormed every 2 months,
vaccinated for encephalomyelitis and tetanus every 6 months
and were free of clinical signs of gastrointestinal disease.
Chronic indwelling gastric cannulas as described by
Campbell-Thompson and Merritt31 had been prepared in these
horses 1 to 24 months prior to this study. All studies were
approved by the University of Florida IACUC.
Experimental preparation
Horses were fasted with free choice water for 20 hours
prior to an experiment. Experiments were performed with no
less than a one week interval between them. The horses were
loosely restrained in the laboratory for the entire

55
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes, while a indwelling
jugular catheter was emplaced. The gastric contents were
i
collected into 1L fluid bags suspended from a surcingle.
Experimental protocol
Gastric contents were collected in 15 minute aliquots
and were filtered through gauze prior to analysis.
Collections were measured for volume and if available, a 50
ml sample was saved for further analyses. Analyses were
performed either immediately or samples were frozen for
later analysis. Each experiment lasted 3 hours. During the
first 45 minutes [basal collection], no treatment was
given. In the treatment experiments, pyrilamine maleate
(Histavet-P, Schering-Plough NJ) was infused IV at 1 mg/kg
over a 15 minute period, beginning at time t=45min. No
additional treatments were given for 30 minutes. In the no
treatment experiments, basal collection was continued during
time t=45-90 min. At time t=90min, an IV infusion of
pentagastrin [6 pg/kg-hr] was administered by infusion pump

56
(Harvard Apparatus, South Natick MA) in all experiments and
continued for the remainder of the experiment.
Each infusion was given in a volume of 60 ml/hr.
Horses were weighed the morning of the experiment to
determine the amount of pentagastrin needed. Pentagastrin
was prepared by dissolving with 0.8 ml of DMSO and 90 mis of
0.9% NaCl and filtered through a 0.22 pm cellulose nitrate
filter (Corning, Corning NY) in preparation for infusion.
Sample analysis
Volume was measured in a graduated cylinder. Aliquots
of gastric contents were analyzed immediately for hydrogen
ion concentration, using a automatic titrator (Radiometer,
Copenhagen Denmark). Hydrogen ion concentration of each
aliquot was measured in duplicate by titration with 0.IN
NaOH to an endpoint of pH of 7.4. Output was calculated on
a per kg body weight basis from the volume and hydrogen ion
concentration and was expressed as j.iEq/kg/15 min.

57
Analysis of data
Statistical analysis was performed on volume, acid
concentration, and acid output data. The last 30 minutes
of basal (t=30&45 min), post-pyrilamine (t=75&90 min), and
two infusion-related collections (early: t=105,120&135 min;
late: t=150,165&180 min) were compared between the studies
with and without pyrilamine pretreatment. Since the same
horses were used in each study, a paired t-test was
performed for each of the four time periods. The time
periods were not compared to each other. A p< 0.05 was
considered significant.
Results
In both studies, the volume and acid output rapidly
increased after pentagastrin infusion began. The horses had
no adverse reactions during or following the administration
of pyrilamine maleate. Physical characteristics of the
gastric collections from both studies were the same. The
mean and SEMs for each time period of both studies are shown
in Table 4.

58
Basal Collections
The volume, acid concentration, and acid output during
the basal time period of both studies did not differ
significantly.
Post-Pyrilamine Collections
In the pyrilamine study, the volume collected during
the 30 minutes following the administration of pyrilamine
was significantly less (p=0.0145) than when no pyrilamine
was given. The acid concentration did not differ between
studies. The acid output was significantly less (p=0.0008)
in the pyrilamine study than when no pyrilamine was given.
Early Infusion Collections
The volume and acid concentration did not differ
significantly between the studies, however, the acid output
was significantly less (p=0.0274) in the pyrilamine studies
than when no pyrilamine was given.

59
TABLE 4.
Mean and SEM Data from Gastric Contents Collected Before and
After Pentagastrin Infusion with and without Pretreatment
with Pyrilamine Maleate.
PYRIL-
BASAL
POST-
EARLY
LATE
AMINE
PYRIL-
INFUSION
INFUSION
AMINE


VOLUME
NO
253.8 +
381.7 +
585.8 +
622.5 +
(ml)
37.2
29.9
74.9
43.7
YES
287.5
181.7
415 +
589.2 +
27.95
34.8
102.2
71.0
[H+]
NO
31.14 +
39.7
31.2 +
48.0 +
(mEq/L)
9.54
11.0
5.5
5.6
YES
39.5 +
31.7 +
36.4 +
51.6 +
6.1
7.0
9.0
8.2
ACID
NO
18.1
34.1 +
46.4 +
76.8 +
OUTPUT
5.2
7.5
5.8
5.6
(fiEq/kg-15
min)
YES
24.5
3.9
12.4 +
2.5'
26.7 +
6.0
56.5 +
4.0
* First half of Pentagastrin Infusion (t=105,120,&135 min)
** Last half of Pentagastrin Infusion (t=150,165,&180 min)
Significantly Less than during No Pyrilamine Study
Late Infusion Collections
As during early infusions, the volume and acid
concentration were not significantly different between the
two studies. Acid output was significantly greater
(p=0.0031) in the study with no pyrilamine pretreatment.

60
Discussion
Pentagastrin infusion resulted in secretion of gastric
acid in both studies; however, the maximal acid output was
affected by the administration of pyrilamine maleate. This
finding was unexpected since pyrilamine pretreatment has
been used as the pretreatment of choice when performing
histamine stimulation in other species;11 where the use of
an H-l specific receptor antagonist does not affect the
secretion of gastric acid during stimulation. In part, the
confusion over whether or not histamine acts directly on
gastric mucosa resulted from early classical studies in
which antihistamines were found to have no inhibitory effect
on histamine induced gastric secretion.27 Better
understanding of histamine receptor classes has helped to
clarify the role of histamine in gastric secretion and
explain these earlier findings,11-12 namely that parietal
cells have H-2 receptors and histamine stimulated gastric
acid secretion appears to be a H-2 specific response.1-2'3'68-69
Histamine receptors are involved in other aspects of
gastric function as well as acid secretion. Three specific
receptor types, H-l, H-2, and H-3 have, to date, been

61
recognized. As well as regulation of acid secretion, these
receptors also play a role in the regulation of gastric
microcirculation and motility.11 Mucosal circulation is
affected by histamine primarily via H-l receptors, although
H-2 and H-3 receptors may be involved. In the rat, for
instance, it appears that both H-l and H-2 receptors are
involved in histamine related vasodilation.72
Vasoconstriction occurs with H-l receptor stimulation in the
rabbit. 72-73 Pyrilamine has been shown to competitively
inhibit histamine related vasodilation in the guinea pig.73
The changes, if any, in equine gastric circulation in
response to histamine or histamine blocking agents are not
known.
The importance of gastric mucosal circulation in the
horse may be most clearly demonstrated by the relative
sensitivity of the horse to gastric ulceration due to
NSAIDs, though no specific studies have quantified equine
gastric mucosal blood flow or the regulation of flow. The
administration of NSAID1s results in gastric ulceration by
inhibition of prostaglandins involved in mucosal blood flow
and cytoprotection.47 Gastrointestinal injury can be seen
endoscopically in horses with or without accompanying

62
clinical signs within a few days of initiation of
administration of even the recommended dose of
phenylbutazone or flunixin meglumine.47 Gastric
microcirculation is a key component of gastric mucosal
protection72 and can be rate-limiting for gastric
secretion.74
Secretagogues involved in stimulating gastric acid
secretion result in increases in blood flow as well.
Histamine, gastrin, and cholinergic agents produce
vasodilator activity associated with the increasing
secretory rate.75 Blood flow has been shown to be rate-
limiting at high levels of stimulation and agents which
decrease blood flow will also inhibit acid secretion.75 A
histamine H-2 antagonist, such cimetidine, has been shown to
decrease blood flow and acid secretion during pentagastrin
stimulation in cats, however, mucosal blood flow was not
decreased under basal conditions. 37,72 Although secretion is
increased by pentagastrin stimulation in this study, the
secretory response may be restricted by limitations on blood
flow.
Histamine H-l receptor antagonists may affect gastric
microcirculation by action at histamine receptors or by

63
atropine-like activity at muscarinic receptors11-76 involved
in vasodilation. In dogs, the cholinolytic properties of
pipolphen, a H-l blocker, have been shown to suppress
I
gastric secretions.77 Agonist to H-3 receptors78'80 and
antagonist of the H-2 receptor11-12-31'78 result in decreased
acid secretion. Pyrilamine has been utilized in numerous
secretion studies and in most species does not elicit this
antisecretory response. 81-82-83 In other equine studies ,
pyrilamine maleate administration was followed by a decrease
in basal secretion, but this decrease was not always
significant.(See Chap. 4 & 5)
Histamine H-3 receptors are found in several locations
including the brain, perivascular nerve terminals, pulmonary
airways, and ECL cells in the gastric mucosa. 36-84 These
receptors appear to be involved in the autoregulation of
histamine release from ECL cells during the stimulation of
gastric acid secretion. 1-24-36-79-80 They may also be involved
in the release of somatostatin which inhibits gastric acid
secretion.78 Certain drugs have demonstrated simultaneous
H-l agonist/H-3 antagonist properties,85 however, it appears
that pyrilamine has a low affinity for H-2 and H-3

64
receptors.86 The distribution of H-l, H-2, and H-3
receptors in the horse has not been documented.
Basal Pretreatment Early Late
Time Block
Figure 3 Mean pentagastrin stimulated acid output with and
without pyrilamine pretreatment. "Basal" refers to acid
output prior to any treatment.(t=30&45 min) "Pretreatment"
indicates output after pretreatment with pyrilamine or from
comparable period with no treatment.(t=75&90 min) "Early"
represents the first half of pentagastrin infusion.
(t=105,120&135 min) Output during the last half of
pentagastrin infusion is labeled "late".(t=150,165&180 min)
In this study, maximal pentagastrin-stimulated acid
output was significantly decreased in horses that received

65
pyrilamine prior to stimulation. This finding is contrary
to the results in other species where H-l receptor
antagonist do not inhibit gastric acid secretion. Because
the precise mechanism for this action is not clear, it is
apparent that this may be yet another important equine
specific finding that warrants further investigation.
Therefore, equine gastric secretion in response to
pentagastrin differs not only in composition from the
classical parietal response of other species and the
histamine response in the horse (See Chap.2), but also by
the ability of pyrilamine to inhibit a maximal acid
response.

CHAPTER 4
PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL CONTENTS
IN HORSES WITH CHRONIC GASTRIC CANNULAS AND ITS EFFECT ON
GASTRIC SECRETION
Introduction
The contents of various parts of the gastrointestinal
system differ in chemical and physical characteristics
between location and species. Much of the normal
gastrointestinal function of the individual species relates
to the anatomy of their alimentary system and the type of
diet which they consume. Increasing our understanding the
normal function is often complicated by those same
differences. Equine gastric secretion and the composition
of the contents under various conditions have been studied
by numerous investigators utilizing several
techniques.31'44'48-54 The development of a chronic gastric
cannula31 for collection of gastric contents has added
greatly to the knowledge regarding equine gastric
physiology.
66

67
Study of the function of the equine proximal duodenum,
biliary system, and pancreas has been even more difficult
due to an anatomical location which strictly limits surgical
exposure.87'88 Up to now, attempts to study the proximal
duodenum and associated structures have met with serious
difficulties and been basically unsuccessful in providing
additional information on the physiology of this region.
The reflux of duodenal contents into the empty equine
stomach has been observed during endoscopic gastric
examination even when there is no evidence of underlying
pathology.50'51 The importance, frequency and volume of
reflux have not been evaluated. Nor has the composition of
the duodenal contents which are mixing with the gastric
contents been fully analyzed. Reflux of large volumes of
small intestinal contents into the stomach is reported
during various disease conditions such as anterior enteritis
and small intestinal obstruction.89,90
The presence of chronic indwelling gastric cannulas in
research horses has made access to the duodenum much easier
for investigator and animal. This study describes how, with
the aid of an endoscope passed up through a gastric cannula,
a catheter can be placed into the equine duodenum for the

68
collection of fluid. The two objectives of this study were
to determine the composition of the duodenal fluid and
whether the presence of the catheter passing into the
duodenum had an effect on the gastric contents collected
from the cannula before and during stimulation of secretion
with pentagastrin.
Materials and Methods
Horses
Five Thoroughbreds(TB) two mixed breed (MB) horses,
and one Arabian (AR) [3 mares, 5 geldings] between 3 and
20 years in age, were used in these studies.(TABLE 5) For
TABLE 5.
Horses used in Gastric Collection Studies.
ID
AGE
BREED
SEX
B
5
y
ARAB
G
D
7
Y
TB
G
E
20
Y
TB
M
H
5
Y
TB
G
I
6
Y
TB
M
J
3
Y
MIXED
G
M
7
Y
MIXED
M
T
5
Y
TB
G

69
both catheter studies, six of the horses (5TB,1AR) were
selected. The no catheter/pentagastrin study was performed
on four (2MB,1AR,1TB) horses. Two horses (1TB,1AR) were
involved in both studies.(TABLE 6) The horses were all
healthy and ranged in weight from 430 to 510 kg. They were
maintained on grass pasture and provided coastal hay ad lib
and 12% protein grain twice daily. All horses were dewormed
every 2 months, vaccinated for encephalomyelitis/tetanus
every 6 months and were free of clinical signs of
gastrointestinal disease. A chronic indwelling gastric
cannula as described by Campbell-Thompson and Merritt31 had
TABLE 6.
Descriptions and Abbreviations for Each Study.
EXPERIMENT
INFUSION
CATHETER
HORSES USED
ABBREVIATION
(secretagogue)
(via cannula)
PG/NOC
Pentagastrin
None
B, E, J, M
PG/CATH
Pentagastrin
Intraduodenal
B, D, E,H,I,T
been prepared
in these horses
1 to 24 months
prior to this
study. All studies were approved by the University of
Florida IACUC.

70
Experimental preparation
Experiments were performed with no less than a one
week interval between them. The horses were fasted with
free choice water for 20 hours prior to an experiment. They
were loosely restrained in the laboratory for the entire
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes while a indwelling
jugular catheter was emplaced. For the catheter studies, a
video endoscope (WelchAllyn, Skaneateles Fall, NY) was
inserted through the gastric cannula into the stomach and
steered into the duodenum to a point approximately 30 cm
past the area of the duodenal diverticulum. A 4.5m long
stylet was threaded through the biopsy port of the endoscope
until it was seen passing from the distal end of the scope.
The endoscope was slowly withdrawn as the stylet was
threaded through the biopsy port, watching that it stayed in
place as the scope was removed. The distance from the
pylorus to the end of the gastric cannula was noted. The
presence of the stylet passing through the pylorus was
visually confirmed prior to removing the endoscope from the
cannula. The stylet was marked at the end of the cannula,
after which a specially modified stallion urinary catheter

71
(see below) was passed over it. The mark on the stylet was
used to assure that it remained in position as the catheter
was introduced through the cannula into the stomach, then
through the pylorus and into the duodenum. The stylet was
left in place until catheter placement was believed to be
complete. The completed setup (fig. 4) resulted in the
Figure 4 Cross sectional view of duodenal catheter passing
through the gastric cannula into the stomach and entering
the proximal duodenum.

72
ability to collect gastric contents from the cannula and
duodenal contents from the catheter into separate
containers. The fluids were collected into 1L fluid bags
suspended from a surcingle. The cannula and catheter were
both allowed to drain by gravity for 15 minutes after
completion of catheter placement. In the studies where
there was no intraduodenal catheter (NOC) in place, gastric
contents only were collected by gravity into 1L fluid bags.
Catheter Design
The specialized catheter was fashioned from a 137 cm
stallion urinary catheter(Jorgensen Laboratories, Inc.,
Loveland, Co), (fig.5) It's end was opened to allow free
passage of the stylet and several additional 5mm side holes
were placed in the 15cm closest to the tip. It was
distinctly marked at 20 cm from the tip and this mark was
considered the "0cm" mark. Additional marks were made
every 5cm markings from that point to the end. To fix the
catheter in position, a 10cm section of silastic tubing
[16mm I.D.] was placed over a 5cm section of the barrel of a
12ml syringe (Monoject, St. Louis, MO.) and the catheter

73
passed tightly through the wall of the silastic tubing into
the lumen and out through the syringe barrel lumen.
Figure 5 Specialized catheter for collection of duodenal
contents. The bold mark is signified by and is located
20 cm from tip. Multiple fenestrations within that 20 cm
region of the catheter.
One end of the syringe barrel locked into the end of the
silastic gastric cannula and the other was attached to the
short segment of silastic tubing which locked the catheter
in a fixed position. The long stylet was made by joining
together 3 stylets provided with stallion catheters. The

74
catheter was passed until the bold mark [Ocm] was 5cm aborad
to the pylorus.
Experimental protocol
Gastric (in all studies) and duodenal contents (only in
the "catheter" studies [CATH]) were collected in 15 minute
aliquots. Gastric samples were filtered through gauze prior
to analysis. Volume of both gastric and duodenal
collections was measured and, if available, a 50 ml sample
was saved for sample analyses. Analyses were performed
either immediately or samples were frozen for later
analysis. Each experiment lasted 3 hours. During the first
45 minutes [basal collection], no treatment was given.
Beginning at time t=45min, pyrilamine maleate (Histavet-P,
Schering-Plough NJ) was infused IV at 1 mg/kg over a 15
minute period. No additional treatments were given for 30
minutes. At time t=90min, an IV infusion of pentagastrin
[6 pg/kg-hr] was administered by infusion pump (Harvard
Apparatus, South Natick MA) and continued for the remainder
of the experiment. At the conclusion of the catheter

75
experiments, the catheter position was rechecked before the
catheter was withdrawn, and the cannula closed.
Each infusion was given in a volume of 60 mls/hr.
Crystalline pentagastrin (Sigma Chemical Co., St. Louis MO)
was prepared by dissolving with 0.8 ml of DMSO and 90 mis of
0.9% NaCl before filtering through a 0.22 pm cellulose
nitrate filter (Corning, Corning NY) in preparation for
infusion.
Sample analysis
Gastric and duodenal sample volume was measured in a
graduated cylinder and then an aliquot was analyzed
immediately for chloride ion concentration. Gastric samples
were also analyzed immediately for hydrogen ion
concentration. Duodenal samples were kept in an ice bath
until they were analyzed for bicarbonate ion concentration.
Both gastric and duodenal samples were frozen for later
measurement of sodium and potassium ion concentration.
Using a automatic titrator (Radiometer, Copenhagen
Denmark), hydrogen ion concentration was measured in
duplicate by titration with 0.IN NaOH to an endpoint of 7.4.

76
Chloride ion concentration was measured in duplicate by a
digital chloridometer (Buchler Instruments Div., Nuclear
Chicago, Fort Lee NJ) with acid reagent (Labconco, Kansas
City, Mo). Chloride standard (Labconco, Kansas City, Mo)
was used to calibrate the machine prior to each experiment
and after every 20 tests. Bicarbonate ion concentration was
determined by back-titration method of Isenberg et al.91
with the automatic titrator (Radiometer, Copenhagen Denmark)
using 0.IN NaOH to titrate to an endpoint of 8.4. Sample
solutions were gassed with nitrogen washed in barium
hydroxide to remove carbon dioxide prior to and during the
titration and were analyzed in triplicate. Standard
solutions prepared in laboratory were measured in
quadruplicate prior to each experiment. Sodium and
potassium ion concentration were measured by flame
photometry (Instrumentation Laboratories Inc., Lexington MA)
on samples which had been frozen at -20C. Samples were
thawed to room temperature, and diluted in an internal
standard lithium solution (Dilumat, Fisher Scientific). The
machine was calibrated with known [Na+] / [K+] standards
(Instrumentation Laboratories Inc., Lexington MA) prior to
any analyses and after every 5 samples.

77
Analysis of data
For the purpose of this paper, duodenal contents were
analyzed to determine electrolyte concentration ranges, but
these data were not statistically evaluated. Statistical
analysis was performed on volume, acid concentration, acid
output, sodium concentration, and sodium output from the
gastric samples. Output was calculated on a per kg body
weight basis from the volume and hydrogen or sodium ion
concentration and was expressed as |.iEq/kg-15min. The last
30 minutes of basal collections, post-pyrilamine
collections, and the first and last 30 minutes of infusion-
related collections were compared between studies. A
two-way ANOVA was performed for factors of time (basal,
post-pyrilamine, early infusion, and late infusion), and
duodenal catheter (yes or no) and interactions of these
factors. A p<0.05 was considered significant and all
pairwise multiple comparisons by Tukey test were performed.

78
Results
Gastric Contents
Volume.(Table 7) The volume of gastric collection
differed significantly (p<0.01) between the designated time
blocks. The volume was significantly greater (p<0.05)
during the late infusion block than during all other blocks.
The early infusion volume was significantly greater (p<0.05)
than the post-pyrilamine volume, but did not differ
significantly from the basal volumes. The basal and post-
pyrilamine volumes did not differ significantly. The
volumes collected during the CATH study were significantly
(p<0.01) greater than during the NOC study. There was no
significant interaction between time blocks and catheter
status.
Acid Concentration,(Table 7) Acid concentration varied
significantly (p=0.001) among the time blocks with a
significantly higher (p<0.05) concentration during late
infusion. The [H+] was not significantly different between
basal, post-pyrilamine and early infusion blocks. The NOC
study had a significantly (p=0.016) higher concentration of

79
acid than the CATH study. No significant interactions were
found between time blocks and catheter.
TABLE 7.
Data from Study With and Without Duodenal Catheter During
Pentagastrin Stimulation (Mean and SEM's)
STUDY
BASAL
PYRILAMINE
EARLY
LATE
VOLUME
(ml/15
min)
NOC
287.5
28.0
171.3 +
27.0
405.0
125.4
568.8 +
83.4
CATH*
541.7
29.7
396.6 +
32.1
653.3 +
66.0
885.8 +
26.7
[H+]
(mEq/L)
NOC**
39.5 +
6.1
32.3 5.2
31.9 +
10.0
52.4 +
9.4
CATH
26.5
4.1
28.9 3.3
20.4 +
3.7
42.4 +
2.2
ACID
OUTPUT
(|iEq/kg-
15min)
NOC
24.5 +
3.9
12.1 + 1.9
22.5 +
6.5
57.4 +
3.8
CATH*
31.9
6.2
24.9 + 3.7
30.2 +
6.8
80.2 +
4.9
[Na+]
(mEq/L)
NOC
106.1 +
6.1
110.8 +
5.7
108.3 +
10.0
93.4 +
8.2
CATH
106.8 +
6.0
104.4 +
3.3
107.4 +
4.2
88.2 +
3.3
NA
OUTPUT
((.lEq/kg-
15min)
NOC
72.5
10.0
44.8 + 8.5
107.3 +
40.0
133.8 +
29.2
CATH*
122.1 +
8.4
88.0 + 8.0
146.4 +
13.6
167.5 +
9.9
* Significantly greater than NOC
** Significantly greater than CATH
Significantly greater than all other time blocks
Significantly greater than post-pyrilamine time block
Significantly less than all other time blocks
Significantly greater than basal & post-pyrilamine time
blocks

80
Acid Output. (Table 7) The output of acid decreased
after the pyrilamine infusion and increased during
pentagastrin infusion. These changes in acid output over
time differed significantly (p<0.001). Acid output (AO) was
significantly greater (p<0.05) during late infusion than
during all other periods, however, the differences between
outputs during each of the other times did not differ
significantly. The AO was significantly greater (p=0.001)
during the CATH study than the NOC study.
Sodium Concentration. (Table 7) The [Na+] was
relatively constant until the late infusion block during
which time the concentration decreased significantly
(p=0.01). There was no significant difference in the
concentration between CATH and NOC studies.
Sodium Output.(Table 7) There was a significant
(pcO.OOl) effect of time on sodium output. The output
during late infusion was significantly greater (p<0.05) than
during basal or post-pyrilamine periods, but not
significantly greater than during the early infusion period.
Early infusion sodium output was also significantly greater
than post-pyrilamine, though it was not significantly

81
greater than the basal output. The output during the CATH
study was significantly greater (p=0.001) than during the
NOC study.
Duodenal Contents
Duodenal fluid was generally thick and mucoid and
tended to be dark yellow to green, in color. The
bicarbonate ion concentration ranged between 19-40 mEq/L;
TABLE 8.
Electrolyte Composition of Fluid from Duodenal Catheter
During Basal, Post-Pyrilamine, and Pentagastrin Infusion
Collection Periods. [Mean + SEM]
DUODENAL
BASAL
PYRILAMINE
INFUSION
[hco3]
(mEq/L)
23.2 + 2.6
16.2 + 1.5
33.0 + 2.3
[Na+]
(mEq/L)
147.5 3.9
151.5 6.7
144.9 + 2.4
[K+]
(mEq/L)
4.5 0.2
4.4 + 0.3
3.6 + 0.1
[Cl']
(mEq/L)
118.1 5.5
119.6 + 5.2
115.1 6.1
it decreased noticeably in the post-pyrilamine collections
and was increased during pentagastrin infusion. The fluid
had a high concentration of sodium (120-190 mEq/L) and low
concentration of potassium (2.4-5.5 mEq/L) compared to that
of gastric contents, in which the [Na+] ranged between 25-

82
125 mEq/L and [K+] between 6-20 mEq/L. Chloride ion
concentrations were in the range of 95-160 mEq/L, whereas
the gastric contents had [Cl'] ranging from 130 to 180
mEq/L. The mean concentrations of sodium, potassium, and
chloride were consistent throughout the experiment.
Discussion
The placement of a duodenal catheter through the
gastric cannula required variable amounts of manipulation of
the videoendoscope. The time required for introduction of
the video endoscope into the duodenum and passage of the
stylet and threading of the catheter ranged from 10 to 25
minutes. The differences related in position of the pylorus
relative to the cannula and the dexterity of the
investigator on that day. The horses did not appear to be
bothered by the process nor by the presence of the catheter
during the experiments. Catheter experiments proceeded as
the no catheter experiments did. Gastric contents were
easily collected from the cannula even with the catheter in
place. During some time periods, no fluid was collected
from the duodenal catheter. However, this did not indicate

83
blockage as fluid was collected during the next time period
as patency was checked injection of air through the
catheter.
In the catheter experiments, gastric contents had
significantly greater volume, acid output, and sodium output
as well as a significantly lower [H+] The presence of the
catheter passing through the pylorus may have allowed
additional fluid reflux from the duodenum into the stomach.
This may have occurred due to capillary action along the
catheter or by preventing complete closure of the pylorus.
The duodenal fluid had a high concentration of sodium and
reflux of this fluid may account for increased sodium output
and volume of gastric contents in CATH experiments. The
acid response to pentagastrin with the duodenal catheter was
similar to previous studies in the horse;31'44 however, during
pentagastrin stimulation, the gastric contents [H+] in the
CATH study was less than in the NOC study. We suggest that
this may have been due to dilution of the gastric
secretions by the fluid refluxing from the duodenum around
the catheter.
The increased acid output observed in the CATH study
was not related to the reflux of duodenal fluid. The post-

84
pyrilamine period decrease in acid output in the CATH study
was not as dramatic in the NOC study. The increasing acid
output during the early and late infusion periods of the
CATH were closer to the normal pentagastrin response
observed in horses without pyrilamine pretreatment(See
Chap.3) than to an unusually profound response to pyrilamine
in the NOC study. Decreased maximal acid output in horses
stimulated with pentagastrin following the administration of
pyrilamine maleate may be due to decreased mucosal blood
flow.(See Chap. 3) The placement of the duodenal catheter
may also potentiate gastric acid secretion by mechanical
stimulation2-3-8-17'18 in the gastric antrum resulting in the
local release of gastrin or acetylcholine, thereby lessening
the effect of the pyrilamine. In humans and dogs,
distention of the antral region has been shown to augment
histamine or gastrin- related secretion of acid.2-3-13
Although the catheter was not large and did not distend the
antrum, it did contact the gastric mucosa and may have
stimulated local intramural reflexes2-3-17-18 involved in the
secretory response.
Sodium output increased dramatically during
pentagastrin infusion in both the CATH and NOC studies,

85
although, the output was significantly greater in the CATH
studies. The infusion related increase in sodium output was
consistent with the apparently equine specific response to
pentagastrin.31-44-51 Monitoring of sodium ions in the stomach
has been used to assess duodenogastric reflux in humans.92-93
The sodium rich fluid collected from the equine gastric
cannulas is probably of duodenal origin50-51 and the reflux of
this sodium rich duodenal fluid around the duodenal catheter
could explain the increased sodium output during the CATH
study.
The equine gastric cannula model has been beneficial in
the understanding of equine gastric physiology and the
development pharmaceuticals for the treatment of gastric
ulcers. 31-49-53-54 It appears that this model may also allow
further investigation of equine gastric and small intestinal
physiology. The duodenal contents had a high concentration
of sodium and chloride and low concentration of potassium
and is most likely the fluid which dilutes parietal
secretions during gastric collections. The passage of a
duodenal catheter and collection of duodenal contents does
not prevent normal acid stimulation in response to
pentagastrin, but may enhance reflux of duodenal contents
into the stomach.

CHAPTER 5
THE EFFECT OF PYLORIC OBSTRUCTION ON EQUINE BASAL AND
STIMULATED GASTRIC SECRETION
Introduction
In horses, the maximal secretory response to
pentagastrin (PG) comprises a large volume of sodium-rich
fluid of relatively low acidity ( [H+] (40-60 mEq/1) .31.44,49.51
This is different from other monogastric species that have
been studied, where the gastric contents under maximal PG
stimulation have high H+ and low Na+ concentrations,
comparable to that seen in response to histamine
stimulation. 30-37'42 On the other hand, the acid and sodium
concentrations of equine gastric contents under maximal
histamine stimulation are similar to those seen in other
monogastric species in that the [H+] ranges between 80-110
mEq/1 and the [Na+] is relatively low. (See Chap.2) The
maximal acid output (MAO) was equivalent to that during
pentagastrin infusion, however, the sodium outputs differed
greatly. In other monogastric species, the difference
86

87
between histamine and pentagastrin stimulation is the
relative sensitivity to each, rather than the composition of
the resultant secretions.17-28-30
Furthermore, when PG-induced gastric acid secretion of
horses is inhibited by either a histamine-2 receptor
antagonist or a proton pump blocking agent, a large volume
of basic, sodium-rich fluid can still be collected from the
stomach. 31- 49-51-53-54- This is also distinctly different from
the response in other monogastrics, where inhibition of acid
secretion results in coincident reduction in the volume of
gastric contents. 37-94 Whether the origin of this fluid is
primarily gastric or extragastric in origin has not been
identified. The objective of this study was to determine
more exactly the source of this large "nonparietal"
component of equine gastric contents that is seen in
response to PG stimulation.
Materials and Methods
Horses
Five Thoroughbreds and one Arabian [2 mares, 4
geldings] ranging from 3 to 20 years were used in this

88
study. The horses were all healthy and weighed between 430
and 510 kg. They were maintained on grass pasture and
provided coastal hay free choice, and 12% protein grain
twice daily.- They were dewormed every 2 months, vaccinated
for encephalomyelitis and tetanus every 6 months and were
free of clinical signs of any disease. Chronic indwelling
gastric cannulas as described by Campbell-Thompson and
Merritt31 had been prepared in these horses from 1 to 24
months prior to this study. All studies were approved by
the University of Florida IACUC.
Experimental protocol
Horses were fasted with free choice water for 20 hours
prior to an experiment. Experiments were performed with no
less than a one week interval between them. The horses were
loosely restrained in the laboratory for the entire
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes, while a indwelling
jugular catheter(Abbocath) was emplaced. Videoendoscopy was
used to place a specially designed catheter into the
duodenum, as described by Kitchen et al.(See Chap. 4) The
catheter was further adapted in half of the experiments by

89
the addition of an inflatable balloon, which could be
inflated or deflated by a three-way stopcock near the
proximal end of the catheter.(fig. 6) The catheter was
passed until a predetermined mark or the balloon was 5cm
Figure 6 Specialized Balloon catheter. at balloon which
is 20 cm from the end of the catheter. marks the 3-way
stopcock and tubing to fill balloon. - points to the
silastic tube which keeps the catheter fixed in place and
allows collection of gastric contents.
aborad to the pylorus. The balloon was inflated with a
60 ml syringe until firm resistance was felt. The catheter
was gently pulled to verify its placement was fixed by the
balloon. The completed setup (fig. 7) resulted in the

90
ability to collect gastric contents from the cannula and
duodenal contents from the catheter into separate
containers, which were 1L size bags suspended from a
surcingle. The cannula and catheter were both allowed to
Figure 7 Cross sectional view showing balloon catheter
positioned in the proximal duodenum through the gastric
cannula.
drain by gravity for 15 minutes after completion of catheter
placement and inflation of balloon in those experiments with
pyloric obstruction.

91
Gastric and duodenal contents were continuously
collected by gravity drainage, separately. The containers
were switched every fifteen minutes and samples from each
time block were analyzed. Gastric samples were filtered
through gauze prior to analysis. Volume of both gastric
and duodenal collections was measured and if available, a
50 ml aliquot was saved for sample analyses. Analyses were
performed either immediately or samples were frozen for
later analysis. Each experiment lasted 3 hours. The design
was a 6x6 Latin square repeated measures design randomized
for treatment.(See Table 9.) Three different IV infusions
Table 9.
EXPERIMENTAL DESIGN
INFUSION
CATHETER TYPE
ABBREVIATION
Saline
No Balloon
SAL/NB
Histamine
No Balloon
HIST/NB
Pentagastrin
No Balloon
PG/NB
Saline
Balloon
SAL/B
Histamine
Balloon
HIST/B
Pentagastrin
Balloon
PG/B
No Balloon
= Pylorus Not
Obstructed
Balloon = Pylorus Obstructed
were given, with the duodenal catheter in place, either
with or without an inflated pyloric balloon. During the

92
first 45 minutes [basal collection], no treatment was given.
Beginning at time t=45min, pyrilamine maleate (Histavet-P,
Schering-Plough NJ) was infused IV at 1 mg/kg over a 15
minute period. No additional treatments were given for 30
minutes. At time t=90min, an IV infusion of either 0.9%
saline [60 mls/hr], histamine [30 pg/kg-hr], or pentagastrin
[6 fjg/kg-hr] was administered by infusion pump (Harvard
Apparatus, South Natick MA) and continued for the remainder
of the experiment. Infusions were prepared as previously
described.(See Chap. 4) At the conclusion of the
experiment, the intraduodenal catheter position was
rechecked before it was withdrawn, and the cannula closed.
Sample analysis
Volume was measured in a graduated cylinder and
aliquots were analyzed immediately for pH, and chloride ion
concentration. Gastric samples were analyzed immediately
for hydrogen ion concentration. Duodenal samples were kept
in an ice bath until they were analyzed for bicarbonate ion
concentration. Both gastric and duodenal samples were
frozen for later analysis of sodium and potassium ion
concentration. Gastric samples from t=45min were analyzed

93
for bile acids to verify complete occlusion of the pylorus
by the balloon in those experiments.
The pH was determined by glass electrode (Radiometer,
Copenhagen Denmark) calibrated at 20C using commercial
buffer solutions of pH 2 and 7 (pH standard, Fischer
Scientific). Using an automatic titrator (Radiometer,
Copenhagen Denmark), hydrogen ion concentration was measured
in duplicate by titration with 0.IN NaOH to an endpoint of
7.4. Chloride ion concentration was measured in duplicate
by a digital chloridometer (Buchler Instruments Div.,
Nuclear Chicago, Fort Lee NJ) with acid reagent (Labconco,
Kansas City, Mo). Chloride standard (Labconco, Kansas City,
Mo) was used to calibrate the machine prior to each
experiment and after every 20 tests. Bicarbonate ion
concentration was determined by back-titration method of
Isenberg et al.91 with the automatic titrator (Radiometer,
Copenhagen Denmark) using 0.IN NaOH to titrate to an
endpoint of 8.4. Sample aliquots were gassed with nitrogen
washed in barium hydroxide to remove carbon dioxide prior to
and during the titration. Bicarbonate measurements were
done in triplicate, and standard solutions prepared in
laboratory were measured in quadruplicate prior to each
experiment. Sodium and potassium ion concentration were

94
measured in duplicate by flame photometry (Instrumentation
Laboratories Inc., Lexington MA) on samples which had been
frozen at -20C. Samples were thawed to room temperature
and were mixed and diluted in an internal standard lithium
solution (Dilumat, Fischer Scientific), prior to analysis.
The machine was calibrated with known [Na+] / [K+] standards
(Instrumentation Laboratories Inc., Lexington MA) prior to
analysis and after every 5 samples. Bile acid concentration
was determined by an enzymatic, colourimetric test kit
(Enzabile, Nycomed, Norway) in the VMTH Clinical Pathology
Laboratory.
Analysis of data
A complete randomized block design experiment was used.
The treatment order was randomized for each horse. In order
to obtain basal samples and pretreat all horses with
pyrilamine maleate, the first 90 minutes of each experiment
was the same. For statistical analysis and descriptive
purposes, the results from the t=30 and 45 min were averaged
and are referred to as "Rl". The results from collection
following pyrilamine maleate infusion (t=75 & 90min) were
averaged and labeled "R2". The three "Rl" values from

95
experiments without pyloric obstruction and the three "Rl"
values from experiments with pyloric obstruction were
averaged to derive "basal" means. The "R2" values were also
averaged to derive two "pyrilamine" means. The first six
aliquots were grouped as "pre"and the next six aliquots
were grouped as "post" treatment. All outputs were
calculated on a per kg body weight basis from the volume and
ion concentrations and were expressed as |^Eq/kg/l5min.
Volume, pH, electrolyte ion concentration, and electrolyte
ion output data were analyzed by ANOVA for repeated
measures. Differences between drug effects, drug*time
interaction, time, drug*balloon interaction, balloon,
balloon*time interaction and drug*balloon*time interaction
were analyzed. Least significant difference was used for
pairwise comparison of means. Significance was chosen as
p<0.05.
Results
The horses maintained their bodyweight or gained weight
during the course of the study, and they did not appear to
be painful or anxious during the experiments. They stood
quietly in the lab throughout and behaved similarly with or

96
without pyloric obstruction. The duodenal mucosa appeared
healthy in all studies and no changes were observed in the
area where the inflated balloon was positioned. No colics
were observed in these horses during or after these studies.
Rarely, a small piece of mucosa would pass from the duodenal
catheter. The size of these pieces was consistent with the
holes in the catheter and may have occurred by suction of
the catheter onto the mucosa. No residual scarring was
visible endoscopically.
Pre-infusion
Gastric samples
(See Table 10,11,12,13,14)
The gastric samples collected after inflation of the
balloon to obstruct the pylorus were clear and watery,
although clear mucus and white foam was sometimes present in
the collection. Gastric samples collected with the duodenal
catheter and no obstruction of the pylorus were yellow to
greenish-yellow and cloudy as observed in other gastric
cannula studies.31-44 Time was statistically significant in
most parameters measured and related to the administration
of pyrilamine maleate. The time effect was significant
(p<0.05) for all parameters except chloride ion

97
concentration, and was consistent between treatment groups.
After treatment with pyrilamine maleate, the collection
volume (p=0.0001), acid concentration (p=0.0001), acid
output (p=0.0001) sodium output (p=0.0001), potassium
concentration (p=0.0001), potassium output (p=0.0001), and
chloride output (p=0.0001) were decreased significantly,
while pH (p=0.0457) and sodium concentration (p=0.0001)
significantly increased. The balloon [obstruction vs. no
obstruction of the pylorus] affected all parameters, except
pH, [Na+] and [K*] The experiments with the balloon had
significantly lower volume (p<0.00001), and acid
(p=0.02517), sodium (p<0.00001), potassium (p<0.00001), and
chloride (p<0.00001) outputs than those without balloon.
Acid (p=0.02075) and chloride (p=0.00102) concentrations
were significantly higher in the experiments with pyloric
obstruction. As expected, no significant differences were
found between groups with regard to which infusion was to be
given. Therefore, two "basal" and "pyrilamine" values were
calculated from mean of the "Rl" and "R2" of either
experiments with balloon, or experiments without balloon.

98
Post-infusion
Gastric samples
Volume. (Table 10) After starting infusion, the
volume of gastric collections increased significantly
(p=0.0001) through the time course (t=105 to 180). A
significant drug*time interaction was observed (p=0.0001).
Pentagastrin experiments resulted in a rapid, marked
increase that was significantly greater than saline
(p=0.0001), but not significantly greater than the increase
with histamine, which was also significantly greater than
saline (p=0.0003). The balloon*time interaction was also
significant (p=0.0214), since the relative volume increase
was greater in the studies with pyloric obstruction than in
those with no obstruction. In all infusions, the volume of
gastric contents collected was significantly greater
(p<0.00001) with no balloon. The drug effect was also
highly significant (p<0.00001). Specifically, pentagastrin
induced volumes significantly greater than saline
(p<0.00001) and histamine (p=0.00001), and histamine volumes
were also significantly greater than saline (p=0.00003).
There was a significant (p= 0.04437) drug*balloon

99
interaction. Further comparison demonstrated the following
gastric volume differences: PG/NB was significantly
greater than HIST/NB (p<0.00001) or SAL/NB (p<0.00001),
HIST/NB was significantly greater than SAL/NB (p=0.00178),
PG/B was significantly greater than HIST/B (p=0.04694) or
SAL/B (p<0.00001), and HIST/B was significantly greater than
SAL/B (p=0.00154).
Table 10.
VOLUME AND pH OF GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
VOLUME
ml/15min
SAL *
472.93 0.5
NB
466.158.4
361.6+51.1
HIST *
664.251.5
+
PG *
885.83 9.5
VOLUME
ml/l5min
SAL *
226.942.5
B4
251.04 8.9
153.930.1
HIST *
445.556.0
+
PG *
523.8+52.4
pH
SAL
2.450.70
NB
2.100.48
2.430.64
HIST §
1.330.07
+
PG
1.590.05
PH
SAL
2.450.91
B
1.950.41
2.64+0.85
HIST §
1.21+0.04
+
PG
1.27+0.02
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
§ HIST significantly less (p<0.05) than other infusions
+ Pyrilamine significantly different than other time blocks

100
pH. (Table 10) The only significant effect on pH
(p=0.02600) was related to the drug of infusion. Histamine
infusion resulted in pH significantly lower than saline
(p=0.00866), but not significantly different from
pentagastrin.
Potassium ion concentration (Table 11) The
concentration of potassium ion increased significantly
(p=0.0001) after initiation of the infusions. The drug*time
interaction was also significant (p=0.0001). Histamine
infusion rapidly resulted in [K+] significantly greater than
pentagastrin (p=0.0029) or saline (p=0.0001). Time-related
changes in [K+] did not differ significantly between
pentagastrin and saline infusions. The [K+] was
significantly greater (p=0.00004) in experiments with the
balloon than in no balloon experiments. There was a
significant (p<0.00001) drug effect. The [K+] during
histamine infusion was significantly greater than during
pentagastrin (p=0.00007) or saline (p<0.00001) infusion, and
the pentagastrin induced [K+] was significantly greater than
that of saline (p=0.00168). The drug*balloon interaction
was significant (p=0.01112) with the following specific
concentration differences: HIST/NB was significantly

101
greater than SAL/NB (p=0.00023) and PG/NB (p=0.00039),
HIST/B was significantly greater than SAL/B (p<0.00001) and
PG/B (p=0.01767), and PG/B was significantly greater than
SAL/B (p=0.00006).
Table 11.
POTASSIUM IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[K+]
mEq/L
SAL
9.8+0.64
NB
9.80.92
8.10.64
HIST *
14.00.90
+
PG
10.30.53
[K+]
mEq/L
SAL *
9.4+0.77
B
10.3 1.18
8.0+0.67
HIST*
17.7+1.03
+
PG *
14,20.94
K+
OUTPUT
(.lEq/kg/
15min
SAL *
9.80.75
NB
10.22.06
6.41.17
HIST
19.51.27
+
PG
19.51.31
K+
OUTPUT
/xEq/kg/
15min)
SAL *
4.7+1.06
B4
5.91.4 9
2.60.51
HIST
16.4+1.72
+
PG
15.71.91
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
+ Pyrilamine significantly different(p<0.05) from other
time blocks
Potassium ion output. (Table 11) Compared to pre
infusion, the output of potassium increased significantly
(p=0.0001) after infusion was begun. While, the actual

102
output stimulated by the infusion of pentagastrin and
histamine did not differ significantly, both were
significantly greater (p<0.00001) than that during saline
infusion. Also, K+ output was significantly greater
(p<0.00001) in experiments with no balloon than those with a
balloon obstructing the pylorus, irrespective of infusion
composition.
Chloride ion concentration. (Table 12) The chloride
ion concentration was relatively constant among all
experiments. The only significant difference was balloon
experiment results were higher (p=0.00035) than when there
was no balloon.
Chloride ion output. (Table 12) Because of minimal
changes in [Cl'] the chloride output related closely to
changes in volume. The output of chloride ion increased
significantly (p=0.0001) throughout the infusion period and
the drug*time interaction was significant (p=0.0001), since
pentagastrin rapidly induced a marked increase, that was
significantly greater than that of histamine (p=0.0495) or
saline (p=0.0001). Histamine alsoproduced an increased
output over time that was significantly greater than that of
saline (p=0.0013). The drug*balloon interaction was

103
significant (p=0.04872). In SAL/NB experiments, the output
of chloride ion was significantly less than either HIST/NB
(p=0.00059) or PG/NB (p<0.00001), and during PG/NB, output
was significantly greater than during HIST/NB (p=0.00001).
Table 12.
CHLORIDE IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[C1-]
mEq/L
SAL
143.23.82
NB
143.4+5.6
143.16.32
HIST
144.9+3.62
PG
144.06.68
[ci-]
mEq/L
SAL
151.35.07
B4
151.15.2
153.35.57
HIST
156.93.53
PG
154.02.56
CL'
OUTPUT
iEq/kg/
15min
SAL *
143.38.82
NB
138.822.7
111.117.8
HIST*
207.320.45
+
PG *
272.919.47
CL'
OUTPUT
¡lEq/kg/
15min
SAL *
73.7+14.07
Bf
82.2+16.93
51.010.44
HIST*
14 9.2 + 19.53
+
PG *
172.0+19.07
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
+ Pyrilamine significantly different(p<0.05) from other
time
In the balloon experiments, pentagastrin stimulated outputs
that were significantly greater than histamine (p=0.04704)

104
and saline (p<0.00001) and histamine stimulated outputs that
were significantly greater than saline(p=0.00024). Overall,
the balloon experiments resulted in significantly less
chloride output (p<0.00001) than the no balloon experiments.
The drug effect on chloride output was significant
(p<0.00001) and all three infusions differed significantly.
Hydrogen ion (acid) concentration. (Table 13) As
infusions were begun, the acid concentration increased
significantly (p=0.0001) over time. The different infusions
responded significantly differently (p=0.0001) over time.
Saline slowly increased from the "R2" period, while
pentagastrin (p=0.0341) and histamine (p=0.0001) increased
significantly more rapidly. The histamine response was also
significantly (p=0.0023) more profound than that of
pentagastrin. The difference between those experiments with
the balloon and those without balloon was also significant
(p<0.00001). In addition, the [H+] in PG/NB was
significantly less (p<0.00005) for all time points than
PG/B. During the last three collections, HIST/B had a
significantly greater (p<0.03) [H+] than HIST/NB.
The overall drug effect on [H+] was significant
(p<0.00001) and there were significant differences between

105
each of the infusions, as well. Histamine infusion produced
[H+] significantly greater than pentagastrin (p=0.00002) or
saline (p<0.00001), and pentagastrin infusion was
significantly greater than saline (p=0.00003) There was a
significant (p=0.00327) drug*balloon interaction. The [H+]
during HIST/NB was significantly greater than SAL/NB
(p<0.00001) or PG/NB (p<0.00001), while there was no
significant difference in [H+] between SAL/NB and PG/NB. In
the balloon experiment, there was no significant difference
in [H+] for HIST/B and PG/B; however SAL/B produced an [H+]
significantly less (p<0.00001) than either HIST/B or PG/B.
Acid output. (Table 13) Acid output was significantly
(p=0.0001) affected by time and by drug*time interaction.
The output increased following the initiation of infusion.
The pattern of increasing acid output was not significantly
different between histamine and pentagastrin infusions,
though each led to significantly greater (p=0.0001) output
changes than during saline infusion. All three infusions
resulted in significantly different (p<0.00001) acid
outputs. Histamine-induced outputs were significantly
greater than those of pentagastrin (p=0.00120), and outputs

106
under both histamine and pentagastrin were significantly
greater (p<0.00001) than that of saline.
Table 13.
ACID IN THE GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[H+]
mEq/L
SAL *
28.95.47
NB
33.8+6.53
27.66.59
HIST§
80.34.86
+
PG
42.43.14
[H+]
mEq/L
SAL *
38.759.09
B4
47.010.15
32.819.32
HIST
103.12 3.48
+
PG
84.17+4.94
H+0UTPUT
(.lEq/kg/
15min
SAL *
28.65.51
NB
35.510.23
22.57.43
HIST§
112.6+8.31
+
PG
80.2+6.99
H'OUTPUT
/iEq/kg/
15min
SAL *
21.78+6.99
B4
29.52+9.53
12.78 5.14
HIST
97.03+10.82
+
PG
91.22+5.85
+ Pyrilamine significantly less (p<0.0 5) than other time
blocks
B significantly different (p<0.05) from NB
§ Histamine significantly different(p<0.05) than other
infusions
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Acid output was also significantly affected (p=0.00054)
by the drug*balloon interaction. In the no balloon
experiments, all three infusions resulted in different
outputs of acid. HIST/NB resulted in outputs significantly

107
greater (p<0.00001) than both PG/NB and SAL/NB. PG/NB
outputs were also significantly greater (p=0.00001) than
SAL/NB. The addition of the balloon dramatically changed
the output differences, since HIST/B was not significantly
different than PG/B. However, both PG/B and HIST/B produced
outputs significantly greater (p<0.00001) than SAL/B.
Sodium ion concentration. (Table 14) The
concentration of sodium decreased significantly (p=0.0001)
over the time course of infusion. A significant (p=0.0001)
drug*time interaction was observed. Specifically, the
decrease following histamine infusion was significantly more
dramatic than with pentagastrin (p=0.0002) or saline
(p=0.0001). Pentagastrin and saline did not differ
significantly.
The effect of the balloon on [Na+] was also significant
(p=0.00002), and under balloon conditions the [Na+] differed
significantly (p<0.00001) in response to each of the
infusion compositions. Sodium concentration was
significantly less during histamine infusion than either
pentagastrin (p=0.00001) or saline (p<0.00001), and was
significantly less (p=0.00020) during pentagastrin infusion
than during saline infusion. At all time points, the PG/B

108
experiments yielded a [Na+] that was significantly less
(p<0.01) than during the PG/NB experiments.
Table 14 .
SODIUM IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[Na+]
mEq/L
SAL *
108.0+4.64
NB
101.5+8.15
107.0+6.08
HIST§
52.55.22
+
PG
88.2+4.78
[Nai
mEq/L
SAL *
91.569.54
B
89.639.17
102.04+9.1
HIST§
31.104.15
+
PG
57.73 6.08
Na+
OUTPUT
^Eq/kg/
15min
SAL *
108.88.80
NB
99.2+12.27
82.2+12.03
HIST§
77.1+12.91
+
PG
167,414.69
Na+
OUTPUT
/xEq/kg/
15min)
SAL
44.87+7.07
B4
45.817.44
32.52 4.98
HIST
30.10+6.60
+
PG
68.62 + 16.24
+ Pyrilamine significantly less (p<0.05) than other time
blocks
B significantly different (p<0.05) from NB
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
§ Histamine significantly different(p<0.05) than other
infusions
t Pentagastrin significantly different(p<0.05)than
histamine
Sodium output. (Table 14) Time (p=0.0488),
balloon*time interaction (p=0.0105), drug*time interaction
(p=0.0008), balloon (p<0.00001), drug (p<0.00001), and

109
drug*balloon interaction (p=0.00023) are all significant for
sodium output. Over time, histamine and saline resulted in
relatively constant sodium outputs, whereas, pentagastrin
resulted significantly different (p=0.0001, and 0.0277,
respectively) fluctuations in sodium output. Sodium output
during pentagastrin infusion was significantly greater than
during histamine (p<0.00001) and saline (0.00003) infusion.
It was also significantly greater (p=0.00137) during saline
than histamine infusion. The output during PG/NB was
significantly greater (p<0.00001) than either HIST/NB or
SAL/NB, while SAL/NB was significantly greater (p=0.00141)
than HIST/NB. Sodium output during SAL/B was not
significantly different than either PG/B or HIST/B; however,
output during HIST/B was significantly less (p=0.01197) than
PG/B. Most importantly, throughout the infusions, the
output during PG/NB was significantly greater (p<0.00001)
than PG/B, HIST/NB was significantly greater (p<0.003) than
HIST/B. and SAL/NB was significantly greater (p<0.0002) than
SAL/B.

110
Pre-infusion
Duodenal samples
(See Tables 15,16,17,18,19)
The presence or absence of the pyloric obstruction did
not change the appearance of the fluid collected from the
duodenal catheter. Duodenal samples were transparent dark
yellow to dark green colored and generally thick and mucoid.
The volume collected was related to viscosity of samples and
limited by the small diameter of the catheter; therefore,
outputs of electrolytes were not calculated. Duodenal fluid
was observed to be less viscid, however, during times in
which a high volume was collected. No fluid was obtained
from the duodenal catheter during 19 (11 pre infusion; 8
post infusion: 16 without obstruction; 3 with obstruction)
of the 432 samples collected. The only significant
difference was in balloon status for volume and bicarbonate
ion concentration. The volume from the duodenal catheter
was significantly (p<0.00001) greater in experiments with
the balloon obstructing the pylorus. Bicarbonate ion
concentration was also significantly (p=0.00353) greater in
experiments with pyloric obstruction. As with gastric
samples, "basal" and "pyrilamine" values were derived from

Ill
"Rl" and "R2" since there were no significant differences
between results of each infusion during this pre-infusion
time.
Post-infusion
Duodenal samples
Bicarbonate ion concentration. (Table 15) The
concentration of bicarbonate ion was significantly greater
(p=0.00397) in collections made while the balloon was in
place. There was also a significant (p=0.00002) drug effect
on [HC03'] Pentagastrin infusion resulted in [HC03']
Table 15.
BICARBONATE IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[HC03-]
mEq/L
SAL
23.6 2.7
NB
23.22.6
16.21.5
HIST
22.9 2.3
PG *
33.0 2.3
[HCO3-]
mEq/L
SAL
28.5 4.7
B
28.5+2.7
28.72.7
HIST
28.3 1.9
PG *
37.1 2.1
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB

112
significantly greater than histamine (p=0.00016) and saline
(p=0.00001). The [HC03] did not differ significantly
between histamine and saline.
Sodium'ion concentration. (Table 16) The only
significant effect observed for [Na+] in duodenal collection
was a drug effect (p=0.0467). During histamine infusion,
the fluid collected had a significantly lower [Na*] than
during pentagastrin (p=0.04231) or saline (p=0.02316)
infusion.
Table 16.
SODIUM IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[Na+]
mEq/L
SAL
149.0+5.6
NB
147.53.9
151.56.7
HIST *
135.03.0
PG
144.92.4
[Na+]
mEq/L
SAL
147.8+5.5
B
143.15.5
142.9+6.1
HIST *
143.1+2.2
PG
152.65.2
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Potassium ion concentration. (Table 17) Over the 90
minutes of infusion, there was a significant (p=0.0019) time
effect of decreasing [K+] The drug effect was also
significant (p=0.00906), with concentrations after starting

113
infusions of histamine (p=0.00783) or pentagastrin
(p=0.00653) decreasing significantly compared to saline.
Table 17.
POTASSIUM IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[K+]
mEq/L
SAL *
4.2 60.2 7
NB
4.50.2
4.40.3
HIST
3.900.20
PG
3.64 + 0.10
[K+]
mEq/L
SAL *
3.940.14
B
4.10.2
4.00.2
HIST
3.69+0.12
PG
3.74+0.27
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Table 18.
CHLORIDE IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[Cl']
mEq/L
SAL *
135.65.5
NB
118.15.5
119.65.2
HIST
103.37.0
PG
115.16.1
[Cl']
mEq/L
SAL *
129.2 + 6.3
B
126.6+7.1
123.94.4
HIST
112.52.7
PG
108.52.7
* Response to this infusion significantly different
(p<0.05) from responses to other infusions
Chloride ion concentration. (Table 18) The drug
effect on [C1] was significant (p<0.00001). The [Cl'] was

114
significantly greater (p=0.00001) during saline infusion
than during either histamine or pentagastrin infusion.
Volume. (Table 19) The volume of fluid collected from
the duodenal catheter increased significantly (p=0.0378)
compared to pre-infusion during the first 30 minutes after
the infusions started and then gradually decreased
throughout the remaining 60 minutes of infusion to volumes
slightly greater than basal. The presence of pyloric
obstruction by the balloon significantly (p<0.00001)
increased the volume collected. The infusion composition
resulted in significant differences (p=0.00005), with
pentagastrin yielding volumes significantly greater than
either histamine (p=0.00008) or saline (p=0.00009), while
histamine and saline did not differ significantly from each
other. In the experiments without the balloon, there was no
significant difference between infusion volume; however,
with balloon, pentagastrin-induced volumes were
significantly greater than during either histamine
(p<0.00001) or saline (p<0.00001) infusion.

Table 19.
VOLUME OF DUODENAL CONTENTS
Mean + SEM
115
B/NB
BASAL
PYRILAMINE
INFUSIONS
VOLUME
ml/l5min
SAL
75.0+24.8
NB
64.325.9
64.5+18.3
HIST
58.924.8
PG
64.515.7
VOLUME
ml/15min
SAL
181.0+49.8
B4
217.2 4 9.5
214.645.0
HIST
155.616.4
PG*
409+111.5
* Significantly different (p<0.05) from other infusions
B significantly different (p<0.05) from NB
Bile Acids
Bile acid concentration was measured in a selected
number of the 45 minute collection. The lower limit of the
Enzabile test was 5 pmol/L. Bile acid concentrations during
the balloon experiments were significantly less than no
balloon experiments (p=0.000981) In the occlusion studies,
the bile acid concentration was <5 pmol/L in 12 of 18
trials. The remaining balloon trials had concentrations of
5 (.tmol/L in 4 trials, 6 pmol/L in 1 trial, and 7 pmol/L in 1
trial. The concentration ranged from 21 to 77 pmol/L in the
NB studies, with a mean of 42 pmol/L.

116
Discussion
The placement of a duodenal catheter through the
indwelling gastric cannula has been used to analyze duodenal
contents and has been shown to allow simultaneous collection
of gastric and duodenal contents during both resting and
stimulated conditions.(See Chap. 4) This technique was
further modified in this study to provide a method to
occlude the pylorus to collect gastric contents that were
devoid of reflux from the duodenum. The previous studies
with the catheter suggest the reflux of duodenal fluid which
has been shown during endoscopic examination to occur
spontaneously in fasted animals50-51 may be enhanced by the
presence of the catheter passing through the pylorus.(See
Chap. 4) The absence of bile acids in the gastric contents
during the balloon experiments confirmed that reflux of
duodenal contents was eliminated. This technique allowed
us, therefore, to collect purely gastric or duodenal
contents during the balloon experiments, whereas, in the no
balloon experiments, the gastric contents were comparable to

117
those of previous equine secretory studies without any kind
of catheter in place.
The pretreatment of the horses with pyrilamine maleate
in all experiments was necessary to allow for comparison of
histamine and pentagastrin. The results of the pyrilamine
pretreatment were not significantly different between
groups, however, they were significantly different from
basal collections prior to treatment. These results are
consistent with previous findings suggesting that the equine
acid secretory response may be dampened by the
administration of an H-l receptor antagonist.(See Chap. 3)
In this study, as predicted, collection volume, acid
concentration, and acid, sodium, potassium and chloride
outputs decreased following infusion of pyrilamine maleate,
while the pH and sodium concentration of the gastric
contents increased.
The trends observed during the NB experiments were
consistent with the species specific equine response that
has been observed in earlier studies as distinct from the
results observed in other species during similar
stimulation.31-44 The infusion of both pentagastrin and
histamine resulted in the stimulation of increased acid

118
output.31'44 (See Chap. 2) Nevertheless, the peak acid
concentrations were significantly higher with histamine
stimulation than with pentagastrin stimulation, and sodium
output increased during pentagastrin stimulation and
decreased slightly during histamine stimulation.
In the preinfusion time blocks, the volume of gastric
collections were significantly less in the B than the NB
experiments, suggesting that an extragastric source of fluid
might be contributing to the volume collected from the
gastric cannula in horses. The fluid collected in the B
experiments also had a higher concentration of HCl than that
of the NB experiments, which added credence to the dilution
theory. Since the [Na+] and [K+] did not differ between B
and NB experiments, this extragastric fluid apparently
contains these ions. Duodenal fluid has a high
concentration of sodium, a slightly lower concentration of
potassium and chloride, and an approximately isotonic
concentration of bicarbonate compared to gastric fluid.(See
Chap. 4) The introduction of duodenal fluid into the
gastric collection may be enhanced by the presence of the
catheter in the NB experiments, but its reflux into the

119
stomach appears to be a consistent feature of equine upper
GI function, even without transpyloric catheterization.
During infusions, the volume continued to be
significantly greater in the NB experiments than the B
experiments. Pentagastrin experiments resulted in greater
volumes than histamine experiments, which in turn had
greater volumes than the saline experiments. The
differences were markedly greater in the NB experiments than
the B experiments. These finding were consistent,
irregardless of balloon status. Therefore, pentagastrin
infusion appears to stimulate a larger fluid response than
does histamine, while both result in equivalent maximal acid
outputs. A portion of this fluid is of gastric origin,
since pyloric obstruction does not eliminate the volume
differences. The absolute volume differences between PG/B
and HIST/B were not large as those between either of these
and SAL/B, however, the difference was significant. The
suggestion is that a nonparietal component of gastric
secretion may be responsive to stimulation by pentagastrin.
It is also possible that this discrepancy results from
unnoticed leakage around the balloon, since in preliminary
trials with this system, we discovered that additional air

120
had to be injected into the balloon during initiation of
pentagastrin infusion to prevent visible leakage of yellow
duodenal contents. Gastrin receptors have been identified
on smooth muscle cells in the gastric antrum in dogs and
gastrin has been shown to relax the pylorus to enhance
gastric emptying.9S-96 Pentagastrin may stimulate these
smooth muscle receptors in the horse and allow additional
reflux of duodenal contents.
As expected, and in accordance with previous studies,
potassium concentration and output increased in parallel
with an increasing acid concentration and output during
stimulation.44 However, the output of potassium was
significantly greater in the NB experiments, suggesting that
it is one of the components of the extragastric fluid which
is separated out by the occlusion of the pylorus.
Whereas, the lower [Cl'] in the NB experiments was
likely secondary to the dilutional effect of the
extragastric portion of these collections, chloride output
was greater in the NB experiments, inferring that the
extragastric fluid contains chloride, but at a lesser
concentration than that of gastric secretions.
Significantly greater chloride output during pentagastrin
infusion in both NB and B experiments in contrast to the

121
histamine response, further implies a special pentagastrin
effect.
The finding that during the NB experiments the maximal
acid concentration induced by histamine was significantly
greater than that induced by pentagastrin, whereas, in the B
experiments, maximal histamine and pentagastrin related acid
concentrations were equivalent suggests that the equine
stomach per se, responds to these 2 secretagogues in a
Time (minutes)
Figure 8 Acid concentration. A curvilinear line derived
from mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials marks mean for NB trials.

122
manner similar to that seen in other monogastric species.
(See fig. 8) In some of the HIST/NB experiments, the acid
concentration was less than corresponding HIST/B
experiments, this is probably related to dilution by some
extragastric fluid that is responsible for a portion of the
increased volume of collection, but not to the same
magnitude stimulated by pentagastrin.
Time (minutes)
Figure 9 Acid output. A curvilinear line derived from mean
sodium output during pentagastrin and histamine infusions
comparison of B and NB experiments, a marks mean for B
trials n marks mean for NB trials.

123
Acid output in the B experiments was equal during
pentagastrin and histamine stimulation, however, in the NB
experiments, histamine related acid output was greater than
that of pentagastrin.(See fig. 9) Several factors seem to
be involved in this unexpected finding. The HIST/NB maximal
acid output was greater than HIST/B during some of the time
blocks, while the opposite relationship was noted for PG/B
and PG/NB. The lower maximal acid output in the PG/NB may
be the result of the loss of hydrogen ions through chemical
reaction with bicarbonate ions from the extragastric
component of NB collections.
Even more dramatic than the effects on acid were those
on sodium recorded in these experiments.(See fig. 10) As
with acid concentration, the pattern of the [Na+] response
to PG/B was that expected of the classic parietal secretory
response rather than the profound nonparietal response seen
in previous equine pentagastrin studies. The comparison of
sodium outputs under B vs. NB conditions was still more
spectacular.(See fig. 11) Sodium output was greater in all
NB experiments than those with the balloon, which is
consistent with the suggestion that the extragastric

124
presumably duodenal, fluid that accounts for the additional
volume is sodium rich.
Figure 10 Sodium concentration. A curvilinear line derived
from mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials a marks mean for NB trials.
The duodenal contents sampled by the intraduodenal
catheter are presumably composed of a combination of
biliary, duodenal, and pancreatic secretions. Not
surprisingly, the volume of collection was much greater in
the experiments with pyloric obstruction, which likely

125
resulted in the accumulation of these secretions in the
proximal duodenum. The significantly greater volumes
observed during pentagastrin infusions were of particular
Figure 11 Sodium output. A curvilinear line derived from
mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials marks mean for NB trials.
interest. Furthermore, the fluid collected during these
experiments appeared to be less viscous than in experiments
with either histamine or saline infusion. The duodenal
contents collected during pentagastrin infusion also had a

126
higher concentration of bicarbonate. These findings are
consistent with a report by Alexander and Hickson that
pentagastrin is a strong stimulant of equine pancreatic
secretion.55
The suggestion that the equine gastric contents might
contain fluid originating from the duodenum is not new or
without warrant.50'51 Anatomically, the position of the
proximal duodenum in relation to the stomach allows gravity
to aid in this reflux. In addition, the bile and pancreatic
ducts of horses enter the duodenum relatively near to the
pyloric sphincter, and reflux of duodenal contents into the
gastric lumen has been seen during endoscopic
examination.50-51 In man, duodenogastric reflux has been
recognized and is quantified by the measurement of sodium
ions in gastric contents.92'93
Pancreatic secretion in the horse is reported to be
continuous and profuse with a higher concentration of
chloride and lower concentration of bicarbonate than that of
other monogastric species.55'57 The fivefold increase in
pancreatic secretion after the administration of
pentagastrin appears to be unique to the horse, among the
species that have been studied.55 In most species,

127
pancreatic fluid and electrolyte secretion is regulated
primarily by secretin with some modulation via vagal
reflexes, whereas enzyme secretion is primarily controlled
by CCK and vagal input. 59-60 Secretin induces pancreatic duct
cells to produce increased volumes of fluid and as the
secretory rate increases, there is a reciprocal switch in
the bicarbonate and chloride concentrations.63 In the
horse, the concentration of bicarbonate is never greater
than that of chloride, even during maximal secretion.55
Enzyme content of pancreatic secretions increase with the
stimulation of CCK-A receptors on the pancreatic acinar
cells in most species.60-61 The concentration of enzymes in
equine pancreatic secretion is very low under both basal and
stimulated conditions.55 Gastrin, which acts at CCK-B
receptors, is a weak stimulant of pancreatic enzyme and
fluid secretion in species other than the horse.62 The
relative prevalence of CCK-A and CCK-B receptors within the
equine gastrointestinal tract has not been reported. The
results of this study and the report of Alexander and
Hickson might mean that the equine pancreas, and in
particular pancreatic duct cells, has an abundance of CCK-B
receptors.

128
Biliary secretion has an electrolyte composition
similar to that of the pancreas, and ductular secretion is
stimulated by secretin with a corresponding increased
bicarbonate concentration.97 Gastrin, but not pentagastrin,
has been shown to increase biliary flow in dogs.97 The
horse lacks a gallbladder and is reported to have continuous
biliary flow55, though which substances are involved in the
regulation of this flow, has not been reported. Increased
biliary secretion in response to pentagastrin is also a
possible source of some of the extragastric fluid in equine
gastric collections.
This study clearly demonstrates that pentagastrin
stimulates the secretion of an extragastric fluid which
dilutes the gastric contents during gastric collection from
the gastric cannula model. With separation of gastric and
extragastric secretions by obstruction of the pylorus, it
becomes apparent that pentagastrin does stimulate parietal
secretion comparable to that of histamine, similarly
comparable to that of other monogastric species. Although,
the exact origin of this extragastric fluid requires further
investigation, it is most likely of pancreatic and/or
biliary origin. The remarkable volume response to

12 9
pentagastrin when collecting gastric contents from the horse
via the cannula is related primarily to increased
duodenogastric reflux of sodium rich isotonic fluid.
Histamine infusion, on the other hand, stimulates the
parietal cells, but does not stimulate the secretion of the
extragastric secretion. Thus, the equine specific gastric
secretory response to pentagastrin is the result of
extragastric actions of pentagastrin rather than species
variation in the acid secretory response.

CHAPTER 6
SUMMARY AND CONCLUSIONS
Summary
Histamine infusion at a dose of 30 (ig/kg-hr to horses
resulted in a maximal acid output response comparable to the
maximal response to pentagastrin infusion and, on a
bodyweight basis is similar to that of humans. Thus, the
gastric contents collected during histamine infusion
differed significantly in electrolyte concentrations and
sodium output from those collected during pentagastrin
infusion. The character of the histamine-stimulated gastric
contents resembles the classic "parietal" response described
in other species and did not include the voluminous sodium-
rich component described in studies with
pentagastrin. 31.44,49,51,53.54
Prior to this study, we had some concerns about the
reaction of horses to the histamine infusion. In the pilot
130

study, no adverse reactions were observed during the
histamine infusions; however, some horses became anxious
during and for approximately 15 minutes after the pyrilamine
maleate administration. The second histamine dose-response
study was designed with a slower infusion of pyrilamine,
which eliminated the excitement problem. It is the results
of this second histamine study that are presented in Chapter
2. The study was designed with 4 doses of histamine, yet
only 3 doses were statistically analyzed. We were able to
complete the all 4 doses in only one horse, due to metabolic
complications in the other horses associated with the loss
of large amounts of HC1, not a direct histamine effect.
Histamine infusion with associated gastric collection done
in later studies (See Chap. 5) was free of such
complications.
Pretreatment with pyrilamine maleate or another H-l
receptor antagonist was necessary to prevent CNS and
respiratory complication during histamine infusion.65 In
these studies, it was observed that acid output decreased
after pyrilamine, in contrast to what is seen in other
species.29'71-77-82'83 In preparation for later studies
comparing histamine to pentagastrin, we decided to

132
investigate the effect of pyrilamine maleate pretreatment on
pentagastrin stimulated gastric contents. Chapter 3
presents the surprising results of this study. Acid output
after pyrilamine maleate was significantly decreased from
basal, and the secretory response to pentagastrin
stimulation was also diminished.
The primary goal of this project was to determine
whether the large sodium-rich component of gastrin contents
in response to pentagastrin stimulation was of gastric or
extragastric origin. After attempts to surgically isolate
the stomach from the proximal duodenum failed, a technique
was developed to obstruct the pylorus temporarily. This
involved the passage of an endoscope through the gastric
cannula into the stomach and then guiding it into the
proximal duodenum. The process of passing the endoscope
into the duodenum, introducing the stylet through the biopsy
channel, removing the endoscope with the stylet still in
place and then threading the specially designed catheter
over the stylet took 15 to 30 minutes.
Because the duodenal catheterization involved
manipulation within the gastric lumen and resulted in
an'object traversing the pylorus throughout the entire

133
experiment, data were analyzed that compared the composition
of contents collected from the gastric cannula with and
without the catheter present. This was not a specific
study, but a statistical evaluation of data collected under
the two conditions. To balance the design, the "no
catheter" data were those of the horses in the pyrilamine
study described in Chapter 3. Chapter 4 discusses the
methods and materials of the catheterization technique and
the results of the comparison. The sodium output was
significantly increased in the horses with an intraduodenal
catheter in place and the relative electrolyte
concentrations were significantly different from those where
there was no catheter. The acid concentration was decreased
in those experiments with the catheter present, though
volume and acid output were increased.
The duodenal contents were also characterized in this
chapter. Compared to the gastric contents, the fluid was
found to have a higher concentration of sodium, and a lower
concentration of potassium and chloride. The bicarbonate
concentration was similar to plasma.
The final step in testing the hypothesis is the balloon
(B) vs. no balloon (NB) study condensed into Chapter 5. The

134
inflation of the balloon on the intraduodenal catheter
allowed obstruction of the pylorus in an attempt to
prevented duodenogastric reflux. Within 15 minutes of
correct positioning and adequate inflation of the balloon,
it was evident that obstruction had occurred. In the no
balloon experiments, the gastric contents were yellow-green
and frothy in appearance.(See fig. 12) These contents had a
mean bile acid concentration of 42 (.unol/L. Once the balloon
Figure 12 Collections from catheter or cannula. KDZD is
duodenal contents collected through the catheter. KDZG is
gastric content collected from the cannula with the pylorus
obstructed. KDUG is gastric contents collected from the
cannula with no balloon on the catheter.

135
occluded the pylorus, the gastric contents were clear and
watery, and did not contain measurable bile acids. Duodenal
contents collected through the catheter with or without the
balloon were thick, mucoid and yellow-green in color.
As well as changing the physical appearance of
collections, obstruction of the pylorus with the balloon
resulted in decreased volume and sodium and chloride output
from the gastric cannula during both basal and stimulated
time blocks. With the B experiments, histamine and
pentagastrin infusions had comparable results, whereas, in
the NB experiments, maximal pentagastrin infusion resulted
in a lower acid concentration and significantly greater
sodium output. That is, in the B studies, acid and sodium
concentration were inversely proportional in response to
both histamine and pentagastrin, and maximal acid
concentration and output was equivalent.
Duodenal contents were not quantified in these
experiments, as the catheter diameter was a limiting factor
in the collection of this thick, often mucoid fluid.
Consistently, the fluid was more profuse, less viscid and
the bicarbonate concentration increased during pentagastrin

136
infusion. Chloride was the predominate anion even during
stimulation, and sodium was the predominant cation.
Conclusions
This series of studies build on each other to support
the hypothesis of this dissertation. Reviewing the results
of these studies, the following conclusions concerning the
composition of equine gastric contents collected from a
cannula are:
1. Histamine stimulates a purely parietal secretion, while
pentagastrin induces both parietal and non-parietal
secretory activity.
2. Pyrilamine maleate appears to decrease equine basal
gastric acid secretion and may attenuate the acid
secretory response to pentagastrin infusion.
3. The presence of a catheter passing through the pylorus
into the duodenum does not prevent a normal acid
secretory response to pentagastrin, but may enhance the
reflux of duodenal contents into the stomach.
4. The voluminous sodium-rich fluid component of gastric
contents in response to pentagastrin, is due, in large
part, to duodenal reflux. The extragastric fluid
refluxing into the gastric contents is most likely of
pancreatic and/or biliary origin.
In addition to answering the hypothesis, these studies
also led to more questions regarding equine gastric

137
physiology. The decreased acid output resulting from
pyrilamine maleate pretreatment appears to be yet another
species specific response in horses. Further investigation
is necessary to determine the mechanism for this response.
Although the study was able to determine that the equine-
specific response to pentagastrin stimulation is of
extragastric origin, still more investigation will be
required to determine the exact origin of this fluid.

APPENDIX A
HISTAMINE DOSE-RESPONSE DATA
Horses used in Histamine Study
NAME
BREED
SEX
AGE
WEIGHT
Buddy
Arabian
G
s y
445 kg
Dick
Thoroughbred
G
6 y
481 kg
Ethel
Thoroughbred
M
19 y
4 93 kg
Harry
Thoroughbred
G
4 y
495 kg
Lucy
Thoroughbred
M
9 y
5 06 kg
Tom
Thoroughbred
G
4 y
482 kg
138

HISTAMINE DOSE-RESPONSE DATA
Volume and pH
139
TIME
DOSE
VOLUME
PH
minutes
^ig/kg-hr
ml
MEAN
SEM
MEAN
SEM
15
0
480
35
1.685
0.066
30
0
405
54
1.66
0.064
45
0
452
45
1.65
0.071
60
HVP
438
45
1.597
0.076
75
307
62
1.707
0.098
90
407
35
1.872
0.123
105
7.5
473
40
1.695
0.116
120
7.5
528
55
1.502
0.098
135
7.5
550
53
1.468
0.133
150
7.5
633
63
1.445
0.126
165
15
598
69
1.46
0.137
180
15
578
50
1.423
0.146
195
15
605
41
1.505
0.205
210
15
578
41
1.452
0.172
225
30
600
48
1.282
0.039
240
30
578
53
1.266
0.038
255
30
466
90
1.296
0.059
270
30
563
52
1.29
0.021
285
45
470
130
1.285
0.005
300
45
430
100
1.42
0.12
315
45
455
35
1.51
0.24
330
ND
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done

140
HISTAMINE DOSE-RESPONSE DATA
Acid Concentration and Output
TIME
DOSE
ACID CONCENTRATION
ACID OUTPUT
minutes
Hg/kg-hr
mEq/L
¡aeQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
37
4
37.3
6
30
0
41.1
5
36.6
9.4
45
0
44
6.3
42.9
9.1
60
HVP
42.9
6.7
39
8
75
38.3
5.1
26.6
7.1
90
28.8
4.3
25.1
5.7
105
7.5
47.2
8.8
47.1
10.2
120
7.5
65.2
7.1
73.3
14.3
135
7.5
71.9
5.5
82.3
11.5
150
7.5
72.5
5.95
93.8
10.8
165
15
75.2
6.3
93
14.8
180
15
82.8
6.6
97.8
9.8
195
15
79.7
7.2
99.7
12.1
210
15
82.9
7.8
99.3
12
225
30
78.2
8.5
94.9
7.1
240
30
80.2
7.7
93.8
7
255
30
79.8
10.3
80.7
17.2
270
30
86.9
9.4
100
4.6
285
45
101.7
8.1
96.3
20.6
300
45
105.8
6.6
92.3
17
315
45
111.4
0.48
104.3
9.7
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done

141
HISTAMINE DOSE-RESPONSE DATA
Sodium Concentration and Output
TIME
DOSE
Na+ CONCENTRATION
SODIUM OUTPUT
minutes
pg/kg-hr
mEq/L
peQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
76.38
11.25
78.22
13.85
30
0
77.08
10.99
65.13
12.31
45
0
74.35
10.20
71.21
11.86
60
HVP
73.32
9.91
65.23
9.93
75
76.98
10.74
50.80
14.18
90
82.03
11.41
70.35
12.85
105
7.5
75.64
10.46
74.06
11.18
120
7.5
54.93
8.95
60.80
11.04
135
7.5
47.96
8.49
56.17
11.25
150
7.5
49.58
8.84
67.29
14.16
165
15
50.75
9.12
64.10
12.95
180
15
46.18
8.87
56.99
12.36
195
15
49.90
9.27
63.97
14.41
210
15
43.44
8.96
52.97
13.04
225
30
46.30
10.27
59.24
14.90
240
30
49.28
12.19
62.50
18.25
255
30
45.21
12.95
44.20
18.68
270
30
40.15
13.66
51.50
21.55
285
45
29.58
9.38
31.26
17.33
300
45
31.03
10.23
29.69
15.76
315
45
23.15
2.85
21.89
4.60
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done

142
HISTAMINE DOSE-RESPONSE DATA
Potassium Concentration and Output
TIME
DOSE
K+ CONCENTRATION
POTASSIUM OUTPUT
minutes
(.ig/kg-hr
mEq/L
|.ieQ/kg-15min
4
MEAN
SEM
MEAN
SEM
15
0
7.7
1.2
7.99
1.64
30
0
8.3
1.3
7.38
1.9
45
0
7.7
1.3
7.75
1.93
60
HVP
7.1
1.04
6.38
1.26
75
5.6
0.68
3.75
1.03
90
5.9
1
5.2
1.27
105
7.5
8.3
1.5
8.47
2.11
120
7.5
10.6
1.46
12.02
2.53
135
7.5
9.4
1.3
10.95
2.14
150
7.5
10.7
1.7
14.13
3.12
165
15
11.4
2
14.37
3.66
180
15
12.6
2.3
15.1
3.47
195
15
12.5
2.3
15.75
3.39
210
15
12.5
2.1
14.87
2.85
225
30
10.6
2.1
12.62
2.07
240
30
11.2
2.3
12.94
2.3
255
30
10.2
2.3
10.38
3.13
270
30
11.7
3.2
13.36
3.33
285
45
12.6
2.4
11.5
1.16
300
45
13.8
2.9
11.61
0.4
315
45
12.9
2.1
11.89
0.84
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done

143
HISTAMINE DOSE-RESPONSE DATA
Chloride Concentration and Output
TIME
DOSE
CL- CONCENTRATION
CHLORIDE OUTPUT
minutes
l-ig/kg-hr
mEq/L
|.ieQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
72.87
1.15
72.19
4.85
30
0
72.02
1.50
60.01
7.19
45
0
71.71
1.55
67.20
7.24
60
HVP
70.86
1.21
63.93
6.16
75
72.45
1.23
45.91
8.77
90
69.65
2.09
58.02
3.65
105
7.5
74.94
2.38
72.90
5.33
120
7.5
77.70
2.20
84.98
8.91
135
7.5
76.34
2.27
86.41
7.48
150
7.5
77.81
0.79
101.99
10.08
165
15
76.48
1.58
94.74
11.49
180
15
77.49
1.25
92.69
7.90
195
15
76.11
1.38
95.43
7.11
210
15
77.83
1.36
93.72
8.10
225
30
77.09
1.74
96.30
8.19
240
30
76.92
1.67
92.54
9.05
255
30
75.78
1.90
75.53
16.06
270
30
78.09
0.56
92.96
10.10
285
45
75.70
3.25
72.41
17.96
300
45
78.50
1.50
69.20
15.65
315
45
76.28
0.88
71.27
5.54
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done

APPENDIX B
PYRILAMINE PRETREATMENT STUDY DATA
VOLUME (ml)
TIME
TREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
247.50
51.21
180.00
29.44
30
BASAL
BASAL
275.00
55.75
210.00
35.36
45
BASAL
BASAL
300.00
20.82
297.50
62.77
60
HVP
BASAL
272.50
13.15
317.50
60.05
75
P-P
BASAL
155.00
22.17
287.50
75.54
90
P-P
BASAL
187.50
52.18
330.00
82.87
105
PENTAGASTRIN
352.50
198.80
295.00
90.60
120
PENTAGASTRIN
457.50
179.04
327.50
76.64
135
PENTAGASTRIN
435.00
203.20
432.50
110.63
150
PENTAGASTRIN
630.00
148.72
707.50
156.86
165
PENTAGASTRIN
535.00
120.45
617.50
108.35
180
PENTAGASTRIN
602.50
131.24
627.50
69.69
195
PENTAGASTRIN
ND
ND
590.00
72.23
210
PENTAGASTRIN
ND
ND
650.00
101.41
225
PENTAGASTRIN
ND
ND
667.50
102.26
240
PENTAGASTRIN
ND
ND
645.00
41.33
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine
144

145
PYRILAMINE PRETREATMENT STUDY DATA
ACID CONCENTRATION (mEq/L)
TIME
PRETREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
40.25
12.69
27.15
16.06
30
BASAL
BASAL
40.15
10.14
22.20
15.65
45
BASAL
BASAL
38.78
8.43
28.69
16.29
60
HVP
BASAL
37.85
10.33
30.58
10.32
75
P-P
BASAL
38.61
7.90
37.90
13.30
90
P-P
BASAL
26.00
5.99
32.11
13.50
105
PENTAGASTRIN
26.36
12.53
38.09
14.55
120
PENTAGASTRIN
37.46
17.04
34.95
12.28
135
PENTAGASTRIN
45.45
19.60
28.71
14.98
150
PENTAGASTRIN
49.89
18.06
27.75
5.37
165
PENTAGASTRIN
54.91
15.54
37.05
8.02
180
PENTAGASTRIN
49.86
13.01
47.00
10.51
195
PENTAGASTRIN
ND
ND
50.66
9.84
210
PENTAGASTRIN
ND
ND
46.25
11.38
225
PENTAGASTRIN
ND
ND
45.01
10.37
240
PENTAGASTRIN
ND
ND
43.76
4.85
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine

146
PYRILAMINE PRETREATMENT STUDY DATA
ACID OUTPUT ((aEq/kg-15 min)
TIME
PRETREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
21.01
8.14
11.22
6.23
30
BASAL
BASAL
22.96
6.33
12.63
8.70
45
BASAL
BASAL
26.01
5.34
16.91
8.60
60
HVP
BASAL
23.28
5.81
21.62
7.86
75
P-P
BASAL
13.65
2.93
25.26
10.99
90
P-P
BASAL
10.49
2.63
29.02
10.83
105
PENTAGASTRIN
12.33
4.91
34.37
11.61
120
PENTAGASTRIN
32.59
10.20
35.64
12.52
135
PENTAGASTRIN
35.23
12.93
35.47
14.39
150
PENTAGASTRIN
54.67
10.46
46.96
5.93
165
PENTAGASTRIN
56.43
6.69
56.64
7.58
180
PENTAGASTRIN
58.40
4.55
77.53
12.48
195
PENTAGASTRIN
ND
ND
77.90
9.28
210
PENTAGASTRIN
ND
ND
74.98
10.13
225
PENTAGASTRIN
ND
ND
76.32
10.87
240
PENTAGASTRIN
ND
ND
78.40
9.56
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine

APPENDIX C
DATA FROM BALLOON/NO BALLOON STUDY
Volume of Gastric Contents
(ml/15 minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
490.0
44.12
497.5
60.63
523.3
49.12
30
BASAL
420.8
54.93
464.3
68.79
541.7
45.20
45
BASAL
405.8
56.12
422.5
82.52
541.7
42.93
60
HVP
429.5
71.64
439.2
53.87
470.8
34.84
75
350.5
61.29
328.3
46.72
409.8
55.93
90
361.7
45.86
335.8
60.27
383.3
36.46
105
INFUSION
393.3
74.37
419.2
40.38
505.8
70.36
120
INFUSION
456.8
58.95
569.2
52.26
800.8
74.17
135
INFUSION
493.3
27.89
598.3
52.75
899.2
62.67
150
INFUSION
491.7
22.42
665.0
49.58
923.3
41.20
165
INFUSION
465.8
21.85
650.8
49.27
886.7
38.36
180
INFUSION
480.0
39.24
677.5
53.69
885.0
40.72
HVP = Pyrilamine maleate infusion
147

148
Volume of Gastric Contents
(ml/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
272.0
45.13
266.2
56.27
229.5
46.22
30
BASAL
245.5
53.38
246.7
69.62
251.0
34.30
45
BASAL
252.3
40.58
251.5
58.20
259.0
37.07
60
HVP
194.7
36.72
237.7
54.05
233.3
26.09
75
139.3
31.75
148.2
33.19
164.0
27.99
90
138.0
24.72
170.0
35.33
163.7
27.86
105
INFUSION
200.0
29.34
207.7
49.00
269.7
26.40
120
INFUSION
215.0
33.74
299.2
77.17
427.5
39.99
135
INFUSION
211.7
29.67
326.3
54.89
468.3
24.45
150
INFUSION
219.3
31.58
386.8
61.57
450.0
26.61
165
INFUSION
233.2
39.58
436.0
53.74
550.0
66.72
180
INFUSION
220.7
45.42
455.0
58.30
497.5
38.03
HVP = Pyrilamine maleate infusion

149
pH of Gastric Contents
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
2.37
0.792
1.67
0.167
2.71
0.927
30
BASAL
2.39
0.839
1.55
0.055
2.39
0.629
45
BASAL
2.69
1.044
1.73
0.136
1.83
0.148
60
HVP
2.67
1.106
2.53
0.835
1.70
0.088
75
2.68
0.966
2.40
0.790
1.69
0.073
90
3.05
1.062
2.69
0.699
2.07
0.257
105
INFUSION
2.91
1.008
1.72
0.130
3.46
0.869
120
INFUSION
2.81
0.894
1.36
0.050
2.90
0.810
135
INFUSION
2.73
0.758
1.33
0.060
1.85
0.136
150
INFUSION
2.34
0.447
1.34
0.056
1.67
0.062
165
INFUSION
2.48
0.719
1.32
0.055
1.61
0.047
180
INFUSION
2.42
0.673
1.34
0.084
1.57
0.052
HVP = Pyrilamine maleate infusion

150
pH of Gastric Contents
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
1.59
0.124
1.77
0.164
2.38
0.904
30
BASAL
1.52
0.095
2.00
0.407
1.54
0.131
45
BASAL
1.54
0.094
2.93
0.940
2.18
0.778
60
HVP
1.72
0.208
3.49
1.259
2.45
1.060
75
2.04
0.343
3.56
1.217
2.53
1.072
90
2.23
0.419
2.89
0.962
2.59
1.083
105
INFUSION
2.77
0.726
1.90
0.269
1.52
0.109
120
INFUSION
2.40
0.743
1.33
0.040
1.32
0.028
135
INFUSION
2.35
0.783
1.25
0.020
1.26
0.034
150
INFUSION
2.62
0.895
1.23
0.026
1.27
0.031
165
INFUSION
2.47
0.888
1.22
0.033
1.28
0.028
180
INFUSION
2.42
0.926
1.20
0.041
1.26
0.022
HVP = Pyrilamine maleate infusion

151
Potassium Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
11.67
1.09
10.76
0.92
9.97
0.91
30
BASAL
10.88
1.05
9.73
0.77
9.76
0.76
45
BASAL
10.55
1.25
8.32
0.97
9.65
0.69
60
HVP
10.38
1.07
7.91
0.82
9.76
0.77
75
8.89
0.81
7.60
0.54
8.62
0.54
90
8.38
1.00
7.44
0.50
7.63
0.44
105
INFUSION
9.28
0.72
10.16
0.87
7.82
0.38
120
INFUSION
9.31
0.52
14.43
0.85
9.78
0.81
135
INFUSION
9.68
0.80
14.87
0.98
10.03
0.61
150
INFUSION
9.78
0.85
14.19
0.86
10.49
0.42
165
INFUSION
9.68
0.50
14.08
0.79
10.01
0.40
180
INFUSION
9.97
0.78
13.95
1.01
10.66
0.66
HVP = Pyrilamine maleate infusion

152
Potassium Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
11.07
1.60
9.14
1.17
9.97
1.54
30
BASAL
9.84
1.09
9.69
1.25
10.44
1.45
45
BASAL
9.04
0.92
9.44
1.27
10.40
1.19
60
HVP
8.73
1.08
8.58
1.08
10.74
1.11
75
7.52
0.91
6.87
0.56
8.52
0.73
90
7.34
0.95
7.31
0.65
8.33
0.69
105
INFUSION
9.25
1.40
10.56
1.08
11.26
1.10
120
INFUSION
9.90
1.32
17.70
0.84
13.99
1.35
135
INFUSION
9.95
1.54
18.62
1.03
14.81
1.30
150
INFUSION
9.45
1.00
18.21
0.95
13.88
1.15
165
INFUSION
9.06
0.95
18.11
1.03
13.12
1.06
180
INFUSION
8.80
1.16
17.20
1.03
13.44
1.01
HVP = Pyrilamine maleate infusion

153
Potassium Output in Gastric Contents
(jiEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
12.24
1.85
11.24
1.54
11.33
1.82
30
BASAL
10.16
2.39
10.02
1.98
11.53
1.73
45
BASAL
9.67
2.22
8.26
2.31
11.42
1.75
60
HVP
10.11
2.34
7.75
1.67
9.91
1.33
75
6.70
1.40
5.21
0.75
7.84
1.47
90
6.65
1.27
5.40
1.22
6.37
0.93
105
INFUSION
7.96
1.88
9.07
1.24
8.54
1.39
120
INFUSION
9.06
1.39
17.36
1.62
16.72
2.03
135
INFUSION
10.19
1.13
18.57
1.18
18.94
1.02
150
INFUSION
10.29
1.23
19.81
1.14
20.64
1.21
165
INFUSION
9.54
0.55
19.28
1.21
18.90
1.02
180
INFUSION
10.06
0.95
19.77
1.33
20.13
1.59
HVP = Pyrilamine maleate infusion

154
Potassium Output in Gastric Contents
(pEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
6.64
1.49
5.74
1.91
5.17
1.32
30
BASAL
5.21
1.20
5.92
2.04
5.88
1.21
45
BASAL
4.90
0.92
5.68
1.78
5.89
1.10
60
HVP
3.56
0.74
4.83
1.51
5.45
0.94
75
2.16
0.55
2.19
0.50
2.78
0.35
90
2.15
0.44
2.65
0.60
2.93
0.53
105
INFUSION
3.88
0.74
4.90
1.47
6.55
1.06
120
INFUSION
4.60
0.99
11.08
2.51
12.55
1.67
135
INFUSION
4.49
0.90
12.69
1.79
14.41
0.68
150
INFUSION
4.36
0.83
14.64
1.91
13.00
0.73
165
INFUSION
4.48
0.90
16.55
1.84
15.22
2.29
180
INFUSION
4.26
1.23
16.19
1.60
14.09
1.49
HVP = Pyrilamine maleate infusion

155
Chloride Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
139.3
4.24
133.9
5.04
140.2
6.07
30
BASAL
144.5
4.91
135.9
7.54
148.3
4.71
45
BASAL
144.0
5.59
137.0
4.76
150.8
5.98
60
HVP
147.2
4.63
137.8
7.93
151.2
5.70
75
142.5
4.84
136.9
8.94
150.3
5.34
90
142.6
5.66
138.0
6.63
148.0
6.50
105
INFUSION
146.1
7.90
145.0
6.08
134.4
7.84
120
INFUSION
147.5
4.80
143.6
5.54
144.9
5.06
135
INFUSION
146.2
5.19
144.4
4.43
143.2
5.51
150
INFUSION
141.2
4.95
147.0
3.45
144.7
3.87
165
INFUSION
143.1
4.02
143.3
4.50
143.5
5.65
180
INFUSION
143.4
3.62
146.5
2.74
144.5
7.71
HVP = Pyrilamine maleate infusion

156
Chloride Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
151. l
3 08
148.8
4.56
149.5
6.68
30
BASAL
152.2
3.72
151.2
3 07
151.0
6.54
45
BASAL
150.9
3.22
152.3
7.46
149.0
7.34
60
HVP
151.2
4.80
155.4
7.89
145.8
4.11
75
148.5
4.72
160.9
6.01
146.7
5.79
90
149.1
4.84
167.6
5.10
147.4
6.99
105
INFUSION
149.7
4.78
162.0
4.15
147.8
3.70
120
INFUSION
148.8
5.79
165.4
3.68
156.5
4.60
135
INFUSION
150.3
4.43
159.4
5.31
149.0
3.04
150
INFUSION
151.0
6.58
153.6
5.87
151.7
3.69
165
INFUSION
151.8
4.77
156.4
2.70
153.6
2.64
180
INFUSION
150.7
5.37
157.5
4.37
154.5
2.47
HVP = Pyrilamine maleate infusion

157
Chloride Output in Gastric Contents
(f.iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
144.8
13.33
143.8
21.01
156.3
17.09
30
BASAL
131.3
20.66
136.3
24.94
136.3
24.94
45
BASAL
127.2
22.11
127.7
27.93
174.3
15.53
60
HVP
137.2
25.79
131.8
22.06
151.9
14.06
75
107.0
21.14
95.9
17.18
134.9
21.76
90
109.9
15.54
98.2
19.95
120.6
11.46
105
INFUSION
119.9
24.13
131.5
16.56
145.8
23.74
120
INFUSION
139.8
14.24
176.2
18.91
245.7
18.13
135
INFUSION
152.6
8.15
185.2
18.92
277.9
30.20
150
INFUSION
147.1
6.86
210.4
20.33
287.4
22.51
165
INFUSION
141.3
6.74
200.8
20.12
272.9
20.35
180
INFUSION
145.2
10.89
213.8
20.78
272.9
18.58
HVP = Pyrilamine maleate infusion

158
Chloride Output in Gastric Contents
(|iEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
88.2
15.26
87.2
19.95
73.1
15.61
30
BASAL
79.8
17.74
82.0
23.35
82.4
13.43
45
BASAL
81.9
13.99
83 .2
19.33
83.6
13.72
60
HVP
64.3
13.67
80.5
19.12
73.2
9.44
75
45.8
11.54
51.2
11.59
51.5
9.49
90
44.7
8.84
59.7
10.71
52.9
10.47
105
INFUSION
64.4
10.03
70.9
16.58
84.3
7.42
120
INFUSION
69.1
11.47
105.0
27.41
141.9
13.99
135
INFUSION
68.6
10.79
111.2
20.15
147.7
6.90
150
INFUSION
70.8
11.25
128.4
23.24
144.5
8.56
165
INFUSION
75.8
13.35
145.6
19.32
180.0
23.38
180
INFUSION
11.7
14.79
152.7
19.74
164.0
14.75
HVP = Pyrilamine maleate infusion

159
Acid Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
37.4
7.52
40.8
7.40
26.5
7.61
30
BASAL
38.2
6.73
41.8
4.39
25.1
6.65
45
BASAL
35.2
9.27
34.3
6.65
27.9
5.49
60
HVP
37.7
8.25
29.1
9.23
32.5
4.99
75
31.8
7.06
32.6
9.30
32.9
2.71
90
22.2
7.44
21.6
7.20
24.8
5.82
105
INFUSION
22.6
6.58
35.9
6.59
16.6
4.52
120
INFUSION
23.2
6.32
71.2
4.64
24.1
5.90
135
INFUSION
21.9
5.56
81.0
5.96
30.5
5.37
150
INFUSION
24.5
7.19
77.7
5.56
35.7
3.59
165
INFUSION
29.0
5.51
78.0
4.53
40.1
2.90
180
INFUSION
28.8
5.43
82.7
5.18
44.7
3.38
HVP = Pyrilamine maleate infusion

160
Acid Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
53.3
9.93
37.8
9.37
46.9
12.28
30
BASAL
53.9
9.84
40.1
10.79
52.4
8.95
45
BASAL
48.6
7.96
35.8
12.98
51.1
10.41
60
HVP
44.2
10.13
33.8
13.03
53.5
10.97
75
34.9
9.16
28.8
12.79
44.5
9.29
90
27.1
7.73
22.8
8.82
38.9
8.13
105
INFUSION
27.0
8.34
39.7
11.10
50.8
7.52
120
INFUSION
34.0
8.61
85.4
6.65
73.6
5.09
135
INFUSION
39.3
9.89
96.0
3.93
85.6
2.59
150
INFUSION
39.1
11.03
101.1
3.37
85.2
4.23
165
INFUSION
38.4
9.88
102.1
3.76
82.2
5.22
180
INFUSION
39.1
8.30
104.2
3.21
86.1
4.66
HVP = Pyrilamine maleate infusion

161
Acid Output in Gastric Contents
(|iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
38.4
9.03
42.4
9.53
31.0
10.00
30
BASAL
36.1
10.09
42.3
9.50
29.9
9.07
45
BASAL
34.7
11.53
35.9
12.09
34.0
9.09
60
HVP
39.5
11.10
31.0
12.55
34.2
7.87
75
25.8
8.35
24.4
9.93
29.1
5.01
90
17.7
7.01
17.1
8.95
20.8
5.35
105
INFUSION
18.6
8.29
33.5
9.01
18.9
6.64
120
INFUSION
21.7
7.36
86.9
10.36
41.4
10.44
135
INFUSION
23.1
6.47
100.9
6.59
56.7
10.15
150
INFUSION
26.2
8.64
108.0
6.04
69.7
6.59
165
INFUSION
28.3
5.33
107.5
8.46
75.7
6.25
180
INFUSION
28.8
5.69
117.8
8.16
84.7
7.74
HVP = Pyrilamine maleate infusion

162
Acid Output in Gastric Contents
(f.iEq/kg/l5minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
34.4
9.91
26.2
11.94
26.9
8.50
30
BASAL
32.1
10.71
28.6
13.47
30.1
5.80
45
BASAL
28.4
7.81
27.0
13.07
30.9
6.34
60
HVP
19.8
7.15
24.1
11.66
28.9
6.06
75
11.9
5.09
13.0
8.02
16.3
3.62
90
9.5
3.95
11.1
6.10
14.9
4.05
105
INFUSION
12.7
4.15
21.8
9.64
30.9
6.41
120
INFUSION
17.8
5.01
56.7
16.94
66.5
7.33
135
INFUSION
20.1
5.49
68.1
12.82
84.9
4.36
150
INFUSION
19.6
6.50
82.8
12.28
80.8
4.73
165
INFUSION
22.1
7.22
94.1
10.43
92.9
6.68
180
INFUSION
21.4
6.76
100.0
11.22
89.5
5.02
HVP = Pyrilaraine maleate infusion

163
Sodium Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
104.9
5.98
89.0
6.38
105.1
9.96
30
BASAL
103.1
7.52
88.5
5.40
109.5
9.80
45
BASAL
109.5
11.91
94.1
6.76
104.2
7.54
60
HVP
105.3
10.98
98.9
8.58
100.4
6.57
75
113.1
8.43
94.6
7.16
100.7
2.87
90
120.5
7.27
107.0
5.19
106.2
5.58
105
INFUSION
119.3
6.61
91.3
6.24
109.8
5.51
120
INFUSION
111.8
5.46
60.0
4.87
105.0
6.79
135
INFUSION
115.1
4.96
49.9
6.30
96.4
6.44
150
INFUSION
111. 5
5.10
53.6
5.93
94.4
5.05
165
INFUSION
107.9
4.22
55.1
4.76
86.8
4.72
180
INFUSION
108.1
5.05
49.9
5.68
89.5
4.83
HVP = Pyrilamine maleate infusion

164
Sodium Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
82.9
9.98
99.2
9.54
86.0
12.47
30
BASAL
79.9
10.11
97.8
10.02
80.6
7.77
45
BASAL
87.2
8.80
101.3
11.59
79.7
7.87
60
HVP
91.3
10.21
105.5
12.21
79.9
8.44
75
93.6
9.62
106.2
12.18
88.7
8.49
90
102.8
8.90
115.2
10.43
94.9
9.67
105
INFUSION
100.6
8.95
97.7
13.97
83.2
7.77
120
INFUSION
95.0
8.32
48.8
6.56
62.5
6.43
135
INFUSION
91.9
9.28
35.6
3.42
52.9
5.07
150
INFUSION
88.7
9.41
31.4
3.79
54.1
5.94
165
INFUSION
92.0
9.39
31.7
4.39
56.6
7.70
180
INFUSION
91.2
9.68
30.5
3.92
52.9
6.96
HVP = Pyrilamine maleate infusion

165
Sodium Output in Gastric Contents
(|.iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
109.0
11.10
95.5
13.84
113.7
8.50
30
BASAL
91.0
11.35
87.8
14.97
126.2
16.00
45
BASAL
90.5
10.05
81.8
14.55
118.0
6.73
60
HVP
92.7
15.30
90.8
11.55
98.5
3.46
75
83.6
14.13
65.6
10.22
89.9
14.66
90
92.2
12.04
75.8
12.91
86.2
8.24
105
INFUSION
100.0
18.79
81.3
8.78
114.7
11.91
120
INFUSION
108.9
15.11
73.1
8.47
178.1
16.21
135
INFUSION
120.3
7.38
67.6
12.77
186.3
20.53
150
INFUSION
115.9
5.01
79.3
13.57
187.6
17.53
165
INFUSION
106.9
6.69
78.8
12.33
165.2
14.37
180
INFUSION
110.8
10.91
75.3
13.48
169.7
15.00
HVP = Pyrilamine maleate infusion

166
Sodium Output in Gastric Contents
(|aEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
43.7
4.19
53.7
9.51
38.0
6.96
30
BASAL
36.6
3.82
46.4
10.49
42.1
6.98
45
BASAL
43.9
5.29
48.4
7.26
42.3
6.51
60
HVP
35.7
6.63
46.8
5.68
38.6
5.21
75
26.7
6.13
29.7
2.94
30.0
5.25
90
28.2
3.12
38.4
4.58
33 3
6.34
105
INFUSION
41.1
5.55
37.5
4.55
46.6
4.51
120
INFUSION
40.7
4.48
29.1
6.46
58.0
10.44
135
INFUSION
38.6
2.96
23.7
3.87
52.2
5.34
150
INFUSION
40.0
6.23
26.9
6.67
51.4
5.84
165
INFUSION
42.6
5.33
30.1
6.56
71.6
21.33
180
INFUSION
40.0
7.27
30.1
6.65
58.8
12.68
HVP = Pyrilamine maleate infusion

167
Volume of Duodenal Contents
(ml/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
123.0
22.27
28.7
9.81
29.0
13.71
30
BASAL
89.7
32.49
65.7
34.39
26.2
12.29
45
BASAL
118.3
38.62
56.5
27.10
29.2
10.34
60
HVP
111. 0
24.69
42.4
25.67
28.0
10.73
75
96.3
30.22
63.3
10.02
28.8
9.22
90
85.7
28.71
82.8
20.57
29.8
10.76
105
INFUSION
93.5
36.58
73.7
23.30
79.7
25.35
120
INFUSION
73.7
39.04
87.0
28.56
87.0
16.94
135
INFUSION
63.0
20.85
93.3
41.51
79.3
18.03
150
INFUSION
55.7
17.42
62.5
34.72
59.7
15.05
165
INFUSION
80.3
27.86
63.5
23.35
67.0
18.41
180
INFUSION
69.7
21.81
54.3
26.34
62.0
13.08
HVP = Pyrilamine maleate infusion

168
Volume of Duodenal Contents
(ml/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
250.5
78.73
149.8
41.80
201.3
45.57
30
BASAL
244.7
54.52
178.0
63.34
245.7
37.12
45
BASAL
225.5
51.44
186.8
57.22
222.5
33.31
60
HVP
215.2
53.61
190.8
55.71
212.0
32.13
75
183.2
57.45
228.2
40.55
170.0
24.97
90
222.8
48.59
299.7
53.26
183.5
45.25
105
INFUSION
209.0
51.34
276.2
71.59
559.2
104.8
120
INFUSION
232.5
53.69
218.7
72.12
527.0
108.1
135
INFUSION
219.0
56.42
186.0
41.84
404.0
101.7
150
INFUSION
177.5
44.21
197.3
39.75
503.3
84.9
165
INFUSION
204.5
41.48
166.7
18.67
392.0
117.6
180
INFUSION
157.5
58.14
144.5
14.20
426.0
105.4
HVP = Pyrilamine maleate infusion

169
pH of Duodenal Contents
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
8.22
0.14
8.05
0.21
8.53
0.13
30
BASAL
8.14
0.15
8.00
0.16
8.62
0.04
45
BASAL
8.13
0.17
7.96
0.21
8.52
0.05
60
HVP
8.10
0.16
8.05
0.12
8.46
0.14
75
8.06
0.13
7.84
0.10
8.47
0.09
90
8.10
0.13
7.90
0.11
8.46
0.15
105
INFUSION
8.12
0.13
7.97
0.12
8.42
0.10
120
INFUSION
8.11
0.18
7.90
0.11
8.37
0.13
135
INFUSION
8.14
0.09
7.98
0.15
8.41
0.10
150
INFUSION
8.18
0.14
7.92
0.15
8.37
0.12
165
INFUSION
8.04
0.10
7.98
0.15
8.38
0.10
180
INFUSION
8.04
0.10
7.90
0.17
8.36
0.12
HVP = Pyrilamine maleate infusion

170
pH of Duodenal Contents
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
8.24
0 09
8.25
0.05
8.30
0.14
30
BASAL
8.17
0.12
8.17
0.12
8.25
0.14
45
BASAL
8.20
0.11
8.17
0.14
8.21
0.12
60
HVP
8.16
0.12
8.15
0.15
8.20
0.12
75
8.04
0.13
8.04
0.11
8.18
0.11
90
8.13
0.13
8.02
0.12
8.09
0.13
105
INFUSION
8.06
0.11
8.07
0.16
8.36
0.05
120
INFUSION
8.06
0.12
8.09
0.15
8.33
0.05
135
INFUSION
8.03
0.10
8.05
0.10
8.26
0.07
150
INFUSION
8.08
0.12
7.97
0.09
8.20
0.11
165
INFUSION
8.03
0.10
7.91
0.09
8.24
0.03
180
INFUSION
8.07
0.11
7.93
0.10
8.18
0.07
HVP = Pyrilamine maleate infusion

171
Bicarbonate Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
27.70
2.05
25.39
3.08
23.23
2.92
30
BASAL
24.21
3.24
22.94
2.58
24.06
2.39
45
BASAL
22.36
2.92
22.36
1.98
23.11
2.25
60
HVP
22.12
3.53
23.37
1.81
24.95
2.03
75
24.04
3.17
22.48
1.46
21.69
1.52
90
23.89
2.52
22.51
1.74
24.11
2.02
105
INFUSION
23.61
2.24
25.01
2.15
29.28
2.67
120
INFUSION
23.08
3.65
25.36
2.53
34.28
1.67
135
INFUSION
23.59
4.28
24.38
1.72
35.17
2.21
150
INFUSION
23.95
2.48
22.68
3.36
33.26
1.48
165
INFUSION
24.48
2 64
23.88
1.87
31.82
2.32
180
INFUSION
22.81
2.69
21.86
2.68
34.23
2.36
HVP = Pyrilamine maleate infusion

172
Bicarbonate Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
31.82
2.73
24.05
3.30
25.44
1.90
30
BASAL
29.28
2 81
28.63
2.62
28.82
2.92
45
BASAL
28.40
2.65
28.02
2.05
27.70
2.90
60
HVP
26.29
3.20
29.52
1.61
26.38
2.87
75
30.95
3.74
31.44
0.73
27.34
2.72
90
26.71
4.09
31.55
1.04
23.97
3.83
105
INFUSION
25.97
5.05
33.59
1.42
36.56
1.43
120
INFUSION
27.40
3.77
32.42
2.90
36.04
2.55
135
INFUSION
28.02
2.12
29.70
2.19
36.51
2.85
150
INFUSION
27.36
3.76
28.71
1.67
36.77
2.68
165
INFUSION
30.91
5.98
28.81
1.66
37.08
2.41
180
INFUSION
26.03
3.34
27.83
2.18
37.13
1.87
HVP = Pyrilamine maleate infusion

173
Sodium Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
155.2
4.86
143.2
2.59
144.2
1.95
30
BASAL
154.2
5.54
142.3
1.90
145.4
2.48
45
BASAL
157.2
8.78
141.7
2.28
144.2
2.56
60
HVP
153.6
5.05
142.2
1.99
139.2
4.54
75
151.9
4.72
142.2
2.62
153.4
10.80
90
160.9
11.02
143.2
1.18
157.2
10.15
105
INFUSION
151.1
6.99
141.6
0.87
143.0
1.87
120
INFUSION
162.4
11.23
139.7
1.48
142.1
2.20
135
INFUSION
152.0
9.44
135.8
3 82
142.4
2.82
150
INFUSION
149.3
8.52
138.3
1.70
144.4
3.73
165
INFUSION
151.5
5.31
135.7
2.26
143.7
1.88
180
INFUSION
146.4
5.82
134.4
3.78
146.2
2.95
HVP = Pyrilamine maleate infusion

174
Sodium Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
138.6
8.41
145.0
4.39
133.8
7.76
30
BASAL
138.2
6.98
136.4
5.29
136.9
5.98
45
BASAL
132.4
11.75
134.9
4.39
141.6
6.43
60
HVP
140.3
9.75
131.6
6.30
137.1
4.55
75
134.0
9.88
135.2
6.85
140.0
6.47
90
132.1
6.65
141.5
3.91
136.0
5.97
105
INFUSION
136.9
5.55
137.1
4.63
142.0
5.56
120
INFUSION
133.7
9.76
139.8
4.94
140.4
9.43
135
INFUSION
130.9
12.34
137.0
4.20
142.2
7.90
150
INFUSION
141.0
6.83
141.5
2.20
142.2
7.15
165
INFUSION
141.3
7.44
143.7
2.42
143.0
7.71
180
INFUSION
134.8
6.67
142.5
1.92
143.8
11.14
HVP = Pyrilamine maleate infusion

175
Potassium Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
4.62
0.28
4.40
0.09
4.47
0.08
30
BASAL
4.69
0.30
4.29
0.07
4.45
0.06
45
BASAL
4.88
0.36
4.22
0.17
4.39
0.09
60
HVP
4.68
0.29
4.23
0.14
4.31
0.11
75
4.45
0.28
4.12
0.13
4.68
0.42
90
4.43
0.25
4.13
0.09
4.66
0.37
105
INFUSION
4.57
0.34
3.97
0.09
4.01
0.14
120
INFUSION
4.75
0.45
3.86
0.09
3 82
0.09
135
INFUSION
4.34
0.31
3 88
0.15
3.70
0.09
150
INFUSION
4.53
0.37
3.80
0.10
3.78
0.16
165
INFUSION
4.15
0.26
3.91
0.22
3 65
0.09
180
INFUSION
4.37
0.28
3.90
0.18
3.63
0.12
HVP = Pyrilamine maleate infusion

176
Potassium Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
3 86
0.29
4.17
0.15
3.96
0.29
30
BASAL
3.87
0.28
3 94
0.14
3.91
0.23
45
BASAL
3.72
0.39
3 83
0.11
4.14
0.30
60
HVP
3.95
0.37
3.79
0.18
3.88
0.20
75
3.71
0.36
3.82
0.18
3.95
0.24
90
3.68
0.30
3.96
0.07
3.95
0.29
105
INFUSION
4.19
0.50
3.85
0.12
3.77
0.18
120
INFUSION
3.58
0.35
3.78
0.06
3.50
0.28
135
INFUSION
3.66
0.44
3.67
0.12
3.73
0.34
150
INFUSION
3.87
0.28
3.63
0.10
3.62
0.34
165
INFUSION
3 83
0.30
3.71
0.11
3.57
0.31
180
INFUSION
3.61
0.28
3.68
0.12
3.49
0.39
HVP = Pyrilamine maleate infusion

177
Chloride Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
119.5
3.17
102.9
6.68
118.2
4.80
30
BASAL
123.4
3.98
102.7
4.00
126.6
6.12
45
BASAL
124.6
4.09
101.8
5.92
129.4
8.91
60
HVP
124.8
4.01
105.8
4.99
110.1
6.69
75
123.5
4.73
107.3
3.45
128.6
4.58
90
121.3
7.03
112.6
6.77
124.7
4.78
105
INFUSION
126.5
6.94
116.5
5.52
119.7
7.13
120
INFUSION
136.3
3.41
110.5
4.70
113.4
5.09
135
INFUSION
137.1
6.40
108.1
6.70
112.4
4.49
150
INFUSION
126.2
8.96
102.7
10.25
105.4
7.85
165
INFUSION
136.1
5.70
105.7
7.32
117.8
7.41
180
INFUSION
135.1
5.39
100.9
6.67
112.4
4.72
HVP = Pyrilamine maleate infusion

178
Chloride Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
126.2
4.91
126.2
7.55
122.7
6.69
30
BASAL
125.4
4.45
128.0
8.08
128.1
5.93
45
BASAL
122.4
7.44
125.1
11.79
130.8
4.88
60
HVP
116.9
7.71
126.8
9.98
127.0
5.13
75
120.9
3.78
122.7
3 81
131.4
5.14
90
117.3
2.65
121.9
4.09
129.1
7.06
105
INFUSION
122.0
3.03
118.0
4.37
110.0
3.65
120
INFUSION
123.6
5.12
121.1
4.00
104.1
5.39
135
INFUSION
126.0
5.19
110.3
4.05
110.0
1.95
150
INFUSION
129.6
5.13
115.4
3.75
108.7
3.82
165
INFUSION
128.6
5.72
111. 8
3.33
110.1
2.67
180
INFUSION
129.9
6.85
113.2
2.03
106.9
2.70
HVP = Pyrilamine maleate infusion

APPENDIX D
STATISTICAL ANALYSIS OF HISTAMINE DOSE RESPONSE DATA
Analysis by General Linear Model with One Way ANOVA for
repeated measures using SigmaStat software.
Gastric Content Volume
Source
DF
SS
MS
HORSES
5
1037113.3
207422.7
DOSE
4
1121695.0
280423.7
Residual
18
215095.0
11949.7
Total
27
2313867.9
85698.8
F Value P Value
o. 00000250
23.46696808 0.000000618
Acid Concentration of Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
12717.1
2543.4
0.000791
DOSE
4
51314.1
12828.5
35.833490
0.0000000241
Residual
18
6444.1
358.0
Total
27
69398.9
2570.3
179

Acid Output of Gastric Contents
Source
DF
ss
MS
F Value
P Value
HORSES
5
0.04418
0.008836
0.00000000214
DOSE
4
0.11481
0.028703
0.0140
0.0000000000
Residual
18
0.00369
0.000205
Total
27
0.15768
0.005840
Sodium Concentration of
Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
46911.3
9382.3
0.000000902
DOSE
4
27197.0
6799.2
14.454750403
0.0000188
Residual
18
8466.9
470.4
Total
27
84638.5
3134.8
Sodium i
Output of Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
0.08123
0.016245
0.00000932
DOSE
4
0.00187
0.000468
0.41486401
0.796
Residual
18
0.02029
0.001127
Total
27
0.10473
0.003879
180

APPENDIX E
STATISTICAL ANALYSIS OF PYRILAMINE MALEATE DATA
Analysis performed using SigmaStat software by General
Linear Model as Paired t-test.
Basal Collections
Parameter
t
DF
P Value
Volume
0.284
7
0.7849
Acid Concentration
-0.0792
7
0.9391
Acid Output
-0.189
7
0.8553
Post-pyrilamine Collections
Parameter
t
DF
P Value
Volume
3.23
7
0.0145
Acid Concentration
2.06
7
0.0785
Acid Output
5.61
7
0.0008
181

Early Infusion Collections
Parameter
t
DF
P Value
Volume
1.38
11
0.1953
Acid Concentration
-0.740
11
0.4747
Acid Output
2.54
11
0.0274
Late Infusion Collections
Parameter
t
DF
P Value
Volume
0.523
11
0.6113
Acid Concentration
-0.913
11
0.3807
Acid Output
3.77
11
0.0031

APPENDIX F
STATISTICAL ANALYSIS OF CATHETER/NO CATHETER DATA
Analysis is by General Linear Model with Two Way ANOVA
using SigraaStat software.
Gastric Content Volume
Source
DF
SS
MS
F Value
P Value
CATHETER
1
1310221.008
1310221.008
41.444
<0.001
TIME
3
2035066.025
678355.342
21.457
<0.001
CATH*TIME
3
22197.025
7399.008
0.234
0.872
Residual
72
2276250.917
31614.596
Total
79
5812169.487
73571.766
183

184
Acid
Concentration
of Gastric
Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
1722.366
1722.366
6.093
0.016
TIME
3
4863.528
1621.176
5.735
0.001
CATH*TIME
3
253.190
84.397
0.299
0.826
Residual
72
20353.253
282.684
Total
79
27373.608
346.501
Acid OutDUt of
Gastric Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
3099.751
3099.751
10.970
0.001
TIME
3
29506.653
9835.551
34.808
<0.001
CATH*TIME
3
741.643
247.214
0.875
0.458
Residual
72
20344.690
282.565
Total
79
56625.792
716.782

185
Sodium Concentration of Gastric Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
194.948
194.948
0.612
0.437
TIME
3
3880.260
1293.420
4.059
0.010
CATH*TIME
3
203.853
67.951
0.213
0.887
Residual
72
22941.946
318.638
Total
79
27518.836
348.340
Sodium Outout
of Gastric
Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
32851.071
32851.071
11.703
0.001
TIME
3
76666.512
25555.504
9.104
<0.001
CATH*TIME
3
649.446
216.482
0.0771
0.972
Residual
72
202115.891
2807.165
Total
79
313360.908
3966.594

APPENDIX G
STATISTICAL ANALYSIS OF BALLOON/NO BALLOON DATA
The SAS System
General Linear Models Procedure
Class
Levels
Values
HORSE
6
B D E H I T
BALLOON
2
no yes
DRUG
3
histamine
saline
pentagastrin
TIME
12
15 30 45 60
135 150 165
75 90 105 120
180
Abbreviations for following ANOVA tables:
B or b = Balloon vs. No Balloon
t = time
d = drug
* = interaction
pre = prior to infusion (t=15-90 minutes)
post = during infusion (t=105-180 minutes)
186

187
Gastric Content Volume
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
<
5
1581979.484
316395.897
43.98
0.0001
BALLOON(B)
1
6964934.280
6964934.280
968.07
0.0001
DRUG
2
1965459.060
982729.530
136.59
0.0001
B*DRUG
2
217416.144
108708.072
15.11
0.0001
HORSE*B*DRUG
25
1233421.502
49336.860
6.86
0.0001
TIME
11
4288302.581
389845.689
54.19
0.0001
B*TIME
11
237064.414
21551.310
3.00
0.0008
DRUG*TIME
22
1533188.995
69690.409
9.69
0.0001
B*DRUG*TIME
22
86068.579
3912.208
0.54
0.9552
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
518680.912
103736.182
14.42
0.0001
post,t effect
5
1103288.981
220657.796
30.67
0.0001
pre, b*t
5
13559.245
2711.849
0.38
0.8644
post,b*t
5
96643.Ill
19328.622
2.69
0.0214
pre,drug*t
10
31124.463
3112.446
0.43
0.9302
post,drug*t
10
368044.491
36804.449
5.12
0.0001
pre, b*drug*t
10
26594.907
2659.491
0.37
0.9591
post,b*drug*t
10
34653.361
3465.336
0.48
0.9016
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
2605905.67
2605905.67
92.193
0.00000
post,b effect
1
4485890.67
4485890.67
158.704
0.00000
pre, d effect
2
60907.37
30453.69
1.077
0.35223
post,d effect
2
3038571.73
1519285.87
53.750
0.00000
pre, d*b
2
48270.26
24135.13
0.854
0.43502
post, d*b
2
193966.19
96983.10
3.431
0.04437

188
Gastric
Content dH
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
i
5
193.5264900
38.7052980
34.44
0.0001
BALLOON(B)
1
2.9320558
2.9320558
2.61
0.1072
DRUG
2
19.7845588
9.8922794
8.80
0.0002
B*DRUG
2
13.0219616
6.5109808
5.79
0.0034
HORSE*B*DRUG
25
290.8255252
11.6330210
10.35
0.0001
TIME
11
40.6180692
3.6925517
3.29
0.0003
B*TIME
11
11.5292525
1.0481139
0.93
0.5091
DRUG*TIME
22
53.9146301
2.4506650
2.18
0.0019
B*DRUG*TIME
22
28.2382718
1.2835578
1.14
0.3000
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
12.86303704
2.57260741
2.29
0.0457
post,t effect
5
12.51123009
2.50224602
2.23
0.0514
pre, b*t
5
5.23759259
1.04751852
0.93
0.4603
post,b*t
5
3.09004861
0.61800972
0.55
0.7384
pre,drug*t
10
14.60956574
1.46095657
1.30
0.2292
post,drug*t
10
3.51883696
0.35188380
0.31
0.9776
pre, b*drug*t
10
5.42322130
0.54232213
0.48
0.9011
post,b*drug*t
10
5.79351944
0.57935194
0.52
0.8791
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.0030
0.0030
0.00046
0.98295
post,b effect
1
6.1307
6.1307
0.96115
0.33473
pre, d effect
2
2.8688
1.4344
0.22488
0.79995
post,d effect
2
52.7020
26.3510
4.13123
0.02600
pre, d*b
2
22.7303
11.3651
1.78179
0.18567
post, d*b
2
7.3132
3.6566
0.57327
0.56972

189
Acid Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
t
5
32666.61465
6533.32293
39.13
0.0001
BALLOON(B)
1
31688.10187
31688.10187
189.81
0.0001
DRUG
2
34270.57097
17135.28549
102.64
0.0001
B*DRUG
2
12733.08847
6366.54424
38.14
0.0001
HORSE*B*DRUG
25
39094.01299
1563.76052
9.37
0.0001
TIME
11
67444.90174
6131.35470
36.73
0.0001
B*TIME
11
7895.62062
717.78369
4.3
0.0001
DRUG*TIME
22
65110.70292
2959.57741
17.73
0.0001
B*DRUG*TIME
22
3948.51653
179.47802
1.08
0.3725
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
5915.33764
1183.06753
7.09
0.0001
post,t effect
5
25597.12889
5119.42578
30.67
0.0001
pre, b*t
5
662.13023
132 42605
0.79
0.5551
post,b*t
5
1371.83370
274.36674
1.64
0.1480
pre,drug*t
10
1742.00250
174,20025
1.04
0.4064
post,drug*t
10
9913.47028
991.34703
5.94
0.0001
pre, b*drug*t
10
495.34380
49.53438
0.30
0.9817
post,b*drug*t
10
664.93880
66.49388
0.40
0.9470
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
5146.06
5146.06
5.9468
0.02075
post,b effect
1
32403.70
32404.70
37.4457
0.00000
pre, d effect
2
1264.93
632.46
0.7309
0.48971
post,d effect
2
86460.88
43230.44
49.9571
0.00000
pre, d*b
2
3510.22
1755.11
2.0282
0.14889
post, d*b
2
12011.10
6005.55
6.9400
0.00327

190
Acid Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.08082750
0.01616550
106.35
0.0001
BALLOON(B)
1
0.00388800
0.00388800
25.58
0.0001
DRUG
2
0.06885906
0.03442953
226.50
0.0001
B*DRUG
2
0.00859756
0.00429878
28.28
0.0001
HORSE*BDRUG
25
0.03029697
0.00121188
7.97
0.0001
TIME
11
0.16610719
0.01510065
99.34
0.0001
B*TIME
11
0.00125706
0.00011428
0.75
0.6881
DRUG*TIME
22
0.09332317
0.00424196
27.91
0.0001
B*DRUG*TIME
22
0.00770722
0.00035033
2.30
0.0009
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.01059159
0.00211832
13.94
0.0001
post,t effect
5
0.06323181
0.01264636
83.20
0.0001
pre, b*t
5
0.00036315
0.00007263
0.48
0.7928
post,b*t
5
0.00029654
0.00005931
0.39
0.8555
pre,drug*t
10
0.00091566
0.00009157
0.60
0.8118
post,drug*t
10
0.02217682
0.00221768
14.59
0.0001
pre, b*drug*t
10
0.00078794
0.00007879
0.52
0.8770
post,b*drug*t
10
0.00209071
0.00020907
1.38
0.1902
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.00377
0.003767
5.523
0.02517
post,b effect
1
0.00072
0.000719
1.054
0.31240
pre, d effect
2
0.00000
0.000002
0.003
0.99654
post,d effect
2
0.13909
0.069543
101.977
0.00000
pre, d*b
2
0.00028
0.000142
0.208
0.81358
post, d*b
2
0.01314
0.006571
9.636
0.00054

191
Sodium Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
30181.87067
6036.37413
38.97
0.0001
BALLOON(B)
1
24969.04280
24969.04280
161.21
0.0001
DRUG
2
44132.80588
22066.40294
142.47
0.0001
B*DRUG
2
8922.09532
4461.04766
28.80
0.0001
HORSE*B*DRUG
25
46055.64502
1842.22580
11.89
0.0001
TIME
11
73160.32748
6650.93886
42.94
0.0001
B*TIME
11
7086.57970
644.23452
4.16
0.0001
DRUG*TIME
22
56593.70301
2572.44105
16.61
0.0001
B*DRUG*TIME
22
4775.21468
217.05521
1.40
0.1101
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
4954.00037
990.80007
6.40
0.0001
post,t effect
5
24135.98708
4827.19742
31.17
0.0001
pre, b*t
5
437.04981
87.40996
0.56
0.7273
post,b*t
5
1472.39968
294.47994
1.90
0.0936
pre,drug*t
10
1511.62991
151.16299
0.98
0.4641
post,drug*t
10
9416.88083
941.68808
6.08
0.0001
pre, b*drug*t
10
494.41269
49.44127
0.32
0.9759
post,b*drug*t
10
1359.65435
135.96544
0.88
0.5542
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
3703.48
3703.48
3.7088
0.06386
post,b effect
1
26442.69
26442.69
26.4810
0.00002
pre, d effect
2
250.42
125.21
0.1254
0.88262
post,d effect
2
89547.58
44773.79
44.8386
0.00000
pre, d*b
2
8239.65
4119.83
4.1258
0.02636
post, d*b
2
3603.59
1801.79
1.8044
0.18235

Sodium Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.02352621
0.00470524
12.97
0.0001
BALLOON(B)
1
0.43675692
0.43675692
1204.21
0.0001
DRUG
2
0.08437257
0.04218628
116.31
0.0001
B*DRUG
2
0.03794764
0.01897382
52.31
0.0001
HORSE*B*DRUG
25
0.07838351
0.00313534
8.64
0.0001
TIME
11
0.03514183
0.00319471
8.81
0.0001
B*TIME
11
0.01913108
0.00173919
4.80
0.0001
DRUG*TIME
22
0.05861341
0.00266425
7.35
0.0001
B*DRUG*TIME
22
0.01446002
0.00065727
1.81
0.0150
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.01271226
0.00254245
7.01
0.0001
post,t effect
5
0.00408749
0.00081750
2.25
0.0488
pre, b*t
5
0.0079682
0.00015936
0.44
0.8209
post,b*t
5
0.00552939
0.00110588
3.05
0.0105
pre,drug*t
10
0.00294658
0.00029466
0.81
0.6169
post,drug*t
10
0.01127471
0.00112747
3.11
0.0008
pre, b*drug*t
10
0.00221936
0.00022194
0.61
0.8037
post,b*drug*t
10
0.00474130
0.00047413
1.31
0.2251
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.15026
0.15026
85.967
0.00000
post,b effect
1
0.29794
0.29794
170.458
0.00000
pre, d effect
2
0.00323
0.00161
0.923
0.40798
post,d effect
2
0.12425
0.06213
35.544
0.00000
pre, d*b
2
0.00641
0.00321
1.834
0.17659
post, d*b
2
0.03874
0.01937
11.083
0.00023

193
Potassium Concentration in Gastric Contents
Source
DF
Type I SS
HORSE
5
139.934838
BALLOON(B)
1
209.585208
DRUG
2
315.970880
B*DRUG
2
169.367639
HORSE*B*DRUG
25
745.549468
TIME
11
1413.509699
B*TIME
11
195.413403
DRUG*TIME
22
1009.475787
B*DRUG*TIME
22
72.474583
Contrast
DF
Contrast :
pre,t effect
5
229.096343
post,t effect
5
261.283148
pre, b*t
5
6.743009
post,b*t
5
20.045370
pre,drug*t
10
25.108241
post,drug*t
10
157.176574
pre, b*drug*t
10
13.242685
post,b*drug*t
10
24.664352
Source
DF
SS N
pre, b effect
1
1.11
post,b effect
1
377.10
pre, d effect
2
75.94
post,d effect
2
1067.23
pre, d*b
2
32.17
post, d*b
2
171.77
Mean Square
F Value
Pr > F
27.986968
9.51
0.0001
209.585208
71.22
0.0001
157.985440
53.68
0.0001
84.683819
28.78
0.0001
29.821979
10.13
0.0001
128.500882
43.66
0.0001
17.764855
6.04
0.0001
45.885263
15.59
0.0001
3.294299
1.12
0.3235
Mean Square
F Value
Pr > F
45.819269
15.57
0.0001
52.256630
17.76
0.0001
1.348602
0.46
0.8072
4.009074
1.36
0.2381
2.510824
0.85
0.5777
15.717657
5.34
0.0001
1.324269
0.45
0.9207
2.466435
0.84
0.5921
MS_N
F Value
PValue
1.11
0.0679
0.79620
377.098
23.0184
0.00004
37.968
2.3176
0.11581
533.613
32.5723
0.00000
16.085
0.9818
0.38628
85.883
5.2424
0.01112

Potassium Output in Gastric Contents
Source
DF
Type I SS
HORSE
5
0.00124741
t
BALLOON(B)
1
0.00204972
DRUG
2
0.00157501
B*DRUG
2
0.00000867
HORSE*B*DRUG
25
0.00099991
TIME
11
0.00552684
B*TIME
11
0.00006758
DRUG*TIME
22
0.00214371
B*DRUG*TIME
22
0.00008627
Contrast
DF
Contrast ;
pre,t effect
5
0.00065783
post,t effect
5
0.00148549
pre, b*t
5
0.00002122
post,b*t
5
0.00004630
pre,drug*t
10
0.00003189
post,drug*t
10
0.00050381
pre, b*drug*t
10
0.00001878
post,b*drug*t
10
0.00004516
Source
DF
SS_N
pre, b effect
1
0.0010140
post,b effect
1
0.0010358
pre, d effect
2
0.0000404
post,d effect
2
0.0031426
pre, d*b
2
0.0000190
post, d*b
2
0.0000120
Mean Square
F Value
Pr > F
0.00024948
36.27
0.0001
0.00204972
298.00
0.0001
0.00078751
114.49
0.0001
0.00000434
0.63
0.5331
0.00004000
5.81
0.0001
0.00050244
73.05
0.0001
0.00000614
0.89
0.5473
0.00009744
14.17
0.0001
0.00000392
0.57
0.9417
Mean Square
F Value
Pr > F
0.00013157
19.13
0.0001
0.00029710
43.19
0.0001
0.00000424
0.62
0.6869
0.00000926
1.35
0.2444
0.00000319
0.46
0.9127
0.00005038
7.32
0.0001
0.00000188
0.27
0.9867
0.00000452
0.66
0.7645
MS_N
F Value
PValue
0.0010140
43.2643
0.00000
0.0010358
44.1937
0.00000
0.0000202
0.8628
0.43094
0.0015713
67.0422
0.00000
0.0000095
0.4053
0.66991
0.0000060
0.2562
0.77546

195
Chloride Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
23328.25991
4665
. 65198
63.32
0.0001
BALLOON(B)
1
9497.81333
9497
. 81333
128.89
0.0001
DRUG
2
286.39699
143
. 19850
1.94
0.1449
B*DRUG
2
2998.29542
1499
. 14771
20.34
0.0001
HORSE*B*DRUG
25
14493.94120
579
. 75765
7.87
0.0001
TIME
11
1174.29352
106
.75396
1.45
0.1497
B*TIME
11
447.83056
40
. 71187
0.55
0.8663
DRUG*TIME
22
2335.85801
106
.17536
1.44
0.0926
B*DRUG*TIME
22
2402.03069
109
. 18321
1.48
0.0771
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
540.394120
108 .
078824
1.47
0.2002
post,t effect
5
281.454861
56 .
290972
0.76
0.5764
pre, b*t
5
311.874861
62 .
374972
0.85
0.5176
post,b*t
5
111.588194
22 .
317639
0.30
0.9110
pre,drug*t
10
829.902130
82 .
990213
1.13
0.3416
post,drug*t
10
651.967778
65 .
196778
0.88
0.5477
pre, b*drug*t
10
753.623611
75 .
362361
1.02
0.4237
post,b*drug*t
10
578.434444
57 .
843444
0.78
0.6433
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
4280.01
4280
. 01
13.0998
0.00102
post,b effect
1
5242.17
5242
. 17
16.0447
0.00035
pre, d effect
2
133.22
66
. 61
0.2039
0.81663
post,d effect
2
1007.17
503
.58
1.5413
0.22971
pre, d*b
2
3451.26
1725
.63
5.2816
0.01047
post, d*b
2
617.01
308
.50
0.9442
0.39964

196
Chloride Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.28817634
0.05763527
68.08
0.0001
BALLOON(B)
1
0.55019419
0.55019419
649.89
0.0001
DRUG
2
0.18821292
0.09410646
111 16
0.0001
B*DRUG
2
0.02283793
0.01141897
13.49
0.0001
HORSE*B*DRUG
25
0.10821931
0.00432877
5.11
0.0001
TIME
11
0.44263141
0.04023922
47.53
0.0001
B*TIME
11
0.02301873
0.00209261
2.47
0.0055
DRUG*TIME
22
0.16428786
0.00746763
8.82
0.0001
B*DRUG*TIME
22
0.00970540
0.00044115
0.52
0.9650
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.04446698
0.00889340
10.50
0.0001
post,t effect
5
0.11751137
0.02350227
27.76
0.0001
pre, b*t
5
0.00127950
0.00025590
0.30
0.9114
post,b*t
5
0.01036171
0.00207234
2.45
0.0338
pre,drug*t
10
0.00386552
0.00038655
0.46
0.9169
post,drug*t
10
0.04230947
0.00423095
5.00
0.0001
pre, b*drug*t
10
0.00355522
0.00035552
0.42
0.9367
post,b*drug*t
10
0.00467181
0.00046718
0.55
0.8524
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.20167
0.20167
77.933
0.00000
post,b effect
1
0.35991
0.35991
139.084
0.00000
pre, d effect
2
0.00493
0.00246
0.952
0.39547
post,d effect
2
0.30140
0.15070
58.237
0.00000
pre, d*b
2
0.00727
0.00364
1.405
0.25854
post, d*b
2
0.01704
0.00852
3.293
0.04872

197
Duodenal Content Volume
Source
DF
Type I
: SS
Mean Square
F Value
Pr >
HORSE
5
519376
. 657
103875.331
11.67
0.0001
BALLOON(B)
1
3598900
.231
3598900.231
404.20
0.0001
DRUG
2
282222
. 977
141111.488
15.85
0.0001
B*DRUG
2
589677
. 116
294838.558
33.11
0.0001
HORSE*B*DRUG
25
1404835
.398
56193.416
6.31
0.0001
TIME
11
322036
. 602
29276.055
3.29
0.0003
B*TIME
11
191191
. 046
17381.004
1.95
0.0325
DRUG*TIME
22
795468
. 634
36157.665
4.06
0.0001
B*DRUG*TIME
22
392494
. 940
17840.679
2.00
0.0053
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > :
pre,t effect
5
12611.
148
2522.230
0.28
0.9221
post,t effect
5
106365.
370
21273.074
2.39
0.0378
pre, b*t
5
9242 .
093
1848.419
0.21
0.9592
post,b*t
5
57847.
833
11569.567
1.30
0.2637
pre,drug*t
10
84652.
324
8465.232
0.95
0.4867
post,drug*t
10
39452 .
046
3945.205
0.44
0.9245
pre, b*drug*t
10
33904.
713
3390.471
0.38
0.9546
post,b*drug*t
10
46453.
139
4645.314
0.52
0.8747
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1193198.69
1193198.69
36.6589
0.00000
post,b effect
1
2529802.67
2529802.67
77.7238
0.00000
pre, d effect
2
82615.95
41307.98
1.2691
0.29425
post,d effect
2
870971.29
435485.64
13.3795
0.00005
pre, d*b
2
29960.68
14980.34
0.4602
0.63506
post, d*b
2
871853.53
435926.76
13.3931
0.00005

198
Bicarbonate Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
3656.939286
731.387857
60.41
0.0001
(
BALLOON(B)
1
2026.567940
2026.567940
167.39
0.0001
DRUG
2
1257.839878
628.919939
51.95
0.0001
B*DRUG
2
145.312574
72.656287
6.00
0.0028
HORSE*B*DRUG
25
5093.186650
203.727466
16.83
0.0001
TIME
11
1050.913733
95.537612
7.89
0.0001
B*TIME
11
146.883691
13.353063
1.10
0.3583
DRUG*TIME
22
2725.646878
123.893040
10.23
0.0001
B*DRUG*TIME
22
172.989442
7.863156
0.65
0.8860
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
62.627287
12.525457
1.03
0.3973
post,t effect
5
41.990059
8.398012
0.69
0.6286
pre, b*t
5
71.945792
14.389158
1.19
0.3146
post,b*t
5
70.392297
14.078459
1.16
0.3274
pre,drug*t
10
189.799161
18.979916
1.57
0.1153
post,drug*t
10
166.034097
16.603410
1.37
0.1925
pre, b*drug*t
10
81.233137
8.123314
0.67
0.7513
post,b*drug*t
10
76.908444
7.690844
0.64
0.7833
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1079.79
1079.79
10.1461
0.00353
post,b effect
1
1047.96
1047.96
9.8470
0.00397
pre, d effect
2
83.20
41.60
0.3909
0.68008
post,d effect
2
3558.25
1779.13
16.7172
0.00002
pre, d*b
2
98.99
49.50
0.4651
0.63284
post, d*b
2
47.05
23.52
0.2210
0.80307

199
Sodium Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
7953.46635
1590.69327
18.51
0.0001
BALLOON(B)
1
215.44566
215.44566
2.51
0.1143
DRUG
2
8596.82849
4298.41425
50.03
0.0001
B*DRUG
2
2849.44840
1424.72420
16.58
0.0001
HORSE*B*DRUG
25
29255.98279
1170.23931
13.62
0.0001
TIME
11
488.42419
44.40220
0.52
0.8917
B*TIME
11
1771.16769
161.01524
1.87
0.0421
DRUG*TIME
22
1502.28611
68.28573
0.79
0.7322
B*DRUG*TIME
22
1352.52704
61.47850
0.72
0.8235
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
198.754640
39.750928
0.46
0.8039
post,t effect
5
285.193595
57.038719
0.66
0.6512
pre, b*t
5
195.668293
39.133659
0.46
0.8092
post,b*t
5
438.983834
87.796767
1.02
0.4048
pre,drug*t
10
763.087688
76.308769
0.89
0.5446
post,drug*t
10
549.054734
54.905473
0.64
0.7800
pre, b*drug*t
10
877.234602
87.723460
1.02
0.4254
post,b*drug*t
10
468.155314
46.815531
0.54
0.8576
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1000.77
1000.77
1.60532
0.21529
post,b effect
1
220.51
220.51
0.35371
0.55666
pre, d effect
2
3754.18
1877.09
3.01099
0.06493
post,d effect
2
4256.85
2128.43
3.41416
0.04670
pre, d*b
2
1257.56
628.78
1.00861
0.37724
post, d*b
2
1352.38
676.19
1.08466
0.35142

200
Potassium Concentration in Duodenal Contents
Source
DF
Type I SS
HORSE
5
20.55811758
BALLOON(B)
1
7.31931108
DRUG
2
8.98637101
B*DRUG
2
4.32570123
HORSE*B*DRUG
25
38.71792471
TIME
11
10.50411559
B*TIME
11
1.60088225
DRUG*TIME
22
5.83152353
B*DRUG*TIME
22
1.54725131
Contrast
DF
Contrast SS
pre,t effect
5
0.55986461
post,t effect
5
2.00535033
pre, b*t
5
0.22016470
post,b*t
5
0.41056199
pre,drug*t
10
1.12691060
post,drug*t
10
0.85270776
pre, b*drug*t
10
0.70248700
post,b*drug*t
10
0.67188245
Source
DF
SS_N
pre, b effect
1
6.74506
post,b effect
1
1.43206
pre, d effect
2
2.76063
post,d effect
2
9.11095
pre, d*b
2
1.55364
post, d*b
2
2.10887
Mean Square
F Value
Pr > F
4.11162352
40.00
0.0001
7.31931108
71.21
0.0001
4.49318551
43.71
0.0001
2.16285061
21.04
0.0001
1.54871699
15.07
0.0001
0.95491960
9.29
0.0001
0.14553475
1.42
0.1643
0.26506925
2.58
0.0002
0.07032960
0.68
0.8549
Mean Square
F Value
Pr > F
0.11197292
1.09
0.3662
0.40107007
3.90
0.0019
0.04403294
0.43
0.8288
0.08211240
0.80
0.5512
0.11269106
1.10
0.3644
0.08527078
0.83
0.6004
0.07024870
0.68
0.7398
0.06718825
0.65
0.7670
MS_N
F Value
PValue
6.74506
8.25450
0.00760
1.43206
1.75254
0.19609
1.38031
1.68921
0.20266
4.55547
5.57492
0.00906
0.77682
0.95066
0.39842
1.05444
1.29040
0.29078

201
Chloride Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
13649.48336
2729
. 89667
27.42
0.0001
BALLOON(B)
1
638.45276
638
.45276
6.41
0.0118
DRUG
2
11923.06964
5961
. 53482
59.88
0.0001
B*DRUG
2
3441.72173
1720
. 86086
17.28
0.0001
HORSE*B*DRUG
25
17811.55894
712
.46236
7.16
0.0001
TIME
11
2296.74541
208
.79504
2.10
0.0203
B*TIME
11
1781.89427
161
. 99039
1.63
0.0901
DRUG*TIME
22
10931.68930
496
. 89497
4.99
0.0001
B*DRUG*TIME
22
1390.41462
63
.20066
0.63
0.8980
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
512.25045
102 .
45009
1.03
0.4005
post,t effect
5
426.80183
85 .
36037
0.86
0.5101
pre, b*t
5
185.52497
37 .
10499
0.37
0.8672
post,b*t
5
669.93027
133 .
98605
1.35
0.2448
pre,drug*t
10
981.26528
98 .
12653
0.99
0.4558
post,drug*t
10
1767.71427
176 .
77143
1.78
0.0643
pre, b*drug*t
10
712.42045
71.
24205
0.72
0.7098
post,b*drug*t
10
380.28384
38 .
02838
0.38
0.9541
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1365.17
1365
.17
3.4499
0.07229
post,b effect
1
14.35
14
.35
0.0363
0.85013
pre, d effect
2
3905.72
1952
. 86
4.9351
0.01341
post,d effect
2
15066.50
7533
.25
19.0373
0.00000
pre, d*b
2
1398.75
699
.38
1.7674
0.18672
post, d*b
2
2354.94
1177
.47
2.9756
0.06499

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211
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Dimaprit on Gastric Acid Secretion in Conscious Cats.
Agents Actions. 1978; 8(5): 453-457.
83. Holm L, Jagare A. Histamine is Not Involved in
Pentagastrin-induced Gastric Mucosal Vasodilation in the
Rat. Am. J. Physiol. 1994; 266(lPtl): G55-G61.
84. Parsons ME. Histamine Receptors: an Overview.
Scand. J. Gastroenterol. Suppl. 1991; 180: 46-52.
85. Kohno S, Ogawa K, Nebe T, Yamamura H, Ohata K.
Dimaprit, a Histamine H2-agonist, Inhibits Anaphylactic
Histamine Releases from Mast Cells and the Decreased Release
is Restored by Thioperamide (H3-antagonist), but not by
Cimetidine (H2-antagonist). Jpn. J. Pharmacol. 1993;
62 (1) : 75-79.
86. Sharif NA, Su SX, Yanni JM. Emedastine: a Potent,
High Affinity Histamine Hl-receptor-selective Antagonist for
Ocular Use: Receptor Binding and Second Messenger Studies.
J. Ocul. Pharmacol. 1994; 10(4): 653-664.
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Prier JE, eds. Textbook of Large Animal Surgery.
Baltimore: Williams & Wilkins, 1974; 364-449.
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Volume 1. Philadelphia: WB Saunders, 1984; 554-664.
89. Allen D, Clark ES, Murray MJ. Disorders of the
Small Intestine. In: Smith BP, ed. Large Animal Internal
Medicine. St. Louis: CV Mosby, 1990; 654-665.
90. Snyder JR, Spier SJ. Diseases of the Small
Intestine Associated with Acute Abdominal Pain. In: Smith
BP, ed. Large Animal Internal Medicine. St. Louis: CV
Mosby, 1990; 685-693.

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Raven Press, 1987;1557-1573.

BIOGRAPHICAL SKETCH
Diane L. Kitchen is the oldest of two children born to
Hyram and Yvonne Kitchen. Born in Tacoma, Washington, she
lived in several states before graduating from Lenoir City
High School in 1977. She spent a year in England as an AFS
exchange student where she completed her "A level" exams
before returning to the States to enter the University of
Tennessee in Knoxville. During her studies there, she was
elected into the Alpha Zeta, Phi Zeta and Phi Kappa Phi
honorary fraternities. After finishing undergraduate
requirements, Diane returned to England to work in a
veterinary practice until her admission to the College of
Veterinary Medicine. She received her Doctor of Veterinary
Medicine from the University of Tennessee in 1984.
During an internship and residency in Large Animal
Internal Medicine at Texas A & M University, Diane received
the Waddell Scholarship Award for excellence in emergency
and intensive care. In 1990, she passed her qualifying
examination for the American College of Veterinary Internal
213

214
Medicine. Diane began a solo large animal private practice
in Marion County, Florida, in 1989. She has served on the
executive committee for the Marion Veterinary Medical
Association since 1992 and was the president during 1996.
She is also an active member of the American Veterinary
Medical Association and Florida Cattleman Association.

I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Dgctqr of Philosophy.
Alfred M. Merritt, Chair
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
i). g
Claus D. Buergelt
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
Daryl Duss
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
Associate Professor of
Veterinary Medicine

I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
George A1 Gerencser
Professor of Physiology
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
(C3 VTuvK,
Robert J. MacKay
Associate Professor of
Veterinary Medicine
This dissertation was submitted to the Graduate Faculty
of the College of Veterinary Medicine and to the Graduate
School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
May, 1997

AD
¡917
i Ml
UNIVERSITY OF FLORIDA
3 1262 08555 3351



211
82. Carter DC, Impicciatore M, Grossman MI. Effect of
Dimaprit on Gastric Acid Secretion in Conscious Cats.
Agents Actions. 1978; 8(5): 453-457.
83. Holm L, Jagare A. Histamine is Not Involved in
Pentagastrin-induced Gastric Mucosal Vasodilation in the
Rat. Am. J. Physiol. 1994; 266(lPtl): G55-G61.
84. Parsons ME. Histamine Receptors: an Overview.
Scand. J. Gastroenterol. Suppl. 1991; 180: 46-52.
85. Kohno S, Ogawa K, Nebe T, Yamamura H, Ohata K.
Dimaprit, a Histamine H2-agonist, Inhibits Anaphylactic
Histamine Releases from Mast Cells and the Decreased Release
is Restored by Thioperamide (H3-antagonist), but not by
Cimetidine (H2-antagonist). Jpn. J. Pharmacol. 1993;
62 (1) : 75-79.
86. Sharif NA, Su SX, Yanni JM. Emedastine: a Potent,
High Affinity Histamine Hl-receptor-selective Antagonist for
Ocular Use: Receptor Binding and Second Messenger Studies.
J. Ocul. Pharmacol. 1994; 10(4): 653-664.
87. Hofmeyr CFB. The Digestive System. In: Oehme FW,
Prier JE, eds. Textbook of Large Animal Surgery.
Baltimore: Williams & Wilkins, 1974; 364-449.
88. Mcllwraith CW. Equine Digestive System. In:
Jennings PB, ed. The Practice of Large Animal Surgery,
Volume 1. Philadelphia: WB Saunders, 1984; 554-664.
89. Allen D, Clark ES, Murray MJ. Disorders of the
Small Intestine. In: Smith BP, ed. Large Animal Internal
Medicine. St. Louis: CV Mosby, 1990; 654-665.
90. Snyder JR, Spier SJ. Diseases of the Small
Intestine Associated with Acute Abdominal Pain. In: Smith
BP, ed. Large Animal Internal Medicine. St. Louis: CV
Mosby, 1990; 685-693.


65
pyrilamine prior to stimulation. This finding is contrary
to the results in other species where H-l receptor
antagonist do not inhibit gastric acid secretion. Because
the precise mechanism for this action is not clear, it is
apparent that this may be yet another important equine
specific finding that warrants further investigation.
Therefore, equine gastric secretion in response to
pentagastrin differs not only in composition from the
classical parietal response of other species and the
histamine response in the horse (See Chap.2), but also by
the ability of pyrilamine to inhibit a maximal acid
response.


145
PYRILAMINE PRETREATMENT STUDY DATA
ACID CONCENTRATION (mEq/L)
TIME
PRETREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
40.25
12.69
27.15
16.06
30
BASAL
BASAL
40.15
10.14
22.20
15.65
45
BASAL
BASAL
38.78
8.43
28.69
16.29
60
HVP
BASAL
37.85
10.33
30.58
10.32
75
P-P
BASAL
38.61
7.90
37.90
13.30
90
P-P
BASAL
26.00
5.99
32.11
13.50
105
PENTAGASTRIN
26.36
12.53
38.09
14.55
120
PENTAGASTRIN
37.46
17.04
34.95
12.28
135
PENTAGASTRIN
45.45
19.60
28.71
14.98
150
PENTAGASTRIN
49.89
18.06
27.75
5.37
165
PENTAGASTRIN
54.91
15.54
37.05
8.02
180
PENTAGASTRIN
49.86
13.01
47.00
10.51
195
PENTAGASTRIN
ND
ND
50.66
9.84
210
PENTAGASTRIN
ND
ND
46.25
11.38
225
PENTAGASTRIN
ND
ND
45.01
10.37
240
PENTAGASTRIN
ND
ND
43.76
4.85
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine


120
had to be injected into the balloon during initiation of
pentagastrin infusion to prevent visible leakage of yellow
duodenal contents. Gastrin receptors have been identified
on smooth muscle cells in the gastric antrum in dogs and
gastrin has been shown to relax the pylorus to enhance
gastric emptying.9S-96 Pentagastrin may stimulate these
smooth muscle receptors in the horse and allow additional
reflux of duodenal contents.
As expected, and in accordance with previous studies,
potassium concentration and output increased in parallel
with an increasing acid concentration and output during
stimulation.44 However, the output of potassium was
significantly greater in the NB experiments, suggesting that
it is one of the components of the extragastric fluid which
is separated out by the occlusion of the pylorus.
Whereas, the lower [Cl'] in the NB experiments was
likely secondary to the dilutional effect of the
extragastric portion of these collections, chloride output
was greater in the NB experiments, inferring that the
extragastric fluid contains chloride, but at a lesser
concentration than that of gastric secretions.
Significantly greater chloride output during pentagastrin
infusion in both NB and B experiments in contrast to the


6
cellular changes occur with activation of the secondary
messenger system within the parietal cell. The proton pump,
H,K ATPase, is present in the membrane of cytoplasmic
membrane compartments during the resting or unstimulated
state and, after stimulation within the membranes of
extensive apical canaliculi.16 The mechanics of this
transformation are not clearly understood. It is possible
that the cytoplasmic vesicles observed in the resting state
are connected to the apical membrane and that tubules simply
expand to expose the proton pump to the lumen of the gastric
glands. An alternative explanation is that activation of
the cell results in the fusion of cytoplasmic membranes with
the apical membrane.16
Another change occurring following stimulation of the
parietal cell is the activation and transformation of
parallel K and Cl channels, which provide the extracellular
K+ needed for the proton pump.16 The pump requires oxygen
as well as Mg++. The energy required by the proton pumps is
supplied as ATP by the large mitochondrial content in the
parietal cell.16 The proton pump transports H+into the
gastric gland in exchange for K+. In order to maintain
intracellular homeostasis, several membrane exchange


80
Acid Output. (Table 7) The output of acid decreased
after the pyrilamine infusion and increased during
pentagastrin infusion. These changes in acid output over
time differed significantly (p<0.001). Acid output (AO) was
significantly greater (p<0.05) during late infusion than
during all other periods, however, the differences between
outputs during each of the other times did not differ
significantly. The AO was significantly greater (p=0.001)
during the CATH study than the NOC study.
Sodium Concentration. (Table 7) The [Na+] was
relatively constant until the late infusion block during
which time the concentration decreased significantly
(p=0.01). There was no significant difference in the
concentration between CATH and NOC studies.
Sodium Output.(Table 7) There was a significant
(pcO.OOl) effect of time on sodium output. The output
during late infusion was significantly greater (p<0.05) than
during basal or post-pyrilamine periods, but not
significantly greater than during the early infusion period.
Early infusion sodium output was also significantly greater
than post-pyrilamine, though it was not significantly


72
ability to collect gastric contents from the cannula and
duodenal contents from the catheter into separate
containers. The fluids were collected into 1L fluid bags
suspended from a surcingle. The cannula and catheter were
both allowed to drain by gravity for 15 minutes after
completion of catheter placement. In the studies where
there was no intraduodenal catheter (NOC) in place, gastric
contents only were collected by gravity into 1L fluid bags.
Catheter Design
The specialized catheter was fashioned from a 137 cm
stallion urinary catheter(Jorgensen Laboratories, Inc.,
Loveland, Co), (fig.5) It's end was opened to allow free
passage of the stylet and several additional 5mm side holes
were placed in the 15cm closest to the tip. It was
distinctly marked at 20 cm from the tip and this mark was
considered the "0cm" mark. Additional marks were made
every 5cm markings from that point to the end. To fix the
catheter in position, a 10cm section of silastic tubing
[16mm I.D.] was placed over a 5cm section of the barrel of a
12ml syringe (Monoject, St. Louis, MO.) and the catheter


170
pH of Duodenal Contents
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
8.24
0 09
8.25
0.05
8.30
0.14
30
BASAL
8.17
0.12
8.17
0.12
8.25
0.14
45
BASAL
8.20
0.11
8.17
0.14
8.21
0.12
60
HVP
8.16
0.12
8.15
0.15
8.20
0.12
75
8.04
0.13
8.04
0.11
8.18
0.11
90
8.13
0.13
8.02
0.12
8.09
0.13
105
INFUSION
8.06
0.11
8.07
0.16
8.36
0.05
120
INFUSION
8.06
0.12
8.09
0.15
8.33
0.05
135
INFUSION
8.03
0.10
8.05
0.10
8.26
0.07
150
INFUSION
8.08
0.12
7.97
0.09
8.20
0.11
165
INFUSION
8.03
0.10
7.91
0.09
8.24
0.03
180
INFUSION
8.07
0.11
7.93
0.10
8.18
0.07
HVP = Pyrilamine maleate infusion


158
Chloride Output in Gastric Contents
(|iEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
88.2
15.26
87.2
19.95
73.1
15.61
30
BASAL
79.8
17.74
82.0
23.35
82.4
13.43
45
BASAL
81.9
13.99
83 .2
19.33
83.6
13.72
60
HVP
64.3
13.67
80.5
19.12
73.2
9.44
75
45.8
11.54
51.2
11.59
51.5
9.49
90
44.7
8.84
59.7
10.71
52.9
10.47
105
INFUSION
64.4
10.03
70.9
16.58
84.3
7.42
120
INFUSION
69.1
11.47
105.0
27.41
141.9
13.99
135
INFUSION
68.6
10.79
111.2
20.15
147.7
6.90
150
INFUSION
70.8
11.25
128.4
23.24
144.5
8.56
165
INFUSION
75.8
13.35
145.6
19.32
180.0
23.38
180
INFUSION
11.7
14.79
152.7
19.74
164.0
14.75
HVP = Pyrilamine maleate infusion


178
Chloride Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
126.2
4.91
126.2
7.55
122.7
6.69
30
BASAL
125.4
4.45
128.0
8.08
128.1
5.93
45
BASAL
122.4
7.44
125.1
11.79
130.8
4.88
60
HVP
116.9
7.71
126.8
9.98
127.0
5.13
75
120.9
3.78
122.7
3 81
131.4
5.14
90
117.3
2.65
121.9
4.09
129.1
7.06
105
INFUSION
122.0
3.03
118.0
4.37
110.0
3.65
120
INFUSION
123.6
5.12
121.1
4.00
104.1
5.39
135
INFUSION
126.0
5.19
110.3
4.05
110.0
1.95
150
INFUSION
129.6
5.13
115.4
3.75
108.7
3.82
165
INFUSION
128.6
5.72
111. 8
3.33
110.1
2.67
180
INFUSION
129.9
6.85
113.2
2.03
106.9
2.70
HVP = Pyrilamine maleate infusion


73
passed tightly through the wall of the silastic tubing into
the lumen and out through the syringe barrel lumen.
Figure 5 Specialized catheter for collection of duodenal
contents. The bold mark is signified by and is located
20 cm from tip. Multiple fenestrations within that 20 cm
region of the catheter.
One end of the syringe barrel locked into the end of the
silastic gastric cannula and the other was attached to the
short segment of silastic tubing which locked the catheter
in a fixed position. The long stylet was made by joining
together 3 stylets provided with stallion catheters. The


81
greater than the basal output. The output during the CATH
study was significantly greater (p=0.001) than during the
NOC study.
Duodenal Contents
Duodenal fluid was generally thick and mucoid and
tended to be dark yellow to green, in color. The
bicarbonate ion concentration ranged between 19-40 mEq/L;
TABLE 8.
Electrolyte Composition of Fluid from Duodenal Catheter
During Basal, Post-Pyrilamine, and Pentagastrin Infusion
Collection Periods. [Mean + SEM]
DUODENAL
BASAL
PYRILAMINE
INFUSION
[hco3]
(mEq/L)
23.2 + 2.6
16.2 + 1.5
33.0 + 2.3
[Na+]
(mEq/L)
147.5 3.9
151.5 6.7
144.9 + 2.4
[K+]
(mEq/L)
4.5 0.2
4.4 + 0.3
3.6 + 0.1
[Cl']
(mEq/L)
118.1 5.5
119.6 + 5.2
115.1 6.1
it decreased noticeably in the post-pyrilamine collections
and was increased during pentagastrin infusion. The fluid
had a high concentration of sodium (120-190 mEq/L) and low
concentration of potassium (2.4-5.5 mEq/L) compared to that
of gastric contents, in which the [Na+] ranged between 25-


70
Experimental preparation
Experiments were performed with no less than a one
week interval between them. The horses were fasted with
free choice water for 20 hours prior to an experiment. They
were loosely restrained in the laboratory for the entire
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes while a indwelling
jugular catheter was emplaced. For the catheter studies, a
video endoscope (WelchAllyn, Skaneateles Fall, NY) was
inserted through the gastric cannula into the stomach and
steered into the duodenum to a point approximately 30 cm
past the area of the duodenal diverticulum. A 4.5m long
stylet was threaded through the biopsy port of the endoscope
until it was seen passing from the distal end of the scope.
The endoscope was slowly withdrawn as the stylet was
threaded through the biopsy port, watching that it stayed in
place as the scope was removed. The distance from the
pylorus to the end of the gastric cannula was noted. The
presence of the stylet passing through the pylorus was
visually confirmed prior to removing the endoscope from the
cannula. The stylet was marked at the end of the cannula,
after which a specially modified stallion urinary catheter


23
amylase are found during stimulation of the vagus, or during
secretin or pentagastrin administration. The concentration
of sodium and potassium are similar to respective plasma
concentrations and chloride is the predominate anion at all
levels of secretion. The bicarbonate concentration is low
relative to other species and does not increase to the
extent anticipated when the volume of secretion increases.55
That is, in most species, the concentration of bicarbonate
is less than chloride concentration at rest, but increases
to become the predominate anion during maximally stimulated
secretion.55 The composition of the large non-parietal
component of the fasting gastric contents is also similar to
that of equine pancreatic fluid. Therefore, the observed
species-specific particulars of equine pancreatic juice
contents might explain the voluminous fluid response
observed during pentagastrin-stimulated gastric collection.
The pancreas is a multifunctional organ which is
responsible for the secretion of fluid, electrolytes, and
enzymes essential to the normal digestive process and the
endocrine secretion of hormones critical to metabolic
homeostasis.59 Just as with gastric secretion, pancreatic
secretion has traditionally been divided into basal and


61
recognized. As well as regulation of acid secretion, these
receptors also play a role in the regulation of gastric
microcirculation and motility.11 Mucosal circulation is
affected by histamine primarily via H-l receptors, although
H-2 and H-3 receptors may be involved. In the rat, for
instance, it appears that both H-l and H-2 receptors are
involved in histamine related vasodilation.72
Vasoconstriction occurs with H-l receptor stimulation in the
rabbit. 72-73 Pyrilamine has been shown to competitively
inhibit histamine related vasodilation in the guinea pig.73
The changes, if any, in equine gastric circulation in
response to histamine or histamine blocking agents are not
known.
The importance of gastric mucosal circulation in the
horse may be most clearly demonstrated by the relative
sensitivity of the horse to gastric ulceration due to
NSAIDs, though no specific studies have quantified equine
gastric mucosal blood flow or the regulation of flow. The
administration of NSAID1s results in gastric ulceration by
inhibition of prostaglandins involved in mucosal blood flow
and cytoprotection.47 Gastrointestinal injury can be seen
endoscopically in horses with or without accompanying


25
reflex.50 The two classical pancreatic regulatory hormones,
cholecystokinin (CCK) and secretin, and vagal cholinergic
reflexes are involved in the "intestinal" phase.60
i
Postganglionic cholinergic neurons are important in the
regulation of enzyme and bicarbonate secretion by the
release of acetylcholine at muscarinic receptors. Secretin
is the most potent stimulant of the bicarbonate-rich fluid
component of exocrine pancreatic secretion in dogs, cats,
rats, and humans., while the primary hormonal stimulant of
enzyme secretion is CCK.59'60 In the rat, rabbit, pig and
guinea pig, CCK is responsible for a copious fluid and
electrolyte secretion which may have a low concentration of
bicarbonate and a high concentration of chloride.59 Enzyme
secretion is stimulated by the action of CCK at CCK-A
receptors on pancreatic acinar cells.61 Although CCK-
B/gastrin receptors have been identified on pancreatic
acinar cells, their function remains unknown.61 Caerulein
is even more potent than CCK, and both are significantly
more potent than gastrin, at stimulating pancreatic enzyme
and fluid secretion in dogs.62 A multitude of other
receptors are present on pancreatic acinar cells, including
those to bombesins, tachykinins, VIP, somatostatin, insulin,


5 THE EFFECT OF PYLORIC OBSTRUCTION ON EQUINE BASAL AND
STIMULATED GASTRIC SECRETION 86
Introduction 86
Materials and Methods 87
Horses 87
Experimental protocol 88
Sample analysis 92
Analysis of data 94
Results 95
Pre-infusion 96
Gastric samples 96
Post-infusion 98
Gastric samples 98
Pre-infusion 109
Duodenal samples 109
Post-infusion Ill
Duodenal samples Ill
Bile Acids 115
Discussion 116
6 SUMMARY AND CONCLUSIONS 130
Summary 130
Conclusions 13 6
APPENDICES
A HISTAMINE DOSE-RESPONSE DATA 138
B PYRILAMINE PRETREATMENT STUDY DATA 144
C DATA FROM BALLOON/NO BALLOON STUDY 147
D STATISTICAL ANALYSIS OF HISTAMINE DOSE RESPONSE
DATA 179
E STATISTICAL ANALYSIS OF PYRILAMINE MALEATE DATA 181
F STATISTICAL ANALYSIS OF CATHETER/NO CATHETER DATA 183
G STATISTICAL ANALYSIS OF BALLOON/NO BALLOON DATA 186
ix


39
Pyrilamine Infusion
The volume of contents collected ranged from 70 to 550
mis, with a mean of 356.7 +37.3 mls/15 min and was not
significantly different than basal collections. The mean
acid concentration was 33.5 + 3.5 mEq/L, mean sodium
concentration was 79.5 + 7.5 mEq/L, and mean sodium output
was 60.6 + 9.6 ^Eq/kg BW/15 min. Acid output ranged from
3 to 55 j.iEq/kg BW/15 min, with a mean of
25.9 + 4.4 pEq/kg BW/15 min. These results were not
significantly different from the basal time periods.
Histamine dose-response
Gastric collections became progressively more clear as
acid concentration increased. During maximal histamine
stimulation, the contents were colorless and watery.
Volume
Maximal secretory volumes ranged from 360 to 850
ml/l5min. For each increasing dose of histamine, the mean
volume was 591.7, 591.7, and 508.9 ml/l5min, respectively.
The volume collected during each dose of histamine infusion
was significantly greater (pcO.0001) than basal volume;


106
under both histamine and pentagastrin were significantly
greater (p<0.00001) than that of saline.
Table 13.
ACID IN THE GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[H+]
mEq/L
SAL *
28.95.47
NB
33.8+6.53
27.66.59
HIST§
80.34.86
+
PG
42.43.14
[H+]
mEq/L
SAL *
38.759.09
B4
47.010.15
32.819.32
HIST
103.12 3.48
+
PG
84.17+4.94
H+0UTPUT
(.lEq/kg/
15min
SAL *
28.65.51
NB
35.510.23
22.57.43
HIST§
112.6+8.31
+
PG
80.2+6.99
H'OUTPUT
/iEq/kg/
15min
SAL *
21.78+6.99
B4
29.52+9.53
12.78 5.14
HIST
97.03+10.82
+
PG
91.22+5.85
+ Pyrilamine significantly less (p<0.0 5) than other time
blocks
B significantly different (p<0.05) from NB
§ Histamine significantly different(p<0.05) than other
infusions
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Acid output was also significantly affected (p=0.00054)
by the drug*balloon interaction. In the no balloon
experiments, all three infusions resulted in different
outputs of acid. HIST/NB resulted in outputs significantly


205
28. Ernas S, Grossman MI. Comparison of Gastric
Secretion in Conscious Dogs and Cats. Gastroenterology
1967; 52(1) : 29-34.
29. Merritt AM, Brooks FP. Basal and Histamine-
Induced Gastric Acid and Pepsin Secretion in the Conscious
Minature Pig. Gastroenterology 1970; 58(6): 801-814.
30. Mulvihill SJ, Pappas TN, Debas HT.
Characterization of in Vivo acid Secretory Responses of
Rabbit with Comparison to Dog and Rat. Dig. Dis. and Sci.
1989; 34(6) : 895-904.
31. Campbell-Thompson ML, Merritt AM. Effect of
Ranitidine on Gastric Acid Secretion in Young Horses. Am.
J. Vet. Res. 1987; 48(10): 1511-1515.
32. Sachs G. The Gastric Proton Pump: The H+,K+-
ATPase. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Second Edition. New York: Raven
Press, 1987; 865-879.
33. Soli AH, Amirian DA, Thomas LP, Park J, Elashoff
JD, Beaven MA, Yamada T. Gastrin receptors on Nonparietal
Cells Isolated from Canine Fundic Mucosa. Am. J. Physiol.
1984; 247: G715-G723.
34. Campbell-Thompson M. Secretagogue-induced [14C]
Aminopyrine Uptake in Isolated Equine Parietal Cells. Am.
J. Vet. Res. 1994; 55(1): 132-137.
35. Chew CS, Hersey SJ. Gastrin Stimulation of
Isolated Gastric Glands. Am. J. Physiol. 1982; 242: G504-
G512 .
36.Bado A, Moizo L, Laigneu J-P, Lewin MJM.
Pharmacological Characterization of Histamine H3 Receptors
in Isolated Rabbit Gastric Glands. Am. J. Physiol. 1992;
262: G56-G61.


APPENDIX E
STATISTICAL ANALYSIS OF PYRILAMINE MALEATE DATA
Analysis performed using SigmaStat software by General
Linear Model as Paired t-test.
Basal Collections
Parameter
t
DF
P Value
Volume
0.284
7
0.7849
Acid Concentration
-0.0792
7
0.9391
Acid Output
-0.189
7
0.8553
Post-pyrilamine Collections
Parameter
t
DF
P Value
Volume
3.23
7
0.0145
Acid Concentration
2.06
7
0.0785
Acid Output
5.61
7
0.0008
181


84
pyrilamine period decrease in acid output in the CATH study
was not as dramatic in the NOC study. The increasing acid
output during the early and late infusion periods of the
CATH were closer to the normal pentagastrin response
observed in horses without pyrilamine pretreatment(See
Chap.3) than to an unusually profound response to pyrilamine
in the NOC study. Decreased maximal acid output in horses
stimulated with pentagastrin following the administration of
pyrilamine maleate may be due to decreased mucosal blood
flow.(See Chap. 3) The placement of the duodenal catheter
may also potentiate gastric acid secretion by mechanical
stimulation2-3-8-17'18 in the gastric antrum resulting in the
local release of gastrin or acetylcholine, thereby lessening
the effect of the pyrilamine. In humans and dogs,
distention of the antral region has been shown to augment
histamine or gastrin- related secretion of acid.2-3-13
Although the catheter was not large and did not distend the
antrum, it did contact the gastric mucosa and may have
stimulated local intramural reflexes2-3-17-18 involved in the
secretory response.
Sodium output increased dramatically during
pentagastrin infusion in both the CATH and NOC studies,


96
without pyloric obstruction. The duodenal mucosa appeared
healthy in all studies and no changes were observed in the
area where the inflated balloon was positioned. No colics
were observed in these horses during or after these studies.
Rarely, a small piece of mucosa would pass from the duodenal
catheter. The size of these pieces was consistent with the
holes in the catheter and may have occurred by suction of
the catheter onto the mucosa. No residual scarring was
visible endoscopically.
Pre-infusion
Gastric samples
(See Table 10,11,12,13,14)
The gastric samples collected after inflation of the
balloon to obstruct the pylorus were clear and watery,
although clear mucus and white foam was sometimes present in
the collection. Gastric samples collected with the duodenal
catheter and no obstruction of the pylorus were yellow to
greenish-yellow and cloudy as observed in other gastric
cannula studies.31-44 Time was statistically significant in
most parameters measured and related to the administration
of pyrilamine maleate. The time effect was significant
(p<0.05) for all parameters except chloride ion


89
the addition of an inflatable balloon, which could be
inflated or deflated by a three-way stopcock near the
proximal end of the catheter.(fig. 6) The catheter was
passed until a predetermined mark or the balloon was 5cm
Figure 6 Specialized Balloon catheter. at balloon which
is 20 cm from the end of the catheter. marks the 3-way
stopcock and tubing to fill balloon. - points to the
silastic tube which keeps the catheter fixed in place and
allows collection of gastric contents.
aborad to the pylorus. The balloon was inflated with a
60 ml syringe until firm resistance was felt. The catheter
was gently pulled to verify its placement was fixed by the
balloon. The completed setup (fig. 7) resulted in the


132
investigate the effect of pyrilamine maleate pretreatment on
pentagastrin stimulated gastric contents. Chapter 3
presents the surprising results of this study. Acid output
after pyrilamine maleate was significantly decreased from
basal, and the secretory response to pentagastrin
stimulation was also diminished.
The primary goal of this project was to determine
whether the large sodium-rich component of gastrin contents
in response to pentagastrin stimulation was of gastric or
extragastric origin. After attempts to surgically isolate
the stomach from the proximal duodenum failed, a technique
was developed to obstruct the pylorus temporarily. This
involved the passage of an endoscope through the gastric
cannula into the stomach and then guiding it into the
proximal duodenum. The process of passing the endoscope
into the duodenum, introducing the stylet through the biopsy
channel, removing the endoscope with the stylet still in
place and then threading the specially designed catheter
over the stylet took 15 to 30 minutes.
Because the duodenal catheterization involved
manipulation within the gastric lumen and resulted in
an'object traversing the pylorus throughout the entire


12
and appear in lesser numbers in the dog and primates.1-24
Other endocrine cells observed in the gastric mucosa include
enterochromaffin cells which produce 5-hydroxytryptamine
(serotonin), D cells that secrete somatostatin, gastrin-
producing G cells, and P and X cells which have unknown
functions.1 The ECL cells are found near parietal cells
within the gastric glands and have prominent cytoplasmic
extensions.1-24 They contain a large number of cytoplasmic
vesicles and electron-dense granules, and take up aromatic
amino acids and decarboxylate them. Histidine decarboxylase
(HDC) and histamine are also found within these cells.1,24
Histamine is concentrated into cytoplasmic vesicles by a V-
type ATPase which acts as a H+/histamine antiporter.1,22,24
As indicated above, the production and storage of histamine
by the ECL cell makes it the critical interface in the
regulation of gastric acid secretion.1,24 The primary
mediator of histamine release is gastrin acting through the
CCK-B receptor to increase cytosolic Ca++. 1,22,24 Histamine
release can also be stimulated by acetylcholine at
muscarinic Ml receptors, epinephrine through p adrenergic
receptors, isoproterenol, forskolin, interleukin ip and VIP,


112
significantly greater than histamine (p=0.00016) and saline
(p=0.00001). The [HC03] did not differ significantly
between histamine and saline.
Sodium'ion concentration. (Table 16) The only
significant effect observed for [Na+] in duodenal collection
was a drug effect (p=0.0467). During histamine infusion,
the fluid collected had a significantly lower [Na*] than
during pentagastrin (p=0.04231) or saline (p=0.02316)
infusion.
Table 16.
SODIUM IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[Na+]
mEq/L
SAL
149.0+5.6
NB
147.53.9
151.56.7
HIST *
135.03.0
PG
144.92.4
[Na+]
mEq/L
SAL
147.8+5.5
B
143.15.5
142.9+6.1
HIST *
143.1+2.2
PG
152.65.2
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Potassium ion concentration. (Table 17) Over the 90
minutes of infusion, there was a significant (p=0.0019) time
effect of decreasing [K+] The drug effect was also
significant (p=0.00906), with concentrations after starting


127
pancreatic fluid and electrolyte secretion is regulated
primarily by secretin with some modulation via vagal
reflexes, whereas enzyme secretion is primarily controlled
by CCK and vagal input. 59-60 Secretin induces pancreatic duct
cells to produce increased volumes of fluid and as the
secretory rate increases, there is a reciprocal switch in
the bicarbonate and chloride concentrations.63 In the
horse, the concentration of bicarbonate is never greater
than that of chloride, even during maximal secretion.55
Enzyme content of pancreatic secretions increase with the
stimulation of CCK-A receptors on the pancreatic acinar
cells in most species.60-61 The concentration of enzymes in
equine pancreatic secretion is very low under both basal and
stimulated conditions.55 Gastrin, which acts at CCK-B
receptors, is a weak stimulant of pancreatic enzyme and
fluid secretion in species other than the horse.62 The
relative prevalence of CCK-A and CCK-B receptors within the
equine gastrointestinal tract has not been reported. The
results of this study and the report of Alexander and
Hickson might mean that the equine pancreas, and in
particular pancreatic duct cells, has an abundance of CCK-B
receptors.


Potassium Output in Gastric Contents
Source
DF
Type I SS
HORSE
5
0.00124741
t
BALLOON(B)
1
0.00204972
DRUG
2
0.00157501
B*DRUG
2
0.00000867
HORSE*B*DRUG
25
0.00099991
TIME
11
0.00552684
B*TIME
11
0.00006758
DRUG*TIME
22
0.00214371
B*DRUG*TIME
22
0.00008627
Contrast
DF
Contrast ;
pre,t effect
5
0.00065783
post,t effect
5
0.00148549
pre, b*t
5
0.00002122
post,b*t
5
0.00004630
pre,drug*t
10
0.00003189
post,drug*t
10
0.00050381
pre, b*drug*t
10
0.00001878
post,b*drug*t
10
0.00004516
Source
DF
SS_N
pre, b effect
1
0.0010140
post,b effect
1
0.0010358
pre, d effect
2
0.0000404
post,d effect
2
0.0031426
pre, d*b
2
0.0000190
post, d*b
2
0.0000120
Mean Square
F Value
Pr > F
0.00024948
36.27
0.0001
0.00204972
298.00
0.0001
0.00078751
114.49
0.0001
0.00000434
0.63
0.5331
0.00004000
5.81
0.0001
0.00050244
73.05
0.0001
0.00000614
0.89
0.5473
0.00009744
14.17
0.0001
0.00000392
0.57
0.9417
Mean Square
F Value
Pr > F
0.00013157
19.13
0.0001
0.00029710
43.19
0.0001
0.00000424
0.62
0.6869
0.00000926
1.35
0.2444
0.00000319
0.46
0.9127
0.00005038
7.32
0.0001
0.00000188
0.27
0.9867
0.00000452
0.66
0.7645
MS_N
F Value
PValue
0.0010140
43.2643
0.00000
0.0010358
44.1937
0.00000
0.0000202
0.8628
0.43094
0.0015713
67.0422
0.00000
0.0000095
0.4053
0.66991
0.0000060
0.2562
0.77546


Early Infusion Collections
Parameter
t
DF
P Value
Volume
1.38
11
0.1953
Acid Concentration
-0.740
11
0.4747
Acid Output
2.54
11
0.0274
Late Infusion Collections
Parameter
t
DF
P Value
Volume
0.523
11
0.6113
Acid Concentration
-0.913
11
0.3807
Acid Output
3.77
11
0.0031


5
et al.14 that the fundic ECL cells contained histamine,
began the explosion of new concepts in gastric secretory-
regulation which has led to better understanding of the
process.
Review of Literature
Today, it is apparent that gastric acid secretion by
parietal cells results from paracrine histamine released by
nearby ECL cells. The release of histamine is mediated by
many substances including gastrin, acetylcholine,
somatostatin, vasoactive intestinal peptide (VIP),
prostaglandins, calcitonin gene-related peptide, TGF-a, and
even histamine.1 Histamine acts on the basolateral membrane
of parietal cells at H-2 receptors.2,3 Stimulation of these
receptors activates the basolateral adenylate cyclase and
leads to increased intracellular cAMP within the parietal
cell.15 In contrast, parietal cell gastrin receptors and
muscarinic M3 receptors result in increased intracellular
Ca++ when stimulated.16 The increased cAMP and/or Ca++ may
activate protein kinases involved in the phosphorylation of
the apical H,K ATPase as occurs in Na,K ATPases.16
Several


93
for bile acids to verify complete occlusion of the pylorus
by the balloon in those experiments.
The pH was determined by glass electrode (Radiometer,
Copenhagen Denmark) calibrated at 20C using commercial
buffer solutions of pH 2 and 7 (pH standard, Fischer
Scientific). Using an automatic titrator (Radiometer,
Copenhagen Denmark), hydrogen ion concentration was measured
in duplicate by titration with 0.IN NaOH to an endpoint of
7.4. Chloride ion concentration was measured in duplicate
by a digital chloridometer (Buchler Instruments Div.,
Nuclear Chicago, Fort Lee NJ) with acid reagent (Labconco,
Kansas City, Mo). Chloride standard (Labconco, Kansas City,
Mo) was used to calibrate the machine prior to each
experiment and after every 20 tests. Bicarbonate ion
concentration was determined by back-titration method of
Isenberg et al.91 with the automatic titrator (Radiometer,
Copenhagen Denmark) using 0.IN NaOH to titrate to an
endpoint of 8.4. Sample aliquots were gassed with nitrogen
washed in barium hydroxide to remove carbon dioxide prior to
and during the titration. Bicarbonate measurements were
done in triplicate, and standard solutions prepared in
laboratory were measured in quadruplicate prior to each
experiment. Sodium and potassium ion concentration were


165
Sodium Output in Gastric Contents
(|.iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
109.0
11.10
95.5
13.84
113.7
8.50
30
BASAL
91.0
11.35
87.8
14.97
126.2
16.00
45
BASAL
90.5
10.05
81.8
14.55
118.0
6.73
60
HVP
92.7
15.30
90.8
11.55
98.5
3.46
75
83.6
14.13
65.6
10.22
89.9
14.66
90
92.2
12.04
75.8
12.91
86.2
8.24
105
INFUSION
100.0
18.79
81.3
8.78
114.7
11.91
120
INFUSION
108.9
15.11
73.1
8.47
178.1
16.21
135
INFUSION
120.3
7.38
67.6
12.77
186.3
20.53
150
INFUSION
115.9
5.01
79.3
13.57
187.6
17.53
165
INFUSION
106.9
6.69
78.8
12.33
165.2
14.37
180
INFUSION
110.8
10.91
75.3
13.48
169.7
15.00
HVP = Pyrilamine maleate infusion


155
Chloride Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
139.3
4.24
133.9
5.04
140.2
6.07
30
BASAL
144.5
4.91
135.9
7.54
148.3
4.71
45
BASAL
144.0
5.59
137.0
4.76
150.8
5.98
60
HVP
147.2
4.63
137.8
7.93
151.2
5.70
75
142.5
4.84
136.9
8.94
150.3
5.34
90
142.6
5.66
138.0
6.63
148.0
6.50
105
INFUSION
146.1
7.90
145.0
6.08
134.4
7.84
120
INFUSION
147.5
4.80
143.6
5.54
144.9
5.06
135
INFUSION
146.2
5.19
144.4
4.43
143.2
5.51
150
INFUSION
141.2
4.95
147.0
3.45
144.7
3.87
165
INFUSION
143.1
4.02
143.3
4.50
143.5
5.65
180
INFUSION
143.4
3.62
146.5
2.74
144.5
7.71
HVP = Pyrilamine maleate infusion


reported for horses stimulated with pentagastrin.
Pyrilamine maleate dampened the gastric acid secretory-
response to pentagastrin infusion. The introduction of an
intraduodenal catheter did not alter the maximal acid output
to pentagstrin, although it may have enhanced the reflux of
duodenal fluid into the gastric lumen. Most importantly,
the obstruction of the pylorus with the balloon catheter
significantly decreased the sodium output in gastric
collections suggesting that the vigorous sodium-rich
component of pentagastrin stimulated secretion is primarily
of extragastric origin.
xv


11
determination of the central role of histamine in the
secretory response.22 As a result, numerous H-2 blockers
have become a mainstay in the treatment of peptic ulcers.21
Substituted benzimidazoles, such as omeprazole, have more
recently joined the battery of antiulcer medication due to
their inhibition of the H,K ATPase.21 Certain prostaglandin
E2 analogues also have an antisecretory effect, due to
actions at CNS as well as ECL cell level.1,21 Gastrin
receptor antagonists (ie. Proglumide) are also capable of
inhibiting acid secretion.21 The target of some presently
available drugs and many of the drugs of the future may not
be parietal cells directly, but other cells within the
gastric mucosa which act on the parietal cell.23
Accordingly, the increasing understanding of the role of the
ECL cell is likely to make it the target of investigational
agents for the regulation of acid secretion.
The gastric ECL cell is considered to be one of the
amine precursor uptake decarboxylation (APUD) series of
cells.1,24 Numerous endocrine cells are found scattered
within the gastric mucosa and may represent from 0.5% to 2%
of the cells present. The prevalence of ECL cells vary
among species, as they are particularly common in the rat


8
intestinal.2-3'17'18 The link between the brain and gastric
function has been speculated about since the early 1800's.19
Sight, smell, taste, thought, and swallowing stimulate
gastric acid secretion during the cephalic phase.2-3'9'10 The
vagus nerve is the key link in the cephalic phase through
its stimulation of gastrin release as well as direct
innervation of the parietal cell.2'17'18 As mentioned, these
effects may be mediated through ECL cells rather than
directly through receptors on the parietal cell. Many
neurotransmitters and certain peptides have been shown to
act centrally on the regulation of acid secretion.19
Cholinergic agonists, prostaglandin inhibitors, GABAergic
agonists, gastrin/CCK, TRH-related peptides, and
somatostatin-related peptides administered into the CSF
stimulate gastric acid secretion. Inhibition occurs
following CSF injection of cholinergic antagonists,
adrenergic agonists, prostaglandins, serotonin, bombesin
like peptides, opioid peptides, CRF-like peptides, and
calcitonin-related peptides.19
The gastric phase of stimulated secretory response
is a result of gastric distension or chemical stimulation of
the gastric mucosa.2'3-17'18 This phase is mediated primarily


63
atropine-like activity at muscarinic receptors11-76 involved
in vasodilation. In dogs, the cholinolytic properties of
pipolphen, a H-l blocker, have been shown to suppress
I
gastric secretions.77 Agonist to H-3 receptors78'80 and
antagonist of the H-2 receptor11-12-31'78 result in decreased
acid secretion. Pyrilamine has been utilized in numerous
secretion studies and in most species does not elicit this
antisecretory response. 81-82-83 In other equine studies ,
pyrilamine maleate administration was followed by a decrease
in basal secretion, but this decrease was not always
significant.(See Chap. 4 & 5)
Histamine H-3 receptors are found in several locations
including the brain, perivascular nerve terminals, pulmonary
airways, and ECL cells in the gastric mucosa. 36-84 These
receptors appear to be involved in the autoregulation of
histamine release from ECL cells during the stimulation of
gastric acid secretion. 1-24-36-79-80 They may also be involved
in the release of somatostatin which inhibits gastric acid
secretion.78 Certain drugs have demonstrated simultaneous
H-l agonist/H-3 antagonist properties,85 however, it appears
that pyrilamine has a low affinity for H-2 and H-3


78
Results
Gastric Contents
Volume.(Table 7) The volume of gastric collection
differed significantly (p<0.01) between the designated time
blocks. The volume was significantly greater (p<0.05)
during the late infusion block than during all other blocks.
The early infusion volume was significantly greater (p<0.05)
than the post-pyrilamine volume, but did not differ
significantly from the basal volumes. The basal and post-
pyrilamine volumes did not differ significantly. The
volumes collected during the CATH study were significantly
(p<0.01) greater than during the NOC study. There was no
significant interaction between time blocks and catheter
status.
Acid Concentration,(Table 7) Acid concentration varied
significantly (p=0.001) among the time blocks with a
significantly higher (p<0.05) concentration during late
infusion. The [H+] was not significantly different between
basal, post-pyrilamine and early infusion blocks. The NOC
study had a significantly (p=0.016) higher concentration of


107
greater (p<0.00001) than both PG/NB and SAL/NB. PG/NB
outputs were also significantly greater (p=0.00001) than
SAL/NB. The addition of the balloon dramatically changed
the output differences, since HIST/B was not significantly
different than PG/B. However, both PG/B and HIST/B produced
outputs significantly greater (p<0.00001) than SAL/B.
Sodium ion concentration. (Table 14) The
concentration of sodium decreased significantly (p=0.0001)
over the time course of infusion. A significant (p=0.0001)
drug*time interaction was observed. Specifically, the
decrease following histamine infusion was significantly more
dramatic than with pentagastrin (p=0.0002) or saline
(p=0.0001). Pentagastrin and saline did not differ
significantly.
The effect of the balloon on [Na+] was also significant
(p=0.00002), and under balloon conditions the [Na+] differed
significantly (p<0.00001) in response to each of the
infusion compositions. Sodium concentration was
significantly less during histamine infusion than either
pentagastrin (p=0.00001) or saline (p<0.00001), and was
significantly less (p=0.00020) during pentagastrin infusion
than during saline infusion. At all time points, the PG/B


32
Histamine-2 receptor antagonists have been used successfully
to treat horses with clinical signs related to gastric
ulceration.64
In order to better characterize equine gastric
physiology, investigation of the effects of a secretagogue
other than pentagastrin is essential. Histamine seems the
obvious choice, but its use in horses has been avoided due
to the presumed equine respiratory and CNS hypersensitivity
to this agent. Ideally, "Histalog", a specific H-2 agonist,
might be used, but it is no longer available. In other
species, the undesirable side-effects of histamine have been
largely avoided by pretreatment with an H-l antagonist29,
and such a protocol was chosen for the studies described
herein. Specific objectives of the study were to: 1)
determine the dose of histamine needed to elicit a maximal
acid secretory response in the horse and how equidae compare
with other species, and; 2) see if the non-parietal
component of the secretory response to histamine is similar
to, or different from, that seen with pentagastrin
stimulation.


59
TABLE 4.
Mean and SEM Data from Gastric Contents Collected Before and
After Pentagastrin Infusion with and without Pretreatment
with Pyrilamine Maleate.
PYRIL-
BASAL
POST-
EARLY
LATE
AMINE
PYRIL-
INFUSION
INFUSION
AMINE


VOLUME
NO
253.8 +
381.7 +
585.8 +
622.5 +
(ml)
37.2
29.9
74.9
43.7
YES
287.5
181.7
415 +
589.2 +
27.95
34.8
102.2
71.0
[H+]
NO
31.14 +
39.7
31.2 +
48.0 +
(mEq/L)
9.54
11.0
5.5
5.6
YES
39.5 +
31.7 +
36.4 +
51.6 +
6.1
7.0
9.0
8.2
ACID
NO
18.1
34.1 +
46.4 +
76.8 +
OUTPUT
5.2
7.5
5.8
5.6
(fiEq/kg-15
min)
YES
24.5
3.9
12.4 +
2.5'
26.7 +
6.0
56.5 +
4.0
* First half of Pentagastrin Infusion (t=105,120,&135 min)
** Last half of Pentagastrin Infusion (t=150,165,&180 min)
Significantly Less than during No Pyrilamine Study
Late Infusion Collections
As during early infusions, the volume and acid
concentration were not significantly different between the
two studies. Acid output was significantly greater
(p=0.0031) in the study with no pyrilamine pretreatment.


142
HISTAMINE DOSE-RESPONSE DATA
Potassium Concentration and Output
TIME
DOSE
K+ CONCENTRATION
POTASSIUM OUTPUT
minutes
(.ig/kg-hr
mEq/L
|.ieQ/kg-15min
4
MEAN
SEM
MEAN
SEM
15
0
7.7
1.2
7.99
1.64
30
0
8.3
1.3
7.38
1.9
45
0
7.7
1.3
7.75
1.93
60
HVP
7.1
1.04
6.38
1.26
75
5.6
0.68
3.75
1.03
90
5.9
1
5.2
1.27
105
7.5
8.3
1.5
8.47
2.11
120
7.5
10.6
1.46
12.02
2.53
135
7.5
9.4
1.3
10.95
2.14
150
7.5
10.7
1.7
14.13
3.12
165
15
11.4
2
14.37
3.66
180
15
12.6
2.3
15.1
3.47
195
15
12.5
2.3
15.75
3.39
210
15
12.5
2.1
14.87
2.85
225
30
10.6
2.1
12.62
2.07
240
30
11.2
2.3
12.94
2.3
255
30
10.2
2.3
10.38
3.13
270
30
11.7
3.2
13.36
3.33
285
45
12.6
2.4
11.5
1.16
300
45
13.8
2.9
11.61
0.4
315
45
12.9
2.1
11.89
0.84
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done


34
minutes allowing emptying of residual gastric contents.
During the experiments, gastric contents were collected in
15 minute aliquots. The volume was measured to the nearest
5 ml in a graduated cylinder. Samples were filtered through
gauze to remove feed particles and foam. The pH was
determined using a glass electrode (Radiometer, Copenhagen,
Denmark) calibrated at 20C using commercial buffer
solutions of pH 2 and 7 (pH standard, Fisher Scientific).
Hydrogen ion concentration was measured in duplicate by
electrometric titration with 0.IN NaOH to an endpoint of
7.4. (Radiometer, Copenhagen, Denmark) Sodium ion
concentration was measured by flame photometry
(Instrumentation Laboratories Inc.-, Lexington, MA) on
samples diluted in an internal standard lithium solution
(Dilumat, Fisher Scientific). The machine was calibrated
with known [Na*] / [K+] standards (Instrumentation
Laboratories Inc., Lexington, MA) prior to analysis and
after every 5 samples. Acid and sodium outputs were
calculated for each time period on a per kg body weight
basis.
The first three 15-minute time periods were during
basal (no treatment) gastric collections. At time t=45


200
Potassium Concentration in Duodenal Contents
Source
DF
Type I SS
HORSE
5
20.55811758
BALLOON(B)
1
7.31931108
DRUG
2
8.98637101
B*DRUG
2
4.32570123
HORSE*B*DRUG
25
38.71792471
TIME
11
10.50411559
B*TIME
11
1.60088225
DRUG*TIME
22
5.83152353
B*DRUG*TIME
22
1.54725131
Contrast
DF
Contrast SS
pre,t effect
5
0.55986461
post,t effect
5
2.00535033
pre, b*t
5
0.22016470
post,b*t
5
0.41056199
pre,drug*t
10
1.12691060
post,drug*t
10
0.85270776
pre, b*drug*t
10
0.70248700
post,b*drug*t
10
0.67188245
Source
DF
SS_N
pre, b effect
1
6.74506
post,b effect
1
1.43206
pre, d effect
2
2.76063
post,d effect
2
9.11095
pre, d*b
2
1.55364
post, d*b
2
2.10887
Mean Square
F Value
Pr > F
4.11162352
40.00
0.0001
7.31931108
71.21
0.0001
4.49318551
43.71
0.0001
2.16285061
21.04
0.0001
1.54871699
15.07
0.0001
0.95491960
9.29
0.0001
0.14553475
1.42
0.1643
0.26506925
2.58
0.0002
0.07032960
0.68
0.8549
Mean Square
F Value
Pr > F
0.11197292
1.09
0.3662
0.40107007
3.90
0.0019
0.04403294
0.43
0.8288
0.08211240
0.80
0.5512
0.11269106
1.10
0.3644
0.08527078
0.83
0.6004
0.07024870
0.68
0.7398
0.06718825
0.65
0.7670
MS_N
F Value
PValue
6.74506
8.25450
0.00760
1.43206
1.75254
0.19609
1.38031
1.68921
0.20266
4.55547
5.57492
0.00906
0.77682
0.95066
0.39842
1.05444
1.29040
0.29078


26
endothelin, insulin-like growth factor and epidermal growth
factor.61 Much of the electrolyte secretion by the pancreas
is secreted by duct cells rather than acinar cells.63 The
electrolyte composition of pancreatic secretions vary with
the rate. Bicarbonate and chloride concentrations have a
reciprocal relationship, but the cumulative anion
concentration remains constant.63 As the secretory rate
increases, bicarbonate concentrations increase and chloride
concentrations decrease.63 The volume of the secretion in
response to secretin vary with species. Cats, dogs, pigs
and man have greater secretory rates per gram of gland than
rats and rabbits.63 The specific differences observed in
the limited studies on equine pancreatic secretion are
unique to the horse and similar secretory patterns have not
been reported in other species.
Development of Hypothesis
After reviewing the overwhelming information about
gastric secretory physiology in general, and equine gastric
secretion specifically, it is apparent that equine gastric
physiology requires still more investigation. The


95
experiments without pyloric obstruction and the three "Rl"
values from experiments with pyloric obstruction were
averaged to derive "basal" means. The "R2" values were also
averaged to derive two "pyrilamine" means. The first six
aliquots were grouped as "pre"and the next six aliquots
were grouped as "post" treatment. All outputs were
calculated on a per kg body weight basis from the volume and
ion concentrations and were expressed as |^Eq/kg/l5min.
Volume, pH, electrolyte ion concentration, and electrolyte
ion output data were analyzed by ANOVA for repeated
measures. Differences between drug effects, drug*time
interaction, time, drug*balloon interaction, balloon,
balloon*time interaction and drug*balloon*time interaction
were analyzed. Least significant difference was used for
pairwise comparison of means. Significance was chosen as
p<0.05.
Results
The horses maintained their bodyweight or gained weight
during the course of the study, and they did not appear to
be painful or anxious during the experiments. They stood
quietly in the lab throughout and behaved similarly with or


140
HISTAMINE DOSE-RESPONSE DATA
Acid Concentration and Output
TIME
DOSE
ACID CONCENTRATION
ACID OUTPUT
minutes
Hg/kg-hr
mEq/L
¡aeQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
37
4
37.3
6
30
0
41.1
5
36.6
9.4
45
0
44
6.3
42.9
9.1
60
HVP
42.9
6.7
39
8
75
38.3
5.1
26.6
7.1
90
28.8
4.3
25.1
5.7
105
7.5
47.2
8.8
47.1
10.2
120
7.5
65.2
7.1
73.3
14.3
135
7.5
71.9
5.5
82.3
11.5
150
7.5
72.5
5.95
93.8
10.8
165
15
75.2
6.3
93
14.8
180
15
82.8
6.6
97.8
9.8
195
15
79.7
7.2
99.7
12.1
210
15
82.9
7.8
99.3
12
225
30
78.2
8.5
94.9
7.1
240
30
80.2
7.7
93.8
7
255
30
79.8
10.3
80.7
17.2
270
30
86.9
9.4
100
4.6
285
45
101.7
8.1
96.3
20.6
300
45
105.8
6.6
92.3
17
315
45
111.4
0.48
104.3
9.7
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done


19
until the 1980s. The apparent increase in gastric and
duodenal ulcer disease in horses provoked a particular
interest in equine gastric physiology.31-44 Gastric mucosal
4
ulceration has been observed in horses as a sequela to the
administration of nonsteroidal anti-inflammatory drugs, and
as a spontaneously occurring problem of unknown etiology.44'47
Intermittent aspiration of gastric contents via nasogastric
tube, placement of indwelling pH probes nasogastrically, and
chronic indwelling gastric cannulas to collect contents by
drainage have been used in recent studies of equine gastric
secretion. 31- 44-48'52 Only the cannula allows complete
collection of gastric contents, but these studies can only
be performed on fasted animals. Intermittent aspiration
also requires fasted horses, but may not collect gastric
contents in their entirety. The indwelling pH probe makes
it possible to monitor the intragastric environment for a
long periods of time in either fed or fasted states.
Basal secretion in horses has been described as
continuously variable, with periods of spontaneous
alkalinization as has also been observed in humans, pigs,
rodents, monkeys, and chickens. 31-44-48-50 Thus, the hydrogen
ion concentration and acid output range widely during


167
Volume of Duodenal Contents
(ml/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
123.0
22.27
28.7
9.81
29.0
13.71
30
BASAL
89.7
32.49
65.7
34.39
26.2
12.29
45
BASAL
118.3
38.62
56.5
27.10
29.2
10.34
60
HVP
111. 0
24.69
42.4
25.67
28.0
10.73
75
96.3
30.22
63.3
10.02
28.8
9.22
90
85.7
28.71
82.8
20.57
29.8
10.76
105
INFUSION
93.5
36.58
73.7
23.30
79.7
25.35
120
INFUSION
73.7
39.04
87.0
28.56
87.0
16.94
135
INFUSION
63.0
20.85
93.3
41.51
79.3
18.03
150
INFUSION
55.7
17.42
62.5
34.72
59.7
15.05
165
INFUSION
80.3
27.86
63.5
23.35
67.0
18.41
180
INFUSION
69.7
21.81
54.3
26.34
62.0
13.08
HVP = Pyrilamine maleate infusion


101
greater than SAL/NB (p=0.00023) and PG/NB (p=0.00039),
HIST/B was significantly greater than SAL/B (p<0.00001) and
PG/B (p=0.01767), and PG/B was significantly greater than
SAL/B (p=0.00006).
Table 11.
POTASSIUM IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[K+]
mEq/L
SAL
9.8+0.64
NB
9.80.92
8.10.64
HIST *
14.00.90
+
PG
10.30.53
[K+]
mEq/L
SAL *
9.4+0.77
B
10.3 1.18
8.0+0.67
HIST*
17.7+1.03
+
PG *
14,20.94
K+
OUTPUT
(.lEq/kg/
15min
SAL *
9.80.75
NB
10.22.06
6.41.17
HIST
19.51.27
+
PG
19.51.31
K+
OUTPUT
/xEq/kg/
15min)
SAL *
4.7+1.06
B4
5.91.4 9
2.60.51
HIST
16.4+1.72
+
PG
15.71.91
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
B significantly different (p<0.05) from NB
+ Pyrilamine significantly different(p<0.05) from other
time blocks
Potassium ion output. (Table 11) Compared to pre
infusion, the output of potassium increased significantly
(p=0.0001) after infusion was begun. While, the actual


APPENDIX F
STATISTICAL ANALYSIS OF CATHETER/NO CATHETER DATA
Analysis is by General Linear Model with Two Way ANOVA
using SigraaStat software.
Gastric Content Volume
Source
DF
SS
MS
F Value
P Value
CATHETER
1
1310221.008
1310221.008
41.444
<0.001
TIME
3
2035066.025
678355.342
21.457
<0.001
CATH*TIME
3
22197.025
7399.008
0.234
0.872
Residual
72
2276250.917
31614.596
Total
79
5812169.487
73571.766
183


190
Acid Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.08082750
0.01616550
106.35
0.0001
BALLOON(B)
1
0.00388800
0.00388800
25.58
0.0001
DRUG
2
0.06885906
0.03442953
226.50
0.0001
B*DRUG
2
0.00859756
0.00429878
28.28
0.0001
HORSE*BDRUG
25
0.03029697
0.00121188
7.97
0.0001
TIME
11
0.16610719
0.01510065
99.34
0.0001
B*TIME
11
0.00125706
0.00011428
0.75
0.6881
DRUG*TIME
22
0.09332317
0.00424196
27.91
0.0001
B*DRUG*TIME
22
0.00770722
0.00035033
2.30
0.0009
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.01059159
0.00211832
13.94
0.0001
post,t effect
5
0.06323181
0.01264636
83.20
0.0001
pre, b*t
5
0.00036315
0.00007263
0.48
0.7928
post,b*t
5
0.00029654
0.00005931
0.39
0.8555
pre,drug*t
10
0.00091566
0.00009157
0.60
0.8118
post,drug*t
10
0.02217682
0.00221768
14.59
0.0001
pre, b*drug*t
10
0.00078794
0.00007879
0.52
0.8770
post,b*drug*t
10
0.00209071
0.00020907
1.38
0.1902
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.00377
0.003767
5.523
0.02517
post,b effect
1
0.00072
0.000719
1.054
0.31240
pre, d effect
2
0.00000
0.000002
0.003
0.99654
post,d effect
2
0.13909
0.069543
101.977
0.00000
pre, d*b
2
0.00028
0.000142
0.208
0.81358
post, d*b
2
0.01314
0.006571
9.636
0.00054


44
minutes of the 15 jxg/kg-hr infusion in the other. These
horses did not exhibit long-term effects following these
episodes, and subsequent histamine infusions were
administered to them without incident.
Antihistaminic agents, such as pyrilamine maleate,
specific to H-l receptors are not expected to have
antisecretory effects and are routinely used as part of the
histamine challenge of gastric secretion in humans.11 A
post-pyrilamine decrease in acid concentration and output
was consistently observed and could reflect receptor
cross-reaction or changes in blood flow to the gastric
mucosa, since both H-l and H-2 receptors are involved in
histamine effects on vasculature.11, H-l receptor blockade
may also affect the delivery of substances to the
basolateral membrane of parietal cells, since H-l receptors
are involved in the regulation of capillary permeability.11
The results indicate that a histamine dose of 30
|ig/kg-hr can be considered as that which will induce a
maximal gastric acid secretory response in the horse.(See
fig.l) In pilot studies for this trial, horses were infused
with 15, 30, and 45 }ig/kg-hr of histamine. However, some
of these horses exhibited signs of metabolic alkalosis


92
first 45 minutes [basal collection], no treatment was given.
Beginning at time t=45min, pyrilamine maleate (Histavet-P,
Schering-Plough NJ) was infused IV at 1 mg/kg over a 15
minute period. No additional treatments were given for 30
minutes. At time t=90min, an IV infusion of either 0.9%
saline [60 mls/hr], histamine [30 pg/kg-hr], or pentagastrin
[6 fjg/kg-hr] was administered by infusion pump (Harvard
Apparatus, South Natick MA) and continued for the remainder
of the experiment. Infusions were prepared as previously
described.(See Chap. 4) At the conclusion of the
experiment, the intraduodenal catheter position was
rechecked before it was withdrawn, and the cannula closed.
Sample analysis
Volume was measured in a graduated cylinder and
aliquots were analyzed immediately for pH, and chloride ion
concentration. Gastric samples were analyzed immediately
for hydrogen ion concentration. Duodenal samples were kept
in an ice bath until they were analyzed for bicarbonate ion
concentration. Both gastric and duodenal samples were
frozen for later analysis of sodium and potassium ion
concentration. Gastric samples from t=45min were analyzed


199
Sodium Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
7953.46635
1590.69327
18.51
0.0001
BALLOON(B)
1
215.44566
215.44566
2.51
0.1143
DRUG
2
8596.82849
4298.41425
50.03
0.0001
B*DRUG
2
2849.44840
1424.72420
16.58
0.0001
HORSE*B*DRUG
25
29255.98279
1170.23931
13.62
0.0001
TIME
11
488.42419
44.40220
0.52
0.8917
B*TIME
11
1771.16769
161.01524
1.87
0.0421
DRUG*TIME
22
1502.28611
68.28573
0.79
0.7322
B*DRUG*TIME
22
1352.52704
61.47850
0.72
0.8235
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
198.754640
39.750928
0.46
0.8039
post,t effect
5
285.193595
57.038719
0.66
0.6512
pre, b*t
5
195.668293
39.133659
0.46
0.8092
post,b*t
5
438.983834
87.796767
1.02
0.4048
pre,drug*t
10
763.087688
76.308769
0.89
0.5446
post,drug*t
10
549.054734
54.905473
0.64
0.7800
pre, b*drug*t
10
877.234602
87.723460
1.02
0.4254
post,b*drug*t
10
468.155314
46.815531
0.54
0.8576
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1000.77
1000.77
1.60532
0.21529
post,b effect
1
220.51
220.51
0.35371
0.55666
pre, d effect
2
3754.18
1877.09
3.01099
0.06493
post,d effect
2
4256.85
2128.43
3.41416
0.04670
pre, d*b
2
1257.56
628.78
1.00861
0.37724
post, d*b
2
1352.38
676.19
1.08466
0.35142


210
73. Curwain BP, Turner NC. The Involvement of
Histamine Receptor Subtypes in Gastric Acid Secretion and
Mucosal Blood Flow in the Anaesthetized Rabbit. J. Physiol.
Lond. 1981; 311: 431-442.
74. Rosie M, Collis CS, Anjelkovic IZ, Segal MB,
Djuric D, Zlokovic BV. The Effects of (R) alpha-methyl
Histamine on the Isolated Guinea Pig Aorta. Agents Action-
Suppl. 1991; 33: 283-287.
75. Kauffman GL. Blood Flow and Gastric Secretion.
Federation Proc. 1982; 41:2080-2083.
76. Kubo N, Shirakawa O, Kuno T, Tanaka C.
Antimuscarinic Effects of Antihistamines: Quantitative
Evaluation by Receptor-binding Assay. Jpn. J. Pharmacol.
1987; 43 (3) : 277-282.
77. Beregovaia TV, Khomenko TA, Gubkin VA. The Effect
of Histamine HI Receptors on the Secretory Function and
Blood Flow in the Gastric Mucosa. Farmakol Toksikol. 1990;
53 (1) :41-43 .
78. Hirschowitz BI, Keeling D, Lewin M, Okabe S,
Parsons M, Sewing K,Wallmark B, Sach G. Pharmacological
Aspects of Acid Secretion. Dig. Dis. Sci. 1995; 40(2
Suppl): 3S-23S.
79. Hollande F, Bali JP, Magous R. Autoregulation of
Histamine Synthesis through H3 receptors in Isolated Fundic
Mucosal Cells. Am. J. Physiol. 1993; 265(6Ptl): G1039-
1044 .
80. Bado A, Hervatin F, Lewin MJM. Pharmacological
Evidence for Histamine H3 Receptor in the Control of Gastric
Acid Secretion in Cats. Am. J. Physiol. 1991; 260(23):
G631-G635.
81. Knight SE, Mclsaac RL, Rennie CD. The Effect of
Histamine and Histamine Antagonists on Gastric Acid
Secretion and Mucosal Blood Flow in Man. Br. J. Surg.
1980; 67 (4) : 266-268.


study, no adverse reactions were observed during the
histamine infusions; however, some horses became anxious
during and for approximately 15 minutes after the pyrilamine
maleate administration. The second histamine dose-response
study was designed with a slower infusion of pyrilamine,
which eliminated the excitement problem. It is the results
of this second histamine study that are presented in Chapter
2. The study was designed with 4 doses of histamine, yet
only 3 doses were statistically analyzed. We were able to
complete the all 4 doses in only one horse, due to metabolic
complications in the other horses associated with the loss
of large amounts of HC1, not a direct histamine effect.
Histamine infusion with associated gastric collection done
in later studies (See Chap. 5) was free of such
complications.
Pretreatment with pyrilamine maleate or another H-l
receptor antagonist was necessary to prevent CNS and
respiratory complication during histamine infusion.65 In
these studies, it was observed that acid output decreased
after pyrilamine, in contrast to what is seen in other
species.29'71-77-82'83 In preparation for later studies
comparing histamine to pentagastrin, we decided to


187
Gastric Content Volume
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
<
5
1581979.484
316395.897
43.98
0.0001
BALLOON(B)
1
6964934.280
6964934.280
968.07
0.0001
DRUG
2
1965459.060
982729.530
136.59
0.0001
B*DRUG
2
217416.144
108708.072
15.11
0.0001
HORSE*B*DRUG
25
1233421.502
49336.860
6.86
0.0001
TIME
11
4288302.581
389845.689
54.19
0.0001
B*TIME
11
237064.414
21551.310
3.00
0.0008
DRUG*TIME
22
1533188.995
69690.409
9.69
0.0001
B*DRUG*TIME
22
86068.579
3912.208
0.54
0.9552
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
518680.912
103736.182
14.42
0.0001
post,t effect
5
1103288.981
220657.796
30.67
0.0001
pre, b*t
5
13559.245
2711.849
0.38
0.8644
post,b*t
5
96643.Ill
19328.622
2.69
0.0214
pre,drug*t
10
31124.463
3112.446
0.43
0.9302
post,drug*t
10
368044.491
36804.449
5.12
0.0001
pre, b*drug*t
10
26594.907
2659.491
0.37
0.9591
post,b*drug*t
10
34653.361
3465.336
0.48
0.9016
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
2605905.67
2605905.67
92.193
0.00000
post,b effect
1
4485890.67
4485890.67
158.704
0.00000
pre, d effect
2
60907.37
30453.69
1.077
0.35223
post,d effect
2
3038571.73
1519285.87
53.750
0.00000
pre, d*b
2
48270.26
24135.13
0.854
0.43502
post, d*b
2
193966.19
96983.10
3.431
0.04437


64
receptors.86 The distribution of H-l, H-2, and H-3
receptors in the horse has not been documented.
Basal Pretreatment Early Late
Time Block
Figure 3 Mean pentagastrin stimulated acid output with and
without pyrilamine pretreatment. "Basal" refers to acid
output prior to any treatment.(t=30&45 min) "Pretreatment"
indicates output after pretreatment with pyrilamine or from
comparable period with no treatment.(t=75&90 min) "Early"
represents the first half of pentagastrin infusion.
(t=105,120&135 min) Output during the last half of
pentagastrin infusion is labeled "late".(t=150,165&180 min)
In this study, maximal pentagastrin-stimulated acid
output was significantly decreased in horses that received


53
Equine gastric contents during maximal stimulation with
histamine have a high concentration of acid and low
concentration of sodium as is characteristic of parietal
secretion in other species,(see Chap. 2) whereas,
pentagastrin-stimulated equine gastric contents have a high
concentration of sodium and a relatively low acidity.44
Histamine stimulation of gastric secretion induces a maximal
acid outputs (MAO) equal to those of pentagastrin-stimulated
horses.(See Chap. 2) In horses, as in other species, it is
necessary to administer an H-l antagonist prior to
histamine infusion to prevent side-ef fects 11-29-6S During
gastric secretory studies on horses stimulated with
histamine, pretreatment with the H-l antagonist, pyrilamine
maleate, resulted in a short-lived decrease in basal
volume, acid concentration and acid output. (See Chap.2) The
effect of this pretreatment on pentagastrin-stimulated
gastric secretion is thus far unknown. Since we planned to
further investigate the species specific disparity in the
histamine and pentagastrin-stimulated secretory responses,
we designed this study to consider the effect of pyrilamine
maleate pretreatment on pentagastrin-stimulated gastric
secretion.


195
Chloride Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
23328.25991
4665
. 65198
63.32
0.0001
BALLOON(B)
1
9497.81333
9497
. 81333
128.89
0.0001
DRUG
2
286.39699
143
. 19850
1.94
0.1449
B*DRUG
2
2998.29542
1499
. 14771
20.34
0.0001
HORSE*B*DRUG
25
14493.94120
579
. 75765
7.87
0.0001
TIME
11
1174.29352
106
.75396
1.45
0.1497
B*TIME
11
447.83056
40
. 71187
0.55
0.8663
DRUG*TIME
22
2335.85801
106
.17536
1.44
0.0926
B*DRUG*TIME
22
2402.03069
109
. 18321
1.48
0.0771
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
540.394120
108 .
078824
1.47
0.2002
post,t effect
5
281.454861
56 .
290972
0.76
0.5764
pre, b*t
5
311.874861
62 .
374972
0.85
0.5176
post,b*t
5
111.588194
22 .
317639
0.30
0.9110
pre,drug*t
10
829.902130
82 .
990213
1.13
0.3416
post,drug*t
10
651.967778
65 .
196778
0.88
0.5477
pre, b*drug*t
10
753.623611
75 .
362361
1.02
0.4237
post,b*drug*t
10
578.434444
57 .
843444
0.78
0.6433
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
4280.01
4280
. 01
13.0998
0.00102
post,b effect
1
5242.17
5242
. 17
16.0447
0.00035
pre, d effect
2
133.22
66
. 61
0.2039
0.81663
post,d effect
2
1007.17
503
.58
1.5413
0.22971
pre, d*b
2
3451.26
1725
.63
5.2816
0.01047
post, d*b
2
617.01
308
.50
0.9442
0.39964


38
output was 68.2 + 8.2 pEq/kg BW/15 min with a range from
17.7 to 101.7 jiEq/kg/15 min.
TABLE 2.
Data from Equine Gastric Contents Collected Before and After
Histamine Infusion.
BASAL
POST-
PYRIL
AMINE
7.5
(pg/kg-
hr)
15
(pg/kg-
hr)
30
(pg/kg-
hr)
Volume
(mis/
15 min)
428.3 +
34.1
356.7 +
37.3
591.7 +
41.4
a, b
591.7
28
a, b
508.9 +
54.8
a, b
PH
1.67
0.036
1.79 +
0.08
1.46
0.09
1.48 +
0.13
1.29 +
0.03
Peak
[H+]
(mEq/1)
42.5 +
3.9
33.5
3.5
72.2
3.9
a, b
81.3 +
5.1
a, b, c
82.9 +
6.8
a, b, c
PeakAcid
Output
(pEq/kg/
15min)
39.8 +
6.6
25.9
4.4
87.9
7.7
a, b
99.5 +
8.1
a, b, c
98.4 +
4.2
a, b, c
Peak
[Na+]
(mEq/1)
75.7 +
7.2
79.5
7.5
48.8
5.8
a, b
46.7
6.2
a, b
39.1 +
9.0
a, b
Peak Na
Output
(pEq/kg/
15min)
68.2 +
8.2
60.6 +
9.6
61.7
8.8
58.5 +
9.4
50.3
14.7
Values expressed as Mean + SEM
Pairwise Multiple Comparison procedure-Student-Newman-Keuls
a-significantly different (p<0.05) than basal
b-significantly different (p<0.05) than post-pyrilamine
c-significantly different (p<0.05) than 7.5 pg/kg-hr
Peak values derived from the final 30 minutes of each
treatment.


214
Medicine. Diane began a solo large animal private practice
in Marion County, Florida, in 1989. She has served on the
executive committee for the Marion Veterinary Medical
Association since 1992 and was the president during 1996.
She is also an active member of the American Veterinary
Medical Association and Florida Cattleman Association.


46
30 ¡ig/kg-hr infusion in these horses. (unpublished results)
As with other species29-41, some individual horses were
maximally stimulated at lower doses, but there was no
"supramaximal depression"40-67 of the mean response seen when
the dose was increased from 15 to 3 0 jag/kg-hr. Thus, the
horse is apparently slightly more sensitive to histamine
than man, in which the infusion of 42 |ag/kg-hr results in
MAO(1); the pig and dog are more resistant, requiring
60 fig/kg-hr29 and 50 (ag/kg-hr24, respectively. The peak
secretory response to histamine in horses was more gradually
attained than the response to pentagastrin infusion.44 This
phenomenon has been previously reported in other species, as
well.41
Mean maximal acid output in horses induced by histamine
was similar to that seen in humans on mEq/kg basis.
Furthermore, the maximal responses to histamine and
pentagastrin are not significantly different in horses, as
was anticipated. Species differences in maximal acid output
and relative sensitivity to histamine and pentagastrin are
numerous.17-68 The majority of "in vivo" gastric secretory
studies have involved dogs, rats, and humans.69 Dogs have


153
Potassium Output in Gastric Contents
(jiEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
12.24
1.85
11.24
1.54
11.33
1.82
30
BASAL
10.16
2.39
10.02
1.98
11.53
1.73
45
BASAL
9.67
2.22
8.26
2.31
11.42
1.75
60
HVP
10.11
2.34
7.75
1.67
9.91
1.33
75
6.70
1.40
5.21
0.75
7.84
1.47
90
6.65
1.27
5.40
1.22
6.37
0.93
105
INFUSION
7.96
1.88
9.07
1.24
8.54
1.39
120
INFUSION
9.06
1.39
17.36
1.62
16.72
2.03
135
INFUSION
10.19
1.13
18.57
1.18
18.94
1.02
150
INFUSION
10.29
1.23
19.81
1.14
20.64
1.21
165
INFUSION
9.54
0.55
19.28
1.21
18.90
1.02
180
INFUSION
10.06
0.95
19.77
1.33
20.13
1.59
HVP = Pyrilamine maleate infusion


97
concentration, and was consistent between treatment groups.
After treatment with pyrilamine maleate, the collection
volume (p=0.0001), acid concentration (p=0.0001), acid
output (p=0.0001) sodium output (p=0.0001), potassium
concentration (p=0.0001), potassium output (p=0.0001), and
chloride output (p=0.0001) were decreased significantly,
while pH (p=0.0457) and sodium concentration (p=0.0001)
significantly increased. The balloon [obstruction vs. no
obstruction of the pylorus] affected all parameters, except
pH, [Na+] and [K*] The experiments with the balloon had
significantly lower volume (p<0.00001), and acid
(p=0.02517), sodium (p<0.00001), potassium (p<0.00001), and
chloride (p<0.00001) outputs than those without balloon.
Acid (p=0.02075) and chloride (p=0.00102) concentrations
were significantly higher in the experiments with pyloric
obstruction. As expected, no significant differences were
found between groups with regard to which infusion was to be
given. Therefore, two "basal" and "pyrilamine" values were
calculated from mean of the "Rl" and "R2" of either
experiments with balloon, or experiments without balloon.


22
endoscopic examination of the stomach.51 The fluid refluxed
could potentially contain a mixture of biliary, pancreatic
and duodenal secretions, since the duodenal diverticulum,
where the bile and minor pancreatic ducts enter, is in
relatively close proximity to the pylorus.51 Furthermore,
the absence of a gallbladder leads to continuous secretion
of bile in horses and equine pancreatic secretion is
reported to be profuse and continuous.55-56
Pancreatic secretion of the horse is distinct from that
of other species. The resting secretion of approximately 25
pl/g gland/min is increased by four to fivefold during
eating, stimulation of the vagus nerve, or after the
administration of secretin or pentagastrin.S5-57 Neither
resting nor vagal-induced pancreatic secretion is abolished
by atropine. 55-58 Vagotomy does not alter the basal
secretion. Studies with ponies fitted with re-entrant
cannula in the pancreatic duct found that they may secrete a
volume equivalent to up to 10% of their own body weight
daily.ss The concentration of amylase and the proteolytic
activity of equine pancreatic juice is particularly low, and
it has a very weak ability to emulsify fat, compared to
other species.55 Small increases in the concentration of


30
that equine pancreatic water and electrolyte secretion is
profuse and continuous and can be stimulated by
pentagastrin. Finally, the stimulation of gastric secretion
with histamine resulted in purely parietal secretion
resembling that of other species. Therefore, the
dissertation hypothesis is as follows. In the equine
gastric cannula model, the vigorous sodium-rich component of
pentagastrin stimulated gastric contents is extragastric in
origin.
A technique of duodenal catheterization through the
chronic gastric cannula was developed to allow for occlusion
of the pylorus during acid secretory studies. Chapter 4
discusses the technique for duodenal catheterization, the
effect of the technique on gastric secretion, and the
composition of duodenal contents. The primary study of this
dissertation, describing results with and without the
obstruction of the pylorus, is presented in chapter 5 and
was designed to definitively determine if the sodium rich
fluid found during pentagastrin stimulation and absent
during histamine stimulation is secreted by the gastric
glandular mucosa or by a extragastric source.


148
Volume of Gastric Contents
(ml/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
272.0
45.13
266.2
56.27
229.5
46.22
30
BASAL
245.5
53.38
246.7
69.62
251.0
34.30
45
BASAL
252.3
40.58
251.5
58.20
259.0
37.07
60
HVP
194.7
36.72
237.7
54.05
233.3
26.09
75
139.3
31.75
148.2
33.19
164.0
27.99
90
138.0
24.72
170.0
35.33
163.7
27.86
105
INFUSION
200.0
29.34
207.7
49.00
269.7
26.40
120
INFUSION
215.0
33.74
299.2
77.17
427.5
39.99
135
INFUSION
211.7
29.67
326.3
54.89
468.3
24.45
150
INFUSION
219.3
31.58
386.8
61.57
450.0
26.61
165
INFUSION
233.2
39.58
436.0
53.74
550.0
66.72
180
INFUSION
220.7
45.42
455.0
58.30
497.5
38.03
HVP = Pyrilamine maleate infusion


193
Potassium Concentration in Gastric Contents
Source
DF
Type I SS
HORSE
5
139.934838
BALLOON(B)
1
209.585208
DRUG
2
315.970880
B*DRUG
2
169.367639
HORSE*B*DRUG
25
745.549468
TIME
11
1413.509699
B*TIME
11
195.413403
DRUG*TIME
22
1009.475787
B*DRUG*TIME
22
72.474583
Contrast
DF
Contrast :
pre,t effect
5
229.096343
post,t effect
5
261.283148
pre, b*t
5
6.743009
post,b*t
5
20.045370
pre,drug*t
10
25.108241
post,drug*t
10
157.176574
pre, b*drug*t
10
13.242685
post,b*drug*t
10
24.664352
Source
DF
SS N
pre, b effect
1
1.11
post,b effect
1
377.10
pre, d effect
2
75.94
post,d effect
2
1067.23
pre, d*b
2
32.17
post, d*b
2
171.77
Mean Square
F Value
Pr > F
27.986968
9.51
0.0001
209.585208
71.22
0.0001
157.985440
53.68
0.0001
84.683819
28.78
0.0001
29.821979
10.13
0.0001
128.500882
43.66
0.0001
17.764855
6.04
0.0001
45.885263
15.59
0.0001
3.294299
1.12
0.3235
Mean Square
F Value
Pr > F
45.819269
15.57
0.0001
52.256630
17.76
0.0001
1.348602
0.46
0.8072
4.009074
1.36
0.2381
2.510824
0.85
0.5777
15.717657
5.34
0.0001
1.324269
0.45
0.9207
2.466435
0.84
0.5921
MS_N
F Value
PValue
1.11
0.0679
0.79620
377.098
23.0184
0.00004
37.968
2.3176
0.11581
533.613
32.5723
0.00000
16.085
0.9818
0.38628
85.883
5.2424
0.01112


45
Figure 1. Mean acid output/15 min. during the last 30
minutes of each treatment. "Basal" indicates the status
prior to any treatment. "Pyrilamine" indicates the output
after treatment with pyrilamine malate (1 mg/kg IV) and
peak outputs during IV histamine infusion of 7.5, 15, and
30 (ag/kg-hr are indicated accordingly. Data are expressed
as mean + SEM.
during the 45 jag/kg-hr infusion; therefore, we elected not
to utilize this higher dose in this trial. Four horses
completed the pilot study and the MAO during the 4 5 |^g/kg-hr
infusion was not significantly different from the MAO during


49
Sodium outputs increased coincident with acid outputs
during pentagastrin stimulation in horses44; whereas, in the
studies described here, sodium concentration decreased as
acid concentrations increased during histamine stimulation,
and the sodium output was constant as the acid output
increased to a maximal level.(fig.2) Thus, in the horse as
in other species, histamine appears to stimulate a purely
parietal secretion, with acid concentrations rising to
expected levels and a reciprocal decrease in sodium
concentration.39'41
Figure 2. Regression analysis of acid vs. sodium outputs
during pentagastrin (o) and histamine (A.) infusion.


175
Potassium Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
4.62
0.28
4.40
0.09
4.47
0.08
30
BASAL
4.69
0.30
4.29
0.07
4.45
0.06
45
BASAL
4.88
0.36
4.22
0.17
4.39
0.09
60
HVP
4.68
0.29
4.23
0.14
4.31
0.11
75
4.45
0.28
4.12
0.13
4.68
0.42
90
4.43
0.25
4.13
0.09
4.66
0.37
105
INFUSION
4.57
0.34
3.97
0.09
4.01
0.14
120
INFUSION
4.75
0.45
3.86
0.09
3 82
0.09
135
INFUSION
4.34
0.31
3 88
0.15
3.70
0.09
150
INFUSION
4.53
0.37
3.80
0.10
3.78
0.16
165
INFUSION
4.15
0.26
3.91
0.22
3 65
0.09
180
INFUSION
4.37
0.28
3.90
0.18
3.63
0.12
HVP = Pyrilamine maleate infusion


166
Sodium Output in Gastric Contents
(|aEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
43.7
4.19
53.7
9.51
38.0
6.96
30
BASAL
36.6
3.82
46.4
10.49
42.1
6.98
45
BASAL
43.9
5.29
48.4
7.26
42.3
6.51
60
HVP
35.7
6.63
46.8
5.68
38.6
5.21
75
26.7
6.13
29.7
2.94
30.0
5.25
90
28.2
3.12
38.4
4.58
33 3
6.34
105
INFUSION
41.1
5.55
37.5
4.55
46.6
4.51
120
INFUSION
40.7
4.48
29.1
6.46
58.0
10.44
135
INFUSION
38.6
2.96
23.7
3.87
52.2
5.34
150
INFUSION
40.0
6.23
26.9
6.67
51.4
5.84
165
INFUSION
42.6
5.33
30.1
6.56
71.6
21.33
180
INFUSION
40.0
7.27
30.1
6.65
58.8
12.68
HVP = Pyrilamine maleate infusion


150
pH of Gastric Contents
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
1.59
0.124
1.77
0.164
2.38
0.904
30
BASAL
1.52
0.095
2.00
0.407
1.54
0.131
45
BASAL
1.54
0.094
2.93
0.940
2.18
0.778
60
HVP
1.72
0.208
3.49
1.259
2.45
1.060
75
2.04
0.343
3.56
1.217
2.53
1.072
90
2.23
0.419
2.89
0.962
2.59
1.083
105
INFUSION
2.77
0.726
1.90
0.269
1.52
0.109
120
INFUSION
2.40
0.743
1.33
0.040
1.32
0.028
135
INFUSION
2.35
0.783
1.25
0.020
1.26
0.034
150
INFUSION
2.62
0.895
1.23
0.026
1.27
0.031
165
INFUSION
2.47
0.888
1.22
0.033
1.28
0.028
180
INFUSION
2.42
0.926
1.20
0.041
1.26
0.022
HVP = Pyrilamine maleate infusion


33
Materials and Methods
Six adult horses, both mares and geldings, were used.
All studies were done with the approval of the University of
Florida IACUC. The horses ranged from 2 to 20 years of age.
The five Thoroughbreds, and one Arabian weighed an average
of 484 kg (range 444-506 kg). All horses were free of
clinical signs of gastrointestinal disease, were dewormed
every 2 months and were vaccinated for encephalitis and
tetanus every 6 months. They were maintained on grass
pasture with coastal hay ad lib and 12% protein grain twice
daily. Each horse was previously prepared with a chronic
indwelling gastric cannula as described by Campbell-Thompson
and Merritt.31
The horses were fasted with free choice water for 20
hours prior to each experiment. At least one week interval
occurred between experiments on any given horse. Studies
were performed while the horse was loosely restrained in the
laboratory.
After placement of an indwelling jugular catheter, the
gastric cannula was opened and drained by gravity for 30


208
55. Alexander F, Hickson JCD. The Salivary and
Pancreatic Secretions of the Horse. In: Phillipson AT, ed.
Physiology of Digestion and Metabolism in the Ruminant.
Newcastle-upon-Tyne: Oriel Press, 1969; 375-389.
56. Bernard C. Memoir on the Pancreas, translated by
J. Henderson, Bailliere: Acad Press, 1856(reprinted 1985);
33-37.
57. Comline RS, Hall LW, Hickson JCD, Murillo F,
Walker RG. Pancreatic Secretion in the Horse. Proceedings
of the Physiology Society. 1969; 10P-11P.
58. Comline RS, Hickson JCD, Message MA. Nervous
Tissue in the Pancreas of Different Species. Proceedings of
the Physiology Society. 1963; 47P-48P.
59. Schulz I. Electrolyte and Fluid Secretion in the
Exocrine Pancreas. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Second Edition. New York: Raven
Press 1987; 1147-1165.
60. Solomon TE. Control of Exocrine Pancreatic
Secretion. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Third Edition. New York: Raven
Press 1994; 1499-1527.
61. Jensen RT. Receptors on Pancreatic Acinar Cells.
In: Johnson LR, ed. Physiology of the Gastrointestinal
Tract, Third Edition. New York: Raven Press 1994; 1377-
1434 .
62. Stening GF, Grossman MI. Gastrin-related Peptides
as Stimulants of Pancreatic and Gastric Secretion. Am. J.
Physiol. 1969; 217(1): 262-266.
63. Argent BE, Case RM. Pancreatic Ducts. In:
Johnson LR, ed. Physiology of the Gastrointestinal Tract,
Third Edition. New York: Raven Press, 1994; 1473-1494.


157
Chloride Output in Gastric Contents
(f.iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
144.8
13.33
143.8
21.01
156.3
17.09
30
BASAL
131.3
20.66
136.3
24.94
136.3
24.94
45
BASAL
127.2
22.11
127.7
27.93
174.3
15.53
60
HVP
137.2
25.79
131.8
22.06
151.9
14.06
75
107.0
21.14
95.9
17.18
134.9
21.76
90
109.9
15.54
98.2
19.95
120.6
11.46
105
INFUSION
119.9
24.13
131.5
16.56
145.8
23.74
120
INFUSION
139.8
14.24
176.2
18.91
245.7
18.13
135
INFUSION
152.6
8.15
185.2
18.92
277.9
30.20
150
INFUSION
147.1
6.86
210.4
20.33
287.4
22.51
165
INFUSION
141.3
6.74
200.8
20.12
272.9
20.35
180
INFUSION
145.2
10.89
213.8
20.78
272.9
18.58
HVP = Pyrilamine maleate infusion


15
secretagogue for investigation of the acid secretory process
and its regulation.1'20'29'30 After Gregory and Tracy found
that an extract of porcine antral mucosa was an effective
stimulant of acid secretion9, gastrin became a popular
investigational tool.28 A synthetic polypeptide analog to
the C terminal tetrapeptide of gastrin is pentagastrin, or
peptavlon, which has become the secretagogue most commonly
used for stimulation of gastrin related secretion.17'19-21'30'31
Today, gastric secretory studies range from chronically
implanted gastric cannulas in intact animal models to
receptor immunochemical studies on ECL cells isolated from
the gastric mucosa.
The hundreds of studies of gastric acid secretion
have accumulated a vast amount of information with marked
similarities in the process and its regulation. However,
some striking differences have also been observed. The
relative sensitivity to specific secretagogue, the rate of
basal secretion, the response to inhibition, and ECL cell
shape and prevalence are markedly different between
species.17 In the rat, the gastric acid secretory process
is highly sensitive to pentagastrin and very resistant to
histamine.17-30 Histamine and gastrin are equally effective


AD
¡917
i Ml
UNIVERSITY OF FLORIDA
3 1262 08555 3351


24
meal-induced patterns, with meal related secretion further
divided into cephalic, gastric, and intestinal phases.60 In
most species, basal enzyme secretion ranges from 10% to 30%
of maximal secretion, whereas, basal bicarbonate secretion
is only 1% to 2% of maximal.60 The regulation of basal
enzyme secretion appears to vary between species, while
basal bicarbonate secretion is dependent primarily on
secretin augmented by cholinergic neural input.60 Basal
enzyme secretion is almost entirely due to cholinergic
stimulation in the rat, whereas, in man, both CCK and
cholinergic stimulation mediate it. Brief bursts of
pancreatic enzyme and bicarbonate secretion are associated
with the migrating myoelectric complex and a circadian
rhythm has also been reported.60 The normal pancreatic
secretory response to a meal is increased enzymatic
secretion to aid digestion and increased bicarbonate
secretion to buffer the chyme and assure the optimum
intraluminal pH for enzymatic activity. As with gastric
secretion, "cephalic" pancreatic secretion seems to be
stimulated either directly or indirectly by the vagus
nerve.50 "Gastro-pancreatic reflexes" are initiated by food
or gastric distension and mediated by cholinergic vagovagal


113
infusions of histamine (p=0.00783) or pentagastrin
(p=0.00653) decreasing significantly compared to saline.
Table 17.
POTASSIUM IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[K+]
mEq/L
SAL *
4.2 60.2 7
NB
4.50.2
4.40.3
HIST
3.900.20
PG
3.64 + 0.10
[K+]
mEq/L
SAL *
3.940.14
B
4.10.2
4.00.2
HIST
3.69+0.12
PG
3.74+0.27
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
Table 18.
CHLORIDE IN DUODENAL CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS
[Cl']
mEq/L
SAL *
135.65.5
NB
118.15.5
119.65.2
HIST
103.37.0
PG
115.16.1
[Cl']
mEq/L
SAL *
129.2 + 6.3
B
126.6+7.1
123.94.4
HIST
112.52.7
PG
108.52.7
* Response to this infusion significantly different
(p<0.05) from responses to other infusions
Chloride ion concentration. (Table 18) The drug
effect on [C1] was significant (p<0.00001). The [Cl'] was


160
Acid Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
53.3
9.93
37.8
9.37
46.9
12.28
30
BASAL
53.9
9.84
40.1
10.79
52.4
8.95
45
BASAL
48.6
7.96
35.8
12.98
51.1
10.41
60
HVP
44.2
10.13
33.8
13.03
53.5
10.97
75
34.9
9.16
28.8
12.79
44.5
9.29
90
27.1
7.73
22.8
8.82
38.9
8.13
105
INFUSION
27.0
8.34
39.7
11.10
50.8
7.52
120
INFUSION
34.0
8.61
85.4
6.65
73.6
5.09
135
INFUSION
39.3
9.89
96.0
3.93
85.6
2.59
150
INFUSION
39.1
11.03
101.1
3.37
85.2
4.23
165
INFUSION
38.4
9.88
102.1
3.76
82.2
5.22
180
INFUSION
39.1
8.30
104.2
3.21
86.1
4.66
HVP = Pyrilamine maleate infusion


EFFECTS OF HISTAMINE
AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS
By
DIANE LYNN KITCHEN
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1997


77
Analysis of data
For the purpose of this paper, duodenal contents were
analyzed to determine electrolyte concentration ranges, but
these data were not statistically evaluated. Statistical
analysis was performed on volume, acid concentration, acid
output, sodium concentration, and sodium output from the
gastric samples. Output was calculated on a per kg body
weight basis from the volume and hydrogen or sodium ion
concentration and was expressed as |.iEq/kg-15min. The last
30 minutes of basal collections, post-pyrilamine
collections, and the first and last 30 minutes of infusion-
related collections were compared between studies. A
two-way ANOVA was performed for factors of time (basal,
post-pyrilamine, early infusion, and late infusion), and
duodenal catheter (yes or no) and interactions of these
factors. A p<0.05 was considered significant and all
pairwise multiple comparisons by Tukey test were performed.


206
37. Guttu K, Resok B, Gislason H, Svanes FK, Gronbech
JE. Gastric Bicarbonate Secretion, Acid Secretion, and
Mucosal Blood Flow during Influence of Pentagastrin and
Omeprazole in the Cat. Scand. J. Gastroenterol 1991; 26:
431-441.
38. Xu R-J, Cranwell PD. Development of Gastric Acid
Secretion in Pigs from Birth to Thirty-six Days of Age: the
Response to Pentagastrin. J. Dev. Physiol. 1990; 13: 315-
326 .
39. Aagaard P, Christiansen J. Gastric Secretion of
Potassium, Sodium, Calcium, and Phosphorus Following
Stimulation by Histamine and Peptavlon. Scand. J.
Gastroent. 1970; 5: 155-160.
40. Hirschowitz BI. Apparent Kinetics of Histamine
Dose-Responsive Gastric Water and Electrolyte Secretion in
the Dog. Gastroenterology 1968; 54(4): 514-522.
41. Hutchison GA, Hirschowitz BI. Two Models of
Gastric H, Na, K, and Cl Secretion in the Dog Using
Histamine and Pentagastrin. Am. J. Physiol. 1969; 216(3):
487-492.
42. Meeroff JC, Rofrano JA, Meeroff M. Electrolytes
of the Gastric Juice in Health and Gastroduodenal Diseases.
Am. J. Dig. Dis. 1973; 18: 865-872.
43. Makhlouf GM. Electrolyte Composition of Gastric
Secretion. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract New York: Raven Press, 1981; 551-
566 .
44. Campbell-Thompson ML, Merritt AM. Basal and
Pentagastrin-stimulated Gastric Secretion in Young Horses.
AM. J. Physiol. 1990; 259: R1259-R1266.
45. Becht JL, Byers TD. Gastroduodenal Ulceration in
Foals. Eq. Vet. J. 1986; 18: 307-312.


54
Materials and Methods
Horses
Two mixed breed, one Thoroughbred and one Arabian [2
mares, 2 geldings] ranging from 3 to 20 years were used in
this study. The horses were all healthy and ranged in
weight from 370 to 490 kg. They were maintained on grass
pasture and provided coastal hay ad lib and 12% protein
grain twice daily. All horses were dewormed every 2 months,
vaccinated for encephalomyelitis and tetanus every 6 months
and were free of clinical signs of gastrointestinal disease.
Chronic indwelling gastric cannulas as described by
Campbell-Thompson and Merritt31 had been prepared in these
horses 1 to 24 months prior to this study. All studies were
approved by the University of Florida IACUC.
Experimental preparation
Horses were fasted with free choice water for 20 hours
prior to an experiment. Experiments were performed with no
less than a one week interval between them. The horses were
loosely restrained in the laboratory for the entire


161
Acid Output in Gastric Contents
(|iEq/kg/15minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
38.4
9.03
42.4
9.53
31.0
10.00
30
BASAL
36.1
10.09
42.3
9.50
29.9
9.07
45
BASAL
34.7
11.53
35.9
12.09
34.0
9.09
60
HVP
39.5
11.10
31.0
12.55
34.2
7.87
75
25.8
8.35
24.4
9.93
29.1
5.01
90
17.7
7.01
17.1
8.95
20.8
5.35
105
INFUSION
18.6
8.29
33.5
9.01
18.9
6.64
120
INFUSION
21.7
7.36
86.9
10.36
41.4
10.44
135
INFUSION
23.1
6.47
100.9
6.59
56.7
10.15
150
INFUSION
26.2
8.64
108.0
6.04
69.7
6.59
165
INFUSION
28.3
5.33
107.5
8.46
75.7
6.25
180
INFUSION
28.8
5.69
117.8
8.16
84.7
7.74
HVP = Pyrilamine maleate infusion


164
Sodium Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
82.9
9.98
99.2
9.54
86.0
12.47
30
BASAL
79.9
10.11
97.8
10.02
80.6
7.77
45
BASAL
87.2
8.80
101.3
11.59
79.7
7.87
60
HVP
91.3
10.21
105.5
12.21
79.9
8.44
75
93.6
9.62
106.2
12.18
88.7
8.49
90
102.8
8.90
115.2
10.43
94.9
9.67
105
INFUSION
100.6
8.95
97.7
13.97
83.2
7.77
120
INFUSION
95.0
8.32
48.8
6.56
62.5
6.43
135
INFUSION
91.9
9.28
35.6
3.42
52.9
5.07
150
INFUSION
88.7
9.41
31.4
3.79
54.1
5.94
165
INFUSION
92.0
9.39
31.7
4.39
56.6
7.70
180
INFUSION
91.2
9.68
30.5
3.92
52.9
6.96
HVP = Pyrilamine maleate infusion


CHAPTER 6
SUMMARY AND CONCLUSIONS
Summary
Histamine infusion at a dose of 30 (ig/kg-hr to horses
resulted in a maximal acid output response comparable to the
maximal response to pentagastrin infusion and, on a
bodyweight basis is similar to that of humans. Thus, the
gastric contents collected during histamine infusion
differed significantly in electrolyte concentrations and
sodium output from those collected during pentagastrin
infusion. The character of the histamine-stimulated gastric
contents resembles the classic "parietal" response described
in other species and did not include the voluminous sodium-
rich component described in studies with
pentagastrin. 31.44,49,51,53.54
Prior to this study, we had some concerns about the
reaction of horses to the histamine infusion. In the pilot
130


102
output stimulated by the infusion of pentagastrin and
histamine did not differ significantly, both were
significantly greater (p<0.00001) than that during saline
infusion. Also, K+ output was significantly greater
(p<0.00001) in experiments with no balloon than those with a
balloon obstructing the pylorus, irrespective of infusion
composition.
Chloride ion concentration. (Table 12) The chloride
ion concentration was relatively constant among all
experiments. The only significant difference was balloon
experiment results were higher (p=0.00035) than when there
was no balloon.
Chloride ion output. (Table 12) Because of minimal
changes in [Cl'] the chloride output related closely to
changes in volume. The output of chloride ion increased
significantly (p=0.0001) throughout the infusion period and
the drug*time interaction was significant (p=0.0001), since
pentagastrin rapidly induced a marked increase, that was
significantly greater than that of histamine (p=0.0495) or
saline (p=0.0001). Histamine alsoproduced an increased
output over time that was significantly greater than that of
saline (p=0.0013). The drug*balloon interaction was


Table 1.
Acid and Sodium Concentration during Histamine Infusion
(n=4 horses)
29
Histamine
Dose
pg/kg-hr
Mean [H+]
mEq/L
Mean [Na+]
mEq/L
Basal
26.5
101.3
15
73.9
57.8
30
95.1
55.5
45
97.5
52.4
In order to perform controlled comparisons between
histamine and pentagastrin, without potential extraneous
factors, it was necessary to evaluate the secretory response
to pentagastrin following pyrilamine maleate pretreatment.
Chapter 3 presents the unexpected results of that study.
Four crucial facets of equine gastric secretion were
considered to develop the dissertation hypothesis. First,
equine basal and pentagastrin-stimulated gastric secretion
has an uncharacteristically low concentration of acid and
high concentration and output of sodium. Second, acid
blockade with numerous agents does not eliminate the
profound sodium-rich nonparietal component of pentagastrin-
stimulated secretion. Third, Hickson and Alexander reported


55
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes, while a indwelling
jugular catheter was emplaced. The gastric contents were
i
collected into 1L fluid bags suspended from a surcingle.
Experimental protocol
Gastric contents were collected in 15 minute aliquots
and were filtered through gauze prior to analysis.
Collections were measured for volume and if available, a 50
ml sample was saved for further analyses. Analyses were
performed either immediately or samples were frozen for
later analysis. Each experiment lasted 3 hours. During the
first 45 minutes [basal collection], no treatment was
given. In the treatment experiments, pyrilamine maleate
(Histavet-P, Schering-Plough NJ) was infused IV at 1 mg/kg
over a 15 minute period, beginning at time t=45min. No
additional treatments were given for 30 minutes. In the no
treatment experiments, basal collection was continued during
time t=45-90 min. At time t=90min, an IV infusion of
pentagastrin [6 pg/kg-hr] was administered by infusion pump


20
unstimulated gastric collection periods.31-44 The basal
equine acid output of approximately 30% of maximal output is
consistent with pigs and rats, and it is greater than that
of humans.44 On a body weight basis, equine basal acid
output over time is similar to that found in man.39-44
Up to now, pentagastrin has been the only
secretagogue used "in vivo" to stimulate equine gastric acid
secretion to characterize the species-specific responses and
to study drugs designed to prevent or treat gastric
ulcers. 48-49-51-S3-54 Its administration to horses results in a
significant increases in both gastric acid and sodium
outputs.44 Acid concentration increases after stimulation,
but not to the maximal magnitude observed in other species.
In addition, the increased sodium output during stimulation
is unique to horses. As the dose of pentagastrin is
increased, the concentration of sodium decreases slowly and
remains greater than the acid concentration, unlike in other
species where the sodium concentration rapidly decreases in
an inversely proportional relationship to the increasing
acid concentration.44 This is a major species-specific
difference in the equine secretory response to pentagastrin.
Thus, it has been suggested pentagastrin stimulates both the


43
malate, a selective H-l receptor blocking agent11,
presumably eliminated any potential respiratory or
neurologic side-effects of histamine infusion.
Histamine-induced dyspnea results from bronchoconstriction
mediated by H-l receptors.11 Both H-l and H-2 receptors are
located in the central nervous system and horses are more
susceptible to pronounced excitation and anxiety than some
other species. The histamine provocation test for studies
of equine bronchial responsiveness requires sedation to
prevent apprehension and anxiety.65
Two experiments were not completed because the horses
developed synchronous diaphragmatic flutter (SDF) and muscle
twitches. It is our belief that this was due to metabolic
alkalosis with hypocalcemia and hypochloremia following
marked HC1 secretion.66 Changes in the ionization
potential during metabolic alkalosis alter the free to bound
calcium ratio and results in SDF.66 Once stimulation of
HC1 secretion ceased and the cannula was occluded, fluid and
electrolyte loss ended and the horses responded rapidly.
These individual horses were apparently hyper-responsive to
histamine, since the MAO was reached during the 7.5
M^j/kg-hr infusion in one horse and after the first 15


TABLE OF CONTENTS
ACKNOWLEDGMENTS iv
LIST OF TABLES xi
LIST OF FIGURES xii
ABSTRACT xiii
CHAPTERS
1 INTRODUCTION AND REVIEW OF LITERATURE 1
Introduction 1
Historical Background . 2
Review of Literature 5
Development of Hypothesis .26
2 EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID
SECRETION 31
Introduction 31
Materials and Methods 33
Results 36
Basal Secretion 37
Pyrilamine Infusion 39
Histamine dose-response 39
Volume 3 9
Acid Concentration 40
Acid Output 4 0
Sodium concentration 41
Sodium Output 42
Pentagastrin Outputs 42
Discussion 42
vii


50
The exact origin of the histamine which stimulates
parietal cells and the mechanisms involved in its release
have not been clearly documented in most species24, but it
<
is known to act via H-2 receptors on parietal cells as a
paracrine mediator.2-20 In rats, enterochromaffinlike (ECL)
cells are the major histamine source in the gastric mucosa
and gastrin has been shown to stimulate its release from
them. 22-24 Rabbit and human gastric mucosal preparations also
release histamine in response to gastrin but the cells
responsible have not been identified.22 Few ECL cells are
found in the normal human and canine mucosa; however, many
mast cells are observed and may serve as the histamine
source.24 Human patients with hypergastrinemia appear to
have increased numbers of ECL cells in their gastric
mucosa.24 The density of ECL cells in equine gastric mucosa
is greatest in the pyloric gland region.70 Fewer ECL cells
have been identified in the fundic gland mucosa and in the
proximal duodenum.
In this study, we determined that histamine can be used
as a stimulant of gastric acid secretion in horses.
Histamine stimulated mean maximal acid output was
comparable to that previously reported with pentagastrin.44


124
presumably duodenal, fluid that accounts for the additional
volume is sodium rich.
Figure 10 Sodium concentration. A curvilinear line derived
from mean sodium output during pentagastrin and histamine
infusions comparison of B and NB experiments. a marks mean
for B trials a marks mean for NB trials.
The duodenal contents sampled by the intraduodenal
catheter are presumably composed of a combination of
biliary, duodenal, and pancreatic secretions. Not
surprisingly, the volume of collection was much greater in
the experiments with pyloric obstruction, which likely


18
plasma.43 No change in nonparietal secretory rate is
observed during stimulation with any of the known gastric
secretagogues. Sodium ions are the predominate cation of
this nonparietal component. The differences in response to
secretagogues of these two components explains the inverse
relationship of sodium and acid concentrations reported
during increasing acid secretory rates.43
Various gastroduodenal diseases are characterized by
alterations in the electrolyte composition of gastric
contents.42 Patients with active duodenal ulcers have
increased acid and chloride concentration and decreased
sodium concentration, while gastric ulcer patients have
increased sodium concentrations in the gastric content
without changes in the concentrations of acid, potassium,
or chloride.42 Other changes in the composition of
electrolytes are suggestive of trophic gastric ulcers,
chronic gastritis, and Zollinger-Ellison syndrome.42 The
characteristic gastric secretory response to stimulated
gastric secretion has been consistently observed in all
species except the horse.44
Due to the relative difficulty in collecting the
contents, little was known about equine gastric secretion


69
both catheter studies, six of the horses (5TB,1AR) were
selected. The no catheter/pentagastrin study was performed
on four (2MB,1AR,1TB) horses. Two horses (1TB,1AR) were
involved in both studies.(TABLE 6) The horses were all
healthy and ranged in weight from 430 to 510 kg. They were
maintained on grass pasture and provided coastal hay ad lib
and 12% protein grain twice daily. All horses were dewormed
every 2 months, vaccinated for encephalomyelitis/tetanus
every 6 months and were free of clinical signs of
gastrointestinal disease. A chronic indwelling gastric
cannula as described by Campbell-Thompson and Merritt31 had
TABLE 6.
Descriptions and Abbreviations for Each Study.
EXPERIMENT
INFUSION
CATHETER
HORSES USED
ABBREVIATION
(secretagogue)
(via cannula)
PG/NOC
Pentagastrin
None
B, E, J, M
PG/CATH
Pentagastrin
Intraduodenal
B, D, E,H,I,T
been prepared
in these horses
1 to 24 months
prior to this
study. All studies were approved by the University of
Florida IACUC.


88
study. The horses were all healthy and weighed between 430
and 510 kg. They were maintained on grass pasture and
provided coastal hay free choice, and 12% protein grain
twice daily.- They were dewormed every 2 months, vaccinated
for encephalomyelitis and tetanus every 6 months and were
free of clinical signs of any disease. Chronic indwelling
gastric cannulas as described by Campbell-Thompson and
Merritt31 had been prepared in these horses from 1 to 24
months prior to this study. All studies were approved by
the University of Florida IACUC.
Experimental protocol
Horses were fasted with free choice water for 20 hours
prior to an experiment. Experiments were performed with no
less than a one week interval between them. The horses were
loosely restrained in the laboratory for the entire
experiment. The gastric cannula was opened and allowed to
drain by gravity for 15 to 20 minutes, while a indwelling
jugular catheter(Abbocath) was emplaced. Videoendoscopy was
used to place a specially designed catheter into the
duodenum, as described by Kitchen et al.(See Chap. 4) The
catheter was further adapted in half of the experiments by


91
Gastric and duodenal contents were continuously
collected by gravity drainage, separately. The containers
were switched every fifteen minutes and samples from each
time block were analyzed. Gastric samples were filtered
through gauze prior to analysis. Volume of both gastric
and duodenal collections was measured and if available, a
50 ml aliquot was saved for sample analyses. Analyses were
performed either immediately or samples were frozen for
later analysis. Each experiment lasted 3 hours. The design
was a 6x6 Latin square repeated measures design randomized
for treatment.(See Table 9.) Three different IV infusions
Table 9.
EXPERIMENTAL DESIGN
INFUSION
CATHETER TYPE
ABBREVIATION
Saline
No Balloon
SAL/NB
Histamine
No Balloon
HIST/NB
Pentagastrin
No Balloon
PG/NB
Saline
Balloon
SAL/B
Histamine
Balloon
HIST/B
Pentagastrin
Balloon
PG/B
No Balloon
= Pylorus Not
Obstructed
Balloon = Pylorus Obstructed
were given, with the duodenal catheter in place, either
with or without an inflated pyloric balloon. During the


197
Duodenal Content Volume
Source
DF
Type I
: SS
Mean Square
F Value
Pr >
HORSE
5
519376
. 657
103875.331
11.67
0.0001
BALLOON(B)
1
3598900
.231
3598900.231
404.20
0.0001
DRUG
2
282222
. 977
141111.488
15.85
0.0001
B*DRUG
2
589677
. 116
294838.558
33.11
0.0001
HORSE*B*DRUG
25
1404835
.398
56193.416
6.31
0.0001
TIME
11
322036
. 602
29276.055
3.29
0.0003
B*TIME
11
191191
. 046
17381.004
1.95
0.0325
DRUG*TIME
22
795468
. 634
36157.665
4.06
0.0001
B*DRUG*TIME
22
392494
. 940
17840.679
2.00
0.0053
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > :
pre,t effect
5
12611.
148
2522.230
0.28
0.9221
post,t effect
5
106365.
370
21273.074
2.39
0.0378
pre, b*t
5
9242 .
093
1848.419
0.21
0.9592
post,b*t
5
57847.
833
11569.567
1.30
0.2637
pre,drug*t
10
84652.
324
8465.232
0.95
0.4867
post,drug*t
10
39452 .
046
3945.205
0.44
0.9245
pre, b*drug*t
10
33904.
713
3390.471
0.38
0.9546
post,b*drug*t
10
46453.
139
4645.314
0.52
0.8747
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1193198.69
1193198.69
36.6589
0.00000
post,b effect
1
2529802.67
2529802.67
77.7238
0.00000
pre, d effect
2
82615.95
41307.98
1.2691
0.29425
post,d effect
2
870971.29
435485.64
13.3795
0.00005
pre, d*b
2
29960.68
14980.34
0.4602
0.63506
post, d*b
2
871853.53
435926.76
13.3931
0.00005


58
Basal Collections
The volume, acid concentration, and acid output during
the basal time period of both studies did not differ
significantly.
Post-Pyrilamine Collections
In the pyrilamine study, the volume collected during
the 30 minutes following the administration of pyrilamine
was significantly less (p=0.0145) than when no pyrilamine
was given. The acid concentration did not differ between
studies. The acid output was significantly less (p=0.0008)
in the pyrilamine study than when no pyrilamine was given.
Early Infusion Collections
The volume and acid concentration did not differ
significantly between the studies, however, the acid output
was significantly less (p=0.0274) in the pyrilamine studies
than when no pyrilamine was given.


BIOGRAPHICAL SKETCH
Diane L. Kitchen is the oldest of two children born to
Hyram and Yvonne Kitchen. Born in Tacoma, Washington, she
lived in several states before graduating from Lenoir City
High School in 1977. She spent a year in England as an AFS
exchange student where she completed her "A level" exams
before returning to the States to enter the University of
Tennessee in Knoxville. During her studies there, she was
elected into the Alpha Zeta, Phi Zeta and Phi Kappa Phi
honorary fraternities. After finishing undergraduate
requirements, Diane returned to England to work in a
veterinary practice until her admission to the College of
Veterinary Medicine. She received her Doctor of Veterinary
Medicine from the University of Tennessee in 1984.
During an internship and residency in Large Animal
Internal Medicine at Texas A & M University, Diane received
the Waddell Scholarship Award for excellence in emergency
and intensive care. In 1990, she passed her qualifying
examination for the American College of Veterinary Internal
213


Kosch for his role as Associate Dean for Research and
Graduate Studies.
Dr. Martha Campbell-Thompson, who is one of the
pioneers in equine gastric secretion, provided a wealth of
t
knowledge and was invaluable in the development of this
project as did her chairman at the Health Sciences Center,
Dr. J. McGuigan. I must also thank Dr. Dan Hogan and Mr. M.
Koss who taught me not only the method for analyzing
bicarbonate concentration, but who were instrumental in the
construction of my specialized duodenal catheter.
For emotional support, I must thank several important
people in my life. I am afraid that most have had to suffer
me during one stage or another of this process and deserve
accolades for this. I thank my mother, Yvonne H. Kitchen,
R.N., for the shoulder. I know it has been a tough several
years, but she were always there with unconditional love and
I do love her for it. Michael S. Kitchen, M.D., my dearest
brother keeps me humble. Dr. Jerry and Gayle Spears have
had to "live" with me day by day and have always been there
for me. I cannot thank them enough. Roger Reynolds gave
me peace of mind and allowed me to focus on my own goals.
Elmer and Harriet Heubeck, Cynthia McFarland, Gail
v


173
Sodium Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
155.2
4.86
143.2
2.59
144.2
1.95
30
BASAL
154.2
5.54
142.3
1.90
145.4
2.48
45
BASAL
157.2
8.78
141.7
2.28
144.2
2.56
60
HVP
153.6
5.05
142.2
1.99
139.2
4.54
75
151.9
4.72
142.2
2.62
153.4
10.80
90
160.9
11.02
143.2
1.18
157.2
10.15
105
INFUSION
151.1
6.99
141.6
0.87
143.0
1.87
120
INFUSION
162.4
11.23
139.7
1.48
142.1
2.20
135
INFUSION
152.0
9.44
135.8
3 82
142.4
2.82
150
INFUSION
149.3
8.52
138.3
1.70
144.4
3.73
165
INFUSION
151.5
5.31
135.7
2.26
143.7
1.88
180
INFUSION
146.4
5.82
134.4
3.78
146.2
2.95
HVP = Pyrilamine maleate infusion


154
Potassium Output in Gastric Contents
(pEq/kg/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
6.64
1.49
5.74
1.91
5.17
1.32
30
BASAL
5.21
1.20
5.92
2.04
5.88
1.21
45
BASAL
4.90
0.92
5.68
1.78
5.89
1.10
60
HVP
3.56
0.74
4.83
1.51
5.45
0.94
75
2.16
0.55
2.19
0.50
2.78
0.35
90
2.15
0.44
2.65
0.60
2.93
0.53
105
INFUSION
3.88
0.74
4.90
1.47
6.55
1.06
120
INFUSION
4.60
0.99
11.08
2.51
12.55
1.67
135
INFUSION
4.49
0.90
12.69
1.79
14.41
0.68
150
INFUSION
4.36
0.83
14.64
1.91
13.00
0.73
165
INFUSION
4.48
0.90
16.55
1.84
15.22
2.29
180
INFUSION
4.26
1.23
16.19
1.60
14.09
1.49
HVP = Pyrilamine maleate infusion


134
inflation of the balloon on the intraduodenal catheter
allowed obstruction of the pylorus in an attempt to
prevented duodenogastric reflux. Within 15 minutes of
correct positioning and adequate inflation of the balloon,
it was evident that obstruction had occurred. In the no
balloon experiments, the gastric contents were yellow-green
and frothy in appearance.(See fig. 12) These contents had a
mean bile acid concentration of 42 (.unol/L. Once the balloon
Figure 12 Collections from catheter or cannula. KDZD is
duodenal contents collected through the catheter. KDZG is
gastric content collected from the cannula with the pylorus
obstructed. KDUG is gastric contents collected from the
cannula with no balloon on the catheter.


36
Maximal acid output per histamine dose was calculated
from the last two 15-minute collections at each dose. Values
were expressed as f.iEq/kg BW/15 min. Results are presented
as mean and SEM for all parameters. Data were subjected to
one-way analysis of variance for repeated measures. A
significance value of p<_0.05 was selected. Pairwise multiple
comparison testing of significance was performed using
Student-Newman-Keuls test. Acid output vs. sodium output
data were subjected to linear regression for comparison to
respective pentagastrin-stimulated outputs from the same
horses.
Results
The horses used had been involved in gastric secretory
studies for at least one year prior to these studies. They
demonstrated no evidence of gastrointestinal disease or
problems related to the gastric cannula. Endoscopic
examination of the gastric and duodenal mucosa as a part of
another project in the laboratory revealed an occasional
Gastrophilus spp. larvae and healthy intact gastric squamous
and glandular mucosas.


146
PYRILAMINE PRETREATMENT STUDY DATA
ACID OUTPUT ((aEq/kg-15 min)
TIME
PRETREATMENT
WITH PYRILAMINE
WITHOUT PYRILAMINE
min
YES
NO
MEAN
SEM
MEAN
SEM
15
BASAL
BASAL
21.01
8.14
11.22
6.23
30
BASAL
BASAL
22.96
6.33
12.63
8.70
45
BASAL
BASAL
26.01
5.34
16.91
8.60
60
HVP
BASAL
23.28
5.81
21.62
7.86
75
P-P
BASAL
13.65
2.93
25.26
10.99
90
P-P
BASAL
10.49
2.63
29.02
10.83
105
PENTAGASTRIN
12.33
4.91
34.37
11.61
120
PENTAGASTRIN
32.59
10.20
35.64
12.52
135
PENTAGASTRIN
35.23
12.93
35.47
14.39
150
PENTAGASTRIN
54.67
10.46
46.96
5.93
165
PENTAGASTRIN
56.43
6.69
56.64
7.58
180
PENTAGASTRIN
58.40
4.55
77.53
12.48
195
PENTAGASTRIN
ND
ND
77.90
9.28
210
PENTAGASTRIN
ND
ND
74.98
10.13
225
PENTAGASTRIN
ND
ND
76.32
10.87
240
PENTAGASTRIN
ND
ND
78.40
9.56
YES = Pyrilamine Maleate Pretreatment
NO = No Pretreatment
ND = Not Done
HVP = Pyrilamine infusion
P-P = Post-Pyrilamine


LIST OF TABLES
Table page
1 Acid and Sodium Concentration Histamine Infusion 2 9
2 Equine Gastric Contents 38
3 Acid and Sodium: Histamine versus Pentagastrin . 48
4 Gastric Contents with and without Pretreatment ... 59
5 Horses used in Gastric Collection Studies 68
6 Descriptions and Abbreviations for Each Study ... 69
7 Data from Study With and Without Duodenal Catheter 79
8 Electrolyte Composition of Duodenal Contents .... 81
9 Experimental Design 91
10 Volume and Ph of Gastric Contents 99
11 Potassium in Gastric Contents 101
12 Chloride in Gastric Contents 103
13 Acid in the Gastric Contents 106
14 Sodium in Gastric Contents 108
15 Bicarbonate in Duodenal Contents Ill
16 Sodium in Duodenal Contents 112
17 Potassium in Duodenal Contents 113
18 Chloride in Duodenal Contents 113
19 Volume of Duodenal Contents 115
xi


133
experiment, data were analyzed that compared the composition
of contents collected from the gastric cannula with and
without the catheter present. This was not a specific
study, but a statistical evaluation of data collected under
the two conditions. To balance the design, the "no
catheter" data were those of the horses in the pyrilamine
study described in Chapter 3. Chapter 4 discusses the
methods and materials of the catheterization technique and
the results of the comparison. The sodium output was
significantly increased in the horses with an intraduodenal
catheter in place and the relative electrolyte
concentrations were significantly different from those where
there was no catheter. The acid concentration was decreased
in those experiments with the catheter present, though
volume and acid output were increased.
The duodenal contents were also characterized in this
chapter. Compared to the gastric contents, the fluid was
found to have a higher concentration of sodium, and a lower
concentration of potassium and chloride. The bicarbonate
concentration was similar to plasma.
The final step in testing the hypothesis is the balloon
(B) vs. no balloon (NB) study condensed into Chapter 5. The


119
stomach appears to be a consistent feature of equine upper
GI function, even without transpyloric catheterization.
During infusions, the volume continued to be
significantly greater in the NB experiments than the B
experiments. Pentagastrin experiments resulted in greater
volumes than histamine experiments, which in turn had
greater volumes than the saline experiments. The
differences were markedly greater in the NB experiments than
the B experiments. These finding were consistent,
irregardless of balloon status. Therefore, pentagastrin
infusion appears to stimulate a larger fluid response than
does histamine, while both result in equivalent maximal acid
outputs. A portion of this fluid is of gastric origin,
since pyloric obstruction does not eliminate the volume
differences. The absolute volume differences between PG/B
and HIST/B were not large as those between either of these
and SAL/B, however, the difference was significant. The
suggestion is that a nonparietal component of gastric
secretion may be responsive to stimulation by pentagastrin.
It is also possible that this discrepancy results from
unnoticed leakage around the balloon, since in preliminary
trials with this system, we discovered that additional air


109
drug*balloon interaction (p=0.00023) are all significant for
sodium output. Over time, histamine and saline resulted in
relatively constant sodium outputs, whereas, pentagastrin
resulted significantly different (p=0.0001, and 0.0277,
respectively) fluctuations in sodium output. Sodium output
during pentagastrin infusion was significantly greater than
during histamine (p<0.00001) and saline (0.00003) infusion.
It was also significantly greater (p=0.00137) during saline
than histamine infusion. The output during PG/NB was
significantly greater (p<0.00001) than either HIST/NB or
SAL/NB, while SAL/NB was significantly greater (p=0.00141)
than HIST/NB. Sodium output during SAL/B was not
significantly different than either PG/B or HIST/B; however,
output during HIST/B was significantly less (p=0.01197) than
PG/B. Most importantly, throughout the infusions, the
output during PG/NB was significantly greater (p<0.00001)
than PG/B, HIST/NB was significantly greater (p<0.003) than
HIST/B. and SAL/NB was significantly greater (p<0.0002) than
SAL/B.


CHAPTER 3
THE EFFECT OF PYRILAMINE MALEATE PRETREATMENT ON
PENTAGASTRIN-STIMULATED EQUINE GASTRIC SECRETION
Introduction
The interaction between gastrin and histamine
receptors has long been controversial.1,2'3 The ability of
histamine receptor antagonists to eliminate pentagastrin-
stimulated gastric acid secretion supports the indirect
action of gastrin on parietal cells 21,31,37,48,49,51 53,54 This
inhibition of gastric secretion has been limited
specifically to histamine H-2 receptor antagonists. The
administration of antihistamines directed at H-l receptors
has not been shown to suppress acid production during
stimulation with various secretagogues, including
pentagastrin.11,29,71 Although differences in the relative
sensitivity to various secretagogues have been observed
between species, the characteristics of gastric contents
during maximal stimulation with histamine or pentagastrin
are similar, with the exception of the horse.
52


27
development of a silastic indwelling gastric cannula by
Campbell-Thompson and Merritt for the collection of equine
gastric secretions was pivotal. The distinct composition of
equine gastric contents, particularly the uncharacteristic
"non-parietal" response to pentagastrin stimulation, is of
special interest. Since pentagastrin has been the only
exogenous secretagogue utilized to date in equine secretory
studies, it would be of interest to see if the horse
responded to other secretagogues in a similar way.
Therefore, the initial project for this series of studies
was to characterize the equine gastric secretory response to
histamine. Pilot studies were performed with moderate
trepidation due to the potential side effects of histamine
administration to horses. These studies required
pretreatment of the horses with a H-l antagonist, pyrilamine
maleate. The results of a small pilot study were the last
key to the development of a hypothesis for this
dissertation.
Histamine-stimulated equine gastric contents were
markedly different than those following pentagastrin
stimulation reported in previous studies. The mean acid
and sodium concentrations from the pilot study are presented


90
ability to collect gastric contents from the cannula and
duodenal contents from the catheter into separate
containers, which were 1L size bags suspended from a
surcingle. The cannula and catheter were both allowed to
Figure 7 Cross sectional view showing balloon catheter
positioned in the proximal duodenum through the gastric
cannula.
drain by gravity for 15 minutes after completion of catheter
placement and inflation of balloon in those experiments with
pyloric obstruction.


APPENDIX C
DATA FROM BALLOON/NO BALLOON STUDY
Volume of Gastric Contents
(ml/15 minutes)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
490.0
44.12
497.5
60.63
523.3
49.12
30
BASAL
420.8
54.93
464.3
68.79
541.7
45.20
45
BASAL
405.8
56.12
422.5
82.52
541.7
42.93
60
HVP
429.5
71.64
439.2
53.87
470.8
34.84
75
350.5
61.29
328.3
46.72
409.8
55.93
90
361.7
45.86
335.8
60.27
383.3
36.46
105
INFUSION
393.3
74.37
419.2
40.38
505.8
70.36
120
INFUSION
456.8
58.95
569.2
52.26
800.8
74.17
135
INFUSION
493.3
27.89
598.3
52.75
899.2
62.67
150
INFUSION
491.7
22.42
665.0
49.58
923.3
41.20
165
INFUSION
465.8
21.85
650.8
49.27
886.7
38.36
180
INFUSION
480.0
39.24
677.5
53.69
885.0
40.72
HVP = Pyrilamine maleate infusion
147


141
HISTAMINE DOSE-RESPONSE DATA
Sodium Concentration and Output
TIME
DOSE
Na+ CONCENTRATION
SODIUM OUTPUT
minutes
pg/kg-hr
mEq/L
peQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
76.38
11.25
78.22
13.85
30
0
77.08
10.99
65.13
12.31
45
0
74.35
10.20
71.21
11.86
60
HVP
73.32
9.91
65.23
9.93
75
76.98
10.74
50.80
14.18
90
82.03
11.41
70.35
12.85
105
7.5
75.64
10.46
74.06
11.18
120
7.5
54.93
8.95
60.80
11.04
135
7.5
47.96
8.49
56.17
11.25
150
7.5
49.58
8.84
67.29
14.16
165
15
50.75
9.12
64.10
12.95
180
15
46.18
8.87
56.99
12.36
195
15
49.90
9.27
63.97
14.41
210
15
43.44
8.96
52.97
13.04
225
30
46.30
10.27
59.24
14.90
240
30
49.28
12.19
62.50
18.25
255
30
45.21
12.95
44.20
18.68
270
30
40.15
13.66
51.50
21.55
285
45
29.58
9.38
31.26
17.33
300
45
31.03
10.23
29.69
15.76
315
45
23.15
2.85
21.89
4.60
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done


189
Acid Concentration in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
t
5
32666.61465
6533.32293
39.13
0.0001
BALLOON(B)
1
31688.10187
31688.10187
189.81
0.0001
DRUG
2
34270.57097
17135.28549
102.64
0.0001
B*DRUG
2
12733.08847
6366.54424
38.14
0.0001
HORSE*B*DRUG
25
39094.01299
1563.76052
9.37
0.0001
TIME
11
67444.90174
6131.35470
36.73
0.0001
B*TIME
11
7895.62062
717.78369
4.3
0.0001
DRUG*TIME
22
65110.70292
2959.57741
17.73
0.0001
B*DRUG*TIME
22
3948.51653
179.47802
1.08
0.3725
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
5915.33764
1183.06753
7.09
0.0001
post,t effect
5
25597.12889
5119.42578
30.67
0.0001
pre, b*t
5
662.13023
132 42605
0.79
0.5551
post,b*t
5
1371.83370
274.36674
1.64
0.1480
pre,drug*t
10
1742.00250
174,20025
1.04
0.4064
post,drug*t
10
9913.47028
991.34703
5.94
0.0001
pre, b*drug*t
10
495.34380
49.53438
0.30
0.9817
post,b*drug*t
10
664.93880
66.49388
0.40
0.9470
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
5146.06
5146.06
5.9468
0.02075
post,b effect
1
32403.70
32404.70
37.4457
0.00000
pre, d effect
2
1264.93
632.46
0.7309
0.48971
post,d effect
2
86460.88
43230.44
49.9571
0.00000
pre, d*b
2
3510.22
1755.11
2.0282
0.14889
post, d*b
2
12011.10
6005.55
6.9400
0.00327


LIST OF REFERENCES 2 02
BIOGRAPHICAL SKETCH 213
x


This dissertation is dedicated to my father, Hyram
Kitchen, D.V.M., Ph.D., who taught me the importance of the
pursuit of excellence. I continuously strive to approach
the high standards he spent a lifetime instilling in me.
Even today, I look to his approval as the ultimate in
reward. Thank you, Daddy, and I do wish you were here to
share this with me.


135
occluded the pylorus, the gastric contents were clear and
watery, and did not contain measurable bile acids. Duodenal
contents collected through the catheter with or without the
balloon were thick, mucoid and yellow-green in color.
As well as changing the physical appearance of
collections, obstruction of the pylorus with the balloon
resulted in decreased volume and sodium and chloride output
from the gastric cannula during both basal and stimulated
time blocks. With the B experiments, histamine and
pentagastrin infusions had comparable results, whereas, in
the NB experiments, maximal pentagastrin infusion resulted
in a lower acid concentration and significantly greater
sodium output. That is, in the B studies, acid and sodium
concentration were inversely proportional in response to
both histamine and pentagastrin, and maximal acid
concentration and output was equivalent.
Duodenal contents were not quantified in these
experiments, as the catheter diameter was a limiting factor
in the collection of this thick, often mucoid fluid.
Consistently, the fluid was more profuse, less viscid and
the bicarbonate concentration increased during pentagastrin


204
19. Tache Y. Central Nervous System Regulation of
Gastric Acid Secretion. In: Johnson LR, ed. Physiology of
the Gastrointestinal Tract, Second Edition. New York: Raven
Press, 1987; 911-928.
20. Loiselle J, Wollin A. Mucosal Histamine
Elimination and Its Effect on Acid Secretion in Rabbit
Gastric Mucosa. Gastroenterology 1993; 104: 1013-1020.
21. Robert A. Effect of Drugs on Gastric Secretion.
In: Johnson LR, ed. Physiology of the Gastrointestinal
Tract, Second Edition. New York: Raven Press, 1987; 1071-
1080.
22. Prinz C, Kajimura M, Scott DR, Mercier F, Helander
HF, Sachs G. Histamine Secretion From Rat
Enterochromaffinlike Cells. Gastroenterology 1993; 105:
449-461.
23. Mezey E, Palkovits M. Localization of Targets for
Anti-Ulcer Drugs in Cells of the Immune System. Science
1992; 258: 1662-1665.
24. Hkanson R, Chen D, Sundler F. The ECL Cells.
In: Johnson LR, ed. Physiology of the Gastrointestinal
Tract, Third Edition. New York: Raven Press, 1994; 1171-
1181.
25. Sandor A, Kidd M, Lawton GP, Miu K, Tang LH,
Modlin IM. Neurohormonal Modulation of Rat
Enterochromaffin-like Cell Histamine Secretion.
Gastroenterology. 1996; 110: 1084-1092.
26. Thompson JE, Vane JR. Gastric Secretion Induced
by Histamine and Its Relationship to the Rate of Blood Flow.
J. Physiol. 1953; 121: 433-444.
27. Born GVR, Vane JR. Gastric Secretion Induced by
Histamine. J. Physiol. 1953; 121: 445-451.


7
pathways are present within the membrane of the parietal
cell including C1/HC03 and Na/H exchangers.15 During
stimulation, the parietal cell secretes H+ actively via the
proton pump, Cl- passively via the Cl channel, and H20
passively into the gastric lumen.15 Parietal secretion of
HC1 provides a high concentration (-140 mEq/L) of acid
within the gastric glands that empty into the lumen of the
stomach.
Gastric secretion is commonly described as either basal
or stimulated. Basal secretion is also termed
interdigestive secretion and occurs without external
stimulation, such as ingestion of food, or conditioned
response.2-17 In terms of volume and acid content, basal
secretion varies greatly between species.17 A circadian
rhythm has been observed in human basal secretion with
higher rates during the evening and low rates in the
morning.2-3'17'18 The rate of basal secretion is independent
of serum gastrin concentration and is not abolished by
vagotomy.2'17
Stimulated gastric secretion is classically divided
into three phases, with some overlap between them. These
phases are commonly termed cephalic, gastric, and


LIST OF REFERENCES
1. Modlin IM, Tang LH. The Gastric Enterochromaffin-
like Cell: An Enigmatic Cellular Link. Gastroenterology
1996; 111:783-810.
2. Wolfe MM, Soil AH. The Physiology of Gastric Acid
Secretion. New Engl J Med 1988 ; 319 (26) :1707-1715.
3. Soil AH, Wolfe MM. Regulation of Gastric Acid
Secretion. Ann Rev Physiol 1979; 41:35-53.
4. Pavlov IP. The Work of the Digestive Glands,
Second Edition. Translated by WH Thompson. London:
Griffin, 1910.
5. Bayliss WM, Starling EH. The Mechanism of
Pancreatic Secretion. J. Physiol. 1902; 28: 325-352.
6. Edkins JS. The Chemical Mechanism of Gastric
Secretion. J. Physiol. 1906; 34:133-144.
7. Komarov SA. Gastrin. Proc. Soc. exp. Biol., N.Y.
1938; 38:510-514.
8. Gregory RA, Ivy AC. The Humoral Stimulation of
Gastric Secretion. Quart. J. exp. Physiol. 1941; 31(2):
111-128.
9. Gregory RA. Secretory Mechanisms of the Gastro
intestinal Tract. London: Edward Arnold Pub. 1962; 61.
10. Macintosh FC. Histamine as a Normal Stimulant of
Gastric Secretion. Quart. J. exp. Physiol. 1938; 28: 87-
98 .
202


98
Post-infusion
Gastric samples
Volume. (Table 10) After starting infusion, the
volume of gastric collections increased significantly
(p=0.0001) through the time course (t=105 to 180). A
significant drug*time interaction was observed (p=0.0001).
Pentagastrin experiments resulted in a rapid, marked
increase that was significantly greater than saline
(p=0.0001), but not significantly greater than the increase
with histamine, which was also significantly greater than
saline (p=0.0003). The balloon*time interaction was also
significant (p=0.0214), since the relative volume increase
was greater in the studies with pyloric obstruction than in
those with no obstruction. In all infusions, the volume of
gastric contents collected was significantly greater
(p<0.00001) with no balloon. The drug effect was also
highly significant (p<0.00001). Specifically, pentagastrin
induced volumes significantly greater than saline
(p<0.00001) and histamine (p=0.00001), and histamine volumes
were also significantly greater than saline (p=0.00003).
There was a significant (p= 0.04437) drug*balloon


104
and saline (p<0.00001) and histamine stimulated outputs that
were significantly greater than saline(p=0.00024). Overall,
the balloon experiments resulted in significantly less
chloride output (p<0.00001) than the no balloon experiments.
The drug effect on chloride output was significant
(p<0.00001) and all three infusions differed significantly.
Hydrogen ion (acid) concentration. (Table 13) As
infusions were begun, the acid concentration increased
significantly (p=0.0001) over time. The different infusions
responded significantly differently (p=0.0001) over time.
Saline slowly increased from the "R2" period, while
pentagastrin (p=0.0341) and histamine (p=0.0001) increased
significantly more rapidly. The histamine response was also
significantly (p=0.0023) more profound than that of
pentagastrin. The difference between those experiments with
the balloon and those without balloon was also significant
(p<0.00001). In addition, the [H+] in PG/NB was
significantly less (p<0.00005) for all time points than
PG/B. During the last three collections, HIST/B had a
significantly greater (p<0.03) [H+] than HIST/NB.
The overall drug effect on [H+] was significant
(p<0.00001) and there were significant differences between


28
in Table 1. It was apparent from these studies that the
horse is capable of developing the "classical" parietal
response to an acid secretagogue that is comparable to that
of other monogastric species. During histamine stimulation,
the maximal acid concentration values were much greater than
those induced by pentagastrin, and sodium concentrations
decreased in the classical reciprocal relationship to acid.
The sodium output over various doses of histamine was
constant, unlike the pentagastrin responses. Yet, the
maximal acid output provoked by histamine was equivalent to
that of pentagastrin stimulated secretion. These pilot
findings made it evident that the stimulation of gastric
acid secretion with histamine could be safely performed in
horses, with certain precautions, and that well-designed
dose response study was needed. This led to the study
described in chapter 2. The predominant conclusion of early
investigation of histamine stimulation was that, as opposed
to pentagastrin, it induced a purely parietal gastric
secretion in horses.


212
91. Isenberg JI, Hogan DL, Koss MA, Selling JA. Human
Duodenal Mucosal Bicarbonate Secretion Evidence for Basal
Secretion and Stimulation by Hydrochloric Acid and a
Synthetic Prostaglandin Ex Analogue. Gastroenterology.
1986; 91: 370-378.
92. Smythe A, O'Leary D, Johnson AG. Duodenogastric
Reflux After Gastric Surgery and in Gastric Ulcer Disease:
Continuous Measurement with a Sodium Ion Selective
Electrode. Gut. 1993; 34(8): 1047-1050.
93. Khodzhaeva NU, Ovchinnikov IV, Bogdanov-
Berezovskii AG, Khudaibergenov ShA. A Comparative
Evaluation of Methods for Detecting Duodenogastric Reflux in
Patients with Peptic Ulcer. Lab. Delo. 1991; 3: 60-61.
94. Lind T, Cederberg C, Ekenved G, Haglund U, Olbe L.
Effect of Omeprazole a Gastric Proton Pump Inhibitor on
Pentagastrin Stimulated Acid Secretion in Man. Gut. 1983;
24: 270-276.
95. Walsh JH. Gastrointestinal Hormones. In:
Johnson OR, ed. Physiology of the Gastrointestinal Tract,
Second Edition. New York: Raven Press, 1987; 182-191.
96. Guyton AC. Movement of Food Through the
Alimentary Tract. In: Guyton AC. Textbook of Medical
Physiology, Seventh Edition. Philadelpha: WB Saunders,
1986; 764.
97. Erlinger S. Physiology of Bile Secretion and
Enterohepatic Circulation. In: Johnson LR, ed. Physiology
of the Gastrintestinal Tract, Second Edition. New York:
Raven Press, 1987;1557-1573.


TABLE 3.
Acid and Sodium Concentrations
Histamine versus Pentagastrin
48
PARAMETER
EQUINE
Pentagastrin
(PG) *
HUMAN
PG or HI**
EQUINE
Histamine
(HI)
Basal
Max.
Stim.
Basal
Max.
Stim.
Basal
Max.
Stim.
[H+] mEq/L
21-45
35-57
10-40
70-120
28-45
75 120
[Na+] mEq/L
45-92
75-146
30-70
15-30
62-123
23-70
* from ref no.66
** from ref no.42
In this study, mean acid concentration during maximal
histamine stimulation was markedly greater than that
observed during maximal pentagastrin stimulation. Maximal
acid concentrations in other species have ranged from
100-140 mEq/L17-39, irrespective of stimulant. Individual
maximal acid concentrations in these horses ranged from
75-125 mEq/L during histamine infusion. In contrast, in
pentagastrin stimulated horses, the maximal acid
concentration rarely reached 75 mEq/L, which was reported44
to be a major difference between horses and other species.
Apparently,a nonparietal sodium rich fluid component of
gastric secretion was strongly stimulated by pentagastrin.


CHAPTER 5
THE EFFECT OF PYLORIC OBSTRUCTION ON EQUINE BASAL AND
STIMULATED GASTRIC SECRETION
Introduction
In horses, the maximal secretory response to
pentagastrin (PG) comprises a large volume of sodium-rich
fluid of relatively low acidity ( [H+] (40-60 mEq/1) .31.44,49.51
This is different from other monogastric species that have
been studied, where the gastric contents under maximal PG
stimulation have high H+ and low Na+ concentrations,
comparable to that seen in response to histamine
stimulation. 30-37'42 On the other hand, the acid and sodium
concentrations of equine gastric contents under maximal
histamine stimulation are similar to those seen in other
monogastric species in that the [H+] ranges between 80-110
mEq/1 and the [Na+] is relatively low. (See Chap.2) The
maximal acid output (MAO) was equivalent to that during
pentagastrin infusion, however, the sodium outputs differed
greatly. In other monogastric species, the difference
86


CHAPTER 4
PLACEMENT OF A CATHETER FOR COLLECTION OF DUODENAL CONTENTS
IN HORSES WITH CHRONIC GASTRIC CANNULAS AND ITS EFFECT ON
GASTRIC SECRETION
Introduction
The contents of various parts of the gastrointestinal
system differ in chemical and physical characteristics
between location and species. Much of the normal
gastrointestinal function of the individual species relates
to the anatomy of their alimentary system and the type of
diet which they consume. Increasing our understanding the
normal function is often complicated by those same
differences. Equine gastric secretion and the composition
of the contents under various conditions have been studied
by numerous investigators utilizing several
techniques.31'44'48-54 The development of a chronic gastric
cannula31 for collection of gastric contents has added
greatly to the knowledge regarding equine gastric
physiology.
66


163
Sodium Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
104.9
5.98
89.0
6.38
105.1
9.96
30
BASAL
103.1
7.52
88.5
5.40
109.5
9.80
45
BASAL
109.5
11.91
94.1
6.76
104.2
7.54
60
HVP
105.3
10.98
98.9
8.58
100.4
6.57
75
113.1
8.43
94.6
7.16
100.7
2.87
90
120.5
7.27
107.0
5.19
106.2
5.58
105
INFUSION
119.3
6.61
91.3
6.24
109.8
5.51
120
INFUSION
111.8
5.46
60.0
4.87
105.0
6.79
135
INFUSION
115.1
4.96
49.9
6.30
96.4
6.44
150
INFUSION
111. 5
5.10
53.6
5.93
94.4
5.05
165
INFUSION
107.9
4.22
55.1
4.76
86.8
4.72
180
INFUSION
108.1
5.05
49.9
5.68
89.5
4.83
HVP = Pyrilamine maleate infusion


118
output.31'44 (See Chap. 2) Nevertheless, the peak acid
concentrations were significantly higher with histamine
stimulation than with pentagastrin stimulation, and sodium
output increased during pentagastrin stimulation and
decreased slightly during histamine stimulation.
In the preinfusion time blocks, the volume of gastric
collections were significantly less in the B than the NB
experiments, suggesting that an extragastric source of fluid
might be contributing to the volume collected from the
gastric cannula in horses. The fluid collected in the B
experiments also had a higher concentration of HCl than that
of the NB experiments, which added credence to the dilution
theory. Since the [Na+] and [K+] did not differ between B
and NB experiments, this extragastric fluid apparently
contains these ions. Duodenal fluid has a high
concentration of sodium, a slightly lower concentration of
potassium and chloride, and an approximately isotonic
concentration of bicarbonate compared to gastric fluid.(See
Chap. 4) The introduction of duodenal fluid into the
gastric collection may be enhanced by the presence of the
catheter in the NB experiments, but its reflux into the


105
each of the infusions, as well. Histamine infusion produced
[H+] significantly greater than pentagastrin (p=0.00002) or
saline (p<0.00001), and pentagastrin infusion was
significantly greater than saline (p=0.00003) There was a
significant (p=0.00327) drug*balloon interaction. The [H+]
during HIST/NB was significantly greater than SAL/NB
(p<0.00001) or PG/NB (p<0.00001), while there was no
significant difference in [H+] between SAL/NB and PG/NB. In
the balloon experiment, there was no significant difference
in [H+] for HIST/B and PG/B; however SAL/B produced an [H+]
significantly less (p<0.00001) than either HIST/B or PG/B.
Acid output. (Table 13) Acid output was significantly
(p=0.0001) affected by time and by drug*time interaction.
The output increased following the initiation of infusion.
The pattern of increasing acid output was not significantly
different between histamine and pentagastrin infusions,
though each led to significantly greater (p=0.0001) output
changes than during saline infusion. All three infusions
resulted in significantly different (p<0.00001) acid
outputs. Histamine-induced outputs were significantly
greater than those of pentagastrin (p=0.00120), and outputs


82
125 mEq/L and [K+] between 6-20 mEq/L. Chloride ion
concentrations were in the range of 95-160 mEq/L, whereas
the gastric contents had [Cl'] ranging from 130 to 180
mEq/L. The mean concentrations of sodium, potassium, and
chloride were consistent throughout the experiment.
Discussion
The placement of a duodenal catheter through the
gastric cannula required variable amounts of manipulation of
the videoendoscope. The time required for introduction of
the video endoscope into the duodenum and passage of the
stylet and threading of the catheter ranged from 10 to 25
minutes. The differences related in position of the pylorus
relative to the cannula and the dexterity of the
investigator on that day. The horses did not appear to be
bothered by the process nor by the presence of the catheter
during the experiments. Catheter experiments proceeded as
the no catheter experiments did. Gastric contents were
easily collected from the cannula even with the catheter in
place. During some time periods, no fluid was collected
from the duodenal catheter. However, this did not indicate


108
experiments yielded a [Na+] that was significantly less
(p<0.01) than during the PG/NB experiments.
Table 14 .
SODIUM IN GASTRIC CONTENTS
Mean + SEM
B/NB
BASAL
PYRILAMINE
INFUSIONS (max)
[Na+]
mEq/L
SAL *
108.0+4.64
NB
101.5+8.15
107.0+6.08
HIST§
52.55.22
+
PG
88.2+4.78
[Nai
mEq/L
SAL *
91.569.54
B
89.639.17
102.04+9.1
HIST§
31.104.15
+
PG
57.73 6.08
Na+
OUTPUT
^Eq/kg/
15min
SAL *
108.88.80
NB
99.2+12.27
82.2+12.03
HIST§
77.1+12.91
+
PG
167,414.69
Na+
OUTPUT
/xEq/kg/
15min)
SAL
44.87+7.07
B4
45.817.44
32.52 4.98
HIST
30.10+6.60
+
PG
68.62 + 16.24
+ Pyrilamine significantly less (p<0.05) than other time
blocks
B significantly different (p<0.05) from NB
* Response to this infusion significantly different(p<0.05)
from responses to other infusions
§ Histamine significantly different(p<0.05) than other
infusions
t Pentagastrin significantly different(p<0.05)than
histamine
Sodium output. (Table 14) Time (p=0.0488),
balloon*time interaction (p=0.0105), drug*time interaction
(p=0.0008), balloon (p<0.00001), drug (p<0.00001), and


126
higher concentration of bicarbonate. These findings are
consistent with a report by Alexander and Hickson that
pentagastrin is a strong stimulant of equine pancreatic
secretion.55
The suggestion that the equine gastric contents might
contain fluid originating from the duodenum is not new or
without warrant.50'51 Anatomically, the position of the
proximal duodenum in relation to the stomach allows gravity
to aid in this reflux. In addition, the bile and pancreatic
ducts of horses enter the duodenum relatively near to the
pyloric sphincter, and reflux of duodenal contents into the
gastric lumen has been seen during endoscopic
examination.50-51 In man, duodenogastric reflux has been
recognized and is quantified by the measurement of sodium
ions in gastric contents.92'93
Pancreatic secretion in the horse is reported to be
continuous and profuse with a higher concentration of
chloride and lower concentration of bicarbonate than that of
other monogastric species.55'57 The fivefold increase in
pancreatic secretion after the administration of
pentagastrin appears to be unique to the horse, among the
species that have been studied.55 In most species,


79
acid than the CATH study. No significant interactions were
found between time blocks and catheter.
TABLE 7.
Data from Study With and Without Duodenal Catheter During
Pentagastrin Stimulation (Mean and SEM's)
STUDY
BASAL
PYRILAMINE
EARLY
LATE
VOLUME
(ml/15
min)
NOC
287.5
28.0
171.3 +
27.0
405.0
125.4
568.8 +
83.4
CATH*
541.7
29.7
396.6 +
32.1
653.3 +
66.0
885.8 +
26.7
[H+]
(mEq/L)
NOC**
39.5 +
6.1
32.3 5.2
31.9 +
10.0
52.4 +
9.4
CATH
26.5
4.1
28.9 3.3
20.4 +
3.7
42.4 +
2.2
ACID
OUTPUT
(|iEq/kg-
15min)
NOC
24.5 +
3.9
12.1 + 1.9
22.5 +
6.5
57.4 +
3.8
CATH*
31.9
6.2
24.9 + 3.7
30.2 +
6.8
80.2 +
4.9
[Na+]
(mEq/L)
NOC
106.1 +
6.1
110.8 +
5.7
108.3 +
10.0
93.4 +
8.2
CATH
106.8 +
6.0
104.4 +
3.3
107.4 +
4.2
88.2 +
3.3
NA
OUTPUT
((.lEq/kg-
15min)
NOC
72.5
10.0
44.8 + 8.5
107.3 +
40.0
133.8 +
29.2
CATH*
122.1 +
8.4
88.0 + 8.0
146.4 +
13.6
167.5 +
9.9
* Significantly greater than NOC
** Significantly greater than CATH
Significantly greater than all other time blocks
Significantly greater than post-pyrilamine time block
Significantly less than all other time blocks
Significantly greater than basal & post-pyrilamine time
blocks


196
Chloride Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.28817634
0.05763527
68.08
0.0001
BALLOON(B)
1
0.55019419
0.55019419
649.89
0.0001
DRUG
2
0.18821292
0.09410646
111 16
0.0001
B*DRUG
2
0.02283793
0.01141897
13.49
0.0001
HORSE*B*DRUG
25
0.10821931
0.00432877
5.11
0.0001
TIME
11
0.44263141
0.04023922
47.53
0.0001
B*TIME
11
0.02301873
0.00209261
2.47
0.0055
DRUG*TIME
22
0.16428786
0.00746763
8.82
0.0001
B*DRUG*TIME
22
0.00970540
0.00044115
0.52
0.9650
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.04446698
0.00889340
10.50
0.0001
post,t effect
5
0.11751137
0.02350227
27.76
0.0001
pre, b*t
5
0.00127950
0.00025590
0.30
0.9114
post,b*t
5
0.01036171
0.00207234
2.45
0.0338
pre,drug*t
10
0.00386552
0.00038655
0.46
0.9169
post,drug*t
10
0.04230947
0.00423095
5.00
0.0001
pre, b*drug*t
10
0.00355522
0.00035552
0.42
0.9367
post,b*drug*t
10
0.00467181
0.00046718
0.55
0.8524
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.20167
0.20167
77.933
0.00000
post,b effect
1
0.35991
0.35991
139.084
0.00000
pre, d effect
2
0.00493
0.00246
0.952
0.39547
post,d effect
2
0.30140
0.15070
58.237
0.00000
pre, d*b
2
0.00727
0.00364
1.405
0.25854
post, d*b
2
0.01704
0.00852
3.293
0.04872


122
manner similar to that seen in other monogastric species.
(See fig. 8) In some of the HIST/NB experiments, the acid
concentration was less than corresponding HIST/B
experiments, this is probably related to dilution by some
extragastric fluid that is responsible for a portion of the
increased volume of collection, but not to the same
magnitude stimulated by pentagastrin.
Time (minutes)
Figure 9 Acid output. A curvilinear line derived from mean
sodium output during pentagastrin and histamine infusions
comparison of B and NB experiments, a marks mean for B
trials n marks mean for NB trials.


169
pH of Duodenal Contents
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
8.22
0.14
8.05
0.21
8.53
0.13
30
BASAL
8.14
0.15
8.00
0.16
8.62
0.04
45
BASAL
8.13
0.17
7.96
0.21
8.52
0.05
60
HVP
8.10
0.16
8.05
0.12
8.46
0.14
75
8.06
0.13
7.84
0.10
8.47
0.09
90
8.10
0.13
7.90
0.11
8.46
0.15
105
INFUSION
8.12
0.13
7.97
0.12
8.42
0.10
120
INFUSION
8.11
0.18
7.90
0.11
8.37
0.13
135
INFUSION
8.14
0.09
7.98
0.15
8.41
0.10
150
INFUSION
8.18
0.14
7.92
0.15
8.37
0.12
165
INFUSION
8.04
0.10
7.98
0.15
8.38
0.10
180
INFUSION
8.04
0.10
7.90
0.17
8.36
0.12
HVP = Pyrilamine maleate infusion


184
Acid
Concentration
of Gastric
Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
1722.366
1722.366
6.093
0.016
TIME
3
4863.528
1621.176
5.735
0.001
CATH*TIME
3
253.190
84.397
0.299
0.826
Residual
72
20353.253
282.684
Total
79
27373.608
346.501
Acid OutDUt of
Gastric Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
3099.751
3099.751
10.970
0.001
TIME
3
29506.653
9835.551
34.808
<0.001
CATH*TIME
3
741.643
247.214
0.875
0.458
Residual
72
20344.690
282.565
Total
79
56625.792
716.782


149
pH of Gastric Contents
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
2.37
0.792
1.67
0.167
2.71
0.927
30
BASAL
2.39
0.839
1.55
0.055
2.39
0.629
45
BASAL
2.69
1.044
1.73
0.136
1.83
0.148
60
HVP
2.67
1.106
2.53
0.835
1.70
0.088
75
2.68
0.966
2.40
0.790
1.69
0.073
90
3.05
1.062
2.69
0.699
2.07
0.257
105
INFUSION
2.91
1.008
1.72
0.130
3.46
0.869
120
INFUSION
2.81
0.894
1.36
0.050
2.90
0.810
135
INFUSION
2.73
0.758
1.33
0.060
1.85
0.136
150
INFUSION
2.34
0.447
1.34
0.056
1.67
0.062
165
INFUSION
2.48
0.719
1.32
0.055
1.61
0.047
180
INFUSION
2.42
0.673
1.34
0.084
1.57
0.052
HVP = Pyrilamine maleate infusion


68
collection of fluid. The two objectives of this study were
to determine the composition of the duodenal fluid and
whether the presence of the catheter passing into the
duodenum had an effect on the gastric contents collected
from the cannula before and during stimulation of secretion
with pentagastrin.
Materials and Methods
Horses
Five Thoroughbreds(TB) two mixed breed (MB) horses,
and one Arabian (AR) [3 mares, 5 geldings] between 3 and
20 years in age, were used in these studies.(TABLE 5) For
TABLE 5.
Horses used in Gastric Collection Studies.
ID
AGE
BREED
SEX
B
5
y
ARAB
G
D
7
Y
TB
G
E
20
Y
TB
M
H
5
Y
TB
G
I
6
Y
TB
M
J
3
Y
MIXED
G
M
7
Y
MIXED
M
T
5
Y
TB
G


136
infusion. Chloride was the predominate anion even during
stimulation, and sodium was the predominant cation.
Conclusions
This series of studies build on each other to support
the hypothesis of this dissertation. Reviewing the results
of these studies, the following conclusions concerning the
composition of equine gastric contents collected from a
cannula are:
1. Histamine stimulates a purely parietal secretion, while
pentagastrin induces both parietal and non-parietal
secretory activity.
2. Pyrilamine maleate appears to decrease equine basal
gastric acid secretion and may attenuate the acid
secretory response to pentagastrin infusion.
3. The presence of a catheter passing through the pylorus
into the duodenum does not prevent a normal acid
secretory response to pentagastrin, but may enhance the
reflux of duodenal contents into the stomach.
4. The voluminous sodium-rich fluid component of gastric
contents in response to pentagastrin, is due, in large
part, to duodenal reflux. The extragastric fluid
refluxing into the gastric contents is most likely of
pancreatic and/or biliary origin.
In addition to answering the hypothesis, these studies
also led to more questions regarding equine gastric


APPENDIX D
STATISTICAL ANALYSIS OF HISTAMINE DOSE RESPONSE DATA
Analysis by General Linear Model with One Way ANOVA for
repeated measures using SigmaStat software.
Gastric Content Volume
Source
DF
SS
MS
HORSES
5
1037113.3
207422.7
DOSE
4
1121695.0
280423.7
Residual
18
215095.0
11949.7
Total
27
2313867.9
85698.8
F Value P Value
o. 00000250
23.46696808 0.000000618
Acid Concentration of Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
12717.1
2543.4
0.000791
DOSE
4
51314.1
12828.5
35.833490
0.0000000241
Residual
18
6444.1
358.0
Total
27
69398.9
2570.3
179


185
Sodium Concentration of Gastric Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
194.948
194.948
0.612
0.437
TIME
3
3880.260
1293.420
4.059
0.010
CATH*TIME
3
203.853
67.951
0.213
0.887
Residual
72
22941.946
318.638
Total
79
27518.836
348.340
Sodium Outout
of Gastric
Content
Source
DF
SS
MS
F Value
P Value
CATHETER
1
32851.071
32851.071
11.703
0.001
TIME
3
76666.512
25555.504
9.104
<0.001
CATH*TIME
3
649.446
216.482
0.0771
0.972
Residual
72
202115.891
2807.165
Total
79
313360.908
3966.594


71
(see below) was passed over it. The mark on the stylet was
used to assure that it remained in position as the catheter
was introduced through the cannula into the stomach, then
through the pylorus and into the duodenum. The stylet was
left in place until catheter placement was believed to be
complete. The completed setup (fig. 4) resulted in the
Figure 4 Cross sectional view of duodenal catheter passing
through the gastric cannula into the stomach and entering
the proximal duodenum.


Table 19.
VOLUME OF DUODENAL CONTENTS
Mean + SEM
115
B/NB
BASAL
PYRILAMINE
INFUSIONS
VOLUME
ml/l5min
SAL
75.0+24.8
NB
64.325.9
64.5+18.3
HIST
58.924.8
PG
64.515.7
VOLUME
ml/15min
SAL
181.0+49.8
B4
217.2 4 9.5
214.645.0
HIST
155.616.4
PG*
409+111.5
* Significantly different (p<0.05) from other infusions
B significantly different (p<0.05) from NB
Bile Acids
Bile acid concentration was measured in a selected
number of the 45 minute collection. The lower limit of the
Enzabile test was 5 pmol/L. Bile acid concentrations during
the balloon experiments were significantly less than no
balloon experiments (p=0.000981) In the occlusion studies,
the bile acid concentration was <5 pmol/L in 12 of 18
trials. The remaining balloon trials had concentrations of
5 (.tmol/L in 4 trials, 6 pmol/L in 1 trial, and 7 pmol/L in 1
trial. The concentration ranged from 21 to 77 pmol/L in the
NB studies, with a mean of 42 pmol/L.


CHAPTER 2
EQUINE HISTAMINE DOSE-RESPONSIVE GASTRIC ACID SECRETION
Introduction
Previous studies of equine gastric physiology have all
utilized pentagastrin to stimulate gastric secretion.44'50'52
Increased recognition of clinical disease in horses due to
gastric and duodenal ulceration has led to interest in the
potential use of horses as a model for peptic ulcer disease
in humans as well as a desire to increase our knowledge
about horses, themselves. Gastric-ulceration has been shown
to be a widespread phenomenon in horses and foals.64
Compared to other species, pentagastrin-stimulated gastric
contents in horses differs by being relatively low in acid
concentration and high in sodium concentration, even at
maximal secretory responses.44 Nevertheless, the inhibition
of pentagastrin-stimulated gastric acid secretion has been
an important and effective means to evaluate therapeutic
potential of various anti-ulcer agents in this species.31-49
31


42
Sodium Output
Mean maximal sodium outputs decreased from 61.7 +
8.8 pEq/kg/15 min to 50.3 + 14.7 pEq/kg/15 min as the
histamine infusion rates increased from 7.5 (.ig/kg-hr to 30
pg/kg-hr. No significant differences were observed in the
sodium output during basal, post-pyrilamine or histamine-
stimulated collection periods.
Pentagastrin Outputs
The mean maximal acid output during pentagastrin
infusion was 91.8 + 3.5 pEq/kg/15 min. Corresponding mean
peak sodium output during the pentagastrin trial was 100.8 +
5.0 pEq/kg/15 min.
Discussion
As in other species, intravenous administration of
histamine base stimulated gastric acid secretion in horses
resulting in maximal acid outputs (MAO) comparable to those
of pentagastrin-stimulated horses. Infusions were performed
without serious complications. Pretreatment with pyrilamine


172
Bicarbonate Concentration in Duodenal Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
31.82
2.73
24.05
3.30
25.44
1.90
30
BASAL
29.28
2 81
28.63
2.62
28.82
2.92
45
BASAL
28.40
2.65
28.02
2.05
27.70
2.90
60
HVP
26.29
3.20
29.52
1.61
26.38
2.87
75
30.95
3.74
31.44
0.73
27.34
2.72
90
26.71
4.09
31.55
1.04
23.97
3.83
105
INFUSION
25.97
5.05
33.59
1.42
36.56
1.43
120
INFUSION
27.40
3.77
32.42
2.90
36.04
2.55
135
INFUSION
28.02
2.12
29.70
2.19
36.51
2.85
150
INFUSION
27.36
3.76
28.71
1.67
36.77
2.68
165
INFUSION
30.91
5.98
28.81
1.66
37.08
2.41
180
INFUSION
26.03
3.34
27.83
2.18
37.13
1.87
HVP = Pyrilamine maleate infusion


16
on canine mucosa;1730 in rabbits histamine is much more
effective than gastrin.17-30 Basal secretion is minimal in
dogs and cats and high in rats and rabbits, whereas humans,
primates, pigs, and horses fall somewhere in between.17-28'31
Maximal acid outputs on a normalized bodyweight basis
induced by either histamine or pentagastrin, also differ
between species. Maximal histamine-stimulated output is
greater in rabbits than dogs, while in dogs it is greater
than that of rats, pigs, and cats, which in turn, have
rates of secretion markedly greater than that of primates
and man. 17-29-30 During pentagastrin-induced acid secretion,
rabbit and dog have a comparable maximal response, but that
of rats is significantly less.30 As with histamine, pig,
rat, and cat maximal acid secretory rates in response to
pentagastrin are comparable. 29-30-37-38 Maximal acid output is
used to determine the necessary dosage of either
secretagogue for the purpose of most experimental work;
however, the gastric contents collected during these studies
consist of fluid containing many electrolytes, pepsin, mucus
and other substances, as well as acid.
The electrolyte composition of gastric secretion other
than H+ also changes with the secretory rate. The secretory


198
Bicarbonate Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
3656.939286
731.387857
60.41
0.0001
(
BALLOON(B)
1
2026.567940
2026.567940
167.39
0.0001
DRUG
2
1257.839878
628.919939
51.95
0.0001
B*DRUG
2
145.312574
72.656287
6.00
0.0028
HORSE*B*DRUG
25
5093.186650
203.727466
16.83
0.0001
TIME
11
1050.913733
95.537612
7.89
0.0001
B*TIME
11
146.883691
13.353063
1.10
0.3583
DRUG*TIME
22
2725.646878
123.893040
10.23
0.0001
B*DRUG*TIME
22
172.989442
7.863156
0.65
0.8860
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
62.627287
12.525457
1.03
0.3973
post,t effect
5
41.990059
8.398012
0.69
0.6286
pre, b*t
5
71.945792
14.389158
1.19
0.3146
post,b*t
5
70.392297
14.078459
1.16
0.3274
pre,drug*t
10
189.799161
18.979916
1.57
0.1153
post,drug*t
10
166.034097
16.603410
1.37
0.1925
pre, b*drug*t
10
81.233137
8.123314
0.67
0.7513
post,b*drug*t
10
76.908444
7.690844
0.64
0.7833
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1079.79
1079.79
10.1461
0.00353
post,b effect
1
1047.96
1047.96
9.8470
0.00397
pre, d effect
2
83.20
41.60
0.3909
0.68008
post,d effect
2
3558.25
1779.13
16.7172
0.00002
pre, d*b
2
98.99
49.50
0.4651
0.63284
post, d*b
2
47.05
23.52
0.2210
0.80307


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67
Study of the function of the equine proximal duodenum,
biliary system, and pancreas has been even more difficult
due to an anatomical location which strictly limits surgical
exposure.87'88 Up to now, attempts to study the proximal
duodenum and associated structures have met with serious
difficulties and been basically unsuccessful in providing
additional information on the physiology of this region.
The reflux of duodenal contents into the empty equine
stomach has been observed during endoscopic gastric
examination even when there is no evidence of underlying
pathology.50'51 The importance, frequency and volume of
reflux have not been evaluated. Nor has the composition of
the duodenal contents which are mixing with the gastric
contents been fully analyzed. Reflux of large volumes of
small intestinal contents into the stomach is reported
during various disease conditions such as anterior enteritis
and small intestinal obstruction.89,90
The presence of chronic indwelling gastric cannulas in
research horses has made access to the duodenum much easier
for investigator and animal. This study describes how, with
the aid of an endoscope passed up through a gastric cannula,
a catheter can be placed into the equine duodenum for the


159
Acid Concentration in Gastric Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
37.4
7.52
40.8
7.40
26.5
7.61
30
BASAL
38.2
6.73
41.8
4.39
25.1
6.65
45
BASAL
35.2
9.27
34.3
6.65
27.9
5.49
60
HVP
37.7
8.25
29.1
9.23
32.5
4.99
75
31.8
7.06
32.6
9.30
32.9
2.71
90
22.2
7.44
21.6
7.20
24.8
5.82
105
INFUSION
22.6
6.58
35.9
6.59
16.6
4.52
120
INFUSION
23.2
6.32
71.2
4.64
24.1
5.90
135
INFUSION
21.9
5.56
81.0
5.96
30.5
5.37
150
INFUSION
24.5
7.19
77.7
5.56
35.7
3.59
165
INFUSION
29.0
5.51
78.0
4.53
40.1
2.90
180
INFUSION
28.8
5.43
82.7
5.18
44.7
3.38
HVP = Pyrilamine maleate infusion


152
Potassium Concentration in Gastric Contents
(mEq/L)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
11.07
1.60
9.14
1.17
9.97
1.54
30
BASAL
9.84
1.09
9.69
1.25
10.44
1.45
45
BASAL
9.04
0.92
9.44
1.27
10.40
1.19
60
HVP
8.73
1.08
8.58
1.08
10.74
1.11
75
7.52
0.91
6.87
0.56
8.52
0.73
90
7.34
0.95
7.31
0.65
8.33
0.69
105
INFUSION
9.25
1.40
10.56
1.08
11.26
1.10
120
INFUSION
9.90
1.32
17.70
0.84
13.99
1.35
135
INFUSION
9.95
1.54
18.62
1.03
14.81
1.30
150
INFUSION
9.45
1.00
18.21
0.95
13.88
1.15
165
INFUSION
9.06
0.95
18.11
1.03
13.12
1.06
180
INFUSION
8.80
1.16
17.20
1.03
13.44
1.01
HVP = Pyrilamine maleate infusion


188
Gastric
Content dH
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
i
5
193.5264900
38.7052980
34.44
0.0001
BALLOON(B)
1
2.9320558
2.9320558
2.61
0.1072
DRUG
2
19.7845588
9.8922794
8.80
0.0002
B*DRUG
2
13.0219616
6.5109808
5.79
0.0034
HORSE*B*DRUG
25
290.8255252
11.6330210
10.35
0.0001
TIME
11
40.6180692
3.6925517
3.29
0.0003
B*TIME
11
11.5292525
1.0481139
0.93
0.5091
DRUG*TIME
22
53.9146301
2.4506650
2.18
0.0019
B*DRUG*TIME
22
28.2382718
1.2835578
1.14
0.3000
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
12.86303704
2.57260741
2.29
0.0457
post,t effect
5
12.51123009
2.50224602
2.23
0.0514
pre, b*t
5
5.23759259
1.04751852
0.93
0.4603
post,b*t
5
3.09004861
0.61800972
0.55
0.7384
pre,drug*t
10
14.60956574
1.46095657
1.30
0.2292
post,drug*t
10
3.51883696
0.35188380
0.31
0.9776
pre, b*drug*t
10
5.42322130
0.54232213
0.48
0.9011
post,b*drug*t
10
5.79351944
0.57935194
0.52
0.8791
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.0030
0.0030
0.00046
0.98295
post,b effect
1
6.1307
6.1307
0.96115
0.33473
pre, d effect
2
2.8688
1.4344
0.22488
0.79995
post,d effect
2
52.7020
26.3510
4.13123
0.02600
pre, d*b
2
22.7303
11.3651
1.78179
0.18567
post, d*b
2
7.3132
3.6566
0.57327
0.56972


35
minutes, pyrilamine malate ("Histavet-P", Schering-Plough,
NJ) was infused IV at 1 mg/kg over the entire 15 minute
collection period. No treatment was given during the
subsequent two collection periods (t=60-90 minutes).
Histamine infusion (7.5 |.ig/kg-hr) was begun at time t = 90
minutes and continued for 60 minutes. Two additional 60
minute infusions of histamine, of 15 ^g/kg-hr and 30
(ag/kg-hr respectively, followed. Therefore, the whole
experiment lasted for 4.5 hours.
Crystalline histamine (Sigma Chemical Co., St. Louis
Mo) was dissolved in 60 mis of 0.9% NaCl and filtered
through a 0.22 ^m cellulose nitrate filter (Corning, Corning
NY) in preparation for infusion, given by infusion pump.
(Harvard Apparatus, South Natick MA)
In a separate trial, the horses were maximally
stimulated with pentagastrin44 for collection of data for
comparison. The horses were prepared as described for
histamine trial. After two hours of basal collection,
pentagastrin was infused at 6 |^g/kg-hr for two hours.
Gastric collections were analyzed as during the histamine
trials.


Sodium Output in Gastric Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
0.02352621
0.00470524
12.97
0.0001
BALLOON(B)
1
0.43675692
0.43675692
1204.21
0.0001
DRUG
2
0.08437257
0.04218628
116.31
0.0001
B*DRUG
2
0.03794764
0.01897382
52.31
0.0001
HORSE*B*DRUG
25
0.07838351
0.00313534
8.64
0.0001
TIME
11
0.03514183
0.00319471
8.81
0.0001
B*TIME
11
0.01913108
0.00173919
4.80
0.0001
DRUG*TIME
22
0.05861341
0.00266425
7.35
0.0001
B*DRUG*TIME
22
0.01446002
0.00065727
1.81
0.0150
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
0.01271226
0.00254245
7.01
0.0001
post,t effect
5
0.00408749
0.00081750
2.25
0.0488
pre, b*t
5
0.0079682
0.00015936
0.44
0.8209
post,b*t
5
0.00552939
0.00110588
3.05
0.0105
pre,drug*t
10
0.00294658
0.00029466
0.81
0.6169
post,drug*t
10
0.01127471
0.00112747
3.11
0.0008
pre, b*drug*t
10
0.00221936
0.00022194
0.61
0.8037
post,b*drug*t
10
0.00474130
0.00047413
1.31
0.2251
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
0.15026
0.15026
85.967
0.00000
post,b effect
1
0.29794
0.29794
170.458
0.00000
pre, d effect
2
0.00323
0.00161
0.923
0.40798
post,d effect
2
0.12425
0.06213
35.544
0.00000
pre, d*b
2
0.00641
0.00321
1.834
0.17659
post, d*b
2
0.03874
0.01937
11.083
0.00023


HISTAMINE DOSE-RESPONSE DATA
Volume and pH
139
TIME
DOSE
VOLUME
PH
minutes
^ig/kg-hr
ml
MEAN
SEM
MEAN
SEM
15
0
480
35
1.685
0.066
30
0
405
54
1.66
0.064
45
0
452
45
1.65
0.071
60
HVP
438
45
1.597
0.076
75
307
62
1.707
0.098
90
407
35
1.872
0.123
105
7.5
473
40
1.695
0.116
120
7.5
528
55
1.502
0.098
135
7.5
550
53
1.468
0.133
150
7.5
633
63
1.445
0.126
165
15
598
69
1.46
0.137
180
15
578
50
1.423
0.146
195
15
605
41
1.505
0.205
210
15
578
41
1.452
0.172
225
30
600
48
1.282
0.039
240
30
578
53
1.266
0.038
255
30
466
90
1.296
0.059
270
30
563
52
1.29
0.021
285
45
470
130
1.285
0.005
300
45
430
100
1.42
0.12
315
45
455
35
1.51
0.24
330
ND
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done


I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Dgctqr of Philosophy.
Alfred M. Merritt, Chair
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
i). g
Claus D. Buergelt
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
Daryl Duss
Professor of Veterinary
Medicine
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality, as
a dissertation for the degree of Doctor of Philosophy.
Associate Professor of
Veterinary Medicine


207
46.Campbell-Thompson ML, Brown MP, Slone DE, Merritt
AM,Levy M, Moll D. Gastroenterostomy for Treatment of
Duodenal Ulcer Disease in 14 Foals. JAVMA 1986; 188: 840-
844 .
47. Murray MJ. Nonsteroidal Antiinflammatory Drug
Toxicity. In: Smith BP, ed. Large Animal Internal
Medicine St. Louis: C. V. Mosby Co., 1990; 665-668.
48. Sangiah S, MacAllister CC, Amouzadeh HR. Effects
of Misoprostol and Omeprazole on Basal Gastric pH and Free
Acid Content in Horses. Res. Vet. Sci. 1989; 47:350-354.
49. Andrews FM, Jenkins CC, Blackford JT, Frazier DL,
Olovsson SG, Mattsson H. Effect of Oral Omeprazole on Basal
and Pentagastrin-stimulated Gastric Secretion in Young
Female Horses. Eq. Vet. J. Suppl. 1992; 13: 80-83.
50. Baker SJ, Gerring EL. Technique for Prolonged,
Minimally Invasive Monitoring of Intragastric pH in Ponies.
Am. J. Vet. Res. 1993; 54(10): 1725-1734.
51. Merritt AM, Burrow JA, Horbal MJ, Madison JB, Tran
T. Effect of Omeprazole on Sodium and Potassium Output in
Pentagastrin-stimulated Equine Gastric Contents. Am. J.
Vet. Res. 1996; 57(11): 1640-1644.
52. Andrews FM, Jenkins CC, Frazier D, Blackford JT.
Gastric Secretion Studies in Foals: Measurement by
Nasogastric Intubation with Constant Infusion and
Aspiration. Eq. Vet. J. 1992; 24(13): 75-79.
53. Jenkins CC, Frazier DL, Blackford JT, Andrews FM,
Mattsson H, Olovsson S-G, McCleod M. Pharmacokinetics and
Antisecretory Effects of Intravenous Omeprazole in Horses.
Eq. Vet. J. Suppl. 1992; 13: 84-88.
54. Jenkins CC, Blackford JT, Andrews F, Frazier DL,
Mattsson H, Olovsson S-G, Peterson A. Duration of
Antisecretory Effects of Oral Omeprazole in Horses with
Chronic Gastric Cannulae. Eq. Vet. J. Suppl. 1992; 13: 89-
92 .


171
Bicarbonate Concentration in Duodenal Contents
(mEq/L)
No Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
27.70
2.05
25.39
3.08
23.23
2.92
30
BASAL
24.21
3.24
22.94
2.58
24.06
2.39
45
BASAL
22.36
2.92
22.36
1.98
23.11
2.25
60
HVP
22.12
3.53
23.37
1.81
24.95
2.03
75
24.04
3.17
22.48
1.46
21.69
1.52
90
23.89
2.52
22.51
1.74
24.11
2.02
105
INFUSION
23.61
2.24
25.01
2.15
29.28
2.67
120
INFUSION
23.08
3.65
25.36
2.53
34.28
1.67
135
INFUSION
23.59
4.28
24.38
1.72
35.17
2.21
150
INFUSION
23.95
2.48
22.68
3.36
33.26
1.48
165
INFUSION
24.48
2 64
23.88
1.87
31.82
2.32
180
INFUSION
22.81
2.69
21.86
2.68
34.23
2.36
HVP = Pyrilamine maleate infusion


94
measured in duplicate by flame photometry (Instrumentation
Laboratories Inc., Lexington MA) on samples which had been
frozen at -20C. Samples were thawed to room temperature
and were mixed and diluted in an internal standard lithium
solution (Dilumat, Fischer Scientific), prior to analysis.
The machine was calibrated with known [Na+] / [K+] standards
(Instrumentation Laboratories Inc., Lexington MA) prior to
analysis and after every 5 samples. Bile acid concentration
was determined by an enzymatic, colourimetric test kit
(Enzabile, Nycomed, Norway) in the VMTH Clinical Pathology
Laboratory.
Analysis of data
A complete randomized block design experiment was used.
The treatment order was randomized for each horse. In order
to obtain basal samples and pretreat all horses with
pyrilamine maleate, the first 90 minutes of each experiment
was the same. For statistical analysis and descriptive
purposes, the results from the t=30 and 45 min were averaged
and are referred to as "Rl". The results from collection
following pyrilamine maleate infusion (t=75 & 90min) were
averaged and labeled "R2". The three "Rl" values from


75
experiments, the catheter position was rechecked before the
catheter was withdrawn, and the cannula closed.
Each infusion was given in a volume of 60 mls/hr.
Crystalline pentagastrin (Sigma Chemical Co., St. Louis MO)
was prepared by dissolving with 0.8 ml of DMSO and 90 mis of
0.9% NaCl before filtering through a 0.22 pm cellulose
nitrate filter (Corning, Corning NY) in preparation for
infusion.
Sample analysis
Gastric and duodenal sample volume was measured in a
graduated cylinder and then an aliquot was analyzed
immediately for chloride ion concentration. Gastric samples
were also analyzed immediately for hydrogen ion
concentration. Duodenal samples were kept in an ice bath
until they were analyzed for bicarbonate ion concentration.
Both gastric and duodenal samples were frozen for later
measurement of sodium and potassium ion concentration.
Using a automatic titrator (Radiometer, Copenhagen
Denmark), hydrogen ion concentration was measured in
duplicate by titration with 0.IN NaOH to an endpoint of 7.4.


Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
EFFECTS OF HISTAMINE AND PENTAGASTRIN ON FASTING EQUINE
GASTRIC AND DUODENAL CONTENTS
By
Diane Lynn Kitchen
May 1997
Chairperson: Alfred M. Merritt, II
Major Department: Veterinary Medicine
The composition of equine gastric contents has been
determined to differ markedly from that of other monogastric
species. In the fasted animal, there is a voluminous
sodium-rich fluid component which becomes greater during
pentagastrin infusion, which is not eliminated by acid
blockade. Potential pancreatic stimulation by pentagastrin
was suggested by Alexander and Hickson. Histamine infusion,
however, seemed to cause a classic parietal secretion, as
opposed to the mixed parietal and nonparietal response to
pentagastrin. These findings led to the formulation of the
hypothesis for this dissertation: In the equine gastric
xiii


137
physiology. The decreased acid output resulting from
pyrilamine maleate pretreatment appears to be yet another
species specific response in horses. Further investigation
is necessary to determine the mechanism for this response.
Although the study was able to determine that the equine-
specific response to pentagastrin stimulation is of
extragastric origin, still more investigation will be
required to determine the exact origin of this fluid.


21
parietal and nonparietal components of gastric secretion in
the horse.44 A variety of compounds have been shown to
inhibit equine basal and pentagastrin-stimulated gastric
acid secretion, such as histamine H-2 antagonist ranitidine,
the proton pump blocking agent omeprazole, and the
prostaglandin misoprostol.31'48'49'51'53,54 The profound sodium
rich nonparietal secretion characteristic of the equine
response to pentagastrin is evident even after omeprazole
has effectively inhibited the acid secretory response.51
The origin of this voluminous nonparietal component of
gastric contents has not been clearly defined.
The periods of high pH of gastric contents during basal
secretion have raised much speculation about the equine
gastric secretory capacity, gastric emptying rates, and the
buffering capacity of the various secretory products.50
Potential buffering fluids include saliva, gastric
nonparietal secretions, and duodenogastric reflux.44 Saliva
is not a likely candidate since the production of saliva in
the horse is minimal except during mastication.55 Fasting
equine gastric contents are frequently dark green to yellow
in color and viscous, suggesting possible contamination with
bile.44 Duodenogastric reflux has been observed during


162
Acid Output in Gastric Contents
(f.iEq/kg/l5minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
34.4
9.91
26.2
11.94
26.9
8.50
30
BASAL
32.1
10.71
28.6
13.47
30.1
5.80
45
BASAL
28.4
7.81
27.0
13.07
30.9
6.34
60
HVP
19.8
7.15
24.1
11.66
28.9
6.06
75
11.9
5.09
13.0
8.02
16.3
3.62
90
9.5
3.95
11.1
6.10
14.9
4.05
105
INFUSION
12.7
4.15
21.8
9.64
30.9
6.41
120
INFUSION
17.8
5.01
56.7
16.94
66.5
7.33
135
INFUSION
20.1
5.49
68.1
12.82
84.9
4.36
150
INFUSION
19.6
6.50
82.8
12.28
80.8
4.73
165
INFUSION
22.1
7.22
94.1
10.43
92.9
6.68
180
INFUSION
21.4
6.76
100.0
11.22
89.5
5.02
HVP = Pyrilaraine maleate infusion


209
64. Murray MJ. Disorders of the Stomach. In: Smith
BP,ed. Large Animal Internal Medicine. St. Louis: Mosby,
1990; 648-653.
65. Aguilera-Tejero E, Pascoe JR, Woliner MJ.
Modulation of Bronchial Responsiveness in Horses by
Phenylbutazone and Furosemide. Am. J. Vet. Res. 1993;
54 (10) : 1703-1709.
66. Carlson GP. Physiologic Response to Endurance
Exercise. Proc. 25th Ann. Conv. AAEP (1979). 1980: 459-
468 .
67. Hirschowitz BI. Histamine Dose-responses in
Gastric Fistula Dogs Decreasing Secretion with Time.
Gastroenterology. 1968; 54: 523-531.
68. Soil AH, Berglindh T. Receptors that Regulate
Gastric Acid-Secretory Function. In: Johnson LR, ed.
Physiology of the Gastrointestinal Tract, Third Edition.
New York: Raven Press, 1994; 1139-1170.
69. Soil AH, Berglindh T. Physiology of Isolated
Gastric Glands and Parietal Cells: Receptors and Effectors
Regulating Function. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Second edition, NewYork: Raven
Press, 1987; 883-909.
70. Ceccarelli P, Pedini V, Gargiulo AM. Serotonin-
containing Cells in the Horse Gastrointestinal Tract. Anat.
Histol. Embryol. 1995; 24: 97-99.
71. Hirst BH. Investigation of Mechanism of Fade of
Gastrin-stimulated Gastric Secretion in the Cat. J.
Physiol. Lond. 1988; 395: 319-331.
72. Guth PH, Leung FW. Physiology of the Gastric
Circulation. In: Johnson LR, ed. Physiology of the
Gastrointestinal Tract, Second Edition. New York: Raven
Press, 1987; 1031-1047.


110
Pre-infusion
Duodenal samples
(See Tables 15,16,17,18,19)
The presence or absence of the pyloric obstruction did
not change the appearance of the fluid collected from the
duodenal catheter. Duodenal samples were transparent dark
yellow to dark green colored and generally thick and mucoid.
The volume collected was related to viscosity of samples and
limited by the small diameter of the catheter; therefore,
outputs of electrolytes were not calculated. Duodenal fluid
was observed to be less viscid, however, during times in
which a high volume was collected. No fluid was obtained
from the duodenal catheter during 19 (11 pre infusion; 8
post infusion: 16 without obstruction; 3 with obstruction)
of the 432 samples collected. The only significant
difference was in balloon status for volume and bicarbonate
ion concentration. The volume from the duodenal catheter
was significantly (p<0.00001) greater in experiments with
the balloon obstructing the pylorus. Bicarbonate ion
concentration was also significantly (p=0.00353) greater in
experiments with pyloric obstruction. As with gastric
samples, "basal" and "pyrilamine" values were derived from


201
Chloride Concentration in Duodenal Contents
Source
DF
Type I SS
Mean Square
F Value
Pr > F
HORSE
5
13649.48336
2729
. 89667
27.42
0.0001
BALLOON(B)
1
638.45276
638
.45276
6.41
0.0118
DRUG
2
11923.06964
5961
. 53482
59.88
0.0001
B*DRUG
2
3441.72173
1720
. 86086
17.28
0.0001
HORSE*B*DRUG
25
17811.55894
712
.46236
7.16
0.0001
TIME
11
2296.74541
208
.79504
2.10
0.0203
B*TIME
11
1781.89427
161
. 99039
1.63
0.0901
DRUG*TIME
22
10931.68930
496
. 89497
4.99
0.0001
B*DRUG*TIME
22
1390.41462
63
.20066
0.63
0.8980
Contrast
DF
Contrast SS
Mean Square
F Value
Pr > F
pre,t effect
5
512.25045
102 .
45009
1.03
0.4005
post,t effect
5
426.80183
85 .
36037
0.86
0.5101
pre, b*t
5
185.52497
37 .
10499
0.37
0.8672
post,b*t
5
669.93027
133 .
98605
1.35
0.2448
pre,drug*t
10
981.26528
98 .
12653
0.99
0.4558
post,drug*t
10
1767.71427
176 .
77143
1.78
0.0643
pre, b*drug*t
10
712.42045
71.
24205
0.72
0.7098
post,b*drug*t
10
380.28384
38 .
02838
0.38
0.9541
Source
DF
SS_N
MS_N
F Value
PValue
pre, b effect
1
1365.17
1365
.17
3.4499
0.07229
post,b effect
1
14.35
14
.35
0.0363
0.85013
pre, d effect
2
3905.72
1952
. 86
4.9351
0.01341
post,d effect
2
15066.50
7533
.25
19.0373
0.00000
pre, d*b
2
1398.75
699
.38
1.7674
0.18672
post, d*b
2
2354.94
1177
.47
2.9756
0.06499


Acid Output of Gastric Contents
Source
DF
ss
MS
F Value
P Value
HORSES
5
0.04418
0.008836
0.00000000214
DOSE
4
0.11481
0.028703
0.0140
0.0000000000
Residual
18
0.00369
0.000205
Total
27
0.15768
0.005840
Sodium Concentration of
Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
46911.3
9382.3
0.000000902
DOSE
4
27197.0
6799.2
14.454750403
0.0000188
Residual
18
8466.9
470.4
Total
27
84638.5
3134.8
Sodium i
Output of Gastric Contents
Source
DF
SS
MS
F Value
P Value
HORSES
5
0.08123
0.016245
0.00000932
DOSE
4
0.00187
0.000468
0.41486401
0.796
Residual
18
0.02029
0.001127
Total
27
0.10473
0.003879
180


60
Discussion
Pentagastrin infusion resulted in secretion of gastric
acid in both studies; however, the maximal acid output was
affected by the administration of pyrilamine maleate. This
finding was unexpected since pyrilamine pretreatment has
been used as the pretreatment of choice when performing
histamine stimulation in other species;11 where the use of
an H-l specific receptor antagonist does not affect the
secretion of gastric acid during stimulation. In part, the
confusion over whether or not histamine acts directly on
gastric mucosa resulted from early classical studies in
which antihistamines were found to have no inhibitory effect
on histamine induced gastric secretion.27 Better
understanding of histamine receptor classes has helped to
clarify the role of histamine in gastric secretion and
explain these earlier findings,11-12 namely that parietal
cells have H-2 receptors and histamine stimulated gastric
acid secretion appears to be a H-2 specific response.1-2'3'68-69
Histamine receptors are involved in other aspects of
gastric function as well as acid secretion. Three specific
receptor types, H-l, H-2, and H-3 have, to date, been


168
Volume of Duodenal Contents
(ml/15minutes)
Balloon
TIME
TREATMENT
SALINE
HISTAMINE
PENTAGASTRIN
min
Mean
SEM
Mean
SEM
Mean
SEM
15
BASAL
250.5
78.73
149.8
41.80
201.3
45.57
30
BASAL
244.7
54.52
178.0
63.34
245.7
37.12
45
BASAL
225.5
51.44
186.8
57.22
222.5
33.31
60
HVP
215.2
53.61
190.8
55.71
212.0
32.13
75
183.2
57.45
228.2
40.55
170.0
24.97
90
222.8
48.59
299.7
53.26
183.5
45.25
105
INFUSION
209.0
51.34
276.2
71.59
559.2
104.8
120
INFUSION
232.5
53.69
218.7
72.12
527.0
108.1
135
INFUSION
219.0
56.42
186.0
41.84
404.0
101.7
150
INFUSION
177.5
44.21
197.3
39.75
503.3
84.9
165
INFUSION
204.5
41.48
166.7
18.67
392.0
117.6
180
INFUSION
157.5
58.14
144.5
14.20
426.0
105.4
HVP = Pyrilamine maleate infusion


143
HISTAMINE DOSE-RESPONSE DATA
Chloride Concentration and Output
TIME
DOSE
CL- CONCENTRATION
CHLORIDE OUTPUT
minutes
l-ig/kg-hr
mEq/L
|.ieQ/kg-15min
MEAN
SEM
MEAN
SEM
15
0
72.87
1.15
72.19
4.85
30
0
72.02
1.50
60.01
7.19
45
0
71.71
1.55
67.20
7.24
60
HVP
70.86
1.21
63.93
6.16
75
72.45
1.23
45.91
8.77
90
69.65
2.09
58.02
3.65
105
7.5
74.94
2.38
72.90
5.33
120
7.5
77.70
2.20
84.98
8.91
135
7.5
76.34
2.27
86.41
7.48
150
7.5
77.81
0.79
101.99
10.08
165
15
76.48
1.58
94.74
11.49
180
15
77.49
1.25
92.69
7.90
195
15
76.11
1.38
95.43
7.11
210
15
77.83
1.36
93.72
8.10
225
30
77.09
1.74
96.30
8.19
240
30
76.92
1.67
92.54
9.05
255
30
75.78
1.90
75.53
16.06
270
30
78.09
0.56
92.96
10.10
285
45
75.70
3.25
72.41
17.96
300
45
78.50
1.50
69.20
15.65
315
45
76.28
0.88
71.27
5.54
330
45
ND
ND
ND
ND
HVP = Pyrilamine maleate infusion
ND = Not Done


APPENDIX G
STATISTICAL ANALYSIS OF BALLOON/NO BALLOON DATA
The SAS System
General Linear Models Procedure
Class
Levels
Values
HORSE
6
B D E H I T
BALLOON
2
no yes
DRUG
3
histamine
saline
pentagastrin
TIME
12
15 30 45 60
135 150 165
75 90 105 120
180
Abbreviations for following ANOVA tables:
B or b = Balloon vs. No Balloon
t = time
d = drug
* = interaction
pre = prior to infusion (t=15-90 minutes)
post = during infusion (t=105-180 minutes)
186


10
resting state. Acidification of the gastric contents
inhibits gastrin release by release of somatostatin from
antral D cells.18 The presence of acid, fat, or
i
hyperosmolar solutions within the small intestine inhibits
the acid secretory response through one or more of the
peptides such as secretin, peptide YY, neurotensin, VIP
(vasoactive intestinal peptide), GIP (gastric inhibitory
peptide), and enteroglucagon released by cells within the
small intestinal mucosa.17-18 These inhibitory substances
have receptors on the ECL cell and have been shown to
inhibit the release of histamine from these cells.1
Histamine also exerts negative feedback on ECL cells via H-l
and H-3 receptors.1 The rapid catabolism of histamine and
its speedy removal from the extracellular space surrounding
the parietal cell eliminates the stimulation of these cells
and terminates the secretory process.20
Many drugs have demonstrated antisecretory actions that
have been crucial in clarifying the mechanisms of acid
secretion and in treatment of pathologic conditions related
the secretion of gastric acid.21 Histamine H-2 receptor
antagonists are able to prevent gastrin, food, and vagal-
induced acid secretion. This finding was pivotal in the