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Whole-body retention and excretion of magnesium in humans

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Title:
Whole-body retention and excretion of magnesium in humans : I. Biological Half-life in normals and selected disease states; II. Radiation dosimetry.
Added title page title:
Magnesium in humans.
Creator:
Roessler, Genevieve Schleret ( Dissertant )
Dunavant, Billy G. ( Thesis advisor )
Bolch, W. Emmet ( Reviewer )
Williams, Clyde M. ( Reviewer )
Putnam, Hugh ( Reviewer )
Whig, Robert E. ( Degree grantor )
Place of Publication:
Gainesville, Fla.
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University of Florida
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xi, 173 leaves. illus. 28 cm.

Subjects

Subjects / Keywords:
Crystals ( jstor )
Dosage ( jstor )
Excretion ( jstor )
Feces ( jstor )
Half lives ( jstor )
Isotopes ( jstor )
Magnesium ( jstor )
Metabolism ( jstor )
Urine ( jstor )
Whole body counting ( jstor )
Dissertations, Academic -- UF -- Environmental Engineering Sciences
Environmental Engineering Sciences thesis Ph. D.
Magnesium -- Physiological effect
City of Gainesville ( local )

Notes

Abstract:
Thirty-one whole-body retention and excretion measurements were made on 13 normal subjects and 12 patients with selected disease conditions to determine as accurately as possible the biological half-lives from a single intravenous administration of 28Mg int he form of MgCl2. the prime objective of this research was to contribute information to the currently sparse knowledge on magnesium metabolism in humans. Calculation of radiation dose based on the determined half-lives was an important aspect of the research since the experimental use of 28Mg is increasing rapidly and o dose estimates have been established. the feasibility of this measurement technique for studying abnormalities in disease conditions was also explored. A high specific activity (200-300 microcuries per milligram magnesium) preparation of the radioactive isotope 28Mg (21.3-hour physical half-life) was used in conjunction with the sensitive 4-pi liquid scintillation whole-body counting technique for retention measurements. A NaI(Tl) crystal whole-body counter was employed to measure localization of the magnesium in the body and appropriate low-level counting systems were used for measurement of the isotope in excreta. Whole-body retention data from the determinations of normal subjects were fit to a sum of two exponentials model. The coefficients of the resultant equation are 8.5 and 91.5 and represent the quantities in per cent involved in the turnover of the two compartments. Biological half-lives of 5.4 +/- 2.2 hours for the first compartment and 540 +/- 35 hours for the second compartment were calculated from the rate constants in the exponents of the fitted equation. The radiation dose from this single administration of the 28Mg was calculated to be 2.0 mrad/microcurie. In the normal subjects, excretion measurements on the average accounted for the amount of the 28Mg not retained in the body. Cumulative urinary excretion averaged 3 per cent per day while fecal excretion was approximately 0.5 per cent per day. Whole-body retention values for amyotrophic lateral sclerosis and sub-total gastrectomy patients were significantly lower than normal, while several subjects, one of whom was known to have been on diuretics, had higher than normal retention of the isotope. Repaired gastrectomy patients had retention patterns within the normal range. In the majority of the patients studied, the abnormal retention of the 28Mg was accounted for by amounts int he excreta. However, in several patients, excretion did not account for the total amount of the isotope not retained in the body, resulting in a deficit int he total-measure 28Mg. localization of the isotope in the body as measured by NaI(Tl) crystal whole-body counting showed consistent patterns between results of the normal subjects. An atypical build-up of the isotope was found in the abdominal region of the amyotrophic lateral sclerosis patient who previously exhibited an apparent precipitous whole-body loss of 28Mg. Based on published investigations to date, it is concluded that this turnover study is currently the most accurate. the use of a true tracer dose of 10 microcuries or less of high specific activity 28Mg and the sensitive whole-body counting system allowed administration of a dose which would not upset the physio-chemical balance of the body. also, this procedure permitted measurements up tot six times longer than previously reported studies. The amount of 28Mg to be administered in future investigations with this isotope should be guided by the 2.0 mrad/microcurie dose calculated from the data obtained in this study. Based on the consistent, significantly abnormal retention and excretion patterns shown by certain disease-state measurements in this study, it is concluded that this turnover procedure could serve as a valuable adjunct to other diagnostic techniques.
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Typescript.
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Vita.
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Thesis -- University of Florida.
Bibliography:
Bibliography: leaves 158-172.

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WHIOLE-BODY RETENTION
I. BIOLOGICAL HALF-LIFE
II.


AND EXCRETION OF MAGNESIUM IN EUMANS:
IN NORMALS AND SELECTED DISEASE STATES;
RADIA'TON DOSIMETRY


By
Genevieve Schleret Roessler
















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








UNIVERSITY OF FLORIDA
1972
















ACKNOWLEDGMENTS


Foremost appreciation is expressed to Billy G. Dunavant, Ph.D.,

my committee chairman, for his supervision, inspiration, and guidance,

not only in this phase of graduate work, but also in previous graduate

study and employment. My interest in the area of the use of radioactive

isotopes in the biological field has stemmed from and followed his

interests.

I also gratefully acknowledge the contributions to my research

by the other members of my committee: W. Emmett Bolch, Ph.D., for

guidance in graduate work, for review and critical analysis of manu-

scripts, and for participation in this research as a "normal"; Clyde

Williams, M.D., for clinical advice and direction; and Hugh Putnam, Ph.D.,

for inspiration and advice.

I should also like to acknowledge the support by the College of

Medicine, University of Florida, and, in particular, the many hours

of cooperation by Jared C. Kniffen, M.D., gastroenterologist, and

Donald T. Quick, M.D., neurologist. Others without whose assistance

this research would not have been possible include the staff at the

Clinical Research Center; the staff at the Medical Center Library;

Thomas Bauer, Howard Kavanaugh, Jerry Sawyer, Pat Edgett, Phyllis Durre,

Ann Groves, Lois Fischler, Mike Hewson, James McVey, and Sharon Corbett

of the Radiation Biophysics Section of the Department of Radiology; and

John Thornby, Ph.D., of the Department of Statistics. A special note of

ii












thanks is due Larry Fitzgerald for his motivation and assistance in my

graduate work.

I particularly wish to thank my husband, Chuck, for his assistance,

advice, and encouragement in every phase of my graduate studies and

research. I wish to recognize the assistance of my oldest daughter,

Teresa, with typing, filing, and library work. She and my other

children, Cynthia, Mary, Francis, Kay, Jean, and Anne, have been very

patient and understanding throughout my graduate studies and have assumed

many household duties in order to ease my domestic responsibilities. I

wish to express special appreciation to my father, Leo Schleret, for his

continuing interest in my academic career and, in particular, for his

contribution as a "normal" in this research.

Financial support by the Environmental Protection Agency, Training

Grant Number 2-T01-EP00046-11, is also acknowledged.


iii
















TABLE OF CONTENTS

Page

ACKNOWLEDGMENTS . . . . .. . . . ........ ii

LIST OF TABLES .... . . . . . . . . . vi

LIST OF FIGURES ...... . . . . . . . . .. vii

ABSTRACT . . . . . . . . . . . . . . ix

CHAPTER

I. INTRODUCTION . . . . . . ... . .. 1

II. LITERATURE REVIEW . . . . . . . . . 6

Occurrence of Magnesium in Nature . . . . . 6
Importance of Magnesium to Man. . . . . .. 6
Techniques for Measuring Stable Magnesium . . .. 17
Studies with Magnesium-28 . . . . . . .. 19

III. MATERIALS AND METHODS . . .. .. . .. . . 33

Magnesium-28. . . . . . . . 33
Experimental Conditions and Techniques. . . .. 35
Instrumentation .. . . . . . . . 40
Data Analysis Techniques. . . . . . .. 57

IV. RESULTS AND DISCUSSION . . . . . . .. 61

Whole-Body Retention of 28Mg in Normals . . .. 61
Excretion of 28Mg in Normals . . . . ... 68
Calculation of Radiation Dose .......... 84
Retention and Excretion of 28Mg in Selected Disease
Conditions . . . . .. ....... . 87
Measurements with the NaI(Tl) Crystal Whole-Body
Counter . . . . . . . . . . 103

V. SUMMARY AND CONCLUSIONS . . . . ... . .113

Conclusions . . . . . . . . . . 115

APPENDICES . . . . . . ... . ..... . . . . 117

A. COMPUTATION OF RADIATION DOSE . . . . . ... 118












Page

B. 28Mg BALANCE CHARTS NORMALS AND PATIENTS . . .. .123

C. SWEAT ANALYSIS, STUDY GROUP 7 . . . . ... .154

D. NaI(T1) CRYSTAL WHOLE-BODY COUNTER RETENTION
AND LOCALIZATION DATA . . . . . ... .156

LIST OF REFERENCES ...................... 158

BIOGRAPHICAL SKETCH ...................... 173
















LIST OF TABLES


Table Page

1. SUMMARY OF STUDY GROUPS . . . . . ... .. . .. 37

2. SUMMARY OF DETECTION SYSTEMS . . . . . . ... 41

3. 28Mg TURNOVER RESULTS IN HUMANS . . . . . . .. 81

4. COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT
28Mg STUDIES . . . . . . . . . . . 85

5. PLASMA AND RED BLOOD CELL STABLE MAGNESIUM ANALYSES ... .90

6. COMPARISON OF THE WHOLE-BODY RETENTION MEASUREMENTS BY THE
4-PI LIQUID SCINTILLATION AND THE NaI(T1) CRYSTAL WHOLE-
BODY COUNTERS . . . . . . . . ... . .106















LIST OF FIGURES


Figure Page

1. ISOTOPES OF MAGNESIUM . . . . . . . .... .22

2. RADIOACTIVE DECAY SCHEME OF MAGNESIUM-28 AND ITS
RADIOACTIVE DAUGHTER, ALUMINUM-28 . . . . . 34

3. FLOOR PLAN OF THE RADIATION BIOPHYSICS GRADUATE
PROGRAM FACILITY . . . . . . . .... 42

4. 4-PI LIQUID WHOLE-BODY COUNTER LABORATORY . . . .. 43

5. SUBJECT PREPARING TO ENTER THE 4-PI LIQUID WHOLE-
BODY COUNTER. . . . . . . . .. ..... 44

6. ONE SIDE OF THE 4-PI LIQUID WHOLE-BODY COUNTER SHOWING
SIX PHOTOMULTIPLIER TUBES AND STEEL SHIELD . . . 46

7. 4-PI LIQUID WHOLE-BODY COUNTER INSTRUMENTATION . . .. 47

8. SIGNAL DIAGRAM OF THE 4-PI LIQUID WHOLE-BODY
COUNTING SYSTEM . . . . . . . . .. 48

9. NaI(T1) CRYSTAL WHOLE-BODY COUNTER: WHOLE-BODY COUNT
POSITION . . . . . . . . . . . 50

10. GEOMETRY OF SUBJECT COUNTED ON THE NaI(T1) CRYSTAL
WHOLE-BODY COUNTER . . . . . . . . ... .51

11. NaI(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
HEAD COUNT . . . . . . . . . . . 52

12. NaI(T1) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
CHEST COUNT . . . . . . . . . . . 53

13. NaI(T1) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
ABDOMEN COUNT . . . . . ... . . . 54

14. NaI(T1) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
LEGS COUNT . . . . . . . .. ..... 55

15. LARGE VOLUME WELL COUNTER . . . . . . .. . 56

16. NaI(T1) CRYSTAL COUNTER . . . ... . . . . 58











Figure Page

17. WHOLE-BODY RETENTION OF 28Mg: NORMAL SUBJECTS . . .. .62

18. REPLICATIONS IN MEASUREMENTS OF WHOLE-BODY RETENTION
IN TWO NORMALS . . . . . . . . ... ... 65

19. MODEL FOR 28Mg RETENTION IN NORMAL SUBJECTS . . ... .69

20. TOTAL-MEASURED 28Mg FOR NORMALS NA, NB, AND NC . . .. 71

21. TOTAL-MEASURED 28Mg FOR NORMAL ND, NE, NF, AND NG . .. 72

22. TOTAL-MEASURED 28Mg FOR NORMAL NH, NI, AND NJ . . .. 73

23. TOTAL-MEASURED 28Mg FOR NORMALS NK, NL, AND NM . . .. 74

24. TOTAL-MEASURED 28Mg AVERAGE OF ALL NORMAL . . . 76

25. WHOLE-BODY RETENTION OF 28Mg ALS PATIENTS . . ... .91

26. TOTAL-MEASURED 28Mg PATIENT PA . . . . .... .92

27. TOTAL-MEASURED 28Mg PATIENTS PB, PG, AND PI ..... .93

28. WHOLE-BODY RETENTION OF 28Mg GASTRECTOMY PATIENTS . .. 94

29. TOTAL-MEASURED 28Mg PATIENTS PC, PE, PH, AND PJ .... 95

30. WHOLE-BODY RETENTION OF 28Mg PATIENTS WITH
MISCELLANEOUS DISEASE CONDITIONS . . . . .... .96

31. TOTAL-MEASURED 28Mg PATIENTS PK, PF, PD, AND PL .... 97

32. WHOLE-BODY RETENTION AS MEASURED BY THE NaI(T1) COUNTER . 105

33. REGIONAL RETENTION OF 28Mg . ... . . . . . .... 109


viii








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

WHOLE-BODY RETENTION AND EXCRETION OF MAGNESIUM IN HUMANS:
I. BIOLOGICAL HALF-LIFE IN NORMALS AND SELECTED DISEASE STATES;
II. RADIATION DOSIMETRY

by

Genevieve Schleret Roessler

March, 1972

Chairman: Billy G. Dunavant, Ph.D.
Co-Chairman: W. Emmett Bolch, Ph.D.
Major Department: Environmental Engineering


Thirty-one whole-body retention and excretion measurements

were made on 13 normal subjects and 12 patients with selected disease

conditions to determine as accurately as possible the biological half-

lives from a single intravenous administration of 28Mg in the form of

MgC12. The prime objective of this research was to contribute informa-

tion to the currently sparce knowledge on magnesium metabolism in

humans. Calculation of radiation dose based on the determined half-

lives was an important aspect of the research since the experimental

use of 28Mg is increasing rapidly and no dose estimates have been esta-

blished. The feasibility of this measurement technique for studying

abnormalities in disease conditions was also explored.

A high specific activity (200-300 microcuries per milligram

magnesium) preparation of the radioactive isotope 28Mg (21.3-hour

physical half-life) was used in conjunction with the sensitive 4-pi

liquid scintillation whole-body counting technique for retention

measurements. A NaI(Tl) crystal whole-body counter was employed to

measure localization of the magnesium in the body and appropriate low-

level counting systems were used for measurement of the isotope in

excreta.










Whole-body retention data from the determinations on normal

subjectswere fit to a sum of two exponentials model. The coefficients

of the resultant equation are 8.5 and 91.5 and represent the quantities

in per cent involved in the turnover of the two compartments. Biologi-

cal half-lives of 5.4 2.2 hours for the first compartment and 540

35 hours for the second compartment were calculated from the rate

constants in the exponents of the fitted equation.

The radiation dose from this single administration of 28Mg

was calculated to be 2.0 mrad/microcurie.

In the normal subjects, excretion measurements on the average

accounted for the amount of the 28Mg not retained in the body. Cumula-

tive urinary excretion averaged 3 per cent per day while fecal excretion

was approximately 0.5 per cent per day.

Whole-body retention values for amyotrophic lateral sclerosis

and sub-total gastrectomy patients were significantly lower than

normal, while several subjects, one of whom was known to have been on

diuretics, had higher than normal retention of the isotope. Repaired

gastrectomy patients had retention patterns within the normal range.

In the majority of the patients studied, the abnormal

retention of 28Mg was accounted for by amounts in the excreta. However,

in several patients, excretion did not account for the total amount of

the isotope not retained in the body, resulting in a deficit in the

total-measured 28Mg.

Localization of the isotope in the body as measured by NaI(Tl)

crystal whole-body counting showed consistent patterns between results

of the normal subjects. An atypical build-up of the isotope was found

in the abdominal region of the amyotrophic lateral sclerosis patient

x










who previously exhibited an apparent precipitous whole-body loss of

28Mg.

Based on published investigations to date, it is concluded

that this turnover study is currently the most accurate. The use of a

true tracer dose of 10 microcuries or less of high specific activity

28Mg and the sensitive whole-body counting system allowed administration

of a dose which would not upset the physiochemical balance of the body.

Also, this procedure permitted measurements up to six times longer than

previously reported studies.

The amount of 28Mg to be administered in future investigations

with this isotope should be guided by the 2.0 mrad/microcurie dose

calculated from the data obtained in this study.

Based on the consistent, significantly abnormal retention

and excretion patterns shown by certain disease-state measurements in

this study, it is concluded that this turnover procedure could serve

as a valuable adjunct to other diagnostic techniques.














CHAPTER I

INTRODUCTION


Nothing but a cloud of elements organic,
C. O. H. N. Ferrum, Chor. Flu. Sil. Potassa,
Calc. Sod. Phosph. Magn. Sulphur, Mang.(?) Alumin.(?) Cuprum(?)
Such as man is made of (1).


Oliver Wendell Holmes, in a poem called "DeSauty, an electro-

chemical ecologue," included magnesium in a list of elements of which he

thought man to be composed. Holmes wrote the poem in 1859, almost a

century before an accurate measurement of the human body content of

magnesium was made (2). Although he gave no indication about his

source of information, his prophetical inclusion of magnesium in the

composition of the human body came many years before scientists were to

provide conclusive evidence that magnesium is a required nutrient.

It is now known that magnesium is one of the most biologically

important metallic ions. Magnesium is second only to potassium in

abundance as an intracellular cation in humans (20-30 milliequivalents

per kilogram) (3); the element is known to activate many enzymatic

reactions, it is essential for neuromuscular function and protein

synthesis, and it is an important constituent of bone (4).

Much has been written about the contribution of magnesium to

biological functions and its importance in metabolic processes. Never-

theless, little information is available on magnesium in man (5), although

interest in its metabolism and nutritional significance has increased





2




greatly during the past decade (6). Consequently, as recently as 1969,

researchers deplored the fact that this essential element had not been

investigated to anywhere near the same extent as calcium, phosphorus,

potassium and other fundamental ions (7). Because of the interrelation-

ships of these cations, any lack of information on magnesium limits

the amount of knowledge obtainable on the function of the others.

The study of magnesium metabolism in the human has been

hampered by technological difficulties (4). In spite of recent refine-

ments in classical procedures such as precipitation, fluorimetry,

and the titan yellow method, the element is difficult to measure in

biological materials (8). Over the past decade, routine procedures

have been developed using emission flame spectroscopy and atomic

absorption spectrophotometry for analyses of the metal in body fluids,

tissue, and excreta. These techniques are accurate, but the equipment

is expensive and complex and consequently not available to many clinical

laboratories.

Another more important factor has delayed progress in the study

of the function of magnesium in humans. Although a complete analysis

of stable magnesium can be made from cadaver studies, this "final

analysis" supplies information only on what the content of the living

body was. It can not provide information on the dynamics and function

of magnesium in the living subject. Thus, in vitro measurements of

stable magnesium are made in serum, plasma, urine, feces, and even in

red blood cells, in attempts to establish some means of delineating

normal and abnormal metabolism of the element. The general consensus

of many authors (4,5,7) is that the level of magnesium in the various










body fluids has little relationship to total-body magnesium and probably

predicts very little that is reliable and consistent about its metabolism.

The use of radioactive tracers has provided keys to new know-

ledge about the metabolism of many essential elements. However, it

wasn't until 1953 (9) that a suitable radioisotope of magnesium

(magnesium-28 (28Mg)) was discovered. The first article on the use of

this isotope for biological investigations did not appear until five

years later (10).

Although the use of 28Mg as a tracer overcomes many limita-

tions present in stable analysis, the isotope itself has a limitation;

its short physical half-life (21.3 hours) makes long-term measurements

impossible (3).

Nevertheless, during the past decade, a number of attempts

have been made to further the understanding of magnesium metabolism

by determining the biological half-life and by defining the metabolic

compartmentalization of the element in humans. However, a later discus-

sion will show that results of these studies vary widely. Most of these

studies involve the measurement of excretion rates and/or clearance

from plasma or serum of 28Mg following a single administration of the

isotope in the chloride form. The short physical half-life limited

measurement to only 40 144 hours after administration. In addition,

until recently, only low specific activity 28Mg (<20 microcuries per

milligram (pCi per mg) of magnesium)was available. Investigators who

used this lower specific activity compound report that the dose that

could be administered was "limited by concern for upsetting the magnesium

balance of the system under study" (4) and because of the possibility










of chemical toxicity (11). A number of researchers discontinued their

work with 28Mg because of the restrictions placed on the accuracy of

the results by both the isotopic compound and the measurement techniques

and equipment (12-14).

An opportunity to reduce these technical problems came when

Brookhaven National Laboratory began production of a high specific

activity preparation of 28Mg (200-300 pCi per mg magnesium). This

compound, plus the use of a highly sensitive 4-pi whole-body counter

for measuring whole-body retention of small quantities of the isotope,

made it possible to overcome problems associated with overloading the

system with magnesium. More important, the use of the whole-body

counter permitted measurements with a relatively small dose of the

isotope up to six times as long as was previously possible.

Therefore, a prime objective of this study was to determine

the biological half-life (or half-lives) of 28Mg by measuring whole-body

retention after a single intravenous dose. Excretion was measured in

addition to the whole-body retention as a means of completing total-

balance studies of 28Mg. Another major objective of this study was to

determine the total-body radiation dose from the isotope. This deter-

mination is particularly important now due to the availability and

anticipated frequent use of the higher specific activity 28Mg.

A small number of persons with selected disease conditions

who were suspected of having abnormal magnesium metabolism were included

in the study to examine the possibilities of using this isotope technique

for determining disease state metabolism anomalies. The feasibility

of using either retention or excreta measurements as a part of a diag-

nostic procedure was another facet of this research.






5



The significance of this work as a contribution to the more

complete understanding of the function and metabolism of magnesium in

humans can perhaps be stated in the same way that McCance and Widdowson

(15) evaluated their research in 1939. In regard to experiments they

conducted on the fate of stable magnesium after intravenous administra-

tion to normal persons, these researchers said:

These experiments are only a small contribution toward the
solution of a very large and complicated problem, but they
raise interesting points which deserve consideration.















CHAPTER II

LITERATURE REVIEW


Occurrence of Magnesium in Nature

Magnesium forms about 2.1 per cent of the earth's crust and

is the third most abundant of the industrial metals. It is widely

distributed in nature in a variety of forms; those used most commonly

are carbonate, oxide, and chloride which occur as dolomite, brucite and

carnallite (16). Its name is derived from Magnesia, a Greek city in

Asia Minor, where a large deposit of carbonate is located.

Magnesium has an atomic number of 12 and is usually classi-

fied with the alkaline earth metals calcium, strontium, and others -

although in many ways it has a closer resemblance to zinc and cadmium

(17). Like the other metals of the alkaline earths, it readily forms

divalent ions.


Importance of Magnesium to Man

Magnesium Content in Living Tissue

It is now known that magnesium is present in all living

things (18). However, it wasn't until 1906 that the belief that

magnesium is essential for growth in higher plants was confirmed by

Willstatter, who discovered that it forms an integral part of the

chlorophyll molecule (19). Since that time, it has been shown that

magnesium is present in chlorophyll in all green plants and that it is

a universal microconstituent of lower plants. Higher animals have











considerable quantities of magnesium in all tissues. As the key

element in the maintenance of the anatomic structure of the mito-

chondrion, it is essential for life (6).

Content in the Human Body

The first estimate of the chemical composition of the human

body appeared in 1859 in Moleschatt's handbook of dietetics (20). A

number of other estimates were made during the next 100 years (21-23),

but it wasn't until 1942 that the first reliable approximation of the

total amount of magnesium in the adult human body was made. At that

time, Duckworth (24) reported that an adult weighing 70 kilograms (kg)

had a total content of 29 grams (g) of magnesium, which was somewhat

higher than the 21 g measured by Shohl in 1933 (25). In 1951, Widdow-

son, McCance, and Spray (2) published the first complete chemical

analysis of the human body based on cadaver studies of three adults.

They reported values of 48.4, 42.7, and 43.0 milligrams (mg) of magnesium

per 100 g (i.e.: 33.0, 29.5, and 30.5 g per 70 kg). Currently, it is

generally agreed that the total amount in a 70-kg man is approximately

2,100 milliequivalents (mEq) (25.5 g) (25).

Although magnesium is frequently referred to as a trace element-

it is hardly that being the fourth most abundant cation in the human

body (17). Only sodium, potassium, and calcium exceed it in content.

In 1952, Sherman in his book, The Chemistry of Food and Nutrition, states

that magnesium comprises about 5 per cent of the adult human body (26).

It is located principally in the skeleton and the cells of the soft

tissue. It is primarily intracellular, exceeded in content there only

by one other cation, potassium. Slightly more than half of total-body










magnesium is present in bone; however, its precise location there is

not known (27).

The exchangeable body content of magnesium in humans is 2.6 -

5.3 mEq/kg of body weight, whereas the total-body content is about 30

mEq/kg. The labile pool is contained primarily in connective tissue,

skin, and the soft tissues of the abdominal cavity; the magnesium in

bone, muscle, and red blood cells exchanges slowly (28).

The most recent summaries of magnesium content in humans,

particularly with regard to its biochemistry and its homeostasis,

appeared in reviews by Wacker (29) and Heaton (30) in 1969.

Requirements of Magnesium by the Normal Adult

Although magnesium has always been a part of man's diet

because of its abundance in nature, interest in it as a dietary con-

stituent didn't develop to any extent until the latter part of the

nineteenth century. Reports in 1894 that it was present in animal

tissue (31) led many investigators to believe that magnesium more than

likely was an essential nutrient (32). The report of Sherman and

co-workers (33) in 1910 that magnesium was retained by humans subsisting

on a wide variety of diets was proposed as suggestive evidence of man's

requirement for this element (32).

In 1910, the Office of Experiment Stations of the United

States Department of Agriculture published Bulletin 227 which included

a summary of balance studies on magnesium (33). It was reported in

this bulletin that magnesium is absorbed from the intestinal tract

and deposited in the tissues of the body, especially in bone. However,

the balance data did not show that it was a required nutrient, nor that

it had a definite function.










In 1926, Leroy demonstrated that magnesium is essential in

animal diets (34). This finding prompted numerous studies in the

latter 1920s and early 1930s on magnesium's role in animals and in

man. In 1929, Joachimoglu and Panopoulous (35) analyzed foos typical

of a normal diet and concluded that an adequate amount of magnesium is

obtained by normal intake to meet the body's requirements. In 1932,

the daily need was reported as 300 mg (36), a figure which is still

quoted by some as authoritative (37). A number of reviews of magnesium

metabolism followed including: Shohl, 1933 (25); Schmidt and Greenberg,

1935 (38); and Greenberg, 1939 (39).

A thorough review of magnesium in nutrition in 1939 by Duck-

worth (40) included a summary of metabolism and magnesium deficiency in

addition to a comprehensive synopsis on methods of estimation, occurrence,

and distribution, on the relationship of magnesium to disease, and on

magnesium requirements in domestic animals and in man. In his review

of the literature, he found that estimates of the daily requirements of

magnesium range from 20 298 mEq (24 358 mg). More recent metabolic

balance studies propose an average adult requirement of at least six

mg per kg of body weight per day (420 mg for a 70-kg man) (6).

A summary of the sources of magnesium and an analysis of

the reported data on magnesium balance in normals in different parts

of the world were published in 1964 by Seelig (41). Foods which she

considers as rich in magnesium include cocoa and chocolate, nuts, some

seafoods, bean- and pea-type vegetables, and grains. Green leafy

vegetables, some fruits, and certain meats are listed as foods with a

moderate amount of magnesium. Many foods regularly eaten in a normal











diet are relatively poor in the element. However, according to Seelig,

it is generally agreed that because magnesium is so plentiful in the

normal diet, deficiencies of it cannot develop in the absence of disease.

However, she emphasizes that currently accepted magnesium requirements

should be reevaluated to make certain that the optimal daily intake of

the mineral is correct, since prolonged dietary insufficiency of it may

contribute to the development of chronic disease.

Relationship of Magnesium with Other Tons and Compounds

It has been known since 1909 that a relationship exists between

calcium and magnesium metabolism. Mendel and Benedict (42) showed that

an infusion of calcium in animals produced an increase in their

urinary excretion of magnesium and vice versa, a phenomenon later con-

firmed in man (43,44). Several decades later it was shown that experi-

mental magnesium deficiency produced disturbances in calcium metabolism

(45-47). The absorption of magnesium from the gastrointestinal tract

has also been shown to be influenced by protein intake (48), growth

hormones (49), large doses of vitamin D (50), and certain antibiotics

(51). Vitamin D (52) and certain carbohydrates (53) also affect

magnesium metabolism.

Current reviews of the interrelationship of magnesium with

calcium and phosphorus present data on the complex interactions of

these cations in man and in animals (54-60). Most significant of

these is that magnesium deficiency disturbs calcium metabolism and

that in calcium deficiency, when magnesium is available, it can

replace bone calcium to a limited extent (61). Stearns, speaking for

the Journal of the American Medical Association Council on Foods and









Nutrition, advocates "the maintenance of an adequate, even ample,

intake of calcium, magnesium, and phosphorus throughout the entire

life span" (61). She comments that "calcium, phosphorus, and magnesium

are usually considered together from a nutritional point of view

because all three occur in bone, and, with carbonate, make up the major

part of the bone mineral." Stearns also points out that of the three

elements, magnesium has been studied far less thoroughly because chemical

methods for its determination have been less satisfactory.

Potassium is another element frequently studied with magnesium,

since the two make up the bulk of the intracellular cations. Like calcium

more is known about potassium, primarily because of the ease with which

it can be measured (62). Two recent reviews concentrating on the

interrelationship of magnesium and potassium were published by Hammarsten

et al. (63) and Whang (64). The influence of various nutrients and

hormones on urinary magnesium and other divalent cation excretion was

reviewed in 1969 by Lindeman (65).

Clinical Significance of Magnesium

The first recorded association of magnesium with medicine

dates back to the Renaissance in Italy when various salts of magnesia

were used as laxatives (66). Magnesium sulfate, or epsom salts as it

was known hundreds of years ago, did not actually become popular as a

treatment until 1618 when it was used to "improve gastrointestinal

function" (67). A mineral springs was discovered that year on the manor

of Epsom in a municipal borough of Surrey, England. Although the

mineral composition of the water was not analyzed, its "healing"

qualities became so well known that a spa grew up at Epsom which reached










its zenith a century later (68). More recently it was shown that the

"healing" effect found from drinking the water containing the then

mysterious ingredient apparently was related both to its purgative

action and to its sedative effect.

Magnesium was used in that manner until 1911 when its external

use as sulfate was reported in Lancet (69). Patients suffering from

erysipelas or cellulitis applied a saturated solution of the compound

to painful areas and found relief. Four years later magnesium meta-

bolism was first clinically studied by Holt et al. (70) in infants with

diarrhea by measuring magnesium intake and fecal excretion. However,

as recently as 1931, no clinical significance had been attached to

changes of magnesium in metabolism, even though the manifestations of

magnesium excess in man had been known since 1913, according to the

classic work, Quantitative Clinical Chemistry by Peters and Van Slyke (71).

In 1916, pharmacologic studies of the properties of magnesium as a

potential anticonvulsant and anesthetic agent showed that an excess of

the ion led to impairment of neuromuscular transmission (72). Further

study has shown that even general anesthesia can be produced by infusions

of magnesium; however, concentrations necessary to do this are dangerously

close to those required to produce respiratory paralysis (73). Uninten-

tional production of magnesium excess occurs most frequently in patients

with renal failure (74).

On the other hand, the "indispensibility of magnesium for the

animal organism rested insecurely on a teleological basis" until the

early 1930s when Kruse et al. (75) published their observations on

magnesium deficiencies in the rat. Earlier workers apparently had

failed in attempts to produce clinical changes in animals because of










the difficulty in obtaining a low magnesium diet (76). Kruse described

the classical symptomology of magnesium deficiency and observed that

it resembled that of low-calcium tetany.

During the next few years, there were many attempts to associ-

ate dietary inadequacy of magnesium with increased incidence of malignant

neoplasms. Shear (77), in 1933, reviewed these reports and found the

evidence contradictory and insufficient. A short time later, Walker and

Walker (78) published a work which included an extensive review of the

physiological importance of magnesium and the variations of magnesium

levels in abnormal states. In their study, they compared the range

of serum magnesium in 91 miscellaneous medical and surgical patients

and in a group of persons with hypertension both with and without renal

damage. They concluded that "contrary to certain statements in the

literature, serum magnesium may be elevated in moderate or severe renal

insufficiency, especially if associated with hypertension."

The first investigators to succeed in producing magnesium

deficiency experimentally were Orent and his co-workers (79). They

stated in their 1934 paper that rats in the study showed a depletion

of bone magnesium after being fed a diet containing only 1.8 parts per

million (ppm) of magnesium. After four days on the diet "all exposed

skin areas became vividly red from vasodilation; irritability and

hyperexcitability was exhibited in eight to 10 days; growth stopped

after a week; convulsions began to occur by the 18th day; and death

usually followed the first or subsequent convulsions." That same year,

Hirshfelder (80) described magnesium deficiency in man. However, it

was not until 1959 that the first cure of magnesium deficiency in man











was reported (81). Five patients being fed intravenously developed

severe muscle cramps and convulsions. The symptoms suggested calcium

deficiency, but investigations showed that the patients had been

receiving a sufficient amount of calcium in the liquid nutrient. However,

they had received no magnesium. After intravenous administration of

magnesium sulfate, all of the patients improved within hours and were

soon asymptomatic.

A number of additional attempts to induce magnesium deficiency

took place in the 1930s through the 1960s. Knoop et al. (82), while

studying magnesium and vitamin D relationships in calves fed mineralized

milk, found that the soft-tissue content of magnesium is not appreciably

altered even in severe deficiency. This may be the reason that when

Fitzgerald and Fourman (83) fed a diet containing essentially no

magnesium to normals for 27 days no symptoms of magnesium deficiency

were observed. In addition, they found no differences in the magnesium

blood levels in these subjects between normal and low-magnesium intake

periods. In another case, Barnes et al. (27) did not observe any hypo-

magnesemia or deficiency symptoms in a patient maintained for 38 days

on gastrostomy feedings which contained little magnesium.

In contrast, Shils (84) reported that plasma and red blood

cell magnesium levels fell significantly below normal in two normal

volunteer subjects while they were on a deficient diet for 274 and 414

days. Signs and symptoms of magnesium deficiencies appeared in both

subjects and reversal occurred upon administration of magnesium. In

comparison to the deficiency symptoms first reported in 1934 by Orent

et al. (79), Wacker and Parisi (74) more recently described the syndrome in

man as one involving "neuromuscular dysfunction manifested by hyperexcitability,









sometimes accompanied by behavioral disturbances." These disturbances,

which can be reversed by administration of magnesium, include tetany,

generalized tonic-clonic as well as focal seizures, ataxia, vertigo,

muscular weakness, tremors, depression, irritability, and psychotic

behavior.

Despite the indications of a relationship between disease

conditions and magnesium abnormalities, published articles manifesting

a clinical interest in this cation were few until the 1950s. About

that time, Martin and co-workers (85,86) and Flink and colleagues (87-90)

published results which revived the interest in magnesium abnormalities.

Both groups detected low plasma levels of magnesium in surgical patients

receiving fluids parenterally, in patients receiving diuretic therapy,

and in diabetics.

Then in 1954, a serendipitous occurrence led to the discovery

that patients with chronic alcoholism and delirium tremors are magnesium

deficient. This was discovered when magnesium, because of its sedative

effect, was used by Flink and associates to treat delirium tremors (91).

The manifestations "were promptly alleviated by the administration of

magnesium sulfate intramuscularly in amounts which are not hypnotic."

Flink et al. found the serum levels of all of these patients on admission

to the hospital significantly lower than normal. They reason that

magnesium deficiency in chronic alcoholism is similar to that induced

by a magnesium deficient diet. The caloric requirement.of these patients

is satisfied by alcohol almost exclusively for a long time and, thus,

their diet is low in magnesium.

More recently, other clinicians have reported that, in addition

to a magnesium deficient diet, an alcohol-induced renal excretion is an











important factor in magnesium depletion (92,93). Other studies of

magnesium depletion in alcoholism and reviews of the subject have been

published since that time (94-103).

As a result of Flink's discovery of magnesium deficiency in

alcoholics, extensive research on magnesium metabolism has been

stimulated, not only in alcoholics, but in other disease conditions as

well. Other magnesium insufficiencies have been reported in cases of

malabsorption syndromes, prolonged or severe loss of fluids, lactation,

diuretic therapy, diabetic acidosis, hyperaldosteronism, hypercalcemia

(104), hyper- and hypothyroidism (105), parathyroid disease (106,107),

inflammatory bowel disease (108), celiac disease (109), Kwashiorkor and

protein calorie nutrition (110), Grave's disease (111), and cardiac

necrosis (112). Barnes has evaluated magnesium requirements and

deficiencies in surgical patients (113,114) and Wacker and associates

were the first to describe normocalcemic magnesium deficiency tetany (115).

The relationship of magnesium metabolism and other conditions such as

hyperparathyroidism and osteolytic disease (116), chronic renal disease

(117), hypokalemia (118), gastrointestinal disease (119), and malnutrition

(120) were reviewed in 1969.

Literature reviews of magnesium deficiency are plentiful

(30,87,88,121-131) and they cover studies from the 1930s to the present.

The most recent comprehensive reviews were published in 1965 by Aikawa (132),

and in 1968 by Wacker and Parisi (74,104), and in 1969 by Gitelman and

Welt (133). Reviews of deficiencies in both man and in animals appeared in

the August, 1969, edition of the Annals of the New York Academy of Sciences on

The Pathogenesis and Clinical Significance of Magnesium Deficiency (134-

137). A summary of the experimental production of magnesium deficiency










in man is also in the same edition (138). In that study, magnesium

deficiency was induced in seven volunteer adult human.subjects. All

of the subjects developed neurologic and/or gastrointestinal changes

of varying degrees. All clinical and biochemical changes produced

in the study were reversed by the administration of magnesium. In

another review, conditions associated with abnormalities of magnesium

was reported by Barker (139). Seelig (41), in her review of the

requirements of magnesium by the normal adult, also reviewed the

different aspects of magnesium deficiencies and the role of magnesium

in disease. Magnesium in human nutrition was published as a home econo-

mics report by the U. S. Department of Agriculture in 1962 (140). The

scope of the report included the biological role of magnesium in humans

and a review of data on magnesium in tissues.


Techniques for Measuring Stable Magnesium

The difficulty of making accurate in vivo measurements of

magnesium has always been a limiting factor in its investigation (141).

It is almost entirely this measurement problem that has kept the knowledge

of magnesium years behind that of the other essential elements in the

human body.

This situation has not gone unrecognized. In 1939, an

editorial in the Journal of the American Medical Association (19)

summarized the status of the magnesium problem at that time:

So little is known of the function of magnesium in the
organism that clinically observable abnormalities in man
cannot at present be said with certainty to be due to mag-
nesium deficiency or to a disorder of magnesium metabolism.
The systematic study of magnesium metabolism by accurate
analytical and experimental methods is little more than
begun. Future investigations may be expected to add consider-
ably to our knowledge of this problem.






18

Within a few years, the development of newer and better

techniques for precipitating magnesium in fluids encouraged a few

researchers to examine magnesium levels in body fluids (142). In

1942, Haury (129) reviewed the variation in serum magnesium in health

and disease and concluded that there was not a good correlation between

abnormal serum levels and disease conditions. It was not known then

whether this was due to poor techniques in measuring magnesium, to the

inability of serum to predict accurately total-body magnesium or

disturbance of magnesium within the body, or to the fact that magnesium

levels actually remained unchanged in many diseases.

Nevertheless, during the next 10 years, investigators (143,

144) continued to measure serum and/or plasma magnesium levels. The

older methods of precipitating magnesium as ammonium phosphate or hydrox-

yquinoline (145,146) were replaced by magnesium determinations by the

titan yellow technique (147-150), which was used extensively for some

years. In 1962, an automated fluorimetric method was described by

Hill (151) as an accurate procedure for magnesium analysis. Emission

flame spectrophotometry was another method recommended by Alcock et al. (152)

as a suitable measurement procedure in a wide range of materials. A more

recent publication by Alcock (153) reviewed the development of methods

for the determination of magnesium. She suggests that the best method

for estimation of magnesium in biological specimens is the "atomic

absorption, atomic emission, or the magnesium ammonium phosphate

precipitation method."

In 1963, Maclntyre (8) recommended that the method of choice

for magnesium measurements is absorption flame spectrophotometry. Others

maintain that the most acceptable means for magnesium analysis is the use

of the atomic absorption spectrometer (154-157). Although the instruments











used in this type of analysis are too complicated for routine work in

small laboratories, many large hospitals are set up to do magnesium

and calcium measurements with the atomic absorption spectrophotometer

(158). A number of smaller laboratories send serum and urine samples

out to larger laboratories for analysis (159). Results of the latter

may take up to six days. It appears that the atomic absorption spectro-

meter is an accurate, although certainly not a simple,method for routine

analysis of magnesium in biological fluids.

However, as emphasized previously, most investigators are

uncertain as to what these fluid analyses mean. Thus, the question

which remains to be answered is whether there are ways other than analy-

sis of extracellular magnesium or examination of intake and excreta that

will provide information about magnesium's role in the human body which

is not available with current techniques.


Studies with Magnesium-28

In 1939, Greenberg (39) reviewed calcium, magnesium, and

phosphorus metabolism. He paid particular attention to the development

up to that time in the study of mineral metabolism made possible by

radioactive isotopes. Because of the "revolutionary nature and potential

importance of this subject," Greenberg departed from his usual approach

in a review article to digress on the usefulness of radioactive tracers

in animal organisms. He pointed out the advantages of.this "new tool"

for studying "absorption, permeability, storage, distribution, chemical

transformation, and paths of excretion of the mineral elements." Another

important advantage, he commented,is that in general only very small

doses of the substance need be administered, "thus avoiding the criticism










that the normal body mechanisms are being overtaxed."

Further describing the major advantages of radioisotopes,

Greenberg stated:

In many respects, it is more advantageous to use radio-
active than a non-radioactive isotope because the detection
of the radioactive isotopes is relatively simple . Also
non-radioactive impurities which may be present do not inter-
fere with the measurements and thus very tedious purification
processes can be avoided. Chemically, the radioactive isotopes
behave in identically the same manner as the natural mixture
of isotopes of the elements of the same atomic number because
they have the same nuclear charge.

Since Greenberg's report in 1939, many biologically signifi-

cant radioactive isotopes have been artificially produced to study the

importance of the basic elements to the human system. Yet, Greenberg

was one of the early workers to realize the important factors which

determine whether a radioactive isotope will be suitable for investi-

gative work. These factors, he said, are:

. the degree of stability as measured by the isotope's
half-life and the intensity of the radiation it gives off.
The duration of life of the radioactivity of the element
should be suitably short, so that it may be given in small
quantities as a tracer to animals and man without danger,
. but should be sufficiently long to enable the fate of
the element to be followed until it is eliminated by the
organism.

However, at the time of Greenberg's review, the only known

isotope of magnesium was 27Mg with a physical half-life of less than

10 minutes, a half-life too short to be of significant assistance in

studying magnesium. Consequently, Greenberg's review included results

of radioactive work only on calcium and phosphorus and none on magnesium.

Knowledge of magnesium's function in humans lagged far behind

that of its related elements until the discovery of a new isotope of

magnesium in 1953 by Sheline and Johnson (9) of Florida State University.











Up to that time six isotopes of magnesium were known. (See Figure 1.)

Naturally occurring magnesium is composed of three stable isotopes,

24Mg (78.80 per cent), 25Mg (10.13 per cent), and 26Mg (11.17 per cent).

The three radioactive magnesium isotopes known prior to Sheline and

Johnson's discovery were 22Mg with a 3.9-second half-life, 23Mg with a

12-second half-life, and 27Mg with a 9.5-minute half-life.

Normally, one finds that the half-lives of the isotopes of any

particular element get shorter the farther the isotope is away from the

stable isotopes of the element. (This is depicted as the horizontal

distance in Figure 1.) For example, 22Mg has a shorter half-life than

23Mg because it is farther from stable magnesium on the chart of the

nuclides. Following this "rule," one would expect that 28Mg would have

a half-life shorter than that of 27Mg. If this were the case, efforts

to produce this isotope would be of interest only to nuclear chemists

and physicists and would not be biologically useful. However, nuclear

scientists have found that another rule governs the stability of the

nuclides. So-called "magic numbers" of combinations of neutrons and

protons produce exceptionally stable atomic nuclei (161). These numbers

are 2, 8, 20, 28, 50, 82, and 126. Since 28Mg's atomic mass of 28 is

one of these numbers, it was predicted prior to the production of the

new isotope that the magic number rule would predominate and that 28Mg

would have a greater stability, i. e., a longer half-life, than 27Mg.

With this in mind, Sheline and Johnson went to the University of Chicago

where they used both a betatron and a cyclotron to produce 28Mg. The

nuclear reactions are: 30Si(y,2p)28Mg or 26Mg(a,2p)28Mg. In their report

of the production of 28Mg, the authors expressed the hope that 28Mg would





































M122 M923
2 Mg o
12 24.312 I y .T4,.59 4 A4


Isotopes of Magnesium (160).


Xs, ID 14sca6a 4
K,~ b'.311.34,0J


Figure 1.











find considerable use as a tracer (9).

Shortly after this first production of 28Mg, Brookhaven National

Laboratory (162) began producing it in a nuclear reactor by irradiating

an alloy of 6Li 26Mg with slow neutrons. The two reactions are:

6Li(n,t)4He and 26Mg(t,p)28Mg.

One of the first groups to use 28Mg experimentally as a tracer

was Glicksman et al. (163), who administered it intravenously to six

dogs and two patients. They found that the total-exchangeable magnesium

is much less than the theoretically calculated total amount in the body.

"This," they concluded, "would indicate that during the time of experi-

mental observation (24 hours), a large quantity of magnesium does not

enter into the metabolic pool and appears to be fixed."

In 1958, Zumoff and associates (164) used 28MgC12 to study

"the kinetic behavior of magnesium in intact human subjects." They gave

oral doses of the isotope to study excretion, exchangeable magnesium,

and turnover in plasma. Their results showed that "magnesium kinetics

in diabetes mellitus and myxedema reveal departures from the normal

pattern."

About the same time, Aikawa and his colleagues (165) began

an extensive study in both animals and man with 28Mg. Because of the

conflicting results reported in previous studies using stable magnesium,

Aikawa's group expected that the administration of the radioactive magnes-

ium would prove to be a better way of following the behavior of orally

administered magnesium. In 1959, Aikawa et al. (166-168) observed that

low specific activity 28Mg (t 0.5 pCi per mg magnesium) with the short

21.3-hour half-life made "impossible the use of a truly tracer dose."











Even so, these researchers continued 28Mg studies of magnesium

metabolism in both rabbits (169,170) and in humans (4). In several

reports in 1960, they summarized work to date which included: (1) urin-

ary excretion, tissue distribution, exchangeable magnesium, and the

effect of starvation on urinary magnesium excretion in rabbits and

(2) serum magnesium concentrations, plasma clearance, urinary excretion,

exchangeable magnesium, and urinary and fecal excretion of orally admin-

istered 28Mg in humans.

Other animal studies where 28Mg was used included a number in

1958 and 1959 by Brandt, Glaser, and Jones (171), Langemann (172),

Rogers and Mahon (173), MacIntyre (174), and MacIntyre, Davidsson, and

Leong (175). All these investigators used rats and measured the exchange-

able magnesium in major organs, plasma, bone, and urine. Uptake of 28Mg

in frog muscle was reported in 1960 by Gilbert (176), who found three

turnover components which he attributed to surface absorption, entry

into extracellular water and connective tissue, and entry into the cell.

He found that 75 81 per cent of the magnesium in muscle was non-exchange-

able and difficult to remove by diffusion.

Also in 1960, Graham, Caesar,.and Burgen (177) summarized

their work on gastrointestinal absorption and excretion of 28Mg in man

using oral administration of the isotope in three control subjects. The

same year, Silver, Robertson, and Dahl (178) reported a study of magnesium

turnover in human adults. They followed 10 adults (all but one had

hypertension) who received intravenous or oral doses of 28Mg ranging from

20 to 104 pCi. They had been maintained on a constant diet for five days

before and three days after the administration of the isotope. The











authors concluded that the results should be interpreted with caution

because of the "relatively low specific activity"' (0.07 to 0.12 pCi

per mg magnesium) of the 28Mg.

In 1961, MacIntyre et al. (179) reported on studies of

patients with clinical magnesium deficiency. They carried out balance

studies and bone and muscle biopsies using stable magnesium and used

28Mg in plasma turnover studies. They described 28Mg turnover as a

three-component system. Based on "previous animal work" this suggested

to them that "the three associated compartments were extra-cellular

magnesium with the fastest turnover rate, the vital organs with an inter-

mediate turnover, and muscle with the slowest turnover'. The concept that

bone magnesium can always act as a reservoir was refuted.

McAleese, Bell, and Forbes (180) reported on 28Mg experiments

in lambs in 1961. They used both oral and intravenous doses and followed

the distribution of the isotope in various tissues and excretory path-

ways. They expressed concern for the two limitations of the isotopic

compound: (1) the relatively short half-life and (2) the low specific

activity (0.45 to 0.75 pCi per mg magnesium).

Another approach to the study of magnesium metabolism was

taken by Aikawa et al. (181) who fed adult rabbits a controlled, deficient



1The dose of 104 pCi of the 0.07 pCi per mg preparation
resulted in the administration of =1500 mg of stable magnesium or
=4 x 1023 stable atoms. (The number of atoms of 28Mg in this dose,
=4 x 1012,is insignificant in comparison.) It is not known how many
atoms will upset the magnesium balance of the system being studied. It
is obvious,'however, that the fewer the number of atoms of magnesium
injected instantaneously-into any living system, the less the chances are
of producing chemical toxicity or of disturbing the ion balance.










diet containing stable magnesium and at weekly intervals made an esti-

mate of total-exchangeable magnesium using 28Mg and an isotope dilution

method. At the end of the experimental period, various tissues were

analyzed for magnesium. The deficient diet caused a slight loss in

body weight, a decrease in serum magnesium, a decrease in urinary magnes-

ium excretion, and a progressive decline in total-exchangeable magnesium.

However, the magnesium content of muscle, skin, kidney, heart, and liver

did not change; that of the lung fell by 25 per cent and that of bone

by-only 15 per cent.

This work by Aikawa and his group(181) prompted several perti-

nent comments in an editorial on magnesium metabolism in 1962 in Nutri-

tion Reviews (182). The editor commented that:

(1) It is unfortunate that carrier-free 28Mg is not available
and

(2) . had a true magnesium balance been made (by Aikawa),
it would have been possible to interpret the data on
total-exchangeable magnesium in a more meaningful way.

Studies with 28Mg in the cirrhotic and the alcoholic followed

naturally from the background information reported by Flink (88) and

others on the possibility of magnesium deficiency in these conditions.

Martin and Bauer (183), having found no clear-cut correlation of sympto-

malogy with serum levels of magnesium in these disease states, attempted

to assess exchangeable magnesium using 28Mg. The preparation used to

study seven controls, five cirrhotics, and four acute alcoholics was of a

much higher specific activity (=30 pCi per mg magnesium) than had been

used previously. Four of the five cirrhotics and all of the acute alco-

holics had exchangeable magnesium values below normal.

The higher specific activity 28Mg was also used by Lazzara's










group (184) to evaluate magnesium tissue distribution, kinetics, and

turnover in dogs. In 1962, they reported that important tissues which

did not reach equilibrium after injection of the isotope were the brain

and spinal cord, cortical bone, and skeletal muscle.

Ginsburg, Smith, Ginsburg, Reardon, and Aikawa (185) continued

research of magnesium metabolism in humans and in rabbits and, in 1962,

reported on results of a study in which they attempted to: (1) devise

a reliable method for determining magnesium in erythrocytes; (2) relate

erythrocyte magnesium concentration to reticulocyte count; (3) study the

in vitro uptake of 28Mg by erythrocytes; and (4) study the 28Mg uptake of

various tissues in experimental animals with reticulocytosis induced by

phenylhydrazine. This approach was undertaken because these investi-

gators felt that the "current paucity of information concerning magnesium

metabolism in erythrocytes is due in part to the lack of a reliable method

for determining magnesium in red cells and in part to the fact that a

radioactive isotope of magnesium suitable for tracer studies has only

recently become available."

In 1963, Avioli, Lynch, and Berman (186) reported the first

study in a series on 28Mg kinetics in normals and selected disease states.

They gave intravenous doses of a relatively high specific activity 28Mg

(=17 pCi per mg magnesium) to 10 normal subjects, five patients with

Paget's disease, three hypothyroid, and five hyperthyroid patients. A

digital computer compartmental analysis technique was used to identify and

quantitate exchangeable magnesium in bone, in extracellular fluid, and in

muscle.

Also in 1963, Petersen (187) described the close relationship










of the two major intracellular cations, magnesium and potassium. He

studied the turnover of the two elements in magnesium deficiency and

found indications that the magnesium ion occurs in pools differing in

size and turnover rate. They used a two-compartment model to describe

the turnover of 28Mg in plasma. Petersen concluded that the "total

24-hour exchangeable magnesium was reduced by more than 50 per cent in

magnesium deficiency, due mainly to a decrease in size of a slow pool,

which is believed to include skeletal magnesium."

Mendelson et al. (188) like Martin and Bauer (183) were not

satisfied with the relationship between serum magnesium levels and the

onset of withdrawal symptoms in alcoholics. They suggested that "although

alcohol withdrawal symptoms may be associated with total-body deficit

of magnesium incurred through poor dietary intake, it is also possible

that changes in distribution of magnesium in the extra-cellular intra-

cellular compartments of the body as well as in bone may occur without

concomitant total-body deficit." The authors used 28Mg to determine

exchangeable magnesium in alcoholic patients and,in 1965, reported signi-

ficantly lower exchangeable magnesium values for "tremulous patients" than

for control subjects.

In a report the same year, Wallach and co-workers (189)

discussed results of "radiomagnesium kinetics in normal and uremic

subjects." Using analog computer analyses, they fitted a three compartment

model to plasma specific activity data following intravenous doses of

28Mg. They concluded that hypermagnesemia influences the mechanisms

responsible for cellular transport of magnesium so that fractional influx

of cell magnesium is reduced.

In 1965 and 1966, Aikawa and his group used 28Mg (=40 pCi per mg










magnesium) to study the effect of 2,4-dinitrophenol (190) and sodium

salicylate (191) on magnesium metabolism in the rabbit. About the same

time, Aikawa (192) published a review of "recent developments"in the study

of the role of magnesium in biologic processes. He emphasized that 28Mg,

although expensive and in short supply, had already contributed substanti-

ally to the knowledge concerning the dynamics of magnesium turnover. He

concluded that:

In the final analysis, the ultimate explanation of the fact
that the magnesium ion alone is operative in such diverse but
fundamental cellular processes must be based on the unique
atomic structure of this element. Just how it is unique remains
to be ascertained.

In 1966, Wallach et al.(13) expanded on their study of magnesium in

normal and uremic patients. They gave intravenous injections of 28Mg with

a specific activity of 16 pCi per mg of magnesium to six control subjects

and to six patients with chronic renal disease and moderate to severe

azotemia. The authors utilized conventional analog and digital computer

techniques to analyze plasma concentrations and urinary data. From the

results they proposed a three-compartment model for magnesium transport

in humans.

A similar approach for evaluating magnesium dynamics in vivo

was reported by Avioli and Berman (5) in 1966. Using a 28Mg preparation

with a specific activity of =11 uCi per mg magnesium, these workers

observed the levels of activity in the plasma and excreta in 15 normal

volunteers up to six days after injection. Plasma disappearance of 28Mg

was fitted to a sum of three exponentials model.

In 1966, Yun et al. (11) reported a study of turnover of

magnesium in controls and in patients with idiopathic cardiomyopathy

and congestive heart failure. They said that the reason that the daily










rate of turnover of magnesium was not previously known was because

earlier data, derived from either non-isotopic techniques or by radio-

isotope studies, "are all overestimations because of the loading effect

of the dose of 24Mg administered." Yun and associates used 28Mg with a

specific activity of =200 pCi per mg of magnesium, many times higher than

that previously available. In two controls and four patients, they

measured 28Mg in urine, feces, and plasma up to 70 hours after intra-

venous administration and up to 40 hours after an oral dose.

Skyberg et al. (193) demonstrated the usefulness of 28Mg in

diagnostic procedures in 1968; he used the tracer to show that hypo-

magnesemia was present in an infant and that it was due to a defect in

the intestinal absorption of magnesium. Magnesium-28 (specific activity

of -30 to 500 uCi per mg magnesium) was given orally and excreta was

measured for radioactivity. The numerous routine tests given the infant

including electrocardiography, electroencephalography, and electromyo-

graphy were normal. The urine was chemically and microscopically normal

and the spinal fluid had normal protein concentration and normal cell

count. All blood examinations were normal including the serum concen-

trations. However, by analyzing the urine and feces after peroral and

intravenous administrations of 28Mg, it was found that the child had a

defect in gastrointestinal absorption of magnesium.

Another use of 28Mg (3.2 and 10.6 pCi per mg magnesium) to

examine differences in pathological and normal adults was reported in

1967 by Raynaud and Kellershohn (194). Significant differences were

observed between eight persons described as normal and 22 patients in

plasma, urine, and feces analyses. Seventeen of the patients studied











suffered from nornocalcemic tetanys.

In 1968, Chon6, Jahns, and Misri (37) used 28Mg in an attempt

to define as precisely as possible the proportions of magnesium in

various parts of the human body. Eleven normal subjects received intra-

venous doses of the isotope and were followed up to 120 hours. For the

purposes of localization of magnesium, the body was divided into five

parts; the head, the thorax, the upper abdomen, the lower abdomen, and

the lower extremities. A sodium iodide, thallium-activated (NaI(Tl))

crystal counter was used for the body counts. Whole-body retention was

calculated from these sequential measurements; the data indicated that at

least two compartments were involved in the turnover of 28Mg.

The most recent reports found in the literature on the use

of 28Mg include two in the August, 1969, issue of the New York Academy of

Sciences. Aikawa and David (195) summarized their team's past and also

the most recent results of experiments using 28Mg as a tracer in rabbits.

The investigators report that recent results with the isotope to study

segments of the small intestine from deficient and normal animals suggest

that the "magnesium-absorbing ability of both proximal and distal areas

of the small intestine is enhanced by magnesium deficiency and is not

energy dependent."

Wallach and Dimich (196) reported on turnover studies in hypo-

magnesemic states in which 50 100 pCi of 28Mg with a specific activity

of =17 pCi per mg magnesium was given intravenously. They determined the

plasma specific activity and urinary excretion of the isotope and total

magnesium for 72 hours after injection. The experimental group consisted

of eight alcoholic subjects with hypomagnesemia, three alcoholic subjects





32




with normomagnesemia, one hypomagnesemia subject with periostitis of

unknown etiology and hypercalcemia, and one normomagnesemic subject

with chronic, severe malabsorption who had hypomagnesemia prior to treat-

ment with magnesium infusions.

Pertinent details of many of these recent 28Mg studies will be

discussed later in the results chapter of this study.














CHAPTER III

MATERIALS AND METHODS


Magnesium-28

In the literature review, it was pointed out that in 1939 the

only known radioactive isotope of magnesium was 27Mg with a physical

half-life of less than 10 minutes (39). Although the possibility of

using 27Mg was alluded to, there is no evidence that it was ever used as

a tracer in biological investigations. Its use in this manner is doubt-

ful since it has such a short physical half-life. Normally, tracer

studies are best carried out with an isotope with a half-life on the

order of days, weeks, and sometimes, months.

Although 28Mg has a half-life of only 21.3 hours, it has been

used as a suitable isotope in biological work since shortly after it was

first produced in 1951 (9). Magnesium-28 and its radioactive daughter,

aluminum-28 (28A1), have a number of energetic gamma rays which can be

readily detected by most gamma-counting systems. (See Figure 2.) Alumi-

num-28 with a half-life of 2.24 minutes; rapidly attains secular equili-

brium with 28Mg.

In this study, 28Mg was obtained from Brookhaven National

Laboratory where it is produced in a Van de Graaff accelerator by the

triton proton reaction (26Mg(t,p)28Mg) (197). A 1/4-inch diameter

metallic rod target enriched to 99.77 per cent 26Mg is bombarded with a

beam of 3.4 MeV tritons. After bombardment, a 0.001-inch thick layer








































1.620 MeV
1.373


.972


.031
0


"" -..- 1.779 MeV
Y5 1.373 4.7
Y6 1.589 4.7

28AI B 2.856 100.0
Y 1.779 100.0
Y




0
g28S Stable





Figure 2. Radioactive Decay Scheme of Magnesium-28 and Its Radioactive
Daughter, Aluminum-28. (Based on the Report of Alburger and Harris
(162).)


Radiation Energy Equilibrium
Type (MeV) Intensity
(% per decay)
28Mg 1' .459 95.0%
.212 5.0

Y, .031 95.0
YZ .401 35.9
Ya .941 35.9
v. I "42 40 n











is etched from the end of the rod. This method produces a higher speci-

fic activity than other production methods.

The material was received as 28MgC12 in 0.01 to 0.1 normal

HC1. It was diluted in the laboratory to the desired concentrations

with normal saline, checked for radionuclide purity, and then auto-

claved before administration. The administered material had a specific

activity of 200 300 pCi per mg of magnesium.


Experimental Conditions and Techniques

Fourteen normal subjects between the ages of 28 and 71 and

11 subjects with various disease conditions were measured in seven

groups over a period of 21 months. Two to six subjects were followed

at a time. Each subject was measured by whole-body counting prior to

the injection of the 28Mg to determine the background level of 40K,

137Cs, and any previously administered diagnostic radioisotopes.

Plasma and red blood cell stable magnesium analyses were made prior to

injection of the isotope according to routine procedures of the Clini-

cal Laboratories, J. Hillis Miller Health Center (198). None of the

subjects received medications containing magnesium during the study; no

other restrictions were placed on the quantity and composition of

intake.

One milliliter (ml) of the tracer solution was administered

through the anticubital vein by the "butterfly" infusion method to

subjects in the first six groups. One pCi was given to each subject

in group 1, while 6 to 10 pCi was administered in groups 2 through 7.

In group 7, the isotope solution was injected directly into the vein

since with this method there is less loss of radioactivity.











Whole-Body Retention Measurements

Whole-body retention was followed in a 4-pi liquid scintil-

lation whole-body counter for as long as there was measurable activity.

In group 1, whole-body counts were made five times during the first two

24-hour periods, three times during the next two 24-hour periods, and

then every 24 hours through the seventh day. In groups 2 through 7,

counts were made twice during the first 24 hours after injection and

then every 24 hours (except Sunday) through the tenth day. A summary

of the study parameters is shown in Table 1.

Before measurement in the whole-body counter, each subject

dressed in a cotton "scrub suit." Subject counting times ranged from

0.1 to 10 minutes. Prior to and just after counting each subject, both

a 5-minute background count and a 2-minute count of a reference source

were made. The reference source is a nominal line (or "rod") source

consisting of a 6-foot long plastic tube filled with KC1. It is used

to correct for any variation in overall counter efficiency.

A unit-density phantom (199), containing an amount of 28Mg

approximately equal to that given to the subjects, was counted under

the same conditions as the subjects. The phantom was used to measure

the physical decay of the isotope and to evaluate any resolving time

losses.



1The phantom in groups 1 through 6 consisted of an aqueous
solution in a 50-liter polyethylene carboy. In group 7, a sealed
source of 28Mg was placed in the center of a phantom (designated as
"Tuboy") consisting of a bundle of sealed, sugar-filled polyvinyl
chloride tubes. The phantoms provided similar internal.self-absorp-
tion and scattering of the radioactivity as a human subject and thus
gave comparable count rates and spectrum shape.











TABLE 1

SUMMARY OF STUDY GROUPS


Number of Subjects


28Mg
Administered
(PCi)


1.27

10.00

9.30

6.60

9.70

5.50

10.00


Urine

Urine

Urine

Urine


Urine,feces

Urine,feces

Urine,feces,
sweat


Total


*Includes replication of one normal subject from group 1.
**Includes replication of two patients from group 1.
***Includes replication of one normal subject from group 4.


Group No.


Total


Excreta
Measured


Time
Followed
(days)


Other

2

3**

3

0


Normal


2***


2

4

2**










A shadow shielded NaI(Tl) crystal scintillation whole-body

counter was also used in several of the study groups. Although its

counting efficiency is lower than that of the 4-pi system, it provided

the following useful information:

(1) Because its energy resolution is greater than that of

the 4-pi counter, it was used as a means of identifying unusual back-

ground levels in several patients2;

(2) Since measurements with it are made with the subject in

a sitting position, it was used as an additional means of calculating

whole-body retention on one patient who was unable to lie flat to enter

the 4-pi counter;

(3) Since the detector has some collimation, it was used

in group 7 in an attempt to see if localization of the isotope took

place in the body; and

(4) Also because of its high energy resolution capacities,

it was used in group 7 to determine if the 28Mg 28A1 parent daughter

pair remains in equilibrium throughout its retention in the body.

Five counting positions (to be discussed later) were used for

the group 7 measurements; counting times ranged from 1 to 10 minutes.

The "Tuboy" phantom, described previously, was also counted

each time a set of subjects was counted on the crystal counter. Another

phantom, designated as "Tubman" (199), was used in this study. This

phantom is constructed in seven segments with varying thicknesses to



2It was found that two patients had residual radioactivity due
to having received 60Co in a vitamin B-12 test several years earlier.










simulate the various parts of the human body. The isotope can be distri-

buted throughout the phantom by inserting radioactive sources into

numerous channels within the phantom. Tubman was used to determine the

amount of contribution of the isotope from one part of the body to

another so that accurate corrections for interference could be made.

Excreta Measurements

Twenty-four-hour cumulative urinary excretion of 28Mg was

measured in all groups. An aliquot of the collection was taken for

counting purposes. If the total volume was less than the specified

aliquot, the counting container was filled with distilled water to the

required amount. Urine samples were counted as 780 ml aliquots on a

4-inch by 4-inch NaI(Tl) crystal counter in groups 1 through 4. In

groups 5 through 7, they were counted as 1000 ml aliquots in a large

volume well counter. Counting times ranged from 1 minute to 30 minutes

depending on the amount of radioactivity in the sample. Urine standards

were made up at the same time as the doses for the subjects and phantoms

were prepared. Urine standards with 0.1, 1, and 10 per cent of the

average dose given to the subjects were prepared and counted along with

each set of urine collections.

Fecal excretion was measured in groups 5, 6, and 7; the

total-daily collection was counted for 28Mg in the large volume well

counter.

Measurements of 28Mg in sweat were made in group 7 using the

iontophoresis technique (200). With this technique, pilocarpine is

iontophoresed into the skin by means of a 2.5 milliamp electric current.

In this study, a 2-inch by 2-inch area on the subject's left forearm

was covered with pilocarpine and subjected to the electric current for











10 to 12 minutes. After removal of the iontophoresis electrode, a

pre-weighed 2.75-inch filter paper was transferred to the area, covered

with plastic film, and left in place to collect sweat for 45 minutes.

The filter paper was removed, weighed, and counted on a 4-inch by 4-inch

NaI(Tl) crystal counter. Counting times ranged from 5 to 15 minutes.

Sterile techniques were used throughout the procedure to prevent

possible contamination of the filters with 28Mg from sources other than

sweat.


Instrumentation

The four detection systems used in this research are described

in this chapter and summarized in Table 2.

4-Pi Liquid Scintillation Whole-Body Counter

The University of Florida whole-body counter (62,201) is a

scintillation counter with an approximately 4-pi geometry. It is

located on the ground floor of the J. Hillis Miller Health Center in the

Radiation Biophysics Graduate Program Facility. A floor plan of the

entire facility is shown in Figure 3. Room 17 houses the whole-body

counter and output equipment, while supporting laboratories, sample

preparation areas, and other counting facilities are located in the

adjacent rooms. Figure 4 is a picture of the whole-body counter as seen

from the entrance to the counting room.

Figure 5 shows a closer view of the counter with a subject

preparing to enter the counting chamber. Subjects are centered longi-

tudinally in the counter in a supine position. The detector consists of

liquid scintillator in six tanks that make up an annular configuration

which essentially surrounds the reclining subject. Twelve 16-inch











TABLE 2


SUMMARY OF DETECTION SYSTEMS


System


4-Pi Liquid
Scintillation
Whole-Body Counter


Major Components and Manufacturer

Detector and shield Packard Instrument Co.
Downers Grove, Ill.
400-channel analyzer, Packard Instrument Co.
three-channel scintil-
lation spectrometer


Whole-Body Retention
Measurements


4-inch by 9-inch Harshaw Chemical Co. Whole-Body Retention
Shadow-shielded NaI(Tl) Crystal Cleveland, Ohio Measurements 7
NaI(Tl) Crystal 400-channel analyzer Packard Instrument Co.
Whole-Body Counter Shadow shield and University of Florida Study of Localization 7
supporting frame


4-inch by 4-inch Harshaw Chemical Co.
'NaI(Tl) Crystal NaI(Tl) Crystal Urine Analysis 1-4
Counter 400-channel analyzer Packard Instrument Co.
Shield Custom Fabricated Sweat Analysis 7


Large Volume Detector and shield Custom Fabricated Urine and Feces
Well Counter Two-channel scintil- Packard Instrument Co. Analyses 5-7
lation spectrometer


1-7


Use and Study Group



















I 1


12 13 14 18


0 19 28




6l i \ U



2. Office
S 2, 3. Secretaries' Office
5 4 4. Water Closet
11C 7 5. office
smm -,-,_- 6. Low-Level Counting Laboratory
7. Waiting Room, Calculation Area
8. Dressing Room
9. Shower
10. Dressing Room
2 j i11. Computing Room
12. Graduate Students' Desk Area
13. Storage
14. Sample Preparation
S217. Whole-Body Counter Laboratory
18. Storage
19. Graduate Student Desk Area
20. Office


Figure 3. Floor Plan of the Radiation Biophysics Graduate Program
Facility.


I- I














I1'


4-Pi Liquid Whole-Body Counter Laboratory.


Figure 4.




















































Subject Preparing to Enter the 4-Pi Liquid Whole-Body Counter.


Figure 5.











diameter photomultiplier tubes are positioned so that two are on each

tank of scintillation fluid. (See Figure 6.)

The entire detector is contained in a 6-inch thick shield of

low background steel with a 1/8-inch thick lead lining. Output signals

from the photomultiplier tubes are fed into one of two types of sciatil-

lation spectrometers, a Packard model 3003 three-channel scintillation

spectrometer and a Packard model 115 400-channel analyzer. In Figure

7, the three-channel analyzer is shown on the left and the 400-channel

analyzer is in the center.

In study groups 1 and 2, the 400-channel analyzer was used

because the three-channel system was inoperable. The three-channel

analyzer was operative for use in study group 3 6; however, it was

discovered that resolving time corrections which were necessary in

groups 3 6 could be attributed to the analyzer system rather than to

the counter itself. Therefore, the 400-channel analyzer was used again

for group 7.

Figure 8 shows the signal diagram of the counting system when

the 400-channel analyzer (MCA) is used. Digital output from the system

was obtained by means of a high speed parallel printer and also by inter-

facing an IBM 526 printing summary punch through a Packard model 70

parallel serial converter.

The three-channel analyzer consists of three independent

single-channel analyzers each of which were calibrated to measure the

137Cs, 40K, and the 28Mg 28A1 energy regions. Digital counts were

recorded manually from each scaler.

NaI(Tl) Crystal Whole-Body Counter

The shadow-shielded crystal whole-body counter assembly



















































Figure 6. One Side of the 4-Pi Liquid Whole-Body Counter Showing Six Photomultiplier Tubes
and Steel Shield.




















































4-Pi Liquid Whole-Body Counter Instrumentation.


Figure 7.

















A A2

A4

Rs 82

B4

C2

9 C4



PM PHOTOMULTIPLIER TUBE
PA PREAMPLIFIER
MCA MULTI CHANNEL ANALYZER
IN SIGNAL INVERTER


Figure 8. Signal Diagram of the 4-Pi Liquid Whole-Body Counting System.











(See Figure 9) consists of a 4-inch by 9-inch NaI(Tl), stainless steel-

cased crystal and four 3-inch photomultiplier tubes. The assembly is

enclosed in a lead-filled steel container with a thickness equivalent

to 3.11 inches of lead. No other shielding is used in this counter.

The entire assembly is mounted on a rigid, but movable, steel frame,

which provides a means of gradual rotation of the detector face

through an angle of 90. The crystal shield assembly can also be

raised or lowered a distance of 13 inches. In addition, the crystal

can be moved from a position flat with the end of its shield to a

position 2 inches inside the shield.

The various configurations make it possible to achieve a

number of convenient counting geometries. The subject lies on an

adjustable bed as shown in Figure 9 (the position for a total-body

count). Figure 10 diagramatically summarizes the counting geometries

used in this study.

In addition to the whole-body count position shown in Figure

9, the four other positions used in this research (head, chest, abdo-

men, and legs) are demonstrated by an actual subject in Figures 11 14.

The output system from this counting system consists of

essentially the same equipment as that diagrammed in Figure 8.

Large Volume Well Counter

Radioactivity in urine and feces collections was measured in

an organic scintillation detector with a large volume chamber (202).

(See Figure 15.) The sample is inserted into the center of a right

circular cylinder, 4.5 inches in diameter by 12 inches long. Surround-

ing the sample chamber is a cylindrical tank containing the scintillator;

















































Figure 9. NaI(T1) Crystal Whole-Body Counter: Whole-Body Count Position.















































Position


Angular and Distance Designation


a b c d a+i s 8

Whole-Body 16.5 21.0 4.5 17.0 450 90 00
Head 20.0 21.0 4.5 11.0 600 900 50
Chest 16.5 21.0 4.5 17.0 450 900 50
Abdomen 16.5 21.0 4.5 17.0 450 900 00
Legs 16.5 21.0 4.5 17.0 450 900 00


Figure 10. Geometry of
Counter (201).


Subject Counted on the NaI(T1) Crystal Whole-Body


I I

I-,-C-


















































Figure 11.


NaI(Tl) Crystal Whole-Body Counter: Position for Head Count.



















































Figure 12.


NaI(Tl) Crystal Whole-Body Counter: Position for Chest Count.






































Ur

























Figure 13. NaI(T1) Crystal Whole-Body Counter: Position for Abdomen Count.





































Un
iU1


















Figure 14. NaI(T) Crystal Whole-Body Counter: Position for Legs Count.



Figure 14. NaI(Tl) Crystal Whole-Body Counter: Position for Legs Count.




































































Figure 15. Large Volume Well Counter.











four 5-inch photomultiplier tubes face the end of the tank. The tanks

and photomultiplier tubes are mounted in a 3.37-inch steel plate shield.

Read-out equipment consists of a single-channel analyzer with wide

window capacity, a scaler, and a timer.

NaI(Tl) Crystal Counter

Magnesium-28 in urine samples in groups 1 through 4 and in

sweat samples in group 7 were counted with a 4-inch by 4-inch NaI(T1)

crystal counter. (See Figure 16.) The crystal is housed in a cylindri-

cal cast steel shield, 28 inches high by 36 inches in diameter. The

shield has a 6-inch thick steel equivalent shielding on all sides.

Again, the output system is essentially that shown in Figure 8.


Data Analysis Techniques

Data was recorded manually from the three-channel analyzer,

on paper tape from the 400-channel analyzers, and in group 7 only it

was punched on cards. The data punched on cards represented totals in

the 400-channel analyzer channels and was submitted for summing (inte-

gral counts) of the 28Mg and 28A1 energy regions on an IBM 1800

computer.

Subsequent calculations were performed both with a conven-

tional desk calculator and with Fortran IV programs run on the IBM

360/65 computer by means of a remote 2741 computer terminal located

in the whole-body counter laboratory.

Routine reduction of all counts to net counts per minute

was made on all data. Resolving time corrections were made on the net

subject counts during the first several days in study groups 3 6.

These corrections were made by plotting the phantom measurements versus

































i: ~Tul~s :
i 00


Figure 16. NaI(T1) Crystal Counter.











time after "injection" on semi-logarithmic graph paper. The straight-

line portion of the plot (observed during the last week of measurements),

which corresponds to the portion of the curve where no resolving time

was necessary, was extrapolated back to t = 0. The ratio of difference

between the extrapolated line and the actual line at any time, t, was

used to correct the net subject count.

Further analysis of the retention and excretion data was

carried out according to the method reported by Richmond (203). The

following equation was used to determine whole-body retention:

WBtx/(Stx/Sto)
WBRtx = or
WBto

WBtx/ Stx
WBRtx =
WBt / St
o o

where

WBRt = whole-body retention at time t in counts per
minute (cpm),

WBtx = whole-body activity at time tx in cpm,

WBto = whole-body activity at time to in cpm,

Stx = standard activity at time tx in cpm, and

St = standard activity at time to in cpm.

The whole-body activity was determined directly by whole-

body counting. The standard activities at the various time, tx, were

calculated from a best-fit curve of the phantom measurements. A

computer linear least squares program, Biomedical Computer Program,

BMD02R (204) was used to obtain the phantom decay curve.










Thus,

Stx'/Sto' = Stx'/(Stx'.e-Xt) = e-Xt;

where

St and St are values of St and St predicted from the
X 0 X 0
fitted curve.

The whole-body retention equation then reduces to:

WBRtx = WBtx. e+At/WBto.

By using this technique, the phantom could be measured

only once with each daily set of subjects rather than each time an

individual was counted. Therefore, since the phantom was cumbersome

and the measurements are time-consuming, this technique proved to be an

efficient one. It also produces more statistically accurate values

when an isotope with a short half-life is used. A time lapse of as

much as 30 minutes between a phantom and a subject with 28Mg can

produce an error of 2 per cent. A time lapse of two hours produces

a 7 per cent error.















CHAPTER IV

RESULTS AND DISCUSSION


Whole-Body Retention of 28Mg in Normals

In Figure 17, whole-body retention, expressed as per cent of

the administered dose, for the 13 normal subjects, age 28 to 71, is

plotted by study groups. The subjects included five females, age 43 to

59, and eight males, age 28 to 71.

The two subjects in study group 1, NA and NC, were followed

for the shortest period of time, 165 hours, since they received only

1.3 pCi of 28Mg. This dose level was selected to initiate the study

since it was considered the optimum amount for measurement by the

whole-body counting system. In order to better define the shape of the

curve during the first few days, frequent measurements were made on the

subjects in this group.

The results of group 1 showed that at least two components

are involved in the retention (or turnover) of 28Mg. It was apparent

that a larger dose was needed to permit measurements over a period of

time long enough to accurately establish the second component. Calcula-

tions showed that a factor of eight (23) increase in the dose would

permit meaningful measurements for an additional three days (-three

times the physical half-life of the isotope). Therefore, in subse-

quent study groups the dose was increased to the order of 7 10 pCi

and retention and excretion measurements were possible up to 220 hours.

61










































































20 40 60 80 100 120 140 160
POST INJECTION TIME, HOURS


Figure 17. Whole-Body Retention of 28Mg: Normal Subjects.











The retention results for study groups 1 and 2 define a

fairly smooth, continuous function and have little within-group varia-

tion. In contrast, in groups 3 and 4 there is more within-group

variation and, particularly in group 4, there is a greater departure

from a smooth function. In study group 7, there is good agreement in

the results of the two individuals and it is significant that the data

again more closely resembles that of groups 1 and 2.

Some of the differences in the results of the study groups

can be attributed to differences in instrumentation. The 400-channel

analyzer was used for study groups 1, 2, and 7, while the three-channel

analyzer was used for groups 3 and 4. It appears that there is more

precision in results when the 400-channel analyzer is used. This

assumption is supported by the fact that while resolving losses were

evident for initial high count rate measurements with the three-channel

analyzer, this was not the case for the 400-channel analyzer even with

doses as high as 10 VCi. In addition, the computational steps required

to make resolving loss corrections automatically introduces another

component of variance in the data for groups 3 and 4. Finally, any

error introduced in applying the resolving time corrections would affect

the results in two ways. The magnitude of the high count rate obser-

vations would be directly affected and also all of the observations

would be affected because the value at t = 0 (see page 59) is used as

a denominator in computing each retention value.

However, in spite of the greater variability in some of the

study groups, the average retention values are approximately the same

in all groups.











Two subjects, NC and NH, were measured twice and were used as

a means of establishing the degree of reproducibility of this measure-

ment method. These replications can be seen in the two plots in Figure

18. Subject NC, who was in groups 1 and 2 (time lapse of four months),

had almost identical retention curves with the exception of one point at

165 hours. Because this point represented the last measurement made in

group 1 and the level of activity was low, considerably more counting

error is associated with it than with the measurement made at the same

post-injection time in group 2.

Subject NH was measured both in study groups 4 and 7 (time

lapse of one year and two months). His retention curves are also very

similar with the exception of the 20- and 40-hour points which, as

mentioned previously as a part of the group 4 measurements exhibited

a departure from a smooth function.

Analysis of the results of all of the study groups showed no

pattern due to sex or age. Therefore, both male and female subjects

were considered as representative of a normal population and the results

of all groups, ages, and both sexes were pooled for further analysis.

Determination of the Model for Biological Turnover of 28Mg

A number of estimates of magnesium turnover have been

attempted, both with stable magnesium and more recently with 28Mg. As

discussed in the literature review, researchers in these studies have

been concerned with establishing an accurate biological half-life (or

turnover) of the element in order to provide information on its meta-

bolism in normals and to study its behavior in disease conditions.

The formulation and testing of a model for the retention

data followed suggestions by Mones Berman (205). Berman states that




































100- SUBJECT NC, AGE 36 .


90-





700- NCz

70 REPLICATION GROUP DATE MC
L (NC) 6-69
S2.Z(C2) 2 10-69


p 0 20 40 60 80 100 120 140 S160 18 200 220
z
I-






0 too- SUBJECT NH ,AGE 41, d


90.



80
S-NH


70- REPLICATION GROUP DATE
L(NH) 4 12-69
2.(NHM) 7 2-71


0 20 40 60 80 100 120 140 160 180 200 220
POST-INJECTION TIME HOURS








Figure 18. Replications in Measurements of Whole-Body Retention
in Two Normals.











the first step in the formulation of a model is to choose the type or

class of model applicable. Quite often in tracer kinetics, the model

can be described by a set of linear differential equations, the solu-

tion for which are sums of exponentials (205). Others state that

"clearance curves for radioactive tracers are fit more simply by one or

more negative powers of time"(206).

The two models when used to express retention can be repre-

sented by the following general forms:

Power function: R = At-a + Bt-b + ... + Xt-x.

Sum of exponentials: R = Ae-at + Be-bt + ... + Xe-xt.

A majority of researchers (186,194,196,203,207,208) prefer

the latter model for compartmental analysis. Furthermore, the semi-

logarithmic plot of the data in this research (Figure 17), produced

an exponential-type curve. Therefore, a sum of exponentials model was

selected as the initial approach.

The next step in the analysis was to determine the order

(i.e., the number of independent functions) of the model. Some resear-

chers report a three compartment turnover of 28Mg in serum during the

first 20 hours after injection (196). Others (5,209) predict as many

as ten compartments (with half-lives from 0.623 to 5197 hours) from

turnover of 28Mg in serum.

Visual inspection of the data in this research showed that at

least two compartments were involved in the turnover. However, it is

difficult to resolve more than two components since: (1) the whole-

body retention technique is relatively insensitive to multiple changes

in slope during the first day or so of observation, and (2) the short











physical half-life of the isotope made it extremely difficult to

identify a component with a half-life greater than the total observation

time in the experiment (220 hours).

Berman recommends that for compartmental analysis, the model

with the smallest number of compartments compatible with the data

should be chosen. Therefore, a two compartment model was chosen. The

individual data points were then analyzed by computer using a non-

linear least squares method (Biomedical Computer Program, BMDX851) (210).

The sum of exponentials model used to describe the quantita--

tive 28Mg turnover in normals is:

R = Ae-Xlt + Be-X2t.

The dependent variable,

R = the per cent retention at any time, t, and the independent

variable,

t = the post-injection time in hours.

Parameters A, B, X1, and X2 are as follows:

A = the per cent of the administered dose being excreted

directly from the first compartment;

B = the per cent entering into and being excreted from the

second compartment;

Xi = the turnover rate for the first compartment (in hours);



IThis program obtains a weighted least squares fit, R =
f(tl, ... ti; Pl, .. Pi) + e, of a specified function f to data
values tl, ... ti, R by means of s stepwise Gauss-Newton iterations
on the parameters pl, ... Pi. Within each iteration, parameters are
selected at any given step depending on which one, differentially at
least, makes the greatest reduction in the error sum of squares.











A2 = the turnover rate for the second compartment (in hours).

Biological half-lives for the two compartments can be derived

from this expression and are equal to 0.693/X1 and 0.693/X2.

Figure 19 shows the data points of all the normals. The

retention equation obtained in this study by the non-linear least

squares method is:

R= 8e-0.129t + -0.00128t

This average equation is plotted as the solid line in the

Figure. The broken lines represent the estimated 95 per cent range of

the data or what can be called the "normal retention band." The first

and second coefficients of the retention equation, 8.5 and 91.5, repre-

sent the quantities involved in the turnover of the two compartments.

Turnover rates are 12.9 and 0.128 per cent per hour for the two compart-

ments, respectively. The second turnover rate can also be expressed as

3.07 per cent per day.

Biological half-lives of 5.4 2.2 hours (1 s. d.) for the

first compartment and 540 35 hours for the second compartment were

calculated from the rate constants in the exponents of the fitted

equation.


Excretion of 28Mg in Normals

Magnesium-28 excretion measurements were made on all subjects

in this study in addition to whole-body retention measurements in order

to examine 28Mg balance. One should be able to account for the entire

activity (100 per cent of the administered dose) at any time after

administration of the isotope if all excreta are measured and if both

the whole-body retention and the excreta measurement techniques are

accurate.



















0


0~


5- 0
5.
-5


24

0r


- -


0
-5
* ~ 0
-5
-5
4
a


-5 0
- 5.
5.. 5. -


-5 ~ 0
-5 0
-5..
5-
5-
-5


Fitted Equation R=8.5e-0.1291 91.5e-0.00128t


Compartment First
* Initial Fraction 8.50.97%
* Half-Life 5.4 2.2 hrs.


Second
91.5 0.97%
540 35hrs.


* I.S.D.


20 40 60 80 100 120 140


160 180


POST-INJECTION TIME (t), HOURS


Model for 28Mg Retention in Normal Subjects.


Figure 19.











Total-measured 28Mg diagrams are shown in Figures 20 23 for

the 13 normal subjects. Each diagram shows the subject's whole-body

retention curve; added to it is the cumulative percentage of 28Mg in

urine and feces. The difference between the total-measured 28Mg and

100 per cent is labelled as "deficit" on the Figures. Numerical values

from which these graphs are plotted are tabulated in balance sheets in

Appendix B.

Figures 20 and 21 include results of subjects in groups 1 3

in which urine was the only excreta measured. In general, the results

are near, but somewhat less than the total balance or the 100 per cent

line. Figures 22 and 23 include the subjects in study groups 4 and 7.

Again, for the majority of the subjects, urine was the only excreta

measured. Figure 22 shows the two replications on subject NIH. The

first measurement (labelled NH) in study group 4 where urine was the

only excreta measured, shows a small 4 5 per cent deficit at 220 hours.

However, the second measurement on this subject (NH2) included measure-

ment of feces. This graph shows almost 100 per cent accountability;

a very small deficit is present at 220 hours.

Total-measured 28Mg for the second study group 7 subject, NM,

is shown in Figure 23. Again, there is nearly 100 per cent accounta-

bility of the administered isotope.

Although sweat was also measured in study group 7, it is not

plotted in the Figures since it was determined that the amount of 28Mg

in sweat was not significant. (See Appendix C .)

Since statistical fluctuations are apparent in the total-

measured 28Mg for these 13 normal subjects, an average retention and

































NORMAL SUBJECTS


SUBJECT NA







o-Y



40-4 WHOLE-BODY RETENTION


o!
o 20 40 0 00 100 Ii 140 1o0 100 0 1
POST -*IN ACTION TIME. HOURS



1 SUBJECT NB
io0 *L -- i -- - -- -- -- -- -- -


0.


-t0.


S40.


20.


0 t0 40 00 0 100 120 140 IO 100 00 2i20
POST--INJCTION TIMrl, OURS


SUBJECT NC











WHOLE-BODY RETENTION


0 0 20 40 20 S0 100 10 140 10 1m0 200 2
POST-INJECT10N TIMOt.OURS


SUBJECT NCt





10
so.





40- WHOLE-BODY RETENTION


0O
0 to 40 ;0 80 100 20 140 160 0o to2o 22
POST-IfJECTIOH TIME. HOUttI


Figure 20. Total-Measured 2Mg for Normals NA, NB, and NC.


WHOLE-BODY RETENTION


---






























NORMAL SUBJECTS


SUBJECT NO





4o.04




40- WHOLE ODY RETENTION


0 to 40 40 0o 00 120 40 410 0o t00
POST-IMJECTIO TIME, HOURS


SUBJECT HE











0 WHOLE- *ODY f RTENTION
WOLE- BODY RETENTION


10



.5



I
*



4


go









to0



M4






0


0 20 40 40 0 100 120 140 160 10o o0o ta
POST-1ICTION TIM MOURS


20 40 0 0 i00 t 10 140 10 1;0 200 2:
POST-INJECTIIO TIME.OUtJS


SUBJECT NG


0 20 40 40 OS 1 140 0 4 10 0 200 tI0
POST-JMECTION TIKE.HfOUt


Figure 21. Total-Measured 2"" for Normals ND, NE, NF, and NG.


SUBJECT NF











40- WHOLE BODY RETENTION


WHOLE- BODY RETENTION


I


NORMAL SUBJECTS


1 .


-----------~------~-~~--------
































NORMAL SUBJECTS


20.

tO,


0 0 40 0 0 00 10 0 20 N4 040 160 200 220
POT *-IJECTION TIME. HOUI


SUBJECT NHt





soW




40- WHOLE -BODY RETENTION


0 20 40 0 00 too 0 0 4 6000 010 200 220
POST-INJECTION TItME, HOUS


SUBJECT NJ
S_ . .. ... . *- . . ..,


0 20 40 0 80 100 120 40 410 o 0 200 21.0
POST-INJECTION TIM.EMOU'R


I SUBJECT NT







0-



0 WHOLE -BODY RETENTICN





0.
0 ;o 40 0 0 60 0400 If0o 0 100 200 20
POST-IMJECTION TIME, OURS


Figure 22. Total-Measured 2gMg for Normals NS, NI, and NJ.


0 SUBJECT NH





o0o




0-I WHOLE -BODY RETENTION


H4OLE-BODY RETENTION































SUBJECT NK

----- ---"

^--------^--L
30.. -- Y N





40o


4- WHOLE BODY RETENTION


o1 40 40 i0 1K0 1t 0 140 O tI0 oo00 220
POST1-IJECTION TIMI.HOUR04


to
0






S40


-


24.


NORMAL SUBJECTS


SUBJECT NL








-WHOLEBOY RETENTION

40 WHOLE-BODY RETENTION


0 20 P0 80 '00 120 HO 10 IS0 2 0
POT-14J1CT108 TIVME.HOURS


SUBJECT NM










WHOLE-BODY RETENTION
WHOLE-BODY RfTENTIOH


0 o0 40 O0


10 100 10 1H40 140 I0 00 220
POST*T-INCTION TIME. HOURS


Total-Measured 28Mg for Normals NK, NL, and NM.


Figure 23.











excretion was calculated and is shown in Figure 24. In this Figure, the

whole-body retention curve is the one calculated from the least squares

fit of the data (Figure 19). It was plotted in Figure 24 by substitut-

ing various values of time after administration of the isotope into the

established retention equation, R = S.5e-0.129t + 91.5e-0.00128t. The

curve representing whole-body retention plus total-urinary excretion was

determined by plotting the sum of the whole-body retention and averaged

urinary excretion values versus time. Fecal excretion values were aver-

aged and plotted in the same way.

The most sticking feature of Figure 24 is that, on the average,

the total amount of 28Mg was accounted for at all times after admini-

stration. There is a slight, 1 2 per cent deficit toward the end of

the study, which is probably due to a small accumulative loss and

consequently, non-measurement of excreta.

The total-accountability (i. e., perfect balance) of the 28Mg

on the average in the normal subjects is most significant in that it

verifies the accuracy of the retention measurements. The excreta

measurements also can be assumed to be accurate. Cumulative urinary

excretion averaged 3 per cent per day and fecal excretion was approxi-

mately 0.5 per cent per day.

Comparison of Results to Reports of Other Investigators

Prior to the use of 28Mg, non-isotopic techniques used for

studying magnesium turnover indicated that there are several relatively

small, rapidly equilibrating compartments and that one or more of them

have a slow turnover (178). Early data on magnesium in man suggest that

there are at least three compartments in the body pool of magnesium






















AVERAGE-ALL SUBJECTS


DEFICIT

-10 1 I


o 80-

0
IJ
W 60-
I-
(I,
z

< 40-
LL
0
z
t-
0
C.


T1U -I W S S


20 40 0 80 100 120 14
POST-INJECTION TIME ,HOURS


0 160 !80 200


Figure 24. Total-Measured 28Mg Average of All Normals.


s^' \ \.. i\ iFECAL-__ ,
\'\\\\\\\\\\\\\\\WHO\E-\\-BDY\ RETENTION
^~-\\\~\\^\^\\\\\^\\\\^\\\\\^\^\^\\\\\^^^^^^'^^'^^^-^^^^'^^^^''^^^^^^^^^C <\?\ ^ ---^---^^--^ \\\= URINARY EXCRETION $ $ ;





W----LE--BODY^ RETENTIO
^^ ^" \\\\\\\\\\\\\\\\\ ^*<\\\\\ .\^.\\\\s.^ \\\\ \ ^>^
w |\\VV\\\^ \ \\\\\^\ \<\\ \ \\\\\\
^ --- *^ Vjh,\\\\\ \ \^<\ \V\\\^\







WHOLE-BODY RETENTION


t I











turning over with half-lives of 1, 3, and 14 35 hours, respectiely.

However, 25 50 per cent of the magnesium was thought to be in a

fourth compartment with a turnover rate of less than 2 per cent per day.

Magnesium-28 was used soon after its discovery for the study

of magnesium metabolism; however, in the early 1960s researchers became

concerned that the magnesium content of the low specific activity 28Mg

being administered was capable of upsetting the body-magnesium balance.

Because of this, the validity of the work prior to the availability of

high specific activity preparations is questioned by some researchers

(4, 11, 178). Consequently, only published results where 28Mg of a

specific activity higher than 10 Ci per mg magnesium were considered

in this study for comparative purposes.

One of the first groups to use a high specific activity 28Mg

was Martin and Bauer (183). Their report in 1962 on exchangeable 28Mg

in the cirrhotic and alcoholic showed a significant difference between

patients and controls. However, 28Mg measurements made in serum and

urine samples were followed only 25 hours and no attempt was made to

determine turnover rate.

Avioli et al. (186) have done.extensive work using digital

computer analysis of specific activity data in plasma, urine, and feces

samples after intravenous administration of 28Mg with a specific acti-

vity of =17 yCi per mg. In their work published in 1963, they assumed

a parallel, three-compartment open system. The compartments were tenta-

tively identified as plasma, bone, and muscle. They reported that 35

per cent of muscle magnesium was exchangeable in normal subjects. Later

in 1966, Avioli and Berman (5) reported a metabolic model for magnesium in











man based on measurements of blood, urine, and feces in 15 subjects who

had received 150 175 jpCi of 2Mg (=1l pCi per mg magnesium). They

fitted a sum of three exponentials model to the plasma data to determine

half-lives of 1.1, 7.7, and 187 hours.

In the same paper, Avioli and Berman postulate a more ccrplex

model describing 28Mg kinetics which was later used by Bernard (209) to

obtain the following whole-body retention equation where t is in days;

R = 0.738e-0.00320t + 0.216e-0-164t + 0.034e-4.54t + 0.0115e-26.7t.

This function is obtained as the sum of four separate retention

functions, one for each compartment. The half-lives of the four compart-

ments in hours are: 5197, 101.4, 3.66, and 0.623. Bernard uses this

function to estimate internal dose due to a continuous exposure to 28Mg.

Another measure of magnesium turnover was reported by Petersen

(187) in 1963. He treated his experimental data with the assumption

that plasma activity is a function of immediate dilution in a central

compartment and further transport into two parallel compartments governed

by the rate constants kl and k2. He expressed the concentration in the

central compartment as:

C = ae-klt + be-k2t + c,

where k1 and k2 as determined yield half-lives of about 1 hour and 4

hours.

Several years later, Wallach, Rizek, and Dimich (189) studied

magnesium kinetics in plasma after intravenous administration of 50 -

70 pCi of =16 pCi per mg magnesium. Although measurements were made only

to 72 hours after administration, the total magnesium given was far less

than that used by Avioli et al. (186); therefore, the resultant turnover











rates in plasma are important to consider here. Wallach et al. assumed

that within 13 minutes after injection the isotope had equilibrated with

the extra-cellular magnesium pool and then verified the relation:

SA = Ae-at + Be-bt + Ce-ct,

where SA is the specific activity of 28Mg in plasma. According to

Wallach, one of the simplest models consistent with such a function

which could be applied to metabolism is the parallel three-compartment

open system. Computer derived exponents for the sum of exponentials

model yielded the following turnover times of the isotope in plasma:

0.17, 2.4, and 66 hours.

In 1966, Yun et al. (11) reported the use of a higher specific

activity 28Mg (=20 pCi per mg magnesium) in two normal subjects. They

stated that up until that time, "precise knowledge of the daily rate of

turnover of magnesium in the body" was not known. According to Yun,

earlier data, derived either from non-isotopic techniques or by radio-

isotope studies, are all overestimations because of the "loading effect

of the dose of 24Mg administered."

They administered intravenous doses of 145 and 155 pCi to the

two subjects and followed turnover of 28Mg in plasma and urine. A sum of

three exponentials equation was chosen to describe the rate of urinary

excretion. The following equations express the rate of urinary excre-

tion in per cent of the administered dose per hour for the two subjects:

(1) dU/dt = e-0.4278t + 0.126e-0.077t + 0.106e-0.00236t,

(2) dU/dt = e-0.693t + 0.2e-0.139t + O.11e-0.00173t.

Another measure of magnesium turnover was reported by Raynaud

and Kellershohn (194). They used a sum of exponentials approach to










model results of 28Mg turnover in eight normal subjects. One to three

yCi per kg of weight (=75 to 225 pCi) of 3.2 10.6 vCi per mg 28Mg was

administered to each subject; plasma, urine, and feces samples were

analyzed up to 96 hours after injection. They concluded that "the

analysis of the specific plasmatic radioactivity curve from 9 minutes

after injection until the middle of the third day, a period in which the

existence of a slow exchange becomes apparent, shows that it can be

decomposed into three exponentials in which half-lives are 7.7 minutes,

1.8 hours, and 1.9 days.

The most recent study of 28Mg in humans with which it is

important to compare the results of this study, is the one published in

1968 by Chon6 and co-workers (37). These researchers used a NaI(Tl)

crystal counting system with two 6-inch diameter by 4-inch thick crystals

(201) to scan the body for retention of injected 28Mg in the head,

thorax, upper abdomen, lower abdomen, and lower extremities. The intent

of the study was to define as precisely as possible the proportions of

28Mg in various parts of the body at various times after injection of

2 6 pCi of 28Mg. In addition, whole-body retention was calculated

from the measurements of the various parts of the body. The data was

plotted on semi-logarithmic paper and fitted by hand to produce the

following retention equation:

R = 10e-0.051t + 90e-0.0074t.

Table 3 summarizes the results of all the magnesium studies

just discussed. In order to compare these results to the ones from this

study, it is necessary to examine a number of important parameters; the

number of subjects studied, the total mg of magnesium administered











TABLE 3

28Mg TURNOVER RESULTS IN HUMANS


Half-lives of Compartments*
Number of Dose Specific Total Observed (Hours)
Investigator Subjects (uCi) Activity Mg Hours 28Mg in: 1 2 3 4

Avioli et al. 15 175 =11 16 144 plasma, 1.1 7.7 187 (1000)**
(186) urine

Wallach et al. 6 70 =16 4.3 72 plasma 0.17 2.4 66
(189)

Yun et al. 2 155 =20 7.8 70 plasma, 1.31 6.9 --347.1--
(11) urine

Raynaud, 8 225 10.6 20 96 plasma, 0.13 1.8 46 -
Kellershohn(194) excreta

Chond et al. 11 6 ? ? 120 body -------13.7-------- 933
(37) sections

Roessler 15 10 300 0.3 220 whole- ------- 5.4------- 540
body,
excreta,
body
sections

*Compartments are put in columns according to interpretations by this author as to what
the half-life represents.
**Half-life of a long-term storage site, estimated but not actually measured in the study.












(a combination of total dose and the specific activity of the prepara-

tion), the number of hours followed, the sample measured, and the

results.

The most obvious conclusion that can be made from Table 3 is

that there is no consistency in the results from one study to another.

This could be due to differences in the other parameters tabulated on

the various studies. It can be seen from the Table that in this study

all of these parameters were equal to or better than those of the other

investigators. Of particular importance is the very small amount of

magnesium (0.3 mg) administered. This is many times less than that

given by any other investigator. The total hours that one is able to

follow the activity after administration is also of prime importance

since the total measurement time greatly affects the accuracy of the

determination. This is important primarily in the determination of

turnover times of the longer half-life compartmentss.

Probably the most significant contribution of this study is

that whole-body retention measurements were made directly. The use of

the 4-pi whole-body counter made this possible. Other investigators,

who do not have access to this counting equipment, have to rely on

plasma turnover and/or excretion to estimate whole-body retention. Of

significance also is the fact that excreta measurements which were made

in this study essentially verified the whole-body turnover at all times

after administration of the 28Mg.

It is interesting at this point to examine in more detail

the study by Chone et al. (Table 3). Although measurements were made

by these investigators up to 120 hours after administration compared to











240 hours in this study, the approach is similar enough so that an

almost direct comparison can be made of the two sets of results. The

following comments can be made:

(1) This is the only other study published in which whole-

body retention, although not the primary intent of the study, was

measured directly rather than being calculated from plasma turnover or

from excreta measurements. However, Chon4, used a scanning-type counter

rather than the more sensitive 4-pi liquid counter.

(2) The authors chose a two compartment model for fitting

although they admit that at least one other compartment may exist. They

assume that if a third compartment is present that their first compart-

ment is actually a measure of the first two rapidly exchanging compart-

ments; and

(3) Eleven normal subjects were measured.

Almost identical results are obtained by Chone et al. and by

the measurements in this study for two of the constants in the retention

equation the per cent of the administered magnesium being excreted

directly from the first compartment (Chone et al., 10 per cent -

Roessler, 8.5 per cent) and the per cent of the administered magnesium

entering into and then being excreted from the second compartment.

(Chone et al., 90 per cent Roessler, 91.5 per cent).

However, Chone and his group found half-lives of these two

compartments to be 13.7 and 933 hours, in contrast to the 5.4 and 540

hours found in this study.

An estimate of the degree of accuracy of the results of Chone

et al. is difficult to make since the report gave no indication of the

degree of reproducibility of their measurements. No confidence intervals











were reported on the constants determined for their retention equation.

In addition, only seven points of per cent whole-body retention versus

hours after administration were used to calculate the retention equation.

This small number of points would give a lower degree of confidence for

prediction of any of the four constants in the retention than that in

this study.

In addition to comparisons of the 28Mg biological half-lives,

one can compare the excretion rates of the isotope in this study to

those determined by other investigators. Table 4 summarizes the excreta

results of this study and presents them for the comparison to other

published reports. The urinary excretion for all investigators is quite

consistent. Fecal excretion has only been measured by two other investi-

gators; one of these, Yun et al., report a single value at 70 hours.

The results of this study are about 1 1/2 times those reported by the

two other investigators. Again, the measurement period in this study

was 220 hours compared to 134 hours by Avioli et al. and lesser times

by the other investigators.


Calculation of Radiation Dose

This study and those of others cited here demonstrate the

potential for using 28Mg in studies of magnesium's function and behavior

in humans. Magnesium-28 is currently more available than it was previ-

ously and soon will be produced in a carrier-free form (211). Conse-

quently, it is expected.that its use in human experimentation will

increase significantly.

In all studies where a radionuclide is administered to humans,

one must precede the experimental work with an estimate of the radiation

dose. Radiation dose calculations for 28Mg have typically been based on












TABLE 4

COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT 28Mg STUDIES


Cumulative Excretion (Per Cent of Dose) in Hours After Injection
Urine Feces
Investigator 44 48 70 72 120 134 220 48 70 72 96 134 220

Roessler 9.0 9.3 12.0 13.5 15.0 16.7 27.9 2.0 2.5 2.5 3.0 4.3 5.0

Avioli et al. 10.6 11.6 16.9 1.8 1.2 2.6
(186)
Yun et al. (11) 7.3 10.7 1.4

Wallach et al. 10.4
(189)
Raynaud,
Kellershohn (194) 16.0 1.7











data from the chronic intake of magnesium. The half-life used for such

calculations was obtained from the Report of the ICRP Committee II on

Permissible Dose for Internal Radiation (212) and was estimated from the

biological elimination of the stable element in humans in the absence of

experimental data from radioisotopes. Such a calculation was made of the

anticipated dose to standard man prior to this study. Considering the

radioisotope to be uniformly distributed through the whole-body as a

critical organ, assuming a single exponential turnover with a biological

half-life of 4320 hours as listed by the ICRP (212) and using the classi-

cal method of calculation (213), it was estimated that the radiation

dose per pCi of injected 28Mg would be 2.7 mrad. (See Appendix A.)

In reviewing the results of this study, it can be seen that

the calculation based on a single 4320-hour biological half-life is

inconsistent with the conditions following a single injection. When

the source of the 28Mg is a single administration rather than a chronic

intake, very little of the administered quantity reaches the very

long-lived biological compartment. Because of the short physical half-

life of the isotope, this portion of the administered quantity contri-

butes only a small fraction to the radiation absorbed dose. Accurate

radiation dose calculations for the one-time dose situation should be

based on the model best representative of the biological turnover

following such an administration.

This study represents the longest known determination of both

retention and excretion of 28Mg under these conditions; therefore, the

parameters determined in the retention equation in Figure 19 should

provide the most accurate estimation of the radiation dose to humans












after a single intravenous administration of the isotope.

After the parameters in Figure 19 had been obtained, the

method of the Medical Internal Radiation Dose (MIRD) Committee of the

Society for Nuclear Medicine (214) was followed to recalculate the

radiation dose. (See detailed calculations in Appendix A.) The model

used two uncoupled compartments characterized by the relative activities

and the biological half-lives found in this study. The whole-body was

considered as the target organ and the source for both compartments.

From this data, the radiation dose was calculated as 2.0 mrad per PCi.


Retention and Excretion of 28Mg in Selected Disease Conditions

Because of magnesium's role in neuromuscular function, serum

or plasma levels of this element are routinely examined in patients with

neuromuscular disease. As it was pointed out in the literature review,

this extracellular measurement of a primarily intracellular ion rarely

provides any information with regard to metabolic magnesium abnormali-

ties. Consequently, the measurement of stable magnesium in red blood

cells has been accepted by some clinicians as the method of choice for

determining these abnormalities. Although this determination may be more

sensitive to a disorder in magnesium turnover, it is generally agreed

that red blood cells are "enucleated impotent and dying cells which are

not representative for intracellular metabolism"(215).

Because of these uncertainties in the relationship between

plasma and red blood cell analyses and actual magnesium metabolism,

many clinicians have sought a better means of determining magnesium ab-

normalities. Among these were a gastroenterologist and a neurologist at

the University of Florida who sought help in the use of a radioactive











tracer to study magnesium turnover in neuromuscular patients. Whole-

body turnover of radioisotopes of other essential human elements such as

iron (216), copper (217), and calcium and strontium (218) has been used

successfully to identify abnormalities in other disease conditions.

Therefore, this study was initiated with the objective of determining

whether the measurement of 28Mg turnover could be correlated with select-

ed disease conditions.

This pilot study involved 16 whole-body retention and excretion

determinations following intravenous administration of 28Mg. Another

major objective of the study was to use these determinations to examine

the feasibility and possible applications of this technique as a diag-

nostic test. It was hoped that the 28Mg turnover determination could be

simplified to a one- or two-time measurement that would provide greater

potential in diagnosis than the currently used methods. Of these 16

determinations in this patient study, 10 represent a single turnover

measurement and the others were triplicate measurements at three points

in time on each of two patients.

Patients in the study included three with amyotrophic lateral

sclerosis (ALS) of unknown origin, two who developed ALS symptoms fol-

lowing sub-total gastrectomies, one with infectious polyneuropathy, two

with repaired sub-total gastrectomies, a patient on diuretics, one

renal patient, a patient who had undergone an extensive small bowel

resection, and a patient with a history of hypertension.

In order to correlate the results between the stable magnes-

ium levels, the 28Mg measurements, and these selected disease states,

routine clinical stable magnesium anslyses were made on all subjects in











this study. Table 5 summarizes the results of plasma and red blood

cell analyses. The plasma analyses show that all normals and most of

the patients fall within the normal range. Only patients PF and PK

have values which are lower than normal. The red blood cell measure-

ments show that two normals and four patients have values outside the

normal range. Normals NG and NI have above normal values. Higher than

normal levels were also found in red blood cell measurements of patients

PD, PH, and PJ, while a lower than normal level was observed for patient

PK. Only patient PK has abnormal magnesium levels in both plasma and

red blood cell measurements.

Magnesium-28 retention and excretion results for all patients

are shown in Figures 25 31. Whole-body retention values, grouped by

disease conditions, are superimposed on the normal retention band (from

Figure 19) and shown in Figures 25, 28, and 30. The total-measured 28Mg

results for these patients are shown in Figures 26, 27, 29, and 31.

These can be compared both to the individual normal results (Figures

20 23) and to the average for all normals (Figure 24).

Neuromuscular Patients

The whole-body retention curves for four of the neuromuscular

patients PA, PB, PG, all ALS patients, and PI,.who has infectious poly-

neuropathy, are shown in Figure 25. A number of different, lower than

normal retention patterns are obvious; however, only one, PI, appears

entirely within the normal range. As can be seen from the figure, PB's

retention curve shows the most dramatic departure from normal. In the

first two measurements on this subject, the whole-body retention was

lower than normal and also the resultant curve does not follow the




Full Text
116
could be used. An accurate definition of early retention data could be
obtained from a 1 yCi dose. This would be followed in the same sub
ject (s) at a later date with a much larger dose.
5. The use of a partially collimated Nal(Tl) crystal whole-
body counter,in a pilot study in this research, shox^s promise for future
work. A crystal with better collimation in a shielded room would pro
vide more precise, important information on the localization of magnes
ium in the body. This information would not only be a significant
contribution to normal metabolism studies but would also serve as a
means for studying a number of disease conditions where abnormal
magnesium metabolism is suspected.


145
SUBJECT: PD STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:25 DOSE: 9.105 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.8
100
-
100
10.6
98
2
100
24.3
97
3
100
48.1
95
5
100
73.2
93
6
99
-1
97.7
93
6
99
-1
145.0
88
8
96
-4
168.9
89
9
98
-2
193.0
96
9
105
+5
216.9
110
9
119
+9
240.9
126
10
136
+36
*Expressed as per cent,
rounded off
to the
nearest whole number.
- Means not measured


64
Two subjects, NC and Nil, were measured twice and were used as
a means of establishing the degree of reproducibility of this measure
ment method. These replications can be seen in the two plots in Figure
18. Subject NC, who was in groups 1 and 2 (time lapse of four months),
had almost identical retention curves with the exception of one point at
165 hours. Because this point represented the last measurement made in
group 1 and the level of activity was low, considerably more counting
error is associated with it than with the measurement made at the same
post-injection time in group 2.
Subject NH was measured both in study groups 4 and 7 (time
lapse of one year and two months). His retention curves are also very
similar with the exception of the 20- and 40-hour points which, as
mentioned previously as a part of the group 4 measurements exhibited
a departure from a smooth function.
Analysis of the results of all of the study groups showed no
pattern due to sex or age. Therefore, both male and female subjects
were considered as representative of a normal population and the results
of all' groups, ages, and both sexes were pooled for further analysis.
Determination of the Model for Biological Turnover of 28Mg
A number of estimates of magnesium turnover have been
28
attempted, both with stable magnesium and more recently with Mg. As
discussed in the literature review, researchers in these studies have
been concerned with establishing an accurate biological half-life (or
turnover) of the element in order to provide information on its meta
bolism in normals and to study its behavior in disease conditions.
The formulation and testing of a model for the retention
data followed suggestions by Mones Berman (205). Berman states that


CHAPTER IV
RESULTS AND DISCUSSION
Whole-Body Retention of in Normals
In Figure 17, whole-body retention, expressed as per cent of
the administered dose, for the 13 normal subjects, age 28 to 71, is
plotted by study groups. The subjects included five females, age 43 to
59, and eight males, age 28 to 71.
The two subjects in study group 1, NA and NC, were followed
for the shortest period of time, 165 hours, since they received only
1.3 pCi of 2%g. This dose level was selected to initiate the study
since it was considered the optimum amount for measurement by the
whole-body counting system. In order to better define the shape of the
curve during the first few days, frequent measurements were made on the
subjects in this group.
The results of group 1 showed that at least two components
are involved in the retention (or turnover) of 28^. it was apparent
that a larger dose was needed to permit measurements over a period of
time long enough to accurately establish the second component. Calcula
tions showed that a factor of eight (2^) increase in the dose would
permit meaningful measurements for an additional three days (-three
times the physical half-life of the isotope). Therefore, in subse
quent study groups the dose was increased to the order of 7 10 pCi
and retention and excretion measurements were possible up to 220 hours.
61


I
Figure 9. Nal(Tl) Crystal Whole-Body Counter: Whole-Body Count Position.


20
that the normal body mechanisms are being overtaxed."
Further describing the major advantages of radioisotopes,
Greenberg stated:
In many respects, it is more advantageous to use radio
active than a non-radioactive isotope because the detection
of the radioactive isotopes Is relatively simple . Also
non-radioactive impurities which may be present do not inter
fere with the measurements and thus very tedious purification
processes can be avoided. Chemically, the radioactive isotopes
behave in identically the same manner as the natural mixture
of isotopes of the elements of the same atomic number because
they have the same nuclear charge.
Since Greenberg's report in 1939, many biologically signifi
cant radioactive isotopes have been artifically produced to study the
importance of the basic elements to the human system. Yet, Greenberg
was one of the early workers to realize the important factors which
determine whether a radioactive isotope will be suitable for investi
gative work. These factors, he said, are:
. . the degree of stability as measured by the isotope's
half-life and the intensity of the radiation it gives off.
The duration of life of the radioactivity of the element
should be suitably short, so that it may be given in small
quantities as a tracer to animals and man without danger,
. . but should be sufficiently long to enable the fate of
the element to be followed until it is eliminated by the
organism.
However, at the time of Greenberg's review, the only known
isotope of magnesium was 27^g with a physical half-life of less than
10 minutes, a half-life too short to be of significant assistance in
studying magnesium. Consequently, Greenberg's review included results
of radioactive work only on calcium and phosphorus and none on magnesium.
Knowledge of magnesium's function in humans lagged far behind
that of its related elements until the discovery of a new isotope of
magnesium in 1953 by Sheline and Johnson (9) of Florida State University.


TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ......... ii
LIST OF TABLES vi
LIST OF FIGURES ............. vii
ABSTRACT ix
CHAPTER
I. INTRODUCTION . 1
II.LITERATURE REVIEW 6
Occurrence of Magnesium in Nature 6
Importance of Magnesium to Man 6
Techniques for Measuring Stable Magnesium 17
Studies with Magnesium-28 19
III.MATERIALS AND METHODS . 33
Magnesium-28 33
Experimental Conditions and Techniques 35
Instrumentation 40
Data Analysis Techniques 57
IV.RESULTS AND DISCUSSION 61
Whole-Body Retention of in Normals ........ 61
Excretion of 28^g in Normals 68
Calculation of Radiation Dose 84
Retention and Excretion of 28yjg in Selected Disease
Conditions .......... 87
Measurements with the Nal(Tl) Crystal Whole-Body
Counter 103
V. SUMMARY AND CONCLUSIONS 113
Conclusions 115
APPENDICES 117
A. COMPUTATION OF RADIATION DOSE 118
iv


30
rate of turnover of magnesium was not previously known was because
earlier data, derived from either non-isotopic techniques or by radio
isotope studies, "are all overestimations because of the loading effect
of the dose of 24jqg administered." Yun and associates used 28f{g with a
specific activity of =200 yCi per mg of magnesium, many times higher than
that previously available. In two controls and four patients, they
measured 28Mg in urine, feces, and plasma up to 70 hours after intra
venous administration and up to 40 hours after an oral dose.
Skyberg jet al. (193) demonstrated the usefulness of ^£$Mg
diagnostic procedures in 1968; he used the tracer to show that hypo
magnesemia was present in an infant and that it was due to a defect in
the intestinal absorption of magnesium. Magnesium-28 (specific activity
of =30 to 500 yCi per mg magnesium) was given orally and excreta was
measured for radioactivity. The numerous routine tests given the infant
including electrocardiography, electroencephalography, and electromyo
graphy were normal. The urine was chemically and microscopically normal
and the spinal fluid had normal protein concentration and normal cell
count. All blood examinations were normal including the serum concen
trations. However, by analyzing the urine and feces after peroral and
intravenous administrations of 28^g} it was found that the child had a
defect in gastrointestinal absorption of magnesium.
Another use of ^Mg (3.2 and 10.6 yCi per mg magnesium) to
examine differences in pathological and normal adults was reported in
1967 by Raynaud and Kell*ershohn (194). Significant differences were
observed between eight persons described as normal and 22 patients in
plasma, urine, and feces analyses. Seventeen of the patients studied


60
Thus,
Stx'/St0 = Stx'/(Stx'-e-^t) = e-Xt;
where
St and St are values of St and St predicted from the
x o x o r
fitted curve.
The whole-body retention equation then reduces to:
WBRtx = WBtx* e+*t/WBt0.
By using this technique, the phantom could be measured
only once with each daily set of subjects rather than each time an
individual was counted. Therefore, since the phantom was cumbersome
and the measurements are time-consuming, this technique proved to be an
efficient one. It also produces more statistically accurate values
when an isotope with a short half-life is used. A time lapse of as
much as 30 minutes between a phantom and a subject with can
produce an error of 2 per cent. A time lapse of two hours produces
a 7 per cent error.


170
186.
187.
188.
189.
190.
191.
192.
193.
194.
195.
196.
197.
198.
199.
200.
L. V. Avioli, T. N. Lynch, and M. Berman, "Digital Computer
Compartmental Analysis of 28jqg Kinetics in Normal Subjects,
Paget's Disease, and Thyroid Disease," J, Clin. Invest., 42:
915 (1963).
V. P. Petersen, "Potassium and Magnesium Turnover in Magnesium
Deficiency," Acta Med. Scand., 174:595 (1963).
J. H. Mendelson, B. Barnes, C. Mayman, and M. Victor, "The
Determination of Exchangeable Magnesium in Alcoholic Patients,"
Metabolism,14:88 (1965).
S. Wallach, J. E. Rizek, and A. Dimich, "Radiomagnesium Kinetics
in Normal and Uremic Subjects," J. Clin. Invest., 44:1107 (1965).
J. K. Aikawa and J. Z. Reardon, "Effect of 2,4-Dinitrophenol on
Magnesium Metabolism," Proc. Soc. Expt. Biol. Med., 119:812
(1965).
J. K. Aikawa and J. Z. Reardon, "Effect of Sodium Salicylate on
Magnesium Metabolism in the Rabbit," Proc. Soc. Expt. Biol. Med.,
122:884 (1966).
J. K. Aikawa, The Role of Magnesium in Biologic Processes,
Charles C. Thomas, Publisher, Springfield, Ill. (1963).
D. Skyberg, J. H. Stromme, R. Nesbakken, and K. Harnaes, "Neo
natal Hypomagnesemia with Selective Malabsorption of Magnesium -
A Clinical Entity," Scand. J. Clin. Lab. Invest., 21:355 (1968).
C. Raynud and C.
ment Echangeables
ium a L'aide du 2
Strahlentherapie,
Kellershohn, "Mesure des Compartiments Radipe-
des Taux D'echange et de Transfer du Magnes-
Mg Chez L'adulte Normal et Pathologique,"
65:430 (1967).
J. K. Aikawa and A. P. David, "^Mg Studies in Magnesium-Defi
cient Animals," Ann. N. Y. Acad. Sci., 162:744 (1969).
S. Wallach and A. Dimich, "Radiomagnesium Turnover Studies in
Hypomagnesemia," Ann. N. Y. Acad. Sci.,162:963 (1969).
Powell Richards, Hot Laboratory, Brookhaven National Laboratory,
Upton, L. I., N. Y., Personal Communication.
Clinical Laboratories, J. Hillis Miller Health Center, University
of Florida, Personal Communication.
W. J. Walker, Jr., "The Nature and Control of External Sources
of Variation in Whole-Body Counting," Doctoral Dissertation,
University of Florida (1971).
I. Davidsohn and J. B. Henry, "Sweat Electrolytes by Pilocarpine
Iontophoresis." Clinical Diagnosis by Laboratory Methods, W. B.
Saunders Co., Philadelphia, Pa.> 758 (1969).


17?
215. A. Donath, Bern, Switzerland, Personal Communication.
216. W. Noyes, Department of Medicine, University of Florida, Personal
Communication.
217. S. O'Reilly, T. Strickland, P. M. Weber, W. M. Beckner, and L.
Shipley, "Abnormalities of the Physiology of Copper in Wilson's
Disease," Arch. Neurol., 24:385 (1971).
218. T. Sargent, J. A. Linfoot, and E. L. Isaac, "Whole-Body Counting
of ^7ca and ^Sr in the Study of Bone Diseases," IAEA, Clinical
Uses of Whole-Body Counters, Proceedings of a 1965 Panel,
Vienna, Austria.


WHOLE-BODY RETENTION AND EXCRETION OF MAGNESIUM IN HI
BIOLOGICAL HALF-LIFE IN NORMALS AND SELECTED DISEASE
II. RADIATION DOSIMETRY
By
Genevieve Schleret Roes
ler
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
MANS:
STATES
UNIVERSITY OF FLORIDA
1972


134
SUBJECT: NI STUDY GROUP: 4
DATE, TIME OP INJECTION: 1-6-70, 16:11 DOSE: 6.535 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit
0.9
97
-

97
-3
6.2
89
4
-
93
-7
18.0
80
9
-
89
-11
42.0
84
12
-
96
-4
65.2
79
14
-
93
-7
90.2
83
17
-
100
137.9
77
20
-
97
-3
162.1
71
22
-
93
-7
186.9
72
28
-
100
210.3
75
28
-
103
+3
234.2
80
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


10
diet are relatively poor in the element. However, according to Seelig,
it is generally agreed that because magnesium is so plentiful in the
normal diet, deficiences of it cannot develop in the absence of disease.
However, she emphasizes that currently accepted magnesium requirements
should be reevaluated to make certain that the optimal daily intake of
the mineral is correct, since prolonged dietary insufficiency of it may
contribute to the development of chronic disease.
Relationship of Magnesium with Other Ions and Compounds
It has been known since 1909 that a relationship exists between
calcium and magnesium metabolism. Mendel and Benedict (42) showed that
an infusion of calcium in animals produced an increase in their
urinary excretion of magnesium and vice versa, a phenomenon later con
firmed in man (43,44). Several decades later it was shown that experi
mental magnesium deficiency produced disturbances in calcium metabolism
(45-47). The absorption of magnesium from the gastrointestinal tract
has also been shown to be influenced by protein intake (48), growth
hormones (49), large doses of vitamin D (50), and certain antibiotics
(51). Vitamin D (52) and certain carbohydrates (53) also affect
magnesium metabolism.
Current reviews of the interrelationship of magnesium with
calcium and phosphorus present data on the complex interactions of
these cations in man and in animals (54-60). Most significant of
these is that magnesium deficiency disturbs calcium metabolism and
that in calcium deficiency, when magnesium is available, it can
replace bone calcium to a limited extent (61). Stearns, speaking for
the Journal of the American Medical Association Council on Foods and


77
turning over with half-lives of 1, 3, and 14 ^ 35 hours, respectively.
However, 25 50 per cent of the magnesium was thought to be in a
fourth compartment with a turnover rate of less than 2 per cent per day,
Magnesium-28 was used soon after its discovery for the study
of magnesium metabolism; however, in the early 1960s researchers became
concerned that the magnesium content of the low specific activity 28^g
being administered was capable of upsetting the body-magnesium balance.
Because of this, the validity of the work prior to the availability of
high specific activity preparations is questioned by some researchers
(4, 11, 178). Consequently, only published results where ^8^g 0f a
specific activity higher than 10 yCi per mg magnesium were considered
in this study for comparative purposes.
One of the first groups to use a high specific activity
was Martin and Bauer (183). Their report in 1962 on exchangeable 28^g
in the cirrhotic and alcoholic showed a significant difference between
patients and controls. However, 28^g measurements made in serum and
urine samples were followed only 25 hours and no attempt was made, to
determine turnover rate.
Avioli jet al. (186) have done, extensive work using digital
computer analysis of specific activity data in plasma, urine, and feces
samples after intravenous administration of 28]tfg with a specific acti
vity of =17 yCi per mg. In their work published in 1963, they assumed
a parallel, three-compartment open system. The compartments were tenta
tively identified as plasma, bone, and muscle. They reported that 35
per cent of muscle magnesium was exchangeable in normal subjects. Later
in 1966, Avioli and Berman (5) reported a metabolic model for magnesium in


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TITLE: Whole-body retention and excretion of magnesium in humans: (record
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PUBLICATION DATE: 1972
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!
PAIi£TS
H38T NOeCTfOH T1*t£.HOim
Figure 27. Total-Measured 28Mg Patients PB, ?G, and ?I.
VD
U>


80
model results of 28Mg turnover in eight normal subjects. One to three
yCi per kg of weight (-75 to 225 yCi) of 3.2 10.6 yCi per mg 28^g was
administered to each subject; plasma, urine, and feces samples were
analyzed up to 96 hours after injection. They concluded that "the
analysis of the specific plasmatic radioactivity curve from 9 minutes
after injection until the middle of the third day, a period in which the
existence of a slow exchange becomes apparent, shows that it can be
decomposed into three exponentials in which half-lives are 7.7 minutes,
1.8 hours, and 1.9 days.
The most recent study of ^Mg humans with which it is
important to compare the results of this study, is the one published in
1968 by Chon and co-workers (37). These researchers used a Nal(Tl)
crystal counting system with two 6-inch diameter by 4-inch thick crystals
(201) to scan the body for retention of injected 28jjg the head,
thorax, upper abdomen, lower abdomen, and lower extremities. The intent
of the study was to define as precisely as possible the proportions of
28
Mg in various parts of the body at various times after injection of
2-6 yCi of 28p[g# jn addition, whole-body retention was calculated
from the measurements of the various parts of the body. The data was
plotted on semi-logarithmic paper and fitted by hand to produce the
following retention equation:
R = 10e-0,051t + gOe-0-007^.
Table 3 summarizes the results of all the magnesium studies
just discussed. In order to compare these results to the ones from this
study, it is necessary to examine a number of important parameters; the
number of subjects studied, the total mg of magnesium administered


39
simulate the various parts of the human body. The isotope can be distri
buted throughout the phantom by inserting radioactive sources into
numerous channels within the phantom. Tubman was used to determine the
amount of contribution of the isotope from one part of the body to
another so that accurate corrections for interference could be made.
Excreta Measurements
Twenty-four-hour cumulative urinary excretion of ^Mg was
measured in all groups. An aliquot of the collection was taken for
counting purposes. If the total volume was less than the specified
aliquot, the counting container was filled with distilled water to the
required amount. Urine samples were counted as 780 ml aliquots on a
4-inch by 4-inch Nal(Tl) crystal counter in groups 1 through 4. In
groups 5 through 7, they were counted as 1000 ml aliquots in a large
volume well counter. Counting times ranged from 1 minute to 30 minutes
depending on the amount of radioactivity in the sample. Urine standards
were made up at the same time as the doses for the subjects and phantoms
were prepared. Urine standards with 0.1, 1, and 10 per cent of the
average dose given to the subjects were prepared and counted along with
each set of urine collections.
Fecal excretion was measured in groups 5, 6, and 7; the
total-daily collection was counted for ^8^g the iarge volume well
counter.
Measurements of ^Mg in sweat were made in group 7 using the
iontophoresis technique (200). With this technique, pilocarpine is
iontophoresed into the skin by means of a 2.5 milliamp electric current.
In this study, a 2-inch by 2-inch area on the subjects left forearm
was covered with pilocarpine and subjected to the electric current for


103
(3) The patients who have "recovered" from the ALS associated
with gastrectomies also have normal retention curves and a normal amount
of 28f,jg excreta.
(4) The patient on diuretic therapy and the patient with
hypertension who denied use of diuretics both have higher than normal
retention of the isotope. Interestingly, the diuretic patient has a
retention curve that takes an upward turn at approximately the same time
that the ALS patients' curves turn downward. The latter observation
leads one to consider whether at this point in time the 28>ig is leaving
one compartment of the body in large amounts and entering another. An
abnormal relocation could produce counting efficiency changes which in
turn would result in an incorrect determination of whole-body retention.
These uncertainties led to the use in study group 7 of a
Nal(Tl) crystal whole-body counter to study relocation of the isotope.
Other factors that were also considered in this study group as possible
explanations for the abnormalities included sweat as a source of magnes
ium excretion and the possibility of a change in the equilibrium of the
2^Mg 28^1 parent daughter pair.
Measurements with the Nal(Tl) Crystal Whole-Body Counter
Three types of data evaluation were performed with the results
from the Nal(Tl) crystal counter measurements on the four subjects (PA,
PB, NH, and NM) in study group 7.
(1) Whole-body retention was computed;
(2) The partial-body counts were examined to determine if
localization of ^Mg OCCurred within the body; and
(3) Ratios of the counting rates in the 28Mg and 28a1 photo
peak regions were analyzed for possible variations in this equilibrium.


96
Figure 30. Whole-Body Retention of
Disease Conditions.
28
'Mg Patients with Miscellaneous
I
rr


124
SUBJECT: NA STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:15 DOSE: 1.307 pCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
1.4
99
2
-
101
1
3.5
96
3
-
99
-1
8.1
96
3
-
99
-1
20.5
93
4
-
97
-3
22.7
93
4
-
97
-3
25.8
92
4
-
96
-4
28.2
92
5
-
97
-3
32.2
92
5
-
97
-3
45.3
91
6
-
97
-3
48.3
93
6
-
99
-1
52.3
90
7
-
97
-3
56.5
90
7
-
97
-3
70.1
89
9
-
98
-2
78.9
86
9
-
95
-5
93.4
85
10
-
95
-5
124.5
82
12
-
94
-6
142.5
81
13
-
94
-6
166.3
79
-
-

-
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


165
107. S. Hanna, K. A. K. North, I. MacIntyre, and R. Fraser, "Magnesium
in Parathyroid Disease," Brit. Med, J., 2:1253 (1961).
108. K. Gerlach, D. A. Morowitz, and J. B. Kirsner, "Symptomatic
Hypomagnesemia Complicating Regional Enteritis," Gastroenterology,
59:567 (1970).
109. A. S. Goldman, D. D. Van Fossan, and E. E. Baird, "Magnesium
Deficiency in Celiac Disease," Pditrics, 29:948 (1962).
110. R. D. Montgomery and B. Chir, "Magnesium Balance Studies in
Marasmic Kwashiorkor," J. Ped., 59:119 (1961).
111. L. J. Soffer, C. Cohn, E. B. Grossman, M. Jacobs, and H. Sobotka,
"Magnesium Partition Studies in Grave's Disease and in Clinical
and Experimental Hypothyroidism," J, Clin. Invest., 20:429 (1956).
112. A. H. Heggtveit, L. Herman, and R. K. Mishra, "Cardiac Necrosis and
Calcification in Experimental Magnesium Deficiency," Am. J. Path.,
45:757 (1964).
113. B. A. Barnes, "Current Concepts Relating Magnesium and Surgical
Disease," Am. J. Surg., 103:309 (1962).
114. B. A. Barnes, "Magnesium Conservation: A Study of Surgical Patients,"
Ann. N. Y. Acad. Sci., 162:786 (1969).
115. E. C. Wacker, R. D. Moore, D. D. Ulmer, and B. L. Vallee, "Normo-
calcemic Magnesium Deficiency Tetany," JAMA, 180:161 (1962).
116. L. P. Eliel, W. 0. Smith, R. Chaes, and J. Hawrylko, "Magnesium
Metabolism in Hyperparathyroidism and Osteolytic Disease," Ann.
!Ll Ijl Acad. Sci,, 162:810 (1969).
117. R. E. Randall, Jr., "Magnesium Metabolism in Chronic Renal Disease,"
Ann. N. Y. Acad. Sci., 162:831 (1969).
118. H. J. Gitelman, J. B. Graham, and L. G. Welt, "A Familial Disorder
Characterized by Hypokalemia and Hypomagnesemia," Ann. N. Y. Acad.
Sci., 162:856 (1969).
119. I. MacIntyre and C. J. Robinson, "Magnesium and the Gut: Experimental
and Clinical Observations," Ann. N. Y. Acad. Sci., 162:865 (1969).
120. J. L. Caddell, "Magnesium Deficiency in Protein-Calorie Malnutrition:
A Follow-up Study," Ann. N. Y. Acad. Sci., 162:874 (1969).
121. I. MacIntyre, S. Hanna, C. C. Booth, and A. E. Read, "Intracellular
Magnesium Deficiency in Man," Clin. Sci., 20:297 (1961).
122. I. MacIntyre, "The Interrelation of Calcium and Magnesium Absorp
tion," Proc^ Roy^Soc^ Med^, 53:1037 (1960).


51
Position Angular and Distance Designation
a
b
C
d
a + (3
a
6
Whole-Body
16.5
21.0
4.5
17.0
45
90
0
Head
20.0
21.0
4.5
11.0
60
90
5
Chest
16.5
21.0
4.5
17.0
45
90
5
Ab domen
16.5
21.0
4.5
17.0
45
90
0
Legs
16.5
21.0
4.5
17.0
45
O
O
Oh
0
Figure 10. Geometry of Subject Counted on the Nal(Tl) Crystal Whole-Body
Counter (201).


148
SUBJECT: PG STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70,10:04 DOSE: 4.445 uCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
1.0
100
-
-
100
10.1
90
15
0
105
+5
24.8
82
23
3
108
+8
48.9
79
30
3
112
+12
72.8
76
35
3
114
+14
121.2
64
40
5
109
+9
144.7
59
44
6
109
+9
169.2
55
44
8
107
+7
193.2
53
44
9
106
+6
219.5
49
45
11
105
+5
^Expressed as per cent
, rounded off
to the
nearest
whole number
- Means not measured


107
are compared at several points in time for the three subjects measured
on both counters. The major difference in the results of this compari
son is that the retention measured by the crystal counter is lower; the
greatest difference, about 10 per cent, was found at the 165-hour
measurement.
There are a number of reasons to support the 4-pi counter
results as the true absolute values. First of all, the balance studies
(Figure 25) in this study using the 4-pi counter essentially account for
all of the administered ^^Mg. Therefore, the whole-body retention
determinations were verified. In addition, the 4-pi system shows less
\
variability and produces more accurate absolute values because of its
inherent characteristics and because of the operational experience
with the counter. The geometrical configuration of the 4-pi counter is
one of the superior characteristics it essentially surrounds the sub
ject producing a counting efficiency many times higher than that of the
crystal counter. This configuration is also relatively insensitive to
source location, while the crystal counter geometry is not. The crys
tal counter measures the major portion of the body, but it eliminates the
head and the lower legs. Any non-uniform distribution with respect to
any of the body parts would produce an apparent rate of turnover differ
ent than a true whole-body count. The 4-pi counter also has the advant
ages of lower background due to its fully-shielded room and ventilated
air flow. Another aspect of comparison is that this was the first time
that the crystal counter had been used in a tracer experiment. The
inexperience of the operating personnel in positioning subjects, in
routine handling of the output systems, and in analysis of the data


16A
93. J. Neilson, "Magnesium Metabolism in Acute Alcoholics," Danish
'Med'; Bull., 10:225 (1963).
94. 0. M. Jankelson, J. J. Vitale, and D. M. Hegsted, "Serum Magnesium,
Cholestrol, and Lipoproteins in-Patients with Atherosclerosis and
Alcoholism," Am. J. Clin. Nutr., 7:23 (1959).
95. H. E. Martin, C. McCuskey^Jr., and N. Tupikova, "Electrolyte
Disturbance in Acute Alcoholism with Particular Reference to
Magnesium," Am. J. Clin. Nutr., 7:191 (1959).
96. J. F. Sullivan, J. G. Lankford, M. J. Swartz, and C. Farrell,
"Magnesium Metabolism in Alcoholism," Am, J, Clin. Nutr., 13:297
(1963).
97. J. F. Sullivan, P. W. Wolpert, R. Williams, and J. D. Egan,
"Serum Magnesium in Chronic Alcoholism," Ann. N. Y. Acad. Sci.,
162:947 (1969).
98. R. J. McCollister, E. B. Flink, and R. P. Doe, "Magnesium Balance
Studies in Chronic Alcoholism," J. Lab. Clin. Med., 55:98 (1960).
99. J. H. Mendelson, B. Barnes, C. Mayman, and M. Victor, "The Deter
mination of Exchangeable Magnesium in Alcoholic Patients,"
Metabolism, 14:88 (1965).
100. J. H. Mendelson, M. Ogata, and N. K. Mello, "Effects of Alcohol
Ingestion and Withdrawal on Magnesium States of Alcoholics: Clinical
and Experimental Findings," Ann. N. Y, Acad. Sci., 162:918 (1969).
101. M. S. Seelig, "Electrographic Patterns of Magnesium Depletion
Appearing in Alcoholic Heart Disease," Ann. N. Y. Acad, Sci., 162:
906 (1969).
102. J. E. Jones, S. R. Shane, W. J. Jacobs, and E. B. Flink, "Magnesium
Balance Studies in Chronic Alcoholism," Ann. N. Y. Acad. Sci., 162:
934 (1969).
103. S. M. Wolfe and M. Victor, "The Relationship of Hypomagnesemia and
Alkalosis to Alcohol Withdrawal Symptoms," Ann. N. Y. Acad, Sci.,
162:973 (1969).
104. E. C. Wacker and A. F. Parisi, "Magnesium Metabolism," New Eng. J.
Med., 278:712 (1968).
105. J. E. Jones, P. C. Desper, S. R. Shane, and E. B. Flink, "Magnesium
Metabolism in Hyperthyroidism and Hypothyroidism," J, Clin. Invest.,
45:891 (1966).
106. J. T. Potts and B. Roberts, "Clinical Significance of Magnesium
Deficiency and Its Relation to Parathyroid Disease," Am. J. Med, Sci.,
235:206 (1958).


This dissertation was submitted to the Dean of the College of Engineering
and to the Graduate Council, and was accepted as partial fulfillment of
the requirements for the degree of Doctor of Philosophy.
March, 1972
Dean, Graduate School


125
SUBJECT: NB STUDY GROUP: 1
DATE, TIME OF INJECTION: 9-23-69, 12:20 DOSE: 10.35 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
100
10.1
95
4
99
-1
22.8
96
6
102
+2
46.6
92
9
101
+1
70.1
86
11
97
-3
94.9
82
13
95
-5
142.7
75
16
91
-9
165.9
76
18
94
-6
189.8
73
20
93
-7
213.8
75
23
98
-2
*Expressed in per cent,
rounded off
to the
nearest whole number.
- Means not measured


APPENDIX B
28Mg BALANCE CHARTS
NORMALS AND PATIENTS


TABLE 2
SUMMARY OF DETECTION SYSTEMS
System
Manor Components
and Manufacturer
Use and Study Group
4-Pi Liquid
Detector and shield
Packard Instrument Co.
Downers Grove, Ill.
Whole-Body Retention
Scintillation
Whole-Body Counter
ft
400-channel analyzer,
three-channel scintil
lation spectrometer
Packard Instrument Co.
Measurements
1-7
Shadow-shielded
4-inch by 9-inch
Nal(Tl) Crystal
Harshaw Chemical Co.
Cleveland, Ohio
Whole-Body Retention
Measurements
7
Nal(Tl) Crystal
400-channel analyzer
Packard Instrument Co.
Whole-Body Counter
Shadow shield and
supporting frame
University of Florida
Study of Localization 7
'Nal(Tl) Crystal
4-inch by 4-inch
Nal(Tl) Crystal
Harshaw Chemical Co.
Urine Analysis
1-4
Counter
400-channel analyzer
Packard Instrument Co.
Shield
Custom Fabricated
Sweat Analysis
7
Large Volume
Detector and shield
Custom Fabricated
Urine and Feces
Well Counter
Two-channel scintil
lation spectrometer
Packard Instrument Co.
Analyses
5-7


130
SUBJECT: NF STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 8:58 DOSE: 9.344 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours)Retention* Urine Feces Balance* Deficit*
0.4
100
-
-
100
10.6
96
3
-
99
-1
27.0
92
6
-
98
-2
50.1
90
13
-
103
+3
74.6
86
16
-
102
+2
98.0
84
18
-
102
+2
146.7
79
20
-
99
-1
170.7
76
22
-
98
-2
194.9
70
24
-
94
-6
218.0
70
26
96
-4
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


WHOLE -BODY RETENTION, %
Figure 32. Whole-Body Retention as Measured by the Nal(Tl) Counter.
|


7
considerable quantities of magnesium in all tissues. As the key
element in the maintenance of the anatomic structure of the mito
chondrion, it is essential for life (6),
Content in the Human Body
The first estimate of the chemical composition of the human
body appeared in 1859 in Moleschatt's handbook of dietetics (20). A
number of other estimates were made during the next 100 years (21-23),
but it wasnt until 1942 that the first reliable approximation of the
total amount of magnesium in the adult human body was made. At that
time, Duckworth (24) reported that an adult weighing 70 kilograms (kg)
had a total content of 29 grams (g) of magnesium, which was somewhat
higher than the 21 g measured by Shohl in 1933 (25). In 1951, Widdow-
son, McCance, and Spray (2) published the first complete chemical
analysis of the human body based on cadaver studies of three adults.
They reported values of 48.4, 42.7, and 43.0 milligrams (mg) of magnesium
per 100 g (i.e.: 33.0, 29.5, and 30.5 g per 70 kg). Currently, it is
generally agreed that the total amount in a 70-kg man is approximately
2,100 milliequivalents (mEq) (25.5 g) (25).
Although magnesium is frequently referred to as a trace element-
it is hardly that being the fourth most abundant cation in the human
body (17). Only sodium, potassium, and calcium exceed it in content.
In 1952, Sherman in his book, The Chemistry of Food and Nutrition, states
that magnesium comprises about 5 per cent of the adult human body (26).
It is located principally in the skeleton and the cells of the soft
tissue. It is primarily intracellular, exceeded in content there only
by one other cation, potassium. Slightly more than half of total-body


79
rates in plasma are important to consider here. Wallach e_t al. assumed
that within 13 minutes after injection the isotope had equilibrated with
the extra-cellular magnesium pool and then verified the relation:
SA = Ae-at + Be_bt + Cect,
where SA is the specific activity of 28Mg in plasma. According to
Wallach, one of the simplest models consistent with such a function
which could be applied to metabolism is the parallel three-compartment
open system. Computer derived exponents for the sum of exponentials
model yielded the following turnover times of the isotope in plasma:
0.17, 2.4, and 66 hours.
In 1966, Yun et. al. (11) reported the use of a higher specific
activity 28Mg (-20 pCi per mg magnesium) in too normal subjects. They
stated that up until that time, "precise knowledge of the daily rate of
turnover of magnesium in the body" was not known. According to Yun,
earlier data, derived either from non-isotopic techniques or by radio
isotope studies, are all overestimations because of the "loading effect
of the dose of 24Mg administered."
They administered intravenous doses of 145 and 155 pCi to the
too subjects and followed turnover of 28Mg in plasma and urine. A sum of
three exponentials equation was chosen to describe the rate of urinary
excretion. The following equations express the rate of urinary excre
tion in per cent of the administered dose per hour for the two subjects:
(1) dU/dt = e-0*4278t + 0.126e"0-077t + 0.106e-'00236t,
(2) dU/dt = e-693t + o.2e"-139t + 0.11e--00173t.
Another measure of magnesium turnover was reported by Raynaud
and Kellershohn (194). They used a sum of exponentials approach to


Whole-Body Retention
An alternative method of whole-body retention analysis was
made using the crystal counter results primarily because patient PB was
not able to maintain the supine position necessary for the 4-pi counter
measurement. Results of measurements by the crystal counter on the
three other subjects were used to intercompare results of 4-pi counter
measurements.
Whole-body retention as a function of time after administra
tion of the isotope is shown for the two normals and the two ALS
patients in Figure 32. The two normals, NH and NM, have similar reten
tion functions; at the last observation (=165 hours)* they had retentions
of 69 and 66 per cent, respectively.
The retention of the two patients, PA and PB, was signifi
cantly lower than those of the normal subjects. This difference is
consistent with the observations made with the 4-pi counting system on
ALS and normal subjects. The two patients have similar curves up to
=115 hours; at this point PB's curve takes a sharp upward turn (dashed
curve). This positive change in slope has to be an anomaly in the
counting measurement since it is impossible for the patient to have an
increase in total-body 28Mg.
In general, the retention values for all four subjects meas
ured by the crystal counter are proportional to those measured with the
4-pi counter during the same time period. In Table 6, the two systems
Although these subjects were followed for 220 hours on the
4-pi counter during this study, measurements beyond 165 hours were not
possible with the crystal counter because of its higher minimum detect
able activity level (due to lower counting efficiency and minimum back
ground reduction achieved by only partial shielding.


Figure Page
17. WHOLE-BODY RETENTION OF 28Mg: NORMAL SUBJECTS 62
18. REPLICATIONS IN MEASUREMENTS OF WHOLE-BODY RETENTION
IN TWO NORMALS 65
19. MODEL FOR 28Mg RETENTION IN NORMAL SUBJECTS 69
20. TOTAL-MEASURED 28Mg FOR NORMALS NA, NB, AND NC 71
21. TOTAL-MEASURED 28Mg FOR NORMALS ND, NE, NF, AND NG . . 72
22. TOTAL-MEASURED 28Mg FOR NORMALS NH, NI, AND NJ 73
23. TOTAL-MEASURED 28Mg FOR NORMALS NK, NL, AND NM 74
24. TOTAL-MEASURED 28Mg AVERAGE OF ALL NORMALS 76
25. WHOLE-BODY RETENTION OF 28Mg ALS PATIENTS 91
26. TOTAL-MEASURED 28Mg PATIENT PA 92
27. TOTAL-MEASURED 28Mg PATIENTS PB, PG, AND PI 93
28. WHOLE-BODY RETENTION OF 28Mg GASTRECTOMY PATIENTS .... 94
29. TOTAL-MEASURED 28Mg PATIENTS PC, PE, PH, AND PJ 95
30. WHOLE-BODY RETENTION OF 28Mg PATIENTS WITH
MISCELLANEOUS DISEASE CONDITIONS 96
31. TOTAL-MEASURED 28Mg PATIENTS PK, PF, PD, AND PL 97
32. WHOLE-BODY RETENTION AS MEASURED BY THE Nal(Tl) COUNTER . 105
33. REGIONAL RETENTION OF 28Mg 109
viii


WHOLE-BODY RETENTION AND EXCRETION OF MAGNESIUM IN HI
BIOLOGICAL HALF-LIFE IN NORMALS AND SELECTED DISEASE
II. RADIATION DOSIMETRY
By
Genevieve Schleret Roes
ler
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL
OF THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE DEGREE OF DOCTOR OF PHILOSOPHY
MANS:
STATES
UNIVERSITY OF FLORIDA
1972

ACKNOWLEDGMENTS
Foremost appreciation is expressed to Billy G. Dunavant, Ph.D.,
my committee chairman, for his supervision, inspiration, and guidance,
not only in this phase of graduate work, but also in previous graduate
study and employment. My interest in the area of the use of radioactive
isotopes in the biological field has stemmed from and followed his
interests.
I also gratefully acknowledge the contributions to my research
by the other members of my committee: W. Emmett Bolch, Ph.D., for
guidance in graduate work, for review and critical analysis of manu
scripts, and for participation in this research as a "normal"; Clyde
Williams, M.D., for clinical advice and direction; and Hugh Putnam, Ph.D.,
for inspiration and advice.
I should also like to acknowledge the support by the College of
Medicine, University of Florida, and, in particular, the many hours
of cooperation by Jared C. Kniffen, M.D., gastroenterologist, and
Donald T. Quick, M.D., neurologist. Others without whose assistance
this research would not have been possible include the staff at the
Clinical Research Center; the staff at the Medical Center Library;
Thomas Bauer, Howard Kavanaugh, Jerry Sawyer, Pat Edgett, Phyllis Durre,
Ann Groves, Lois Fischler, Mike Hewson, James McVey, and Sharon Corbett
of the Radiation Biophysics Section of the Department of Radiology; and
John Thomby, Ph.D., of the Department of Statistics. A special note of
ii

thanks is due Larry Fitzgerald for his motivation and assistance in my
graduate work.
I particularly wish to thank my husband, Chuck, for his assistance,
advice, and encouragement in every phase of my graduate studies and
research. I wish to recognize the assistance of my oldest daughter,
Teresa, with typing, filing, and library work. She and my other
children, Cynthia, Mary, Francis, Kay, Jean, and Anne, have been very
patient and understanding throughout my graduate studies and have assumed
many household duties in order to ease my domestic responsibilities. I
wish to express special appreciation to my father, Leo Schleret, for his
continuing interest in my academic career and, in particular, for his
contribution as a "normal" in this research.
Financial support by the Environmental Protection Agency, Training
Grant Number 2-T01-EP00046-11, is also acknowledged.
iii

TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ......... ii
LIST OF TABLES vi
LIST OF FIGURES ............. vii
ABSTRACT ix
CHAPTER
I. INTRODUCTION . 1
II.LITERATURE REVIEW 6
Occurrence of Magnesium in Nature 6
Importance of Magnesium to Man 6
Techniques for Measuring Stable Magnesium 17
Studies with Magnesium-28 19
III.MATERIALS AND METHODS . 33
Magnesium-28 33
Experimental Conditions and Techniques 35
Instrumentation 40
Data Analysis Techniques 57
IV.RESULTS AND DISCUSSION 61
Whole-Body Retention of in Normals ........ 61
Excretion of 28^g in Normals 68
Calculation of Radiation Dose 84
Retention and Excretion of 28yjg in Selected Disease
Conditions .......... 87
Measurements with the Nal(Tl) Crystal Whole-Body
Counter 103
V. SUMMARY AND CONCLUSIONS 113
Conclusions 115
APPENDICES 117
A. COMPUTATION OF RADIATION DOSE 118
iv

Page
B. 28Mg BALANCE CHARTS NORMALS AND PATIENTS ...... 123
C. SWEAT ANALYSIS, STUDY GROUP 7 154
D. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER RETENTION
AND LOCALIZATION DATA 156
LIST OF REFERENCES 158
BIOGRAPHICAL SKETCH 173
v

LIST OF TABLES
Table Page
1. SUMMARY OF STUDY GROUPS 37
2. SUMMARY OF DETECTION SYSTEMS 41
3. 28Mg TURNOVER RESULTS IN HUMANS 81
4. COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT
28Mg STUDIES 85
5. PLASMA AND RED BLOOD CELL STABLE MAGNESIUM ANALYSES 90
6. COMPARISON OF THE WHOLE-BODY RETENTION MEASUREMENTS BY THE
4-PI LIQUID SCINTILLATION AND THE Nal(Tl) CRYSTAL WHOLE-
BODY COUNTERS 106
vi

LIST OF FIGURES
Figure Page
1. ISOTOPES OF MAGNESIUM 22
2. RADIOACTIVE DECAY SCHEME OF MAGNESIUM-28 AND ITS
RADIOACTIVE DAUGHTER, ALUMINUM-28 34
3. FLOOR PLAN OF THE RADIATION BIOPHYSICS GRADUATE
PROGRAM FACILITY 42
4. 4-PI LIQUID WHOLE-BODY COUNTER LABORATORY ... 43
5. SUBJECT PREPARING TO ENTER THE 4-PI LIQUID WHOLE-
BODY COUNTER 44
6. ONE SIDE OF THE 4-PI LIQUID WHOLE-BODY COUNTER SHOWING
SIX PHOTOMULTIPLIER TUBES AND STEEL SHIELD 46
7. 4-PI LIQUID WHOLE-BODY COUNTER INSTRUMENTATION 47
8. SIGNAL DIAGRAM OF THE 4-PI LIQUID WHOLE-BODY
COUNTING SYSTEM 48
9. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: WHOLE-BODY COUNT
POSITION 50
10. GEOMETRY OF SUBJECT COUNTED ON THE Nal(Tl) CRYSTAL
WHOLE-BODY COUNTER 51
11. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
HEAD COUNT 52
12. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
CHEST COUNT 53
13. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
ABDOMEN COUNT 54
14. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
LEGS COUNT 55
15. LARGE VOLUME WELL COUNTER 56
16. Nal(Tl) CRYSTAL COUNTER ......... 58
vii

Figure Page
17. WHOLE-BODY RETENTION OF 28Mg: NORMAL SUBJECTS 62
18. REPLICATIONS IN MEASUREMENTS OF WHOLE-BODY RETENTION
IN TWO NORMALS 65
19. MODEL FOR 28Mg RETENTION IN NORMAL SUBJECTS 69
20. TOTAL-MEASURED 28Mg FOR NORMALS NA, NB, AND NC 71
21. TOTAL-MEASURED 28Mg FOR NORMALS ND, NE, NF, AND NG . . 72
22. TOTAL-MEASURED 28Mg FOR NORMALS NH, NI, AND NJ 73
23. TOTAL-MEASURED 28Mg FOR NORMALS NK, NL, AND NM 74
24. TOTAL-MEASURED 28Mg AVERAGE OF ALL NORMALS 76
25. WHOLE-BODY RETENTION OF 28Mg ALS PATIENTS 91
26. TOTAL-MEASURED 28Mg PATIENT PA 92
27. TOTAL-MEASURED 28Mg PATIENTS PB, PG, AND PI 93
28. WHOLE-BODY RETENTION OF 28Mg GASTRECTOMY PATIENTS .... 94
29. TOTAL-MEASURED 28Mg PATIENTS PC, PE, PH, AND PJ 95
30. WHOLE-BODY RETENTION OF 28Mg PATIENTS WITH
MISCELLANEOUS DISEASE CONDITIONS 96
31. TOTAL-MEASURED 28Mg PATIENTS PK, PF, PD, AND PL 97
32. WHOLE-BODY RETENTION AS MEASURED BY THE Nal(Tl) COUNTER . 105
33. REGIONAL RETENTION OF 28Mg 109
viii

Abstract of Dissertation Presented to the Graduate
Council of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy
WHOLE-BODY RETENTION AND EXCRETION OF MAGNESIUM IN HUMANS:
I. BIOLOGICAL HALF-LIFE IN NORMALS AND SELECTED DISEASE STATES;
II. RADIATION DOSIMETRY
by
Genevieve Schleret Roessler
March, 1972
Chairman: Billy G. Dunavant, Ph.D.
Co-Chairman: W. Emmett Bolch, Ph.D.
Major Department: Environmental Engineering
Thirty-one whole-body retention and excretion measurements
were made on 13 normal subjects and 12 patients with selected disease
conditions to determine as accurately as possible the biological half-
lives from a single intravenous administration of ^%ig in the form of
MgClg. The prime objective of this research was to contribute informa
tion to the currently sparce knowledge on magnesium metabolism in
humans. Calculation of radiation dose based on the determined half-
lives was an important aspect of the research since the experimental
use of 28pig is increasing rapidly and no dose estimates have been esta
blished. The feasibility of this measurement technique for studying
abnormalities in disease conditions was also explored.
A high specific activity (200-300 microcuries per milligram
magnesium) preparation of the radioactive isotope 28Mg (21.3-hour
physical half-life) was uped in conjunction with the sensitive 4-pi
liquid scintillation whole-body counting technique for retention
measurements. A Nal(Tl) crystal whole-body counter was employed to
measure localization of the magnesium in the body and appropriate low-
level counting systems were used for measurement of the isotope in
excreta.
ix

Whole-body retention data from the determinations on normal
subjects were fit to a sum of two exponentials model. The coefficients
of the resultant equation are 8.5 and 91.5 and represent the quantities
in per cent involved in the turnover of the two compartments. Biologi
cal half-lives of 5.4 2.2 hours for the first compartment and 540 1
35 hours for the second compartment were calculated from the rate
constants in the exponents of the fitted equation.
The radiation dose from this single administration of 28Mg
was calculated to be 2.0 mrad/microcurie.
In the normal subjects, excretion measurements on the average
accounted for the amount of the 28y¡g not retained in the body. Cumula
tive urinary excretion averaged 3 per cent per day while fecal excretion
was approximately 0.5 per cent per day.
Whole-body retention values for amyotrophic lateral sclerosis
and sub-total gastrectomy patients were significantly lower than
normal, while several subjects, one of whom was known to have been on
diuretics, had higher than normal retention of the isotope. Repaired
gastrectomy patients had retention patterns within the normal range.
In the majority of the patients studied, the abnormal
retention of 28pjg was accounted for by amounts in the excreta. However,
in several patients, excretion did not account for the total amount of
the isotope not retained in the body, resulting in a deficit in the
total-measured 28j^g,
Localization of the isotope in the body as measured by Nal(Tl)
crystal whole-body counting showed consistent patterns between results
of the normal subjects. An atypical build-up of the isotope was found
in the abdominal region of the amyotrophic lateral sclerosis patient
x

who previously exhibited an apparent precipitous whole-body loss of
28Mg.
Based on published investigations to date, it is concluded
that this turnover study is currently the most accurate. The use of a
true tracer dose of 10 microcuries or less of high specific activity
o o
Mg and the sensitive whole-body counting system allowed administration
of a dose which would not upset the physiochemical balance of the body.
Also, this procedure permitted measurements up to six times longer than
previously reported studies.
The amount of 28Mg to be administered in future investigations
with this isotope should be guided by the 2.0 mrad/microcurie dose
calculated from the data obtained in this study.
Based on the consistent, significantly abnormal retention
and excretion patterns shown by certain disease-state measurements in
this study, it is concluded that this turnover procedure could serve
as a valuable adjunct to other diagnostic techniques.
xi

CHAPTER I
INTRODUCTION
Nothing but a cloud of elements organic,
C. 0. H. N. Ferrum, Chor. Flu. Sil. Potassa,
Calc. Sod. Phosph. Magn. Sulphur, Mang.(?) Alumin.(?) Cuprum(?)
Such as man is made of (1).
Oliver Wendell Holmes, in a poem called "DeSauty, an electro
chemical ecologue," included magnesium in a list of elements of which he
thought man to be composed. Holmes wrote the poem in 1859, almost a
century before an accurate measurement of the human body content of
magnesium was made (2). Although he gave no indication about his
source of information, his prophetical inclusion of magnesium in the
composition of the human body came many years before scientists were to
provide conclusive evidence that magnesium is a required nutrient.
It is now known that magnesium is one of the most biologically
important metallic ions. Magnesium is second only to potassium in
abundance as an intracellular cation in humans (20-30 milliequivalents
per kilogram) (3); the element is knox-m to activate many enzymatic
reactions, it is essential for neuromuscular function and protein
synthesis, and it is an important constituent of bone (A).
Much has been written about the contribution of magnesium to
biological functions and its importance in metabolic processes. Never
theless, little information is available on magnesium in man (5), although
interest in its metabolism and nutritional significance has increased
1

2
greatly during the past decade (6). Consequently, as recently as 1969,
researchers deplored the fact that this essential element had not been
investigated to anywhere near the same extent as calcium, phosphorus,
potassium and other fundamental ions (7). Because of the interrelation
ships of these cations, any lack of information on magnesium limits
the amount of knowledge obtainable on the function of the others.
The study of magnesium metabolism in the. human has been
hampered by technological difficulties (4). In spite of recent refine
ments in classical procedures such as precipitation, fluorimetry,
and the titan yellow method, the element is difficult to measure in
biological materials (8). Over the past decade, routine procedures
have been developed using emission flame spectroscopy and atomic
absorption spectrophotometry for analyses of the metal in body fluids,
tissue, and excreta. These techniques are accurate, but the equipment
is expensive and complex and consequently not available to many clinical
laboratories.
Another more important factor has delayed progress in the study
of the function of magnesium in humans. Although a complete analysis
of stable magnesium can be made from cadaver studies, this "final
analysis" supplies information only on what the content of the living
body was. It can not provide information on the dynamics and function
of magnesium in the living subject. Thus, in vitro measurements of
stable magnesium are made in serum, plasma, urine, feces, and even in
red blood cells, in attempts to establish some means of delineating
normal and abnormal metabolism of the element. The general consensus
of many authors (4,5,7) is that the level of magnesium in the various

3
body fluids has little relationship to total-body magnesium and probably
predicts very little that is reliable and consistent about its metabolism.
The use of radioactive tracers has provided keys to new know
ledge about the metabolism of many essential elements. However, it
wasn't until 1953 (9) that a suitable radioisotope of magnesium
28
(magnesium-28 ( Mg)) was discovered. The first article on the use of
this isotope for biological investigations did not appear until five
years later (10).
Although the use of as a tracer overcomes many limita
tions present in stable analysis, the isotope itself has a limitation;
its short physical half-life (21.3 hours) makes long-term measurements
impossible (3).
Nevertheless, during the past decade, a number of attempts
have been made to further the understanding of magnesium metabolism
by determining the biological half-life and by defining the metabolic
compartmentalization of the element in humans. However, a later discus
sion will show that results of these studies vary widely. Most of these
studies involve the measurement of excretion rates and/or clearance
from plasma or serum of 28j,jg following a single administration of the
isotope in the chloride form. The short physical half-life limited
measurement to only 40 144 hours after administration. In addition,
until recently, only low specific activity (<20 microcuries per
milligram (yCi per mg) of magnesium)was available. Investigators who
used this lower specific activity compound report that the dose that
could be administered was "limited by concern for upsetting the magnesium
balance of the system under study" (4) and because of the possibility

4
of chemical toxicity (11). A number of researchers discontinued their
work with because of the restrictions placed on the accuracy of
the results by both the isotopic compound and the measurement techniques
and equipment (12-14).
An opportunity to reduce these technical problems came when
Brookhaven National Laboratory began production of a high specific
activity preparation of (200-300 ytCi per mg magnesium). This
compound, plus the use of a highly sensitive 4-pi whole-body counter
for measuring whole-body retention of small quantities of the isotope,
made it possible to overcome problems associated with overloading the
system with magnesium. More important, the use of the whole-body
counter permitted measurements with a relatively small dose of the
isotope up to six times as long as was previously possible.
Therefore, a prime objective of this study was to determine
the biological half-life (or half-lives) of by measuring whole-body
retention after a single intravenous dose. Excretion was measured in
addition to the whole-body retention as a means of completing total-
balance studies of 28Mg. Another major objective of this study was to
determine the total-body radiation dose from the isotope. This deter-
' mination is particularly important now due to the availability and
anticipated frequent use of the higher specific activity 28Mg.
A small number of persons with selected disease conditions
who were suspected of having abnormal magnesium metabolism were included
in the study to examine the possibilities of using this isotope technique
for determining disease state metabolism anomalies. The feasibility
of using either retention or excreta measurements as a part of a diag
nostic procedure was another facet of this research.

5
The significance of this work as a contribution to the more
complete understanding of the function and metabolism of magnesium in
humans can perhaps be stated in the same way that McCance and Widdowson
(15) evaluated their research in 1939. In regard to experiments they
conducted on the fate of stable magnesium after intravenous administra
tion to normal persons, these researchers said:
These experiments are only a small contribution toward the
solution of a very large and complicated problem, but they
raise interesting points which deserve consideration.

CHAPTER II
LITERATURE REVIEW
Occurrence of Magnesium in Nature
Magnesium forms about 2.1 per cent of the earth's crust and
is the third most abundant of the industrial metals. It is widely
distributed in nature in a variety of forms; those used most commonly
are carbonate, oxide, and chloride which occur as dolomite, brucite and
carnallite (16). Its name is derived from Magnesia, a Greek city in
Asia Minor, where a large deposit of carbonate is located.
Magnesium has an atomic number of 12 and is usually classi
fied with the alkaline earth metals calcium, strontium, and others -
although in many ways it has a closer resemblance to zinc and cadmium
(17). Like the other metals of the alkaline earths, it readily forms
divalent ions.
Importance of Magnesium to Man
Magnesium Content in Living Tissue
It is now known that magnesium is present in all living
things (18). However, it wasn't until 1906 that the belief that
magnesium is essential for growth in higher plants was confirmed by
Wills tatter, who discovered that it forms an integral part of the
chlorophyll molecule (19*). Since that time, it has been shown that
magnesium is present in chlorophyll in all green plants and that it is
a universal microconstituent of lower plants. Higher animals have
6

7
considerable quantities of magnesium in all tissues. As the key
element in the maintenance of the anatomic structure of the mito
chondrion, it is essential for life (6),
Content in the Human Body
The first estimate of the chemical composition of the human
body appeared in 1859 in Moleschatt's handbook of dietetics (20). A
number of other estimates were made during the next 100 years (21-23),
but it wasnt until 1942 that the first reliable approximation of the
total amount of magnesium in the adult human body was made. At that
time, Duckworth (24) reported that an adult weighing 70 kilograms (kg)
had a total content of 29 grams (g) of magnesium, which was somewhat
higher than the 21 g measured by Shohl in 1933 (25). In 1951, Widdow-
son, McCance, and Spray (2) published the first complete chemical
analysis of the human body based on cadaver studies of three adults.
They reported values of 48.4, 42.7, and 43.0 milligrams (mg) of magnesium
per 100 g (i.e.: 33.0, 29.5, and 30.5 g per 70 kg). Currently, it is
generally agreed that the total amount in a 70-kg man is approximately
2,100 milliequivalents (mEq) (25.5 g) (25).
Although magnesium is frequently referred to as a trace element-
it is hardly that being the fourth most abundant cation in the human
body (17). Only sodium, potassium, and calcium exceed it in content.
In 1952, Sherman in his book, The Chemistry of Food and Nutrition, states
that magnesium comprises about 5 per cent of the adult human body (26).
It is located principally in the skeleton and the cells of the soft
tissue. It is primarily intracellular, exceeded in content there only
by one other cation, potassium. Slightly more than half of total-body

8
magnesium is present in bone; however, its precise location there is
not known (27).
The exchangeable body content of magnesium in humans is 2.6 -
5.3 mEq/kg of body weight, whereas the total-body content is about 30
mEq/kg. The labile pool is contained primarily in connective tissue,
skin, and the soft tissues of the abdominal cavity; the magnesium in
bone, muscle, and red blood cells exchanges slowly (28).
The most recent summaries of magnesium content in humans,
particularly with regard to its biochemistry and its homeostasis,
appeared in reviews by Wacker (29) and Heaton (30) in 1969.
Requirements of Magnesium by the Normal Adult
Although magnesium has always been a part of man's diet
because of its abundance in nature, interest in it as a dietary con
stituent didn't develop to any extent until the latter part of the
nineteenth century. Reports in 1894 that it was present in animal
tissue (31) led many investigators to believe that magnesium more than
likely was an essential nutrient (32). The report of Sherman and
co-workers (33) in 1910 that magnesium was retained by humans subsisting
on a wide variety of diets was proposed as suggestive evidence of man's
requirement for this element (32).
In 1910, the Office of Experiment Stations of the United
States Department of Agriculture published Bulletin 227 which included
a summary of balance studies on magnesium (33). It was reported in
this bulletin that magnesium is absorbed from the intestinal tract
and deposited in the tissues of the body, especially in bone. However,
the balance data did not show that it was a required nutrient, nor that
it had a definite function.

9
In 1926, Leroy demonstrated that magnesium is essential in
animal diets (34). This finding prompted numerous studies in the
latter 1920s and early 1930s on magnesium's role in animals and in
man. In 1929, Joachimoglu and Panopoulous (35) analyzed foods typical
of a normal diet and concluded that an adequate amount of magnesium is
obtained by normal intake to meet the body's requirements. In 1932,
the daily need was reported as 300 mg (36), a figure which is still
quoted by some as authoritative (37). A number of reviews of magnesium
metabolism followed including: Shohl, 1933 (25); Schmidt and Greenberg,
1935 (38); and Greenberg, 1939 (39).
A thorough reviey of magnesium in nutrition in 1939 by Duck
worth (40) included a summary of metabolism and magnesium deficiency in
addition to a comprehensive synopsis on methods of estimation, occurrence,
and distribution, on the relationship of magnesium to disease, and on
magnesium requirements in domestic animals and in man. In his review
of the literature, he found that estimates of the daily requirements of
magnesium range from 20 298 mEq (24 358 mg). More recent metabolic
balance studies propose an average adult requirement of at least six
mg per kg of body weight per day (420 mg for a 70-kg man) (6).
A summary of the sources of magnesium and an analysis of
the reported data on magnesium balance in normals in different parts
of the world were published in 1964 by Seelig (41). Foods which she
considers as rich in magnesium include cocoa and chocolate, nuts, some
seafoods, bean- and pea-typs vegetables, and grains. Green leafy
vegetables, some fruits, and certain meats are listed as foods with a
moderate amount of magnesium. Many foods regularly eaten in a normal

10
diet are relatively poor in the element. However, according to Seelig,
it is generally agreed that because magnesium is so plentiful in the
normal diet, deficiences of it cannot develop in the absence of disease.
However, she emphasizes that currently accepted magnesium requirements
should be reevaluated to make certain that the optimal daily intake of
the mineral is correct, since prolonged dietary insufficiency of it may
contribute to the development of chronic disease.
Relationship of Magnesium with Other Ions and Compounds
It has been known since 1909 that a relationship exists between
calcium and magnesium metabolism. Mendel and Benedict (42) showed that
an infusion of calcium in animals produced an increase in their
urinary excretion of magnesium and vice versa, a phenomenon later con
firmed in man (43,44). Several decades later it was shown that experi
mental magnesium deficiency produced disturbances in calcium metabolism
(45-47). The absorption of magnesium from the gastrointestinal tract
has also been shown to be influenced by protein intake (48), growth
hormones (49), large doses of vitamin D (50), and certain antibiotics
(51). Vitamin D (52) and certain carbohydrates (53) also affect
magnesium metabolism.
Current reviews of the interrelationship of magnesium with
calcium and phosphorus present data on the complex interactions of
these cations in man and in animals (54-60). Most significant of
these is that magnesium deficiency disturbs calcium metabolism and
that in calcium deficiency, when magnesium is available, it can
replace bone calcium to a limited extent (61). Stearns, speaking for
the Journal of the American Medical Association Council on Foods and

11
Nutr.tion, advocates "the maintenance of an adequate, even ample,
intake of calcium, magnesium, and phosphorus throughout the entire
life span" (61). She comments that "calcium, phosphorus, and magnesium
are usually considered together from a nutritional point of view
because all three occur in bone, and, with carbonate, make up the major
part of the bone mineral." Stearns also points out that of the three
elements, magnesium has been studied far less thoroughly because chemical
methods for its determination have been less satisfactory.
Potassium is another element frequently studied with magnesium,
since the two make up the bulk of the intracellular cations. Like calcium
more is known about potassium, primarily because of the ease with which
it can be measured (62) Two recent reviews concentrating on the
interrelationship of magnesium and potassium were published by Hammarsten
et al, (63) and Whang (64) The influence of various nutrients and
hormones on urinary magnesium and other divalent cation excretion was
reviewed in 1969 by Lindeman (65).
Clinical Significance of Magnesium
The first recorded association of magnesium with medicine
dates back to the Renaissance in Italy when various salts of magnesia
were used as laxatives (66) Magnesium sulfate, or epsom salts as it
was known hundreds of years ago, did not actually become popular as a
treatment until 1618 when it was used to "improve gastrointestinal
function" (67). A mineral springs was discovered that year on the manor
of Epsom in a municipal borough of Surrey, England. Although the
mineral composition of the water was not analyzed, its "healing"
qualities became so well known that a spa grew up at Epsom which reached

12
its zenith a century later (68) More recently it was shox^n that the
"healing" effect found from drinking the water containing the then
mysterious ingredient apparently was related both to its purgative
action and to its sedative effect.
Magnesium was used in that manner until 1911 when its external
use as sulfate was reported in Lancet (69) Patients suffering from
erysipelas or cellulitis applied a saturated solution of the compound
to painful areas and found relief. Four years later magnesium meta
bolism was first clinically studied by Holt e_t al. (70) in infants with
diarrhea by measuring magnesium intake and fecal excretion. However,
as recently as 1931, no clinical significance had been attached to
changes of magnesium in metabolism, even though the manifestations of
magnesium excess in man had been known since 1913, according to the
classic work, Quantitative Clinical Chemistry by Peters and Van Slyke (71).
In 1916, pharmacologic studies of the properties of magnesium as a
potential anticonvulsant and anesthetic agent showed that an excess of
the ion led to impairment of neuromuscular transmission (72). Further
study has shown that even general anesthesia can be produced by infusions
of magnesium; however, concentrations necessary to do this are dangerously
close to those required to produce respiratory paralysis (73). Uninten
tional production of magnesium excess occurs most frequently in patients
with renal failure (74).
On the other hand, the "indispensibility of magnesium for the
animal organism rested insecurely on a teleological basis" until the
early 1930s when Kruse jit al. (75) published their observations on
magnesium deficiencies in the rat. Earlier workers apparently had
failed in attempts to produce clinical changes in animals because of

13
the difficulty in obtaining a low magnesium diet (76). Kruse described
the classical symptomology of magnesium deficiency and observed that
it resembled that of low-calcium tetany.
During the next few years, there were many attempts to associ
ate dietary inadequacy of magnesium with increased incidence of malignant
neoplasms. Shear (77), in 1933, reviewed these reports and found the
evidence contradictory and insufficient, A short time later, Walker and
Walker (78) published a work which included an extensive review of the
physiological importance of magnesium and the variations of magnesium
levels in abnormal states. In their study, they compared the range
of serum magnesium in 91 miscellaneous medical and surgical patients
and in a group of persons with hypertension both with and without renal
damage. They concluded that "contrary to certain statements in the
literature, serum magnesium may be elevated in moderate or severe renal
insufficiency, especially if associated with hypertension."
The first investigators to succeed in producing magnesium
deficiency experimentally were Orent and his co-workers (79). They
stated in their 1934 paper that rats in the study showed a depletion
of bone magnesium after being fed a diet containing only 1.8 parts per
million (ppm) of magnesium. After four days on the diet "all exposed
skin areas became vividly red from vasodilation; irritability and
hyperexcitability was exhibited in eight to 10 days; growth stopped
after a week; convulsions began to occur by the 18th day; and death
usually followed the first or subsequent convulsions." That same year,
Hirshfelder (80) described magnesium deficiency in man. However, it
was not until 1959 that the first cure of magnesium deficiency in man

was reported (81). Five patients being fed intravenously developed
severe muscle cramps and convulsions. The symptoms suggested calcium
deficiency, but investigations showed that the patients had been
receiving a sufficient amount of calcium in the liquid nutrient. However,
they had received no magnesium. After intravenous administration of
magnesium sulfate, all of the patients improved within hours and were
soon asymptomatic.
A number of additional attempts to induce magnesium deficiency
took place in the 1930s through the 1960s. Knoop et al. (82), while
studying magnesium and vitamin D relationships in calves fed mineralized
milk, found that the soft-tissue content of magnesium is not appreciably
altered even in severe deficiency. This may be the reason that when
Fitzgerald and Fourman (83) fed a diet containing essentially no
magnesium to normals for 27 days no symptoms of magnesium deficiency
were observed. In addition, they found no differences in the magnesium
blood levels in these subjects between normal and low-magnesium intake
periods. In another case, Barnes et al. (27) did not observe any hypo
magnesemia or deficiency symptoms in a patient maintained for 38 days
on gastrostomy feedings which contained little magnesium.
In contrast, Shils (84) reported that plasma and red blood
cell magnesium levels fell significantly below normal in two normal
volunteer subjects while they were on a deficient diet for 274 and 414
days. Signs and symptoms of magnesium deficiencies appeared in both
subjects and reversal occurred upon administration of magnesium. In
comparison to the deficiency symptoms first reported in 1934 by Orent
et al. (79), Wacker and Paris! (74) more recently described the syndrome in
man as one involving "neuromuscular dysfunction manifested by hyperexcitability,

15
sometimes accompanied by behavioral disturbances." These disturbances,
which can be reversed by administration of magnesium, include tetany,
generalized tonic-clonic as well as focal seizures, ataxia, vertigo,
muscular weakness, tremors, depression, irritability, and psychotic
behavior.
Despite the indications of a relationship between disease
conditions and magnesium abnormalities, published articles manifesting
a clinical interest in this cation were few until the 1950s. About
that time, Martin and co-workers (85,86) and Flink and colleagues (87-90)
published results which revived the interest in magnesium abnormalities.
Both groups detected low plasma levels of magnesium in surgical patients
receiving fluids parenterally, in patients receiving diuretic therapy,
and in diabetics.
Then in 1954, a serendipitous occurrence led to the discovery
that patients with chronic alcoholism and delirium tremors are magnesium
deficient. This was discovered when magnesium, because of its sedative
effect, was used by Flink and associates to treat delirium tremors (91).
The manifestations "were promptly alleviated by the administration of
magnesium sulfate intramuscularly in amounts which are not hypnotic."
Flink e£ al. found the serum levels of all of these patients on admission
to the hospital significantly lower than normal. They reason that
magnesium deficiency in chronic alcoholism is similar to that induced
by a magnesium deficient diet. The caloric requirement, of these patients
is satisfied by alcohol almost exclusively for a long time and, thus,
their diet is low in magnesium.
More recently, other clinicians have reported that, in addition
to a magnesium deficient diet, an alcohol-induced renal excretion is an

16
important factor in magnesium depletion (92,93). Other studies of
magnesium depletion in alcoholism and reviews of the subject have been
published since that time (94-103).
As a result of Flinks discovery of magnesium deficiency in
alcoholics, extensive research on magnesium metabolism has been
stimulated, not only in alcoholics, but in other disease conditions as
well. Other magnesium insufficiencies have been reported in cases of
malabsorption syndromes, prolonged or severe loss of fluids, lactation,
diuretic therapy, diabetic acidosis, hyperaldosteronism, hypercalcemia
(104), hyper- and hypothyroidism (105), parathyroid disease (106,107),
inflammatory bowel disease (108), celiac disease (109) Kwashiorkor and
protein calorie nutrition (110), Grave's disease (111), and cardiac
necrosis (112). Barnes has evaluated magnesium requirements and
deficiencies in surgical patients (113,114) and Wacker and associates
were the first to describe normocalcemic magnesium deficiency tetany (115).
The relationship of magnesium metabolism and other conditions such as
hyperparathyroidism and osteolytic disease (116), chronic renal disease
(117), hypokalemia (118), gastrointestinal disease (119), and malnutrition
(120) were reviewed in 1969.
Literature reviews of magnesium deficiency are plentiful
(30,87,88,121-131) and they cover studies from the 1930s to the present.
The most recent comprehensive reviews were published in 1965 by Aikawa (132),
and in 1968 by Wacker and Parisi (74,104), and in 1969 by Gitelman and
Welt (133). Reviews of deficiencies in both man and in animals appeared in
the August, 1969, edition of the Annals of the New York Academy of Sciences on
The Pathogenesis and Clinical Significance of Magnesium Deficiency (134-
137). A summary of the experimental production of magnesium deficiency

17
in man is also in the same edition (138). In that study, magnesium
deficiency was induced in seven volunteer adult human subjects. All
of the subjects developed neurologic and/or gastrointestinal changes
of varying degrees. All clinical and biochemical changes produced
in the study were reversed by the administration of magnesium. In
another review, conditions associated with abnormalities of magnesium
was reported by Barker (139). Seelig (41), in her review of the
requirements of magnesium by the normal adult, also reviewed the
different aspects of magnesium deficiencies and the role of magnesium
in disease. Magnesium in human nutrition was published as a home econo
mics report by the U. S. Department of Agriculture in 1962 (140). The
scope of the report included the biological role of magnesium in humans
and a review of data on magnesium in tissues.
Techniques for Measuring Stable Magnesium
The difficulty of making accurate in vivo measurements of
magnesium has always been a limiting factor in its investigation (141).
It is almost entirely this measurement problem that has kept the knowledge
of magnesium years behind that of the other essential elements in the
human body.
This situation has not gone unrecognized. In 1939, an
editorial in the Journal of the American Medical Association (19)
summarized the status of the magnesium problem at that time:
So little is known of the function of magnesium in the
organism that clinically observable abnormalities in man
cannot at present be said with certainty to be due to mag
nesium deficiency or to a disorder of magnesium metabolism.
The systematic study of magnesium metabolism by accurate
analytical and experimental methods is little more than
begun. Future investigations may be expected to add consider
ably to our knowledge of this problem.

18
Within a few years, the development of newer and better
techniques for precipitating magnesium in fluids encouraged a few
researchers to examine magnesium levels in body fluids (142). In
1942, Haury (129) reviewed the variation in serum magnesium in health
and disease and concluded that there was not a good correlation between
abnormal serum levels and disease conditions. It was not known then
whether this was due to poor techniques in measuring magnesium, to the
inability of serum to predict accurately total-body magnesium or
disturbance of magnesium within the body, or to the fact that magnesium
levels actually remained unchanged in many diseases.
Nevertheless, during the next 10 years, investigators (143,
144) continued to measure serum and/or plasma magnesium levels. The
older methods of precipitating magnesium as ammonium phosphate or hydrox-
yquinoline (145,146) were replaced by magnesium determinations by the
titan yellow technique (147-150), which was used extensively for some
years. In 1962, an automated fluorimetric method was described by
Hill (151) as an accurate procedure for magnesium analysis. Emission
flame spectrophotometry was another method recommended by Alcock et al. (152)
as a suitable measurement procedure in a wide range of materials. A more
recent publication by Alcock (153) reviewed the development of methods
for the determination of magnesium. She suggests that the best method
for estimation of magnesium in biological specimens is the "atomic
absorption, atomic emission, or the magnesium ammonium phosphate
precipitation method."
In 1963, MacIntyre (8) recommended that the method of choice
for magnesium measurements is absorption flame spectrophotometry. Others
maintain that the most acceptable means for magnesium analysis is the use
of the atomic absorption spectrometer (154-157). Although the instruments

19
used in this type of analysis are too complicated for routine work in
small laboratories, many large hospitals are set up to do magnesium
and calcium measurements with the atomic absorption spectrophotometer
(158). A number of smaller laboratories send serum and urine samples
out to larger laboratories for analysis (159). Results of the latter
may take up to six days. It appears that the atomic absorption spectro
meter is an accurate, although certainly not a simple,method for routine
analysis of magnesium in biological fluids.
However, as emphasized previously, most investigators are
uncertain as to what these fluid analyses mean. Thus, the question
which remains to be answered is whether there are ways other than analy
sis of extracellular magnesium or examination of intake and excreta that
will provide information about magnesiums role in the human body which
is not available with current techniques.
Studies with Magnesium-28
In 1939, Greenberg (39) reviewed calcium, magnesium, and
phosphorus metabolism. He paid particular attention to the development
up to that time in the study of mineral metabolism made possible by
radioactive isotopes. Because of the "revolutionary nature and potential
importance of this subject," Greenberg departed from his usual approach
in a review article to digress on the usefulness of radioactive tracers
in animal organisms. He pointed out the advantages of.this "new tool"
for studying "absorption, permeability, storage, distribution, chemical
transformation, and paths of excretion of the mineral elements." Another
important advantage, he commented,is that in general only very small
doses of the substance need be administered, "thus avoiding the criticism

20
that the normal body mechanisms are being overtaxed."
Further describing the major advantages of radioisotopes,
Greenberg stated:
In many respects, it is more advantageous to use radio
active than a non-radioactive isotope because the detection
of the radioactive isotopes Is relatively simple . Also
non-radioactive impurities which may be present do not inter
fere with the measurements and thus very tedious purification
processes can be avoided. Chemically, the radioactive isotopes
behave in identically the same manner as the natural mixture
of isotopes of the elements of the same atomic number because
they have the same nuclear charge.
Since Greenberg's report in 1939, many biologically signifi
cant radioactive isotopes have been artifically produced to study the
importance of the basic elements to the human system. Yet, Greenberg
was one of the early workers to realize the important factors which
determine whether a radioactive isotope will be suitable for investi
gative work. These factors, he said, are:
. . the degree of stability as measured by the isotope's
half-life and the intensity of the radiation it gives off.
The duration of life of the radioactivity of the element
should be suitably short, so that it may be given in small
quantities as a tracer to animals and man without danger,
. . but should be sufficiently long to enable the fate of
the element to be followed until it is eliminated by the
organism.
However, at the time of Greenberg's review, the only known
isotope of magnesium was 27^g with a physical half-life of less than
10 minutes, a half-life too short to be of significant assistance in
studying magnesium. Consequently, Greenberg's review included results
of radioactive work only on calcium and phosphorus and none on magnesium.
Knowledge of magnesium's function in humans lagged far behind
that of its related elements until the discovery of a new isotope of
magnesium in 1953 by Sheline and Johnson (9) of Florida State University.

21
Up to that time six isotopes of magnesium were known. (See Figure 1.)
Naturally occurring magnesium is composed of three stable isotopes,
2%lg (78.80 per cent), 25>jg (10.13 per cent), and 26>ig (11.17 per cent).
The three radioactive magnesium isotopes known prior to Sheline and
Johnson?s discovery were 22^g with a 3.9-second half-life, 23Mg with a
12-second half-life, and 27>jg with a 9.5-minute half-life.
Normally, one finds that the half-lives of the isotopes of any
particular element get shorter the farther the isotope is away from the
stable isotopes of the element. (This is depicted as the horizontal
distance in Figure 1.) For example, 22^g has a shorter half-life than
23Mg because it is farther from stable magnesium on the chart of the
nuclides. Following this "rule," one would expect that 28>ig would have
a half-life shorter than that of ^Mg. if this were the case, efforts
to produce this isotope would be of interest only to nuclear chemists
and physicists and would not be biologically useful. However, nuclear
scientists have found that another rule governs the stability of the
nuclides. So-called "magic numbers" of combinations of neutrons and
protons produce exceptionally stable atomic nuclei (161). These numbers
are 2, 8, 20, 28, 50, 82, and 126. Since 28^s atomic mass of 28 is
one of these numbers, it was predicted prior to the production of the
new isotope that the magic number rule would predominate and that 28^g
would have a greater stability, i. e., a longer half-life, than
With this in mind, Sheline and Johnson went to the University of Chicago
where they used both a betatron and a cyclotron to produce 28jfg. The
nuclear reactions are: 30si(y,2p)28Mg or 26Mg(aj2p)28Mg. in their report
of the production of ^Mg, the authors expressed the hope that 28^g would

22
12
Mg
Mg ZZ
3.9s
Mg 23
'2*
fr 3.0,-
24.312
y .074..59
y.44
F 4.06
Figure 1
Isotopes of Magnesium (160)

23
find considerable use as a tracer (9).
Shortly after this first production of 28Mg} Brookhaven National
Laboratory (162) began producing it in a nuclear reactor by irradiating
an alloy of ^Li 26]qg with slow neutrons. The two reactions are:
6Li(n,t)%e and 26Mg(t,p)28>ig.
One of the first groups to use ^S^g experimentally as a tracer
was Glicksman et al, (163), who administered it intravenously to six
dogs and two patients. They found that the total-exchangeable magnesium
is much less than the theoretically calculated total amount in the body.
"This," they concluded, "would indicate that during the time of experi
mental observation (24 hours), a large quantity of magnesium does not
enter into the metabolic pool and appears to be fixed."
In 1958, Zumoff and associates (164) used ^^gci^ to study
"the kinetic behavior of magnesium in intact human subjects." They gave
oral doses of the isotope to study excretion, exchangeable magnesium,
and turnover in plasma. Their results showed that "magnesium kinetics
in diabetes mellitus and myxedema reveal departures from the normal
pattern."
About the same time, Aikawa and his colleagues (165) began
an extensive study in both animals and man with 28y[g. Because of the
conflicting results reported in previous studies using stable magnesium,
Aikawa*s group expected that the administration of the radioactive magnes
ium would prove to be a better way of following the behavior of orally
administered magnesium. In 1959, Aikawa et al. (166-168) observed that
low specific activity 28jqg o.5 yCi per mg magnesium) with the short
21.3-hour half-life made "impossible the use of a truly tracer dose."

24
Even so, these researchers continued 28>fg studies of magnesium
metabolism in both rabbits (169,170) and in humans (4). In several
reports in 1960, they summarized work to date which included: (1) urin
ary excretion, tissue distribution, exchangeable magnesium, and the
effect of starvation on urinary magnesium excretion in rabbits and
(2) serum magnesium concentrations, plasma clearance, urinary excretion,
exchangeable magnesium, and urinary and fecal excretion of orally admin
istered 28Mg in humans.
Other animal studies where ^Mg was used included a number in
1958 and 1959 by Brandt, Glaser, and Jones (171), Langemann (172),
Rogers and Mahon (173), MacIntyre (174), and MacIntyre, Davidsson, and
Leong (175). All these investigators used rats and measured the exchange
able magnesium in major organs, plasma, bone, and urine. Uptake of 28^g
in frog muscle was reported in 1960 by Gilbert (176), who found three
turnover components which he attributed to surface absorption, entry
into extracellular water and connective tissue, and entry into the cell.
He found that 75 81 per cent of the magnesium in muscle was non-exchange
able and difficult to remove by diffusion.
Also in 1960, Graham, Caesar,, and Burgen (177) summarized
their work on gastrointestinal absorption and excretion of 28^g in man
using oral administration of the isotope in three control subjects. The
same year, Silver, Robertson, and Dahl (178) reported a study of magnesium
turnover in human adults. They followed 10 adults (all but one had
hypertension) who received intravenous or oral doses of 28jyjg ranging from
20 to 104 pCi. They had been maintained on a constant diet for five days
before and three days after the administration of the isotope. The

25
authors concluded that the results should be interpreted with caution
because of the "relatively low specific activity"! (0.07 to 0.12 pCi
per mg magnesium) of the 28Mg.
In 1961, Maclntyr et al. (179) reported on studies of
patients with clinical magnesium deficiency. They carried out balance
studies and bone and muscle biopsies using stable magnesium and used
28ng in plasma turnover studies. They described 28]^g turnover as a
three-component system. Based on "previous animal work" this suggested
to them that "the three associated compartments were extra-cellular
magnesium with the fastest turnover rate, the vital organs with an inter
mediate turnover, and muscle with the slowest turnovef. The concept that
bone magnesium can always act as a reservoir was refuted.
McAleese, Bell, and Forbes (180) reported on 28Mg experiments
in lambs in 1961. They used both oral and intravenous doses and followed
the distribution of the isotope in various tissues and excretory path
ways. They expressed concern for the two limitations of the isotopic
compound; (1) the relatively short half-life and (2) the low specific
activity (0.45 to 0.75 pCi per mg magnesium).
Another approach to the study of magnesium metabolism was
taken by Aikawa et al. (181) who fed adult rabbits a controlled, deficient
iThe dose of 104 yCi of the 0.07 yCi per mg preparation
resulted in the administration of -1500 mg of stable magnesium or
=4 x 10^3 stable atoms. (The number of atoms of 28j^g in this dose,
=4 x 10l2}is insignificant in comparison.) It is not known how many
atoms will upset the magnesium balance of the system being studied. It
is obvious,'however, that the fewer the number of atoms of magnesium
injected instantaneously-into any living system, the less the chances are
of producing chemical toxicity or of disturbing the ion balance.

26
diet containing stable magnesium and at weekly intervals made an esti
mate of total-exchangeable magnesium using 2S^g and an isotope dilution
method. At the end of the' experimental period, various tissues were
analyzed for magnesium. The deficient diet caused a slight loss in
body weight, a decrease in serum magnesium, a decrease in urinary magnes
ium excretion, and a progressive decline in total-exchangeable magnesium.
However, the magnesium content of muscle, skin, kidney, heart, and liver
did not change; that of the lung fell by 25 per cent and that of bone
by only 15 per cent.
This work by Aikawa and his group(181) prompted several perti
nent comments in an editorial on magnesium metabolism in 1962 in Nutri
tion Reviews (182). The editor commented that:
(1) It is unfortunate that carrier-free 28^g is not available
and
(2) . had a true magnesium balance been made (by Aikawa),
it would have been possible to interpret the data on
total-exchangeable magnesium in a more meaningful way.
Studies with ^Mg the cirrhotic and the alcoholic followed
naturally from the background information reported by Flink (88) and
others on the possibility of magnesium deficiency in these conditions.
Martin and Bauer (183), having found no clear-cut correlation of sympto-
malogy with serum levels of magnesium in these disease states, attempted
to assess exchangeable magnesium using ^Mg. The preparation used to
study seven controls, five cirrhotics, and four acute alcoholics was of a
much higher specific activity (-30 pCi per mg magnesium) than had been
used previously. Four of the five cirrhotics and all of the acute alco
holics had exchangeable magnesium values below normal.
The higher specific activity 28^g was also used by Lazzara's

27
group (184) to evaluate magnesium tissue distribution, kinetics, and
turnover in dogs. In 1962, they reported that important tissues which
did not reach equilibrium after injection of the isotope were the brain
and spinal cord, cortical bone, and skeletal muscle.
Ginsburg, Smith, Ginsburg, Reardon, and Aikawa (185) continued
research of magnesium metabolism in humans and in rabbits and, in 1962,
reported on results of a study in which they attempted to: (1) devise
a reliable method for determining magnesium in erythrocytes; (2) relate
erythrocyte magnesium concentration to reticulocyte count; (3) study the
in vitro uptake of 28yjg by erythrocytes; and (4) study the 28>ig uptake of
various tissues in experimental animals with reticulocytosis induced by
phenylhydrazine. This approach was undertaken because these investi
gators felt that the "current paucity of information concerning magnesium
metabolism in erythrocytes is due in part to the lack of a reliable method
for determining magnesium in red cells and in part to the fact that a
radioactive isotope of magnesium suitable for tracer studies has only
recently become available."
In 1963, Avioli, Lynch, and Berman (186) reported the first
study in a series on 28^g kinetics in normals and selected disease states.
They gave intravenous doses of a relatively high specific activity ^Mg
(-17 yCi per mg magnesium) to 10 normal subjects, five patients with
Pagets disease, three hypothyroid, and five hyperthyroid patients. A
digital computer compartmental analysis technique was used to identify and
quantitate exchangeable magnesium in bone, in extracellular fluid, and in
muscle.
Also in 1963, Petersen (187) described the close relationship

28
of the two major intracellular cations, magnesium and potassium. He
studied the turnover of the two elements in magnesium deficiency and
found indications that the magnesium ion occurs in pools differing in
size and turnover rate. They used a two-compartment model to describe
the turnover of 28Mg in plasma. Petersen concluded that the "total
24-hour exchangeable magnesium was reduced by more than 50 per cent in
magnesium deficiency, due mainly to a decrease in size of a slow pool,
which is believed to include skeletal magnesium."
Mendelson et al. (188) like Martin and Bauer (183) were not
satisfied with the relationship betxjeen serum magnesium levels and the
onset of withdrawal symptoms in alcoholics. They suggested that "although
alcohol withdrawal symptoms may be associated with total-body deficit
of magnesium incurred through poor dietary intake, it is also possible
that changes in distribution of magnesium in the extra-cellular intra
cellular compartments of the body as well as in bone may occur without
concomitant total-body deficit." The authors used 28^g to determine
exchangeable magnesium in alcoholic patients and,in 1965, reported signi
ficantly lower exchangeable magnesium values for "tremulous patients" than
for control subjects.
In a report the same year, Wallach and co-workers (189)
discussed results of "radiomagnesium kinetics in normal and uremic
subjects." Using analog computer analyses, they fitted a three compartment
model to plasma specific activity data following intravenous doses of
Mg. They concluded that hypermagnesemia influences the mechanisms
responsible for cellular transport of magnesium so that fractional influx
of cell magnesium is reduced.
In 1965 and 1966, Aikawa and his group used 28Mg (=40 yCi per mg

29
magnesium) to study the effect of 2,4-dinitrophenol (190) and sodium
salicylate (191) on magnesium metabolism in the rabbit. About the same
time, Aikawa (192) published a review of "recent developments" in the study
of the role of magnesium in biologic processes. He emphasized that 28]*^
although expensive and in short supply, had already contributed substanti
ally to the knowledge concerning the dynamics of magnesium turnover. He
concluded that:
In the final analysis, the ultimate explanation of the fact
that the magnesium ion alone is operative in such diverse but
fundamental cellular processes must be based on the unique
atomic structure of this element. Just how it is unique remains
to be ascertained.
In 1966, Wallach et al.(13) expanded on their study of magnesium in
normal and uremic patients. They gave intravenous injections of 28Mg with
a specific activity of 16 yCi per mg of magnesium to six control subjects
and to six patients with chronic renal disease and moderate to severe
azotemia. The authors utilized conventional analog and digital computer
techniques to analyze plasma concentrations and urinary data. From the
results they proposed a three-compartment model for magnesium transport
in humans.
A similar approach for evaluating magnesium dynamics jLn vivo
was reported by Avioli and Berman (5) in 1966. Using a 28p[g preparation
with a specific activity of =11 yCi per mg magnesium, these workers
observed the levels of activity in the plasma and excreta in 15 normal
volunteers up to six days after injection. Plasma disappearance of 28^g
was fitted to a sum of three exponentials model.
In 1966, Yuri et al. (11) reported a study of turnover of
magnesium in controls and in patients with idiopathic cardiomyopathy
and congestive heart failure. They said that the reason that the daily

30
rate of turnover of magnesium was not previously known was because
earlier data, derived from either non-isotopic techniques or by radio
isotope studies, "are all overestimations because of the loading effect
of the dose of 24jqg administered." Yun and associates used 28f{g with a
specific activity of =200 yCi per mg of magnesium, many times higher than
that previously available. In two controls and four patients, they
measured 28Mg in urine, feces, and plasma up to 70 hours after intra
venous administration and up to 40 hours after an oral dose.
Skyberg jet al. (193) demonstrated the usefulness of ^£$Mg
diagnostic procedures in 1968; he used the tracer to show that hypo
magnesemia was present in an infant and that it was due to a defect in
the intestinal absorption of magnesium. Magnesium-28 (specific activity
of =30 to 500 yCi per mg magnesium) was given orally and excreta was
measured for radioactivity. The numerous routine tests given the infant
including electrocardiography, electroencephalography, and electromyo
graphy were normal. The urine was chemically and microscopically normal
and the spinal fluid had normal protein concentration and normal cell
count. All blood examinations were normal including the serum concen
trations. However, by analyzing the urine and feces after peroral and
intravenous administrations of 28^g} it was found that the child had a
defect in gastrointestinal absorption of magnesium.
Another use of ^Mg (3.2 and 10.6 yCi per mg magnesium) to
examine differences in pathological and normal adults was reported in
1967 by Raynaud and Kell*ershohn (194). Significant differences were
observed between eight persons described as normal and 22 patients in
plasma, urine, and feces analyses. Seventeen of the patients studied

31
suffered from normocalcemic tetanys.
In 1968, Chond, Jahns, and Misri (37) used ^Mg an attempt
to define as precisely as possible the proportions of magnesium in
various parts of the human body. Eleven normal subjects received intra
venous doses of the isotope and were followed up to 120 hours. For the
purposes of localization of magnesium, the body was divided into five
parts; the head, the thorax, the upper abdomen, the lower abdomen, and
the lower extremities. A sodium iodide, thallium-activated (Nal(Tl))
crystal counter was used for the body counts. Whole-body retention was
calculated from these sequential measurements; the data indicated that at
least two compartments were involved in the turnover of ^Mg.
The most recent reports found in the literature on the use
of 2%g include two in the August, 1969, issue of the New York Academy of
Sciences. Aikawa and David (195) summarized their team's past and also
the most recent results of experiments using 28yig as a tracer in rabbits.
The investigators report that recent results with the isotope to study
segments of the small intestine from deficient and normal animals suggest
that the "magnesium-absorbing ability of both proximal and distal areas
of the small intestine is enhanced by magnesium deficiency and is not
energy dependent."
Wallach and Dimich (196) reported on turnover studies in hypo-
magnesemic states in which 50 100 yCi of 28^g with a specific activity
of =17 yCi per mg magnesium was given intravenously. They determined the
plasma specific activity and urinary excretion of the isotope and total
magnesium for 72 hours after injection. The experimental group consisted
of eight alcoholic subjects with hypomagnesemia, three alcoholic subjects

32
with normoinagne.sernia, one hypomagnesemia subject with periostitis of
unknown etiology and hypercalcemia, and one normomagnesemic subject
with chronic, severe malabsorption who had hypomagnesemia prior to treat
ment with magnesium infusions.
Pertinent details of many of these recent 28pig studies will be
discussed later in the results chapter of this study.
*

CHAPTER III
MATERIALS AND METHODS
Magnesium-28
In the literature review, it was pointed out that in 1939 the
only known radioactive isotope of magnesium was ^Mg with a physical
half-life of less than 10 minutes (39). Although the possibility of
?7
using Mg was alluded to, there is no evidence that it was ever used as
a tracer in biological investigations. Its use in this manner is doubt
ful since it has such a short physical half-life. Normally, tracer
studies are best carried out with an isotope with a half-life on the
order of days, weeks, and sometimes, months.
Although 28Mg has a half-life of only 21.3 hours, it has been
used as a suitable isotope in biological work since shortly after it was
first produced in 1951 (9). Magnesium-28 and its radioactive daughter,
aluminum-28 (28ai), have a number of energetic gamma rays which can be
readily detected by most gamma-counting systems. (See Figure 2.) Alumi
num-28 with a half-life of 2.24 minutes; rapidly attains secular equili
brium with ^Mg.
In this study, Mg was obtained from Brookhaven National
Laboratory where it is produced in a Van de Graaff accelerator by the
triton proton reaction (2%g(t,p)2%g) (197). A 1/4-inch diameter
metallic rod target enriched to 99.77 per cent is bombarded with a
beam of 3.4 MeV tritons. After bombardment, a 0.001-inch thick layer
33

34
Mg
21.3h
Radiation
Typa
Energy
(MeV)
Equilibrium
Intimity
(% per decay)
28Mg
a*
.459
.212
95.0%
5.0
y,
.031
95.0
v2
.401
35.9
>3
.941
35.9
v4
1.342
54.0
Ys
1.373
4.7
y6
1.569
4.7
28ai
B~
2.656
100.0
Y
1.779
100.0
1.779 MeV
2s¡
Stable
Figure 2. Radioactive Decay Scheme of Magnesium-28 and Its Radioactive
Daughter, Aluminum-28. (Based on the Report of Alburger and Harris
(162).)

35
is etched from the end of the rod. This method produces a higher speci
fic activity than other production methods.
OO
The material was received as MgC^ in 0.01 to 0.1 normal
HC1. It was diluted in the laboratory to the desired concentrations
with normal saline, checked for radionuclide purity, and then auto
claved before administration. The administered material had specific
activity of 200 300 yCi per mg of magnesium.
Experimental Conditions and Techniques
Fourteen normal subjects between the ages of 28 and 71 and
11 subjects with various disease conditions were measured in seven
groups over a period of 21 months. Two to six subjects were followed
at a time. Each subject was measured by whole-body counting prior to
the injection of the 28Mg to determine the background level of
^^Cs, and any previously administered diagnostic radioisotopes.
Plasma and red blood cell stable magnesium analyses were made prior to
injection of the isotope according to routine procedures of the Clini
cal Laboratories, J. Hillis Miller Health Center (198). None of the
subjects received medications containing magnesium during the study; no
other restrictions were placed on the quantity and composition of
intake.
One milliliter (ml) of the tracer solution was administered
through the anticubital vein by the "butterfly" infusion method to
subjects in the first six groups. One yCi was given to each subject
in group 1, while 6 to 10 yCi was administered in groups 2 through 7.
In group 7, the isotope solution was injected directly into the vein
since with this method there is less loss of radioactivity.

36
Whole-Body Retention Measurements
Whole-body retention was followed in a 4-pi liquid scintil
lation whole-body counter for as long as there was measurable activity.
In group 1, whole-body counts were made five times during the first two
24-hour periods, three times during the next two 24-hour periods, and
then every 24 hours through the seventh day. In groups 2 through 7,
counts were made twice during the first 24 hours after injection and
then every 24 hours (except Sunday) through the tenth day. A summary
of the study parameters is shown in Table 1.
Before measurement in the whole-body counter, each subject
dressed in a cotton "scrub suit." Subject counting times ranged from
0.1 to 10 minutes. Prior to and just after counting each subject, both
a 5-minute background count and a 2-minute count of a reference source
were made. The reference source is a nominal line (or "rod") source
consisting of a 6-foot long plastic tube filled with KC1. It is used
to correct for any variation in overall counter efficiency.
A unit-density phantom-*- (199) containing an amount of
approximately equal to that given to the subjects, was counted under
the same conditions as the subjects. The phantom was used to measure
the physical decay of the isotope and to evaluate any resolving time
losses.
-^The phantom in groups 1 through 6 consisted of an aqueous
solution in a 50-liter polyethylene carboy. In group 7, a sealed
source of ^8j^g was placed in the center of a phantom (designated as
"Tuboy") consisting of a bundle of sealed, sugar-filled polyvinyl
chloride tubes. The phantoms provided similar internal self-absorp
tion and scattering of the radioactivity as a human subject and thus
gave comparable count rates and spectrum shape.

TABLE 1
SUMMARY OF STUDY GROUPS
2^Mg Time
Group No.
Number of
Subjects
Administered
Excreta
Followed
(yci)
Measured
(days)
Normal Other
Total
1
2
2
4
1.27
Urine
7
2
3*
3**
6
10.00
Urine
10
3
3
3
6
9.30
Urine
10
4
5
0
5
6.60
Urine
10
5
0
2
2
9.70
Urine,feces
10
6
0
4
4
5.50
Urine,feces
10
7
2***
2 & >'<
4
10.00
Urine,feces,
10
sweat
Total
15
16
31
^Includes
replication of
one
normal subject
from
group 1.
**Inc.ludes
replication of
two
patients from ,
group
1.
***Includes
replication of
one
normal subject
from
group 4.

38
A shadow shielded Nal(Tl) crystal scintillation whole-body
counter was also used in several of the study groups. Although its
counting efficiency is lower than that of the 4-pi system, it provided
the following useful information:
(1) Because its energy resolution is greater than that of
the 4-pi counter, it was used as a means of identifying unusual back
ground levels in several patients2 ;
(2) Since measurements with it are made with the subject in
a sitting position, it was used as an additional means of calculating
whole-body retention on one patient who was unable to lie flat to enter
the 4-pi counter;
(3) Since the detector has some collimation, it was used
in group 7 in an attempt to see if localization of the isotope took
place in the body; and
(4) Also because of its high energy resolution capacities,
it was used in group 7 to determine if the 28\tg 28^1 parent daughter
pair remains in equilibrium throughout its retention in the body.
Five counting positions (to be discussed later) were used for
the group 7 measurements; counting times ranged from 1 to 10 minutes.
The "Tuboy" phantom, described previously, was also counted
each time a set of subjects was counted on the crystal counter. Another
phantom, designated as "Tubman" (199), was used in this study. This
phantom is constructed in seven segments with varying thicknesses to
2It was found that two patients had residual radioactivity due
to having received &0qo in a vitamin B-12 test several years earlier.

39
simulate the various parts of the human body. The isotope can be distri
buted throughout the phantom by inserting radioactive sources into
numerous channels within the phantom. Tubman was used to determine the
amount of contribution of the isotope from one part of the body to
another so that accurate corrections for interference could be made.
Excreta Measurements
Twenty-four-hour cumulative urinary excretion of ^Mg was
measured in all groups. An aliquot of the collection was taken for
counting purposes. If the total volume was less than the specified
aliquot, the counting container was filled with distilled water to the
required amount. Urine samples were counted as 780 ml aliquots on a
4-inch by 4-inch Nal(Tl) crystal counter in groups 1 through 4. In
groups 5 through 7, they were counted as 1000 ml aliquots in a large
volume well counter. Counting times ranged from 1 minute to 30 minutes
depending on the amount of radioactivity in the sample. Urine standards
were made up at the same time as the doses for the subjects and phantoms
were prepared. Urine standards with 0.1, 1, and 10 per cent of the
average dose given to the subjects were prepared and counted along with
each set of urine collections.
Fecal excretion was measured in groups 5, 6, and 7; the
total-daily collection was counted for ^8^g the iarge volume well
counter.
Measurements of ^Mg in sweat were made in group 7 using the
iontophoresis technique (200). With this technique, pilocarpine is
iontophoresed into the skin by means of a 2.5 milliamp electric current.
In this study, a 2-inch by 2-inch area on the subjects left forearm
was covered with pilocarpine and subjected to the electric current for

40
3.0 to 12 minutes. After removal of the iontophoresis electrode, a
pre-weighed 2.75-inch filter paper was transferred to the area, covered
with plastic film, and left in place to collect sx^eat for 45 minutes.
The filter paper was removed, weighed, and counted on a 4-inch by 4-inch
Nal(Tl) crystal counter. Counting times ranged from 5 to 15 minutes.
Sterile techniques were used throughout the procedure to prevent
possible contamination of the filters with 28j^g from sources other than
sweat.
Instrumentation
The four detection systems used in this research are described
in this chapter and summarized in Table 2.
4-Pi Liquid Scintillation Whole-Body Counter
The University of Florida whole-body counter (62,201) is a
scintillation counter with an approximately 4-pi geometry. It is
located on the ground floor of the J. Hillis Miller Health Center in the
Radiation Biophysics Graduate Program Facility. A floor plan of the
entire facility is shown in Figure 3. Room 17 houses the whole-body
counter and output equipment, while supporting laboratories, sample
preparation areas, and other counting facilities are located in the
adjacent rooms. Figure 4 is a picture of the whole-body counter as seen
from the entrance to the counting room.
Figure 5 shows a closer view of the counter with a subject
preparing to enter the counting chamber. Subjects are centered longi
tudinally in the counter in a supine position. The detector consists of
liquid scintillator in six tanks that make up an annular configuration
which essentially surrounds the reclining subject. Twelve 16-inch

TABLE 2
SUMMARY OF DETECTION SYSTEMS
System
Manor Components
and Manufacturer
Use and Study Group
4-Pi Liquid
Detector and shield
Packard Instrument Co.
Downers Grove, Ill.
Whole-Body Retention
Scintillation
Whole-Body Counter
ft
400-channel analyzer,
three-channel scintil
lation spectrometer
Packard Instrument Co.
Measurements
1-7
Shadow-shielded
4-inch by 9-inch
Nal(Tl) Crystal
Harshaw Chemical Co.
Cleveland, Ohio
Whole-Body Retention
Measurements
7
Nal(Tl) Crystal
400-channel analyzer
Packard Instrument Co.
Whole-Body Counter
Shadow shield and
supporting frame
University of Florida
Study of Localization 7
'Nal(Tl) Crystal
4-inch by 4-inch
Nal(Tl) Crystal
Harshaw Chemical Co.
Urine Analysis
1-4
Counter
400-channel analyzer
Packard Instrument Co.
Shield
Custom Fabricated
Sweat Analysis
7
Large Volume
Detector and shield
Custom Fabricated
Urine and Feces
Well Counter
Two-channel scintil
lation spectrometer
Packard Instrument Co.
Analyses
5-7

1
2
L
r
28'-
Mechanical Equipment
Office
Secretaries' Office
Water Closet
Office
Low-Level Counting Laboratory
Waiting Room, Calculation Area
Dressing Room
Shower
Dressing Room
Computing Room
Graduate Students' Desk Area
Storage
Sample Preparation
Whole-Body Counter Laboratory
Storage
Graduate Student Desk Area
Office
Figure 3. Floor Plan of the Radiation Biophysics Graduate Program
Facility.

Figure 4. 4-Pi Liquid Whole-Body Counter Laboratory

Figure 5. Subject Preparing to Enter the 4-Pi Liquid Whole-Body Counter.

45
diameter photomultiplier tubes are positioned so that two are on each
tank of scintillation fluid. (See Figure 6.)
The entire detector is contained in a 6-inch thick shield of
low background steel with a 1/8-inch thick lead lining. Output signals
from the photomultiplier tubes are fed into one of two types of scintil
lation spectrometers, a Packard model 3003 three-channel scintillation
spectrometer and a Packard model 115 400-channel analyzer. In Figure
7, the three-channel analyzer is shown on the left and the 400-channel
analyzer is in the center.
In study groups 1 and 2, the 400-channel analyzer was used
because the three-channel system was inoperable. The three-channel
analyzer was operative for use in study group 3-6; however, it was
discovered that resolving time corrections which were necessary in
groups 3-6 could be attributed to the analyzer system rather than to
the counter itself. Therefore, the 400-channel analyzer was used again
for group 7.
Figure 8 shows the signal diagram of the counting system when
the 400-channel analyzer (MCA) is used. Digital output from the system
was obtained by means of a high speed parallel printer and also by inter
facing an IBM 526 printing summary punch through a Packard model 70
parallel serial converter.
The three-channel analyzer consists of three independent
single-channel analyzers each of which were calibrated to measure the
137Cs, 4C>k, and the ^Mg 28^ energy regions. Digital counts were
recorded manually from each scaler.
Nal(Tl) Crystal Whole-Body Counter
The shadow-shielded crystal whole-body counter assembly

4>
ON
Figure 6. One Side of the 4-Pi Liquid Whole-Body Counter Showing Six Photomultiplier Tubes
and Steel Shield.
Bl

Figure 7
4-Pi Liquid Whole-Body Counter Instrumentation

Figure 8. Signal Diagram of the 4-Pi Liquid Whole-Body Counting System

49
(See Figure 9) consists of a 4-inch by 9-inch Nal(Tl), stainless steel-
cased crystal and four 3-inch photomultiplier tubes. The assembly is
enclosed in a lead-filled steel container with a thickness equivalent
to 3.11 inches of lead. No other shielding is used in this counter.
The entire assembly is mounted on a rigid, but movable, steel frame,
which provides a means of gradual rotation of the detector face
through an angle of 90. The crystal shield assembly can also be
raised or lowered a distance of 13 inches. In addition, the crystal
can be moved from a position flat with the end of its shield to a
position 2 inches inside the shield.
The various configurations make it possible to achieve a
number of convenient counting geometries. The subject lies on an
adjustable bed as shown in Figure 9 (the position for a total-body
count). Figure 10 diagramatically summarizes the counting geometries
used in this study.
In addition to the whole-body count position shown in Figure
9, the four other positions used in this research (head, chest, abdo
men, and legs) are demonstrated by an actual subject in Figures 11 14.
The output system from this counting system consists of
essentially the same equipment as that diagrammed in Figure 8.
Large Volume Well Counter
Radioactivity in urine and feces collections was measured in
an organic scintillation detector with a large volume chamber (202).
(See Figure 15.) The sample is inserted into the center of a right
circular cylinder, 4.5 inches in diameter by 12 inches long. Surround
ing the sample chamber is a cylindrical tank containing the scintillator;

I
Figure 9. Nal(Tl) Crystal Whole-Body Counter: Whole-Body Count Position.

51
Position Angular and Distance Designation
a
b
C
d
a + (3
a
6
Whole-Body
16.5
21.0
4.5
17.0
45
90
0
Head
20.0
21.0
4.5
11.0
60
90
5
Chest
16.5
21.0
4.5
17.0
45
90
5
Ab domen
16.5
21.0
4.5
17.0
45
90
0
Legs
16.5
21.0
4.5
17.0
45
O
O
Oh
0
Figure 10. Geometry of Subject Counted on the Nal(Tl) Crystal Whole-Body
Counter (201).

'
I
I
i
Figure 11. Nal(Ti) Crystal Whole-Body Counter: Position for Head Count.

Figure 12. Nal(Tl) Crystal Whole-Body Counter: Position for Chest Count.

I
Figure 13. Nal(Tl) Crystal Whole-Body Counter: Position for Abdomen Count.

Figure 14. Nal(TI) Crystal Whole-Body Counter: Position for Legs Count.

56
Figure 15. Large Volume Well Counter

57
four 5-inch photomultiplier tubes face the end of the tank. The tanks
and photomultiplier tubes are mounted in a 3.37-inch steel plate shield.
Read-out equipment consists of a single-channel analyzer with wide
window capacity, a scaler, and a timer.
Nal(Tl) Crystal Counter
Magnesium-28 in urine samples in groups 1 through 4 and in
sweat samples in group 7 were counted with a 4-inch by 4-inch Nal(Tl)
crystal counter. (See Figure 16.) The crystal is housed in a cylindri
cal cast steel shield, 28 inches high by 36 inches in diameter. The
shield has a 6-inch thick steel equivalent shielding on all sides.
Again, the output system is essentially that shown in Figure 8.
Data Analysis Techniques
Data was recorded manually from the three-channel analyzer,
on paper tape from the 400-channel analyzers, and in group 7 only it
was punched on cards. The data punched on cards represented totals in
the 400-channel analyzer channels and was submitted for summing (inte
gral counts) of the 28^g and A1 energy regions on an IBM 1800
computer.
Subsequent calculations were performed both with a conven
tional desk calculator and with Fortran IV programs run on the IBM
360/65 computer by means of a remote 2741 computer terminal located
in the whole-body counter laboratory.
Routine reduction of all counts to net counts per minute
was made on all data. Resolving time corrections were made on the net
subject counts during the first several days in study groups 3-6.
These corrections were made by plotting the phantom measurements versus

Figure 16. Nal(TI) Crystal Counter.
j

59
time after "injection" on semi-logarithmic graph paper. The straight-
line portion of the plot (observed during the last week of measurements),
which corresponds to the portion of the curve where no resolving time
was necessary, was extrapolated back to t = 0. The ratio of difference
between the extrapolated line and the actual line at any time, t, was
used to correct the net subject count.
Further analysis of the retention and excretion data was
carried out according to the method reported by Richmond (203). The
following equation was used to determine whole-body retention:
WBtx/(Stx/St0)
WBRt = or
WBt0
WBtx/ Stx .
WBRtx = 5
WBt / St
o o
where
WBRtx = whole-body retention at time t in counts per
minute (cpm),
WBt = whole-body activity at time tY in cpm,
WBtQ = whole-body activity at time tQ in cpm,
Stx = standard activity at time tx in cpm, and
StQ = standard activity at time tQ in cpm.
The whole-body activity was determined directly by whole-
body counting. The standard activities at the various time, tx, were
calculated from a best-fit curve of the phantom measurements. A
computer linear least squares program, Biomedical Computer Program,
BMD02R (204) was used to obtain the phantom decay curve.

60
Thus,
Stx'/St0 = Stx'/(Stx'-e-^t) = e-Xt;
where
St and St are values of St and St predicted from the
x o x o r
fitted curve.
The whole-body retention equation then reduces to:
WBRtx = WBtx* e+*t/WBt0.
By using this technique, the phantom could be measured
only once with each daily set of subjects rather than each time an
individual was counted. Therefore, since the phantom was cumbersome
and the measurements are time-consuming, this technique proved to be an
efficient one. It also produces more statistically accurate values
when an isotope with a short half-life is used. A time lapse of as
much as 30 minutes between a phantom and a subject with can
produce an error of 2 per cent. A time lapse of two hours produces
a 7 per cent error.

CHAPTER IV
RESULTS AND DISCUSSION
Whole-Body Retention of in Normals
In Figure 17, whole-body retention, expressed as per cent of
the administered dose, for the 13 normal subjects, age 28 to 71, is
plotted by study groups. The subjects included five females, age 43 to
59, and eight males, age 28 to 71.
The two subjects in study group 1, NA and NC, were followed
for the shortest period of time, 165 hours, since they received only
1.3 pCi of 2%g. This dose level was selected to initiate the study
since it was considered the optimum amount for measurement by the
whole-body counting system. In order to better define the shape of the
curve during the first few days, frequent measurements were made on the
subjects in this group.
The results of group 1 showed that at least two components
are involved in the retention (or turnover) of 28^. it was apparent
that a larger dose was needed to permit measurements over a period of
time long enough to accurately establish the second component. Calcula
tions showed that a factor of eight (2^) increase in the dose would
permit meaningful measurements for an additional three days (-three
times the physical half-life of the isotope). Therefore, in subse
quent study groups the dose was increased to the order of 7 10 pCi
and retention and excretion measurements were possible up to 220 hours.
61

WHOLE BODY RETENTION
62
Figure 17. Whole-Body Retention of 2%g; Normal Subjects.

63
The retention results for study groups 1 and 2 define a
fairly smooth, continuous function and have little within-group varia
tion. In contrast, in groups 3 and 4 there is more within-group
variation and, particularly in group 4, there is a greater departure
from a smooth function. In study group 7, there is good agreement in
the results of the two individuals and it is significant that the data
again more closely resembles that of groups 1 and 2.
Some of the differences in the results of the study groups
can be attributed to differences in instrumentation. The 400-channel
analyzer was used for study groups 1, 2, and 7, while the three-channel
analyzer was used for groups 3 and 4. It appears that there is more
precision in results when the 400-channel analyzer is used. This
assumption is supported by the fact that while resolving losses were
evident for initial high count rate measurements with the three-channel
analyzer, this was not the case for the 400-channel analyzer even with
doses as high as 10 yCi. In addition, the computational steps required
to make resolving loss corrections automatically introduces another
component of variance in the data for groups 3 and 4. Finally, any
error introduced in applying the resolving time corrections would affect
the results in two ways. The magnitude of the high count rate obser
vations would be directly affected and also all of the observations
would be affected because the value at t = 0 (see page 59) is used as
a denominator in computing each retention value.
However, in spite of the greater variability in some of the
study groups, the average retention values are approximately the same
in all groups.

64
Two subjects, NC and Nil, were measured twice and were used as
a means of establishing the degree of reproducibility of this measure
ment method. These replications can be seen in the two plots in Figure
18. Subject NC, who was in groups 1 and 2 (time lapse of four months),
had almost identical retention curves with the exception of one point at
165 hours. Because this point represented the last measurement made in
group 1 and the level of activity was low, considerably more counting
error is associated with it than with the measurement made at the same
post-injection time in group 2.
Subject NH was measured both in study groups 4 and 7 (time
lapse of one year and two months). His retention curves are also very
similar with the exception of the 20- and 40-hour points which, as
mentioned previously as a part of the group 4 measurements exhibited
a departure from a smooth function.
Analysis of the results of all of the study groups showed no
pattern due to sex or age. Therefore, both male and female subjects
were considered as representative of a normal population and the results
of all' groups, ages, and both sexes were pooled for further analysis.
Determination of the Model for Biological Turnover of 28Mg
A number of estimates of magnesium turnover have been
28
attempted, both with stable magnesium and more recently with Mg. As
discussed in the literature review, researchers in these studies have
been concerned with establishing an accurate biological half-life (or
turnover) of the element in order to provide information on its meta
bolism in normals and to study its behavior in disease conditions.
The formulation and testing of a model for the retention
data followed suggestions by Mones Berman (205). Berman states that

65
U
oc
>*
a
o
CO
Figure 18. Replications in Measurements of Whole-Body Retention
in Two Normals.

66
the first step in the formulation of a model is to choose the type or
class of model applicable. Quite often in tracer kinetics, the model
can be described by a set of linear differential equations, the solu
tion for which are sums of exponentials (205). Others state that
"clearance curves for radioactive tracers are fit more simply by one or
more negative powers of timeM(206).
The two models when used to express retention can be repre
sented by the following general forms:
Power function: R = At-a + Bt-^ + ... + Xt-x.
Sum of exponentials: R = Ae-at + Bekt + ... + Xe-xt.
A majority of researchers (186,194,196,203,207,208) prefer
the latter model for compartmental analysis. Furthermore, the semi-
logarithmic plot of the data in this research (Figure 17), produced
an exponential-type curve. Therefore, a sum of exponentials model was
selected as the initial approach.
The next step in the analysis was to determine the order
(i.e., the number of independent functions) of the model. Some resear
chers report a three compartment turnover of 28^g in serum during the
first 20 hours after injection (196). Others (5,209) predict as many
as ten compartments (with half-lives from 0.623 to 5197 hours) from
turnover of 28^g in serum.
Visual inspection of the data in this research showed that at
least two compartments were involved in the turnover. However, it is
difficult to resolve more than two components since: (1) the whole-
body retention technique is relatively insensitive to multiple changes
in slope during the first day or so of observation, and (2) the short

67
physical half-life of the isotope made it extremely difficult to
identify a component with a half-life greater than the total observation
time in the experiment (220 hours).
Berman recommends that for compartmental analysis, the model
with the smallest number of compartments compatible with the data
should be chosen. Therefore, a two compartment model was chosen. The
individual data points were then analyzed by computer using a non
linear least squares method (Biomedical Computer Program, BMDX851) (210).
The sum of exponentials model used to describe the quantita-
28
tive Mg turnover in normals is:
R = Ae-^lt + Bex2t.
The dependent variable,
R = the per cent retention at any time, t, and the independent
variable,
t = the post-injection time in hours.
Parameters A, B, Xj, and X2 are as follows:
A = the per cent of the administered dose being excreted
directly from the first compartment;
B = the per cent entering into and being excreted from the
second compartment;
X.i = the turnover rate for the first compartment (in hours);
1This program obtains a weighted least squares fit, R =
f(t-^, ... t^; pjl, .. Pj[) + e, of a specified function f to data
values t^, ... t^, R by means of s stepwise Gauss-Newton iterations
on the parameters p^, ... p^. Within each iteration, parameters are
selected at any given step depending on which one, differentially at
least, makes the greatest reduction in the error sum of squares.

68
A2 = the turnover rate for the second compax'tment (in hours) .
Biological half-lives for the two compartments can be derived
from this expression and are equal to 0.693/A] and 0.693/1?.
Figure 19 shows the data points of all the normals. The
retention equation obtained in this study by the non-linear least
squares method is:
R = 8.5e_0,129t + 91.5e--00128t.
This average equation is plotted as the solid line in the
Figure. The broken lines represent the estimated 95 per cent range of
the data or what can be called the "normal retention band." The first
and second coefficients of the retention equation, 8.5 and 91.5, repre
sent the quantities involved in the turnover of the two compartments.
Turnover rates are 12.9 and 0.128 per cent per hour for the two compart
ments, respectively. The second turnover rate can also be expressed as
3.07 per cent per day.
Biological half-lives of 5.4 1 2.2 hours (Is. d.) for the
first compartment and 540 35 hours for the second compartment were
calculated from the rate constants in the exponents of the fitted
equation.
Excretion of ^Mg jn Normals
Magnesium-28 excretion measurements were made on all subjects
in this study in addition to whole-body retention measurements in order
to examine 28^g balance. One should be able to account for the entire
activity (100 per cent of the administered dose) at any time after
administration of the isotope if all excreta are measured and if both
the whole-body retention and the excreta measurement techniques are
accurate.

WHOLE-BODY RETENTION (R), %
IOO
Figure 19. Model for 28^jg Retention in Normal Subjects

70
Total-measured 2%g diagrams are shown in Figures 20 23 for
the 13 normal subjects. Each diagram shows the subjects whole-body
retention curve; added to it is the cumulative percentage of 28^g j_n
urine and feces. The difference between the total-measured 28j,jg an
100 per cent is labelled as "deficit" on the Figures. Numerical values
from which these graphs are plotted are tabulated in balance sheets in
Appendix B.
Figures 20 and 21 include results of subjects in groups 1-3
in which urine was the only excreta measured. In general, the results
are near, but somewhat less than the total balance or the 100 per cent
line. Figures 22 and 23 include the subjects in study groups 4 and 7.
Again, for the majority of the subjects, urine i^as the only excreta
measured. Figure 22 shows the two replications on subject NH. The
first measurement (labelled NH) in study group 4 where urine was the
only excreta measured, shows a small 4-5 per cent deficit at 220 hours.
However, the second measurement on this subject (NH2) included measure
ment of feces. This graph shows almost 100 per cent accountability;
a very small deficit is present at 220 hours.
Total-measured 28^g for the second study group 7 subject, NM,
is shown in Figure 23. Again, there is nearly 100 per cent accounta
bility of the administered isotope.
Although sweat was also measured in study group 7, it is not
plotted in the Figures since it was determined that the amount of 28j^g
in sweat was not significant. (See Appendix C .)
Since statistical fluctuations are apparent in the total-
measured 28^ig for these 13 normal subjects, an average retention and

NORMAL SUBJECTS
=¡J
Total-Measured -Mg for Normals NA, NB,
Figure 20
and NC

NORMAL SUBJECTS
q
ND,
, and NG.
Figure 21
Total-Measured '28mg for Normal;
NE
NF

NORMAL SUBJECTS
Total-Measured fg for Normals
ijx ana NJf *
Figure 22
ana

Figure 23. Total-Measured 28Mg for Normals NX, Nl, and NM.

75
excretion was calculated and is shown in Figure 24. In this Figure, the
whole-body retention curve is the. one calculated from the least squares
fit of the data (Figure 19). It was plotted in Figure 24 by substitut
ing various values of time after administration of the isotope into the
established retention equation, R = 8.5e*"^*^29t + 91.5e_00128t# The
curve representing whole-body retention plus total-urinary excretion las
determined by plotting the sum of the whole-body retention and averaged
urinary excretion values versus time. Fecal excretion values were aver
aged and plotted in the same way.
The most stiking feature of Figure 24 is that, on the average,
the total amount of ^Mg was accounted for at all times after admini
stration. There is a slight, 1-2 per cent deficit toward the end of
the study, which is probably due to a small accumulative loss and
consequently, non-measurement of excreta.
The total-accountability (i. e. perfect balance) of the
on the average in the normal subjects is most significant in that it
verifies the accuracy of the retention measurements. The excreta
measurements also can be assumed to be accurate. Cumulative urinary
excretion averaged 3 per cent per day and fecal excretion was approxi
mately 0.5 per cent per day.
Comparison of Results to Reports of Other Investigators
Prior to the use of ^Mg, non-isotopic techniques used for
studying magnesium turnover indicated that there are several relatively
small, rapidly equilibrating compartments and that one or more of them
have a slow turnover (178). Early data on magnesium in man suggest that
there are at least three compartments in the body pool of magnesium

AVERAGE-ALL SUBJECTS
2
Mg Average of Ail Normals.
Figure 24. Total-Measured

77
turning over with half-lives of 1, 3, and 14 ^ 35 hours, respectively.
However, 25 50 per cent of the magnesium was thought to be in a
fourth compartment with a turnover rate of less than 2 per cent per day,
Magnesium-28 was used soon after its discovery for the study
of magnesium metabolism; however, in the early 1960s researchers became
concerned that the magnesium content of the low specific activity 28^g
being administered was capable of upsetting the body-magnesium balance.
Because of this, the validity of the work prior to the availability of
high specific activity preparations is questioned by some researchers
(4, 11, 178). Consequently, only published results where ^8^g 0f a
specific activity higher than 10 yCi per mg magnesium were considered
in this study for comparative purposes.
One of the first groups to use a high specific activity
was Martin and Bauer (183). Their report in 1962 on exchangeable 28^g
in the cirrhotic and alcoholic showed a significant difference between
patients and controls. However, 28^g measurements made in serum and
urine samples were followed only 25 hours and no attempt was made, to
determine turnover rate.
Avioli jet al. (186) have done, extensive work using digital
computer analysis of specific activity data in plasma, urine, and feces
samples after intravenous administration of 28]tfg with a specific acti
vity of =17 yCi per mg. In their work published in 1963, they assumed
a parallel, three-compartment open system. The compartments were tenta
tively identified as plasma, bone, and muscle. They reported that 35
per cent of muscle magnesium was exchangeable in normal subjects. Later
in 1966, Avioli and Berman (5) reported a metabolic model for magnesium in

78
man based on measurements of blood, urine, and feces in 15 subjects who
* OO
had received 150 175 yCi of Mg (-11 yCi per mg magnesium). They
fitted a sum of three exponentials model to the plasma data to determine
half-lives of 1.1, 7.7, and 187 hours.
In the same paper, Avioli and Berman postulate a more complex
model describing 23Mg kinetics which was later used by Bernard (209) to
obtain the following whole-body retention equation where t is in days;
R = 0.738e_0'00320t + 0.216e_0-164t + 0.034e-4-54t + 0.0115e"26-7t.
This function is obtained as the sum of four separate retention
functions, one for each compartment. The half-lives of the four compart
ments in hours are: 5197, 101.4, 3.66, and 0.623. Bernard uses this
function to estimate internal dose due to a continuous exposure to 28Mg.
Another measure of magnesium turnover was reported by Petersen
(187) in 1963. He treated his experimental data with the assumption
that plasma activity is a function of immediate dilution in a central
compartment and further transport into two parallel compartments governed
by the rate constants k^ and k^. He expressed the concentration in the
central compartment as:
C = ae-k-^t + be^c2t + c>
where k^ and k^ as determined yield half-lives of about 1 hour and 4
hours.
Several years later, Wallach, Rizek, and Dimich (189) studied
magnesium kinetics in plasma after intravenous administration of 50 -
70 yCi of =16 yCi per mg magnesium. Although measurements were made only
to 72 hours after administration, the total magnesium given was far less
than that used by Avioli et al. (186); therefore, the resultant turnover

79
rates in plasma are important to consider here. Wallach e_t al. assumed
that within 13 minutes after injection the isotope had equilibrated with
the extra-cellular magnesium pool and then verified the relation:
SA = Ae-at + Be_bt + Cect,
where SA is the specific activity of 28Mg in plasma. According to
Wallach, one of the simplest models consistent with such a function
which could be applied to metabolism is the parallel three-compartment
open system. Computer derived exponents for the sum of exponentials
model yielded the following turnover times of the isotope in plasma:
0.17, 2.4, and 66 hours.
In 1966, Yun et. al. (11) reported the use of a higher specific
activity 28Mg (-20 pCi per mg magnesium) in too normal subjects. They
stated that up until that time, "precise knowledge of the daily rate of
turnover of magnesium in the body" was not known. According to Yun,
earlier data, derived either from non-isotopic techniques or by radio
isotope studies, are all overestimations because of the "loading effect
of the dose of 24Mg administered."
They administered intravenous doses of 145 and 155 pCi to the
too subjects and followed turnover of 28Mg in plasma and urine. A sum of
three exponentials equation was chosen to describe the rate of urinary
excretion. The following equations express the rate of urinary excre
tion in per cent of the administered dose per hour for the two subjects:
(1) dU/dt = e-0*4278t + 0.126e"0-077t + 0.106e-'00236t,
(2) dU/dt = e-693t + o.2e"-139t + 0.11e--00173t.
Another measure of magnesium turnover was reported by Raynaud
and Kellershohn (194). They used a sum of exponentials approach to

80
model results of 28Mg turnover in eight normal subjects. One to three
yCi per kg of weight (-75 to 225 yCi) of 3.2 10.6 yCi per mg 28^g was
administered to each subject; plasma, urine, and feces samples were
analyzed up to 96 hours after injection. They concluded that "the
analysis of the specific plasmatic radioactivity curve from 9 minutes
after injection until the middle of the third day, a period in which the
existence of a slow exchange becomes apparent, shows that it can be
decomposed into three exponentials in which half-lives are 7.7 minutes,
1.8 hours, and 1.9 days.
The most recent study of ^Mg humans with which it is
important to compare the results of this study, is the one published in
1968 by Chon and co-workers (37). These researchers used a Nal(Tl)
crystal counting system with two 6-inch diameter by 4-inch thick crystals
(201) to scan the body for retention of injected 28jjg the head,
thorax, upper abdomen, lower abdomen, and lower extremities. The intent
of the study was to define as precisely as possible the proportions of
28
Mg in various parts of the body at various times after injection of
2-6 yCi of 28p[g# jn addition, whole-body retention was calculated
from the measurements of the various parts of the body. The data was
plotted on semi-logarithmic paper and fitted by hand to produce the
following retention equation:
R = 10e-0,051t + gOe-0-007^.
Table 3 summarizes the results of all the magnesium studies
just discussed. In order to compare these results to the ones from this
study, it is necessary to examine a number of important parameters; the
number of subjects studied, the total mg of magnesium administered

TABLE 3
28Mg TURNOVER RESULTS IN HUMANS
Half-lives of Compartments*
Investigator
Number of
Subjects
Dose
(yCi)
Specific
Activity
Total
Mg
Hours
28Mg in:
Observed
1 2
(Hours)
3
4
Avioli et al.
(186)
15
175
=11
16
144
plasma,
urine
1.1
7.7
187
(1000)**
Wallach et al.
(189)
6
70
=16
4.3
72
plasma
0.17
2.4
66
-
Yun et al.
(ID
2
155
=20
7.8
70
plasma,
urine
1.31
6.9

347.1
Raynaud,
Kellershohn(194)
8
225
10.6
20
96
plasma,
excreta
0.13
1.8
46
-
Chon et al.
(37)
11
6
?
?
120
body
sections
-13.7-
- 933
Roessler
15
10
300
0.3
220
whole-
body,
excreta,
body
sections
- 5.4-
- 540
*Compartments are put in columns according to interpretations by this author as to what
the half-life represents.
**Half-life of a long-term storage site, estimated but not actually measured in the study.

82
(a combination of total dose and the specific activity of the prepara
tion) the number of hours followed, the sample measured, and the
results.
The most obvious conclusion that can be made from Table 3 is
that there is no consistency in the results from one study to another.
This could be due to differences in the other parameters tabulated on
the various studies. It can be seen from the Table that in this study
all of these parameters were equal to or better than those of the other
investigators. Of particular importance is the very small amount of
magnesium (0.3 mg) administered. This is many times less than that
given by any other investigator. The total hours that one is able to
follow the activity after administration is also of prime importance
since the total measurement time greatly affects the accuracy of the
determination. This is important primarily in the determination of
turnover times of the longer half-life compartment(s).
Probably the most significant contribution of this study is
that whole-body retention measurements were made directly. The use of
the 4-pi whole-body counter made this possible. Other investigators,
who do not have access to this counting equipment, have to rely on
plasma turnover and/or excretion to estimate whole-body retention. Of
significance also is the fact that excreta measurements which were made
in this study essentially verified the whole-body turnover at all times
28
after administration of the Mg.
It is interesting at this point to examine in more detail
the study by Chon et_ al. (Table 3). Although measurements were made
by these investigators up to 120 hours after administration compared to

83
240 hours in this study, the approach is similar enough so that an
almost direct comparison can be made of the two sets of results. The
following comments can be made:
(1) This is the only other study published in which whole-
body retention, although not the primary intent of the study, was
measured directly rather than being calculated from plasma turnover or
from excreta measurements. However, Chon, used a scanning-type counter
rather than the more sensitive 4-pi liquid counter.
(2) The authors chose a two compartment model for fitting
although they admit that at least one other compartment may exist. They
assume that if a third compartment is present that their first compart
ment is actually a measure of the first two rapidly exchanging compart
ments ; and
(3) Eleven normal subjects were measured.
Almost identical results are obtained by Chon ejt al. and by
the measurements in this study for two of the constants in the retention
equation the per cent of the administered magnesium being excreted
directly from the first compartment (Chon e_t al. 10 per cent -
Roessler, 8.5 per cent) and the per cent of the administered magnesium
entering into and then being excreted from the second compartment.
(Chon et al., 90 per cent Roessler, 91.5 per cent).
However, Chon and his group found half-lives of these two
compartments to be 13.7 and 933 hours, in contrast to the 5.4 and 540
hours found in this study.
An estimate of the degree of accuracy of the results of Chon
et al. is difficult to make since the report gave no indication of the
degree of reproducibility of their measurements. No confidence intervals

84
were reported on the constants determined for their retention equation.
In addition, only seven points of per cent whole-body retention versus
hours after administration were used to calculate the retention equation.
This small number of points would give a lower degree of confidence for
prediction of any of the four constants in the retention than that in
this study.
In addition to comparisons of the 28Mg biological half-lives,
one can compare the excretion rates of the isotope in this study to
those determined by other investigators. Table 4 summarizes the excreta
results of this study and presents them for the comparison to other
published reports. The urinary excretion for all investigators is quite
consistent. Fecal excretion has only been measured by two other investi
gators; one of these, Yun et clL_, report a single value at 70 hours.
The results of this study are about 1 1/2 times those reported by the
two other investigators. Again, the measurement period in this study
was 220 hours compared to 134 hours by Avioli e_t al. and lesser times
by the other investigators.
Calculation of Radiation Dose
This study and those of others cited here demonstrate the
potential for using 28^jg studies of magnesium's function and behavior
in humans. Magnesium-28 is currently more available than it was previ
ously and soon will be produced in a carrier-free form (211). Conse
quently, it is expected,that its use in human experimentation will
increase significantly.
In all studies where a radionuclide is administered to humans,
one must precede the experimental work with an estimate of the radiation
dose. Radiation dose calculations for ^Mg have typically been based on

TABLE 4
COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT 28Mg STUDIES
Cumulative Excretion (Per Cent of Dose) in Hours After Injection
Investigator
44
48
70
Urine
72
120
134
220
48
70
Feces
72 96
134
220
Roessler
9.0
9.3
12.0
13.5
15.0
16.7
27.9
2.0
2.5
2.5
3.0
4.3
5.0
Avioli et al.
(186)
Yun et al. (11)
7.3
10.6
10.7
11.6
16.9
1.8
1.4
1.2
2.6
Wallach et al.
(189)
Raynaud,
Kellershohn (194)
10.4
16.0
1.7

86
data from the chronic intake of magnesium. The half-life used for such
calculations was obtained from the Report of the J.CRP Committee II on
Permissible Dose for Internal Radiation (212) and was estimated from the
biological elimination of the stable element in humans in the absence of
experimental data from radioisotopes. Such a calculation was made of the
anticipated dose to standard man prior to this study. Considering the
radioisotope to be uniformly distributed through the whole-body as a
critical organ, assuming a single exponential turnover with a biological
half-life of 4320 hours as listed by the ICRP (212) and using the classi
cal method of calculation (213), it was estimated that the radiation
dose per yCi of injected 28jqg WOuld be 2.7 mrad. (See Appendix A.)
In reviewing the results of this study, it can be seen that
the calculation based on a single 4320-hour biological half-life is
inconsistent with the conditions following a single injection. When
no
the source of the Mg is a single administration rather than a chronic
intake, very little of the administered quantity reaches the very
long-lived biological compartment. Because of the short physical half-
life of the isotope, this portion of the administered quantity contri
butes only a small fraction to the radiation absorbed dose. Accurate
radiation dose calculations for the one-time dose situation should be
based on the model best representative of the biological turnover
following such an administration.
This study represents the longest known determination of both
retention and excretion of ^Mg uncjer these conditions; therefore, the
parameters determined in the retention equatipn in Figure 19 should
provide the most accurate estimation of the radiation dose to humans

87
after a single intravenous administration of the isotope.
After the parameters in Figure 19 had been obtained, the
method of the Medical Internal Radiation Dose (MIRD) Committee of the
Society for Nuclear Medicine (214) was followed to recalculate the
radiation dose. (See detailed calculations in Appendix A.) The model
used two uncoupled compartments characterized by the relative activities
and the biological half-lives found in this study. The whole-body was
considered as the target organ and the source for both compartments.
From this data, the radiation dose was calculated as 2.0 mrad per yCi.
Retention and Excretion of ^Mg jn Selected Disease Conditions
Because of magnesiums role in neuromuscular function, serum
or plasma levels of this element are routinely examined in patients with
neuromuscular disease. As it was pointed out in the literature review,
this extracellular measurement of a primarily intracellular ion rarely
provides any information with regard to metabolic magnesium abnormali
ties. Consequently, the measurement of stable magnesium in red blood
cells has been accepted by some clinicians as the method of choice for
determining these abnormalities. Although this determination may be more
sensitive to a disorder in magnesium turnover, it is generally agreed
that red blood cells are "enucleated impotent and dying cells which are
not representative for intracellular metabolism"(215).
Because of these uncertainties in the relationship between
plasma and red blood cell analyses and actual magnesium metabolism,
many clinicians have sought a better means of determining magnesium ab
normalities. Among these were a gastroenterologist and a neurologist at
the University of Florida who sought help in the use of a radioactive

88
tracer to study magnesium turnover in neuromuscular patients. Whole-
body turnover of radioisotopes of other essential human elements such as
iron (216), copper (217), and calcium and strontium (218) has been used
successfully to identify abnormalities in other disease conditions.
Therefore, this study was initiated with the objective of determining
whether the measurement of 28Mg turnover could be correlated with select
ed disease conditions.
This pilot study involved 16 whole-body retention and excretion
determinations following intravenous administration of Another
major objective of the study was to use these determinations to examine
the feasibility and possible applications of this technique as a diag
nostic test. It was hoped that the ^%g turnover determination could be
simplified to a one- or two-time measurement that would provide greater
potential in diagnosis than the currently used methods. Of these 16
determinations in this patient study, 10 represent a single turnover
measurement and the others were triplicate measurements at three points
in time on each of two patients.
Patients in the study included three with amyotrophic lateral
sclerosis (ALS) of unknown origin, two who developed ALS symptoms fol
lowing sub-total gastrectomies, one with infectious polyneuropathy, two
with repaired sub-total gastrectomies, a patient on diuretics, one
renal patient, a patient who had undergone an extensive small bowel
resection, and a patient with a history of hypertension.
In order to correlate the results between the stable magnes
ium levels, the ^Mg measurements, and these selected disease states,
routine clinical stable magnesium anslyses were made on all subjects in

89
this study. Table 5 summarizes the results of plasma and red blood
cell analyses. The plasma analyses show that all normals and most of
the patients fall within the normal range. Only patients PF and PK
have values which are lower than normal. The red blood cell measure
ments show that two normals and four patients have values outside the
normal range. Normals NG and NI have above normal values. Higher than
normal levels were also found in red blood cell measurements of patients
PD, PH, and PJ, while a lower than normal level was observed for patient
PK. Only patient PK has abnormal magnesium levels in both plasma and
red blood cell measurements.
Magnesium-28 retention and excretion results for all patients
are shown in Figures 25 31. Whole-body retention values, grouped by
disease conditions, are superimposed on the normal retention band (from
Figure 19) and shown in Figures 25, 28, and 30. The total-measured ^Mg
results for these patients are shown in Figures 26, 27, 29, and 31.
These can be compared both to the individual normal results (Figures
20 23) and to the average for all normals (Figure 24).
Neuromuscular Patients
The whole-body retention curves for four of the neuromuscular
patients PA, PB, PG, all ALS patients, and PI, who has infectious poly
neuropathy, are shown in Figure 25. A number of different, lower than
normal retention patterns are obvious; however, only one, PI, appears
entirely within the normal range. As can be seen from the figure, PB's
retention curve shows the most dramatic departure from normal. In the
first two measurements on this subject, the whole-body retention was
lower than normal and also the resultant curve does not follow the

90
TABLE 5
PLASMA AND RED BLOOD CELL STABLE MAGNESIUM ANALYSES
Subject
Disease Condition
Age
Sex
Magnesium
Plasma Red
(r %)*
oi. d Cell
Normals
NA
28
M
N.A.**
N.A.**
NB
33
M
2.2
6.0
NC
36
M
2.1
5.5
ND
52
M
2.0
5.9
NE
47
M
2.3
5.9
NF
52
F
1.8
5.0
NG
59
F
1.8
7.1
NH
41
M
2.0
5.8
NI
48
M
2.1
6.9
NJ
43
F
2.1
5.8
NK
47
F
2.0
5.4
NL
56
F
2.0
5.8
NM
71
M
N.A.**
N.A.**
Patients
PA
ALS
50
M
2.1
5.6
PB
ALS
51
M
2.1
6.2
PC
Gastrectomy
54
F
2.0
4.6
PD
"Diuretic"
61
M
2.2
6.6
PE
Repaired Gastrectomy
61
F
2.1
4.4
PF
Kidney
23
F
1.6
6.3
PG
ALS
60
M
2.0
5.8
PH
Gastrectomy
52
M
1.8
6.7
PI
Infectious Polyneuropathy
42
M
1.9
5.4
PJ
Repaired Gastrectomy
54
M
2.2
7.1
PK
Bowel Resection
43
F
0.7
3.6
PL
Hypertension
50
M
N.A.**
N.A.**
Established Normal Values:
Mean
Range
2.0
1.7 2.3 4.
5.4
4 6.5
^Results are routinely reported in this unit, mg %, which means
milligrams of magnesium per 100 milligrams.
**N.A. = not analyzed.

91
Figure 25.
Whole-Body Retention of
28jig
ALS Patients.

PATIENTS
Figure 26. Total-Measured Patient FA

!
PAIi£TS
H38T NOeCTfOH T1*t£.HOim
Figure 27. Total-Measured 28Mg Patients PB, ?G, and ?I.
VD
U>

Figure 28.
Whole-Body Retention of
28Mg
Gastrectomy Patients

I
PATIENTS
O
Ln
Figure 29. Total-Measured ^Mg Patients PC, PE, PH, and PJ.

96
Figure 30. Whole-Body Retention of
Disease Conditions.
28
'Mg Patients with Miscellaneous
I
rr

. Total-Measured
2%g
Patients PK, PF, PD,
and PL.
Figure 31

98
typical negative sura of exponentials. The first measurement on this
subject (study group 1) shows a striking departure from the normal curve
beginning at about 100 hours and drops to a 10.5 per cent retention
at 165 hours; normal retention is 70 80 per cent after this same period
of time. PB's retention curve in study group 2 followed essentially the
same pattern with the rapid drop starting at a later point in time.
PB's third whole-body retention measurement was not made on the 4-pi
liquid whole-body counter due to his advanced progression in the disease
and his inability to lie in a supine position.
PA, whose ALS syndrome was described by his physician as one not
progressing as rapidly as PB's, also has lower than normal retention in
all three of the measurements. The first two measurements (PA and PA2),
made two months apart, are nearly identical. The last measurement
(PA3), almost two years later, again shows a low 28^g retention; however,
the resultant curve is shaped similar to PB's and takes a precipitous
drop at 120 hours. Additional information on these patients can be
gained by examining the total-measured ^Mg results shown in Figures
26 and 27. It is interesting to note in Figure 27 that in neither of
the two measurements made on PB is there 100 per cent accountability
of the isotope. At 190 hours the second measurement (PB2) accounted
for only 50 per cent of the administered isotope.
In contrast, although PA's pattern is abnormal (Figure 26), there
is almost total-accountability of ^Mg the first two measurements,
but in the third where the whole-body retention curve departs from the
sum of exponentials model, a deficit similar to PB's exists. In the
first two measurements fecal 28^g was not analyzed; however, normal
excretion would essentially account for PA's administered magnesium.

99
Therefore, it might be concluded that PA's low whole-body retention is
due to a higher than normal urinary excretion of magnesium. At 220 hours
he had a cumulative urinary excretion of about 40 per cent compared
to an average normal excretion of 25 per cent.
The third ALS patient, PG, has a whole-body retention pattern
similar to that of PA's first and second measurements with a signifi
cantly higher than normal excretion of the isotope in both urine and
in feces. However, the total-measured 28Mg for this patient is somewhat
higher than 100 per cent, indicating an overestimation of at least one
of the measurements.
Pi's whole-body retention falls in the normal range and both
urinary and fecal excretion are normal. Again, as with PG, the total-
measured 28Mg
is somewhat over 100 per cent.
Gastrectomy Patients
The four gastrectomy patients' whole-body retention curves are
shown in Figure 28 and their total-measured 28j4g is in Figure 29.
Patients PC and PH had sub-total gastrectomies and manifested ALS-type
symptoms. They also have abnormal retention curves. PC's retention
pattern is similar to that of ALS patients PA and PG and is about 30
per cent lower than an average normal at 220 hours. Figure 29 shows
that PC has almost normal urinary excretion; consequently, the ^Mg
deficit is greater than that which can be attributed to a normal
fecal excretion.
PH's whole-body retention curve is similar in shape to that of
ALS patient PB, but it shows a consistently higher retention; it is
obvious that he had a lower than normal urinary excretion, but his fecal
excretion appears normal. PH's whole-body retention curve shows a drop

100
at about the same time as PB's. Patients PE and PJ sub-total gastrec
tomies were performed prior to this study. More recently they had
reparative surgery to correct a malabsorption problem which was thought
to be causing neuromuscular ALS-type symptoms. After surgery their
symptoms gradually disappeared. Although magnesium retention and
excretion measurements were not made on these individuals while they
manifested neuromuscular disorder, they were studied with ^Mg after
their return to a normal condition. The objective here was to determine
if, in addition to the remission of the neuromuscular condition, these
patients had a normal magnesium turnover. The results show that
although the retention curves are somewhat irregular in pattern, they do
not fall out of the normal retention band. Normal ^Mg urinary and
fecal excretion measurements were also observed.
Other Patient Studies
Patients PK and PF show erratic whole-body retention curves (Figure
30). PF's curve remains within the normal retention band while PK's
rises above the normal band at several points. PF had both kidneys
removed prior to this study and had received a single kidney transplant.
Examination of PFs excretion data in Figure 31 shows a normal amount of
the isotope in the urine. Assuming a normal fecal excretion, there was
essentially total accountability of the administered magnesium in the
study of this patient.
PK, a female patient with an extensive small bowel resection,
excreted almost no ^Mg by the urinary route, but lost a normal amount
in the feces. Throughout the period of study a deficit or imcomplete
accountability of the 2%g exists.
The other two patients in this group, PD and PL, both have higher

101
than normal retention of the isotope (Figure 30). PL, had been under
treatment for many years for hypertension, but denied the use of diure
tics or any medication just prior to or during the study. His retention
curve has a typical sum of exponentials shape, but is consistently higher
than the average normal subject. PD, on the other hand, not only had a
higher than normal retention, but his retention curve increases with
time.
Discussion of 2£$Mg Turnover Results in Patients
Although a small number of patients were studied within the several
groups representing the different disease conditions and the results
are varied, it is possible to make some general observations and also
some suggestions for further study. It is important at this point to
consider not only the erratic pattern of some of the whole-body retention
curves, but also the deficits and excesses which appear in the total-
measured 28y[gt One might speculate at this point that the general-
patterns of abnormal retention and/or excretion of the isotope is
related in some way to clinical abnormalities in the patients.
The behavior of the retention curves can be correlated with the
type of analyzer used in the various study groups. It is obvious in
study groups 3 to 6 that even the normal retention curves (Figure 17)
do not follow as smooth a function as the curves in study groups 1, 2,
and 7. As it was discussed earlier in this chapter, one might conclude
that the erratic behavior of many of the retention curves is related to
the type of analyzer used rather than to a disease condition.
Nevertheless, the most unusual patient results occurred in study
groups 1, 2, and 7 the groups with the least analytical problems.

102
It was in these groups that patient deficits were observed in the total-
measured 2£*Mg determinations. One explanation for a deficit in the
measurements would be incomplete collection of excreta. Although this
cannot be discounted, it is unlikely that in a patient like PB that it
would happen in both study groups 1 and 2 in such a reproducible manner.
The deficit and excess patterns are shown primarily by the
neuromuscular patients in the first case and the patients on or suspected
of being on diuretics in the latter. It appears then that these anoma
lies may be related to clinical conditions. Abnormal relocation of
the 2^Mg isotope in the body has been produced experimentally in a
phantom which simulates an adult human. If this were to occur in a
patient, counting efficiency would be altered to an extent which will
produce the magnitude of excess or deficit seen in this study. It is
possible that the isotope is being routed in large, atypical amounts to
the peripheral blood stream, to fluid of the peritoneal cavity, or to
some internal structure such as bone.
In spite of some of the uncertainties associated with these
results, a pattern of atypical behavior evolves that has a striking
consistency within the disease conditions studied. Specifically, the
following observations can be made:
(1) The patients with ALS (both of unknown origin and due to
gastrectomies) have lower than normal whole-body retention of 28y¡g.
(2) Some of these patients have an unusual retention curve
that drops precipitously around 100 hours after injection. ALS patient
PA did not show this pattern until his last measurement this may be
associated with progression in the disease.

103
(3) The patients who have "recovered" from the ALS associated
with gastrectomies also have normal retention curves and a normal amount
of 28f,jg excreta.
(4) The patient on diuretic therapy and the patient with
hypertension who denied use of diuretics both have higher than normal
retention of the isotope. Interestingly, the diuretic patient has a
retention curve that takes an upward turn at approximately the same time
that the ALS patients' curves turn downward. The latter observation
leads one to consider whether at this point in time the 28>ig is leaving
one compartment of the body in large amounts and entering another. An
abnormal relocation could produce counting efficiency changes which in
turn would result in an incorrect determination of whole-body retention.
These uncertainties led to the use in study group 7 of a
Nal(Tl) crystal whole-body counter to study relocation of the isotope.
Other factors that were also considered in this study group as possible
explanations for the abnormalities included sweat as a source of magnes
ium excretion and the possibility of a change in the equilibrium of the
2^Mg 28^1 parent daughter pair.
Measurements with the Nal(Tl) Crystal Whole-Body Counter
Three types of data evaluation were performed with the results
from the Nal(Tl) crystal counter measurements on the four subjects (PA,
PB, NH, and NM) in study group 7.
(1) Whole-body retention was computed;
(2) The partial-body counts were examined to determine if
localization of ^Mg OCCurred within the body; and
(3) Ratios of the counting rates in the 28Mg and 28a1 photo
peak regions were analyzed for possible variations in this equilibrium.

Whole-Body Retention
An alternative method of whole-body retention analysis was
made using the crystal counter results primarily because patient PB was
not able to maintain the supine position necessary for the 4-pi counter
measurement. Results of measurements by the crystal counter on the
three other subjects were used to intercompare results of 4-pi counter
measurements.
Whole-body retention as a function of time after administra
tion of the isotope is shown for the two normals and the two ALS
patients in Figure 32. The two normals, NH and NM, have similar reten
tion functions; at the last observation (=165 hours)* they had retentions
of 69 and 66 per cent, respectively.
The retention of the two patients, PA and PB, was signifi
cantly lower than those of the normal subjects. This difference is
consistent with the observations made with the 4-pi counting system on
ALS and normal subjects. The two patients have similar curves up to
=115 hours; at this point PB's curve takes a sharp upward turn (dashed
curve). This positive change in slope has to be an anomaly in the
counting measurement since it is impossible for the patient to have an
increase in total-body 28Mg.
In general, the retention values for all four subjects meas
ured by the crystal counter are proportional to those measured with the
4-pi counter during the same time period. In Table 6, the two systems
Although these subjects were followed for 220 hours on the
4-pi counter during this study, measurements beyond 165 hours were not
possible with the crystal counter because of its higher minimum detect
able activity level (due to lower counting efficiency and minimum back
ground reduction achieved by only partial shielding.

WHOLE -BODY RETENTION, %
Figure 32. Whole-Body Retention as Measured by the Nal(Tl) Counter.
|

TABLE 6
COMPARISON OF THE WHOLE-BODY RETENTION MEASUREMENTS BY THE 4-PI LIQUID SCINTILLATION
AND THE Nal(Tl) CRYSTAL WHOLE-BODY COUNTERS
Per Cent Retention
Time After
Subject NH
Subject NM
Patient PA
Injection
(Hours)
4-Pi
Crystal
4-Pi
Crystal
4-Pi
Crystal
Counter
Counter
Counter
Counter
Counter
Counter
30
93
92
90
88
87
78
70
87
76
85
79
82
63
115
84
69
83
75
75
54
165
79
69
78
66
65
54
90 C

107
are compared at several points in time for the three subjects measured
on both counters. The major difference in the results of this compari
son is that the retention measured by the crystal counter is lower; the
greatest difference, about 10 per cent, was found at the 165-hour
measurement.
There are a number of reasons to support the 4-pi counter
results as the true absolute values. First of all, the balance studies
(Figure 25) in this study using the 4-pi counter essentially account for
all of the administered ^^Mg. Therefore, the whole-body retention
determinations were verified. In addition, the 4-pi system shows less
\
variability and produces more accurate absolute values because of its
inherent characteristics and because of the operational experience
with the counter. The geometrical configuration of the 4-pi counter is
one of the superior characteristics it essentially surrounds the sub
ject producing a counting efficiency many times higher than that of the
crystal counter. This configuration is also relatively insensitive to
source location, while the crystal counter geometry is not. The crys
tal counter measures the major portion of the body, but it eliminates the
head and the lower legs. Any non-uniform distribution with respect to
any of the body parts would produce an apparent rate of turnover differ
ent than a true whole-body count. The 4-pi counter also has the advant
ages of lower background due to its fully-shielded room and ventilated
air flow. Another aspect of comparison is that this was the first time
that the crystal counter had been used in a tracer experiment. The
inexperience of the operating personnel in positioning subjects, in
routine handling of the output systems, and in analysis of the data

108
suggests a lower degree of confidence in the crystal counter results.
Another major difference in the results using the crystal
counter is that the retention curve turned upward for PR's determination
at the same time that the curve turned downward in earlier work using
the 4-pi system. (Compare Figures 25 and 32.) This suggests that the
28
Mg may be relocating within the body in such a way that it is measured
with a lower efficiency in the 4-pi counter and a higher efficiency in
the crystal counter.
Localization Measurements of
The necessity for using the crystal counter retention measure
ments on the group 7 subjects also provided an opportunity to evaluate
this crystal system for localization studies.
In its present configxiration, the crystal counter is not
sufficiently collimated to restrict the measurement field to well-defined
regions of the body. Therefore, only four general regions head, chest,
abdomen, and legs were selected for analysis. The chest and abdominal
regions included the upper and lower arms. Corrections were made for
contributions to counts of one region from activity in the others.
Figure 33 shows the regional retention of the isotope (fraction
or per cent of the initial amount in each body section) for the four sub
jects in group 7. The ratios of each of these body regions to the total
amount of 28j^g present in the body initially were calculated as:
head, 7 per cent; chest, 60; abdomen, 19; and legs, 16.
The results for the two normal subjects, NH and NM, show the
following:
(1) The most rapid loss was from the chest region (=45 per
cent regional retention at 165 hours). The curves are almost identical

% OF INITIAL CONTENT IN REGION
109
POST-INJECTION TIME, HOURS
Figure 33. Regional Retention of ^Mg.

no
for the two subjects.
(2) An intermediate loss occurs from the head region (-65
per cent regional retention after 165 hours). The curves are very
similar for the two subjects.
(3) There is an intermediate loss rate in the abdominal
region and a low loss rate in the leg region (>90 per cent regional
retention at 100 hours, >70 per cent at 165 hours). A possible build-up
occurs in both regions in the first 24 48 hours.
In summary, the normal subjects exhibited a higher rate of
loss from the chest region, a less rapid loss from the other regions,
and possible relocation (early build-up) in the abdominal and/or leg
regions.
In comparison, the results for the two patients, PA and PB,
show that:
(1) As with the normals, the most rapid loss was from the
chest region.
(2) The initial loss from the head region is more rapid than
that shown by the normals. Patient PA shows the lowest retention in
the head region of all four subjects. The data for PB suggests a
progressive build-up in this region after 48 hours.
(3) Patterns of the abdominal-regional curves differ between
patients to a greater degree than those of the normals. Patient PA's
curve is not distinguishable from the normal subjects, PB shows a
striking build-up in this region beginning at 24 hours and at 165 hours
reaches a level 2 1/2 times that of the other subjects.
(4) Leg-region curves for the patients are similar to those
of the normals but show a more rapid loss. PB appears to lose a greater

Ill
fraction of the initial activity than PA. Patient PB (with the more
progressive stage of the disease) appears to lose activity more rapidly
from the leg region (or conversely, fails to retain circulating 2%g in
that region) and to deposit it in the abdominal region. The buildup in
the abdominal region helps account for the apparent increase with time
of the patient's whole-body retention measurement. It has subsequently
been shown that with the configuration used at the time, the counting
efficiency is relatively higher for the abdomen than for the other
regions.
Magnesium-28 retention in the legs appears to be related to
age or to the physical activity of the subjects. The normals had
greater retention than the patients; normal NH (age 41) had a greater
retention than NM(age 71) and patient PA (who was still able to walk)
had greater retention than PB (who was confined to a wheelchair).
2^Mg 28Ai Equilibrium
The high energy resolution capability of the Nal(Tl) system
was used as a means of examining the data in study group 7 for possible
changes in the equilibrium of the parent daughter pair. Initial analy
sis of the data included a summing of all counts in two regions, the
2^Mg region, 0.03 to 1.6 MeV (includes interference from the 28^.1 peak)
and the 2A1 region, 1.6 MeV to 2.0 MeV (which is free from 28Mg inter
ference) The ratios of these energy regions were tabulated and examined
for differences between regions of the body, differences between subjects
within the normal and patient groups, and differences with time.
In general, the head and legs showed the lowest ratios (-5.0 -
6.0) while the abdomen and whole-body shoed the highest (-5.5 9.0).
After the first day (ratio =6.1), ratios dropped (=5.0 5.5) and stayed

112
lower for the next three days; then increasing values were observed
for the fifth and sixth days (-5.5 6.5 and =8.0 10.0, respectively).
Ratios fluctuated considerably on the last day of measurements (seventh)s
but this can be attributed largely to the low count rates and consequent
poorer statistics.
The only difference between subjects is limited to an indica
tion of a lower ratio in the chest and a higher ratio in the abdomen and
legs of PB than that observed in the other subjects after the third day.
A decrease in the ratio is due to an increase in the relative number
of counts in the higher energy region, 28^1. This could be a result of:
(1) a biological factor which favors the aluminum element over magnesium
or (2) an increasing average thickness of tissue and thus increasing
attenuation of the photon. An increase in the ratio would be due to
an inverse of the above.
Any interpretations of the data will not be made at this time.
Many variables could contribute to the change in the ratios which have
nothing to do with biological factors. One of these could be spectrum
shifts from day to day or from time to time during the day. Because of
this and the fact that there is no significant and consistent pattern
in the ratios, it is concluded that the 28^g 28^j_ equilibrium remained
constant.
28ng in Sweat
A comparison of the results of sweat analyses between the two
normals and the two patients in study group 7 showed no significant
difference. Results of these measurements are included in Appendix D.
It was concluded that sweat was not the variable involved in the deficit
in total-measured 28p[g in several ALS patients.

CHAPTER V
SUMMARY AND CONCLUSIONS
Thirty-one whole-body retention and excretion measurements
were made on 13 normal subjects and on 10 patients with selected
disease conditions to determine as accurately as possible the biological
half-lives from a single intravenous administration of 28^g in the forra
of MgCl2- The prime objective of this research was to contribute
information to the currently sparce knowledge on magnesium metabolism
in humans. Calculation of radiation dose based on the determined
half-lives was an important aspect of the research since the experi
mental use of 2^Mg is increasing rapidly and no dose estimates have
been established. The feasibility of this measurement technique for
studying abnormalities in disease conditions was also explored.
A high specific activity (=200 300 yCi per mg magnesium)
preparation of the radioactive isotope ^Mg (21.3-hour physical half-
life) was used in conjunction with the sensitive 4-pi liquid scintil
lation whole-body counting technique for retention determinations.
A Nal(Tl) crystal whole-body counter was employed to measure locali
zation of the magnesium in the body and appropriate low-level counting
systems were used for measurement of the isotope in excreta.
The pertinent information gained from this work can be
summarized as follows:
1. The fitting of whole-body retention data from the 15
determinations on normal subjects (including two replications) to a sum
113

1] 4
of two exponentials model resulted in the following equation:
R = 8.5e-0'125t + 91.5e_0-00128t.
The first and second coefficients of the retention equation, 8.5 and
91.5, represent the quantities involved in the turnover of the two
compartments. Biological half-lives of 5.4 2.2 hours for the first
compartment and 540 35 hours for the second compartment were calcula
ted from the rate constants in the exponents of the fitted equation.
2. The resulting radiation dose from this single administra
tion of 2^Mg was calculated to be 2.0 mrad/pCi.
3. In the normal subjects, excretion measurements on the
average accounted for the amount of the 28^g not retained in the body.
Cumulative urinary excretion averaged 3 per cent per day, while fecal
excretion was approximately 0.5 per cent per day.
4. Stable magnesium analyses, made on all subjects in con
junction with the 28Mg measurements, showed no consistent pattern bet
ween normals and patients or between the various disease conditions.
5. Whole-body retention values for ALS and sub-total gastrec
tomy patients were significantly lower than normal, while several sub
jects, one of whom was known to have been on diuretics, had higher than
normal retention of the isotope. Repaired gastrectomy patients had
retention patterns within the normal range.
6. In the majority of the patients studied, the abnormal
retention of 28Mg was accounted for by amounts in the excreta. However,
in several patients, excretion did not account for the total amount
of the isotope not retained in the body, resulting in a deficit in the
total-measured 28^g.

115
7. Sweat analyses, which were performed in an effort to
find the reason for this deficit, showed that this route of excretion
contains an insignificant amount of 28Mg.
8. Localization of the isotope as measured by Nal(Tl) crystal
whole-body counting showed consistent patterns between results cf the
normal subjects. An atypical build-up of the isotope was found in the
abdominal region for the ALS patient who previously exhibited an appar
ent precipitous whole-body loss of ^Mg.
Conclusions
1. Based on published investigations to date, it is con
cluded that this turnover study is currently the most accurate. The
use of a true tracer dose of 10 pCi or less of high specific activity
^Mg and the sensitive whole-body counting system allowed administra
tion of a dose which would not upset the physiochemical balance of the
body. Also, this procedure permitted measurements up to six times longer
than previously reported studies.
O O
2. The amount of Mg to be administered in future investi
gations with this isotope should be guided by the 2.0 mrad/yCi dose
calculated from the data obtained in this study.
3. Based on the consistent, significantly abnormal retention
and excretion patterns shown by certain disease state measurements in
this study, it is concluded that this turnover procedure could serve
as a valuable adjunct to other diagnostic techniques.
4. A review of the results and procedures in this study
shows that if there was sufficient need for continuing the turnover
measurements beyond 10 days a special double measurement technique

116
could be used. An accurate definition of early retention data could be
obtained from a 1 yCi dose. This would be followed in the same sub
ject (s) at a later date with a much larger dose.
5. The use of a partially collimated Nal(Tl) crystal whole-
body counter,in a pilot study in this research, shox^s promise for future
work. A crystal with better collimation in a shielded room would pro
vide more precise, important information on the localization of magnes
ium in the body. This information would not only be a significant
contribution to normal metabolism studies but would also serve as a
means for studying a number of disease conditions where abnormal
magnesium metabolism is suspected.

APPENDICES

APPENDIX A
COMPUTATION OF RADIATION DOSE

119
PRELIMINARY CALCULATION OF RADIATION DOSE
-Using Geometric Factor Method (213) and ICRP Half-Life (212)-
To calculate the total dose per yCi with the activity distri
buted throughout the total body:
Beta Dose: D^ = 73. 8 C E Teff rads.
28Mg: Dg = 7.38 x 1.43 x 1.53 x 8.85 x 10-8 = 1.43 x 10~4 rads.
28A1: Dg = 7.38 x 1.43 x 9.52 x 8.85 x 10-6 = 8.89 x 104 rads,
Gamma Dose: Dy = 33.1 x
Tabulated Computation:
103 c
K g Teff
Total =
rads.
10.32 x
10-4 rads.
Isotope
E
n
ua
K
Dy(rads)
28Mg:
.032
.96
1.1
x 10"4
5.2 x 101
2.6
x 10-4
.40
.31
3.2
x 10-5
6.2 x 101
3.2
x lO"4
.95
.29
3.2
x lO-5
13.6 x 10l
7.1
x 104
1.35
.70
3.1
x 10-5
4.6 x 101
2.3
x 10~4
28A1:
1.78
1.00
2.9
x lO-5
8.0 x 101
0.8
x lO"4
Total
= 16.0
x 10-4
Total Dose:
Dq 1
3+y
= ZDg +
EDy.
Total
dose =(10.3 + i
L6.0)x ;
10-4 rads
= 2.6 x 10'
.O
rads =
= 2.6 mrads.
C = radionuclide concentration in organ =
1 yCi
7 x 104 g
= 1.43 x 105 yCi/g.
Eg = average beta energy, MeV.
Where:

120
28Mg: Eg = 0.459 MeV/3 = 0.153 MeV.
28A1: Eg = 2.856 MeV/3 = 0.952 MeV.
Teff = effective half-life, days = (Tp x Tb)/(Tp + Tb).
Tp = physical half-life = 21.3 hours.
Tb = biological half-life = 4320 hours.
Te££ =(21.3 x 4320)/(21.3 + 4320) hours x 1/24 days/hour
= 0.885 days.
K = specific gamma-ray constant, R cm^/mCi hr
= 1.56 x 10? n E ua.
Y a
n = number of photons per disintegration at energy E.
E-y gamma-ray energy, MeV.
ua= linear absorption coefficient in air for energy E.
g = average geometric factor.

121
COMPUTATION OF RADIATION DOSE
-Using MIRD Method (214)
and Biological Half-Life Determined in this Study-
A. Given:
1. Isotope 28]yig,
2. Critical organ whole body.
3. Administered activity 1 pCi.
4. Physical half-life 21.3 hours.
Biological half-life two components:
a. Uptake of 8.5 per cent with 5.4-hour half-life.
b. Uptake of 91.5 per cent with 540-hour half-life.
Assumptions:
1. Mass of whole body is 70 kilograms.
2. Shape of body is ellipsoidal.
3. Activity is uniformly distributed.
B. Dose Equations average dose to self-irradiated organ (214).
D
y
m L
A 4>
i i
rad.
Where A = cumulated activity, pCi hrs.
m = mass of critical organ, g.
Ai= equilibrium dose constant, g rads/pCi hr.
absorbed fraction for ith radiation in organ.
0.085 x 4.3 =0.53 pCi hrs.
0.915 x 20.49 = 26.99 pCi hrs. '
pCi = 0.085 pCi,
pCi = 0.915 pCi,
half-life, defined previously.
Teff! = (21*3 x 5.4)/(21.3 + 5.4) hrs = 4.3 hrs.
Teff2 = (21.3 x 540)/(21.3 +540) hrs = 20.49 hrs.
In the case of a two-component model:
'Xi 'Xj 'Xj
A = A^ + A£
= 1.44(Aq)^ x 1.44 x
X2 = 1.44(Aq)2 x Teff2= 1.44 x
Where: (A0)^ = 0.085 x 1
(A0)2 = 0.915 x 1
Te££ = effective

122
28 28.1
For Mg Al,
£ Vi can ke coniputed in tabular form:
i
Back Scatter
Radiation
Mean Energy
. ,A.
H
Factor
Ai$i
3i
0.1560
0.332
1.0
-
0.332
82
1.240
2.641
1.0
-
2.641
Auger e
0.0014
0.0002
1.0
__
0.0002
(k shell)
Conversion
0.0029
0.0031
1.0
0.0031
e
Character-
0.0015
=0
1.0
-
0
istic x-ray
y 1
0.0364
0.0620
0.753
1.08
0.0504
y2
0.3998
0.264
0.340
1.05
0.0942
Y3
0.9415
0.562
0.329
1.02
0.1886
Yy
1.342
1.97
0.311
1.02
0.6250
y5
1.779
3.79
0.290
1.02
1.1222
Thus the dose can be computed:
5.0538
a.
D = A J A.$. = 3.93 x 10~4 yCi hrs/g x 5.0538 g rads/yCi hrs
m 7 1 1
m i
= 1.99 mrads

APPENDIX B
28Mg BALANCE CHARTS
NORMALS AND PATIENTS

124
SUBJECT: NA STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:15 DOSE: 1.307 pCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
1.4
99
2
-
101
1
3.5
96
3
-
99
-1
8.1
96
3
-
99
-1
20.5
93
4
-
97
-3
22.7
93
4
-
97
-3
25.8
92
4
-
96
-4
28.2
92
5
-
97
-3
32.2
92
5
-
97
-3
45.3
91
6
-
97
-3
48.3
93
6
-
99
-1
52.3
90
7
-
97
-3
56.5
90
7
-
97
-3
70.1
89
9
-
98
-2
78.9
86
9
-
95
-5
93.4
85
10
-
95
-5
124.5
82
12
-
94
-6
142.5
81
13
-
94
-6
166.3
79
-
-

-
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

125
SUBJECT: NB STUDY GROUP: 1
DATE, TIME OF INJECTION: 9-23-69, 12:20 DOSE: 10.35 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
100
10.1
95
4
99
-1
22.8
96
6
102
+2
46.6
92
9
101
+1
70.1
86
11
97
-3
94.9
82
13
95
-5
142.7
75
16
91
-9
165.9
76
18
94
-6
189.8
73
20
93
-7
213.8
75
23
98
-2
*Expressed in per cent,
rounded off
to the
nearest whole number.
- Means not measured

126
SUBJECT: NC STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:10 DOSE: 1.304 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
1.1
96
4
100
2.6
100
5
105
+5
5.1
97
6
103
+3
21.0
89
7
96
-4
23.2
90
8
98
-2
25.3
89
8
97
-3
27.8
89
9
98
-2
31.8
88
9
97
-3
44.6
86
10
96
-4
47.9
84
11
' 95
-5
52.0
85
11
96
-4
56.0
86
12
98
-2
70.2
80
13
93
-7
74.3
79
14.
93
-7
79.4
78
14
92
-8
93.0
79
15
94
-6
143.9
71
18
89
-11
*Expressed in per cent, rounded
off to the nearest
whole number.
Means not measured

127
SUBJECT: NC2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:35 DOSE: 10.56 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.2
100
-
-
100
9.5
96
6
-
102
+2
21.2
91
8
-
99
-1
44.2
90
11
-
101
+1
69.5
82
15
-
97
-3
93.4
82
17
-
99
-1
141.4
77
23
-
100
169.5
75
24
-
99
-1
192.0
74
25
-
99
-1
215.7
73
30
103
+3
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

128
SUBJECT: ND STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:15 DOSE: 10.20 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
-
100
8.8
97
2
-
99
-1
23.2
95
4
-
99
-1
43.1
94
6
-
100
71.0
87
7
-
94
-6
95.3
84
9
-
93
-7
143.1
81
13
-
94
-6
168.1
78
14
-
92
-8
192.0
75
17
-
92
-8
215.5
79
21
100
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

129
SUBJECT: NE STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:16 DOSE: 9.158 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
-
100
11.1
96
4
-
100
25.9
91
6
-
97
-3
50.0
92
9
-
101
+ 1
73.5
90
10
-
100
97.9
88
12
-
100
145.7
83
17
-
100
169.6
77
20
-
97
-3
193.8
72
21
-
93
-7
217.9
72
22
_
94
-6
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

130
SUBJECT: NF STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 8:58 DOSE: 9.344 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours)Retention* Urine Feces Balance* Deficit*
0.4
100
-
-
100
10.6
96
3
-
99
-1
27.0
92
6
-
98
-2
50.1
90
13
-
103
+3
74.6
86
16
-
102
+2
98.0
84
18
-
102
+2
146.7
79
20
-
99
-1
170.7
76
22
-
98
-2
194.9
70
24
-
94
-6
218.0
70
26
96
-4
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

131
SUBJECT: NG STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:05 DOSE: 9.218 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours)Retention*Urine Feces Balance* Deficit*
0.4
98
-
98
-2
11.9
99
3
102
+2
22.0
83
7
100
45.6
82
9
101
+1
69.6
80
12
92
-8
94.0
80
14
94
-6
142.0
72
18
90
-10
165.2
70
21
91
-9
189.0
70
22
92
-8
213.0
66
24
90
-10
*Expressed in per cent,
rounded off
to the
nearest whole
number.
- Means not measured

132
SUBJECT: NH STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:03 DOSE: 6.368 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.5
99
-
-
99
-1
6.5
94
2
-
96
-4
19.1
85
4
-
89
-1
43.4
84
6
-
90
-10
67.5
85
8
-
93
-7
91.4
86
10
-
96
-4
139.4
84
13
-
97
-3
163.4
78
14
-
92
-8
187.4
77
19
-
96
-4
211.5
78
20
-
98
-2
235.6
73
20
93
-7
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

133
SUBJECT: NH2 STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 11:55 DOSE: 9.373 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
7.2
98
-
-
98
-2
21.5
94
5
1
100
45.2
93
7
2
102
+2
69.5
88
9
2
99
-1
117.3
84
11
4
99
-1
141.5
81
12
5
98
-2
165.3
78
14
5
97
-3
189.3
75
16
5
96
-4
213.8
75
19
6
100
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured.

134
SUBJECT: NI STUDY GROUP: 4
DATE, TIME OP INJECTION: 1-6-70, 16:11 DOSE: 6.535 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit
0.9
97
-

97
-3
6.2
89
4
-
93
-7
18.0
80
9
-
89
-11
42.0
84
12
-
96
-4
65.2
79
14
-
93
-7
90.2
83
17
-
100
137.9
77
20
-
97
-3
162.1
71
22
-
93
-7
186.9
72
28
-
100
210.3
75
28
-
103
+3
234.2
80
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

135
SUBJECT: NJ STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:08 DOSE: 6.599 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
0.6
98
-
-
98
-2
6.1
92
7
-
99
-1
18.0
81
10
-
91
-9
41.9
88
13
-
101
+1
65.1
81
16
-
97
-3
90.0
85
18
-
103
+3
137.9
76
23
-
99
-1
162.0
71
25
-
96
-4
185.7
70
32
-
102
+2
210.0
70
33
-
103
+3
233.8
64
33
97
-3
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured.

136
SUBJECT: NK STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:04 DOSE: 6.630 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.5
99
-
-
99
-1
6.0
94
6
-
100
17.9
81
11
-
92
-8
41.9
88
16
-
104
+4
65.1
81
19
-
100
90.0
84
24
-
108
+8
138.3
o
76
30
-
106
+6
161.8
71
33
-
104
+4
185.6
67
40
-
107
+7
209.7
62
42
-
104
+4
233.5
62
43
105
+5
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured

137
SUBJECT: NL STUDY GROUP: 4
DATE
, TIME OF INJECTION: 1-6-70,
16:20 DOSE:
6.790 yCi
Time
After Injection
Cumulative
Excretion*
Excess or
(Hours) Retention*
Urine Feces
Balance* Deficit*
0.9
97
-
-
97
-3
6.4
95
4
-
99
-1
18.9
81
6
-
87
-13
42.7
82
10
-
92
-8
66.8
78
13
-
91
-9
89.7
80
14
-
94
-6
138.8
79
17
-
96
-4
162.8
72
17
-
89
-11
186.7
71
18
-
89
-11
210.8
75
18
-
93
-7
234.9
67
-
-
-
*Expressed in per cent,
rounded off
to the
nearest
whole number
- Means not measured

138
SUBJECT: NM STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 12:00 DOSE: 9.745 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Exo.
Balance* Def:
6.5
96
-
-
96 -4
20.8
94
5
1
100
26.0
91
7
2
100
45.0
88
9
2
99 -1
68.3
85
12
3
100
116.8
83
13
4
100
140.5
79
14
4
97 -3
164.8
78
16
4
98 -2
187.8
74
19
5
98 -2
213.5
74
-
-
-
*Expressed in per cent,
rounded off
to the
nearest
whole number.
- Means not measured

139
SUBJECT: PA STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:20 DOSE: 1.295 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balanc*
Excess or
Deficit*
1.7
97
3
-
100
3.7
93
5
-
98
-2
8.3
90
6
-
96
-4
21.2
84
10
-
94
-6
23.4
85
11
-
96
-4
26.0
84
12
-
96
-4
28.4
82
13
-
95
-5
32.3
84
14
-
98
-2
46.6
83
15
-
98
-2
48.6
79
16
-
95
-5
52.5
78
17
-
95
-5
56.8
77
18
-
95
-5
71.3
75
19
-
94
-6
74.1
69
21
90
-10
93.9
69
23
-
92
-8
123.3
66
30
-
96
-4
142.1
61
33
-
94
-6
165.6
55
-
-
-
*Expressed as per cent
, rounded off
to the
nearest whole number.
- Means not measured

140
SUBJECT: PA2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 13:00 DOSE: 10.03 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.3
100
-
-
100
8.3
94
9
-
103
+3
21.1
87
13
-
100
45.0
82
18
-
100
69.0
76
21
-
97
-3
93.3
72
24
-
96
-4
141.2
64
31
-
95
-5
165.5
63
34
-
97
-3
189.5
54
37
-
91
-8
213.9
57
42
-
99
-1
237.9
29
51
-
80
-20
* Expressed as per cent
:, rounded off
to the
nearest
whole number.
- Means not measured

141
SUBJECT: PA3 STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 11:53 DOSE: 9.637 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
'Urine Feces
Excess or
Balance*' Deficit*
1.7
100
-
-
100
6.0
90
-
-
90
-10
20.5
90
9
0
99
-1
44.0
86
15
0
101
+1
67.9
81
19
1
101
+1
116.0
75
24
1
100
140.5
71
27
2
100
164.0
65
30
2
97
-3
187.8
55
33
2
90
-10
211.9
38
37
4
79
-21
*Expressed as per cent, rounded off to the nearest whole number.
- Means not measured.

142
SUBJECT: PB STUDY GROUP: 1
DATE, TIME OF
INJECTION: 5-20-69,
12:50
DOSE:
1.265 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balanc*
Deficit*
1.8
99
2
-
101
+1
3.6
98
3
-
101
+1
8.2
92
4
-
96
-4
21.2
91
5
-
96
-4
23.4
88
5
-
93
-7
26.0
88
6
-
94
-6
28.3
89
6
-
95
-5
32.3
88
7
-
95
_5
44.3
85
8
-
93
-7
52.4
84
9
-
93
-7
56.6
84
10
-
94
-6
70.4
82
11
-
93
-7
75.7
77
12
-
89
-11
92.8
78
16
-
94
-6
122.4
65
21
-
86
-14
141.2
50
22
-
72
-28
164.6
11
-
-
-
*Expressed as
per cent, rounded off
to the
nearest
whole number.
- Means not measured

143
SUBJECT: PB2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 13:06 DOSE: 10.01 pCi
Time After Injection
(Hours)
Rtntion*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.2
100
-
-
100
8.3
97
5
-
102
+2
21.2
92
10
-
102
+2
45.2
88
13
-
101
+1
69.5
84
16
-
100
93.5
78
20
-
98
-2
141.5
65
25
-
90
-10
166.1
52
28
-
80
-20
190.1
23
30
-
53
-47
*Expressed as per cent
:, rounded off
to the nearest
whole number.
- Means not measured

144
SUBJECT: PC STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:14 DOSE: 9.298 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours) Rtentiii* Urine Feces Balance* Deficit*
0.7
100
-

100
10.8
91
6
-
97
-3
25.5
82
10
-
92
-8
49.3
76
14
-
90
-10
73.4
71
18
-
89
-11
96.8
68
19
-
87
-13
145.8
58
23
-
81
-19
169.3
58
25
-
83
-17
193.7
55
27
-
82
-16
217.8
53
27
-
80
-20
241.5
54
27

81
-19
*Expressed as per cent, rounded off to the nearest whole number.
- Means not measured.

145
SUBJECT: PD STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:25 DOSE: 9.105 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.8
100
-
100
10.6
98
2
100
24.3
97
3
100
48.1
95
5
100
73.2
93
6
99
-1
97.7
93
6
99
-1
145.0
88
8
96
-4
168.9
89
9
98
-2
193.0
96
9
105
+5
216.9
110
9
119
+9
240.9
126
10
136
+36
*Expressed as per cent,
rounded off
to the
nearest whole number.
- Means not measured

SUBJECT: PE
STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:23 DOSE: 9.061 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
0.7
100
-
-
100
10.4
99
8
-
07
+7
23.9
95
12
-
107
+7
47.8
95
18
-
113
+13
71.8
89
22
-
111
+11
96.3
84
26
-
110
+10
143.8
76
34
-
110
+10
167.7
74
36
-
110
+10
191.8
78
40
-
118
+18
215.7
73
46
-
119
+19
*Expressed as per cent
, rounded off
to the
nearest
whole number

- Means not measured

147
SUBJECT: PF STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:43 DOSE: 10.15 yCi
Time After Injection
Retention*
Cumulative
Excretion*
Balance*
Excess o
Deficit*
(Hours)
Urine
Feces
0.3
100
-
-
100
8.1
99
2
-
101
+1
20.7
98
4
-
102
+2
44.8
93
5
-
98
-2
69.0
87
7
-
94
-6
92.8
88
9
-
97
-3
140.8
83
15
-
98
-2
168.9
80
16
-
96
-4
189.0.
77
17
-
94
-6
213.2
67
21
-
88
-12
236.1
69
30
-
99
-1
*Expressed as per cent
, rounded off
to the
nearest
whole number,

Means not measured.

148
SUBJECT: PG STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70,10:04 DOSE: 4.445 uCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
1.0
100
-
-
100
10.1
90
15
0
105
+5
24.8
82
23
3
108
+8
48.9
79
30
3
112
+12
72.8
76
35
3
114
+14
121.2
64
40
5
109
+9
144.7
59
44
6
109
+9
169.2
55
44
8
107
+7
193.2
53
44
9
106
+6
219.5
49
45
11
105
+5
^Expressed as per cent
, rounded off
to the
nearest
whole number
- Means not measured

149
SUBJECT: PH STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:01 DOSE: 5.336 yCi
Time After Injection
Cumulative
Excretion*
Balance*
Excess or
Deficit*
(Hours)
Retention*
Urine
Fces
0.7
100
-
-
100
6.5
99
-
-
99
-1
24.7
100
3
0
103
+3
48.3
100
5
0
105
+5
72.3
99
6
0
105
+5
120.4
94
7
0
101
+1
144.7
88
7
1
95
-5
168.3
80
8
3
91
-9
192.5
67
8
3
78
-22
216.4
45
10
4
59
-41
*Expressed as per cent
, rounded off
to the
nearest
whole number
- Means not measured

150
SUBJECT: PI STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:02 DOSE: 5.307 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Blarice*
Excess or
Dficit*
0.9
100
-
100
24.3
96
10
0
106
+6
48.7
92
15
0
107
+7
72.7
89
18
2
109
+9
120.9
81
23
4
108
+8
145.4
77
25
4
106
+6
169.0
74
26
4
104
+4
193.4
74
26
6
106
+6
217.2
64
26
6
96
-4
241.6
64

-

^Expressed as per cent
:, rounded off
to the
nearest
whole number.
- Means not measured

151
SUBJECT: PJ STUDY GROUP: 5
DATE, TIME OF INJECTION: 2-10-70, 9:27 DOSE: 9.269 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Dficit*
1.0
100
-
-
100
10.6
95
8
-
101
+1
25.2
84
12
-
96
-4
48.4
78
14
1
93
-7
72.9
78
16
1
95
-5
96.4
75
17
1
93
-7
148.5
83
18
1
102
+2
172.6
82
19
1
102
+2
195.6
70
21
2
93
-7
219.6
61
25
3
89
-11
243.5
57
-
-
-
*Expressed as per cent,
rounded off
to the
nearest
whole number.
Means not measured.

152
SUBJECT: PK STUDY GROUP: 5
DATE, TIME OF INJECTION: 2-10-70, 9:45 DOSE: 9.389 pCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Dficit*
0.5
100
-
-
100
9.6
95
0
0
95
-5
21.6
90
0
1
91
-9
45.7
83
0
2
85
-15
69.8
88
0
3
91
-9
93.8
90
0
3
93
-7
141.7
89
0
4
93
-7
165.7
85
1
4
90
-10
189.7
76
1
5
82
-18
213.8
67
1
7
75
-25
*Expressed as per cent
, rounded off
to the
nearest
whole number.
- Means not measured.

153
SUBJECT: PL STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:00 DOSE: 5.405 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.5
100
-
-
100
9.3
99
2
-
101
+1
24.1
102
3
1
106
+6
48.1
102
5
1
107
+8
72.0
104
6
3
113
+13
120.1
80
9
5
94
-6
144.5
94
10
6
110
+10
168.5
90
12
7
109
+9
192.2
89
12
8
109
+9
216.0
88
12
11
111
+11
240.5
88
- '
-
-
*Expressed as per cent
, rounded off
to the
nearest
whole number

- Means not measured

APPENDIX C
SWEAT ANALYSIS, STUDY GROUP 7

155
Days After Patient PA Patient PB Subject NH Subject NM
Injection
Quantity of Sweat Collected (mg)
1
458.4
468.0
454.6
458.7
2
525.2
395.4
1199.1
501.6
3
459.4
479.8
463.3
455.9
5
478.5
465.9
456.5
451.2
6
441.8
451.4
477.9
481.8
7
476.6
485.3
481.8
458.2
8
541.9
496.9
470.4
460.1
9
489.2
482.6
480.2
467.4
28Mg
in Sweat, %
of Injected Dose
1
O.O(NS)
0.0(NS)
0.0(NS)
0.0(NS)
2
0.003
0.004
0.005
0.004
3
0.009
0.008
0.011
0.035
5
0.019
0.009(NS)
0.006(NS)
0.020
6
0.015(NS)
0.009(NS)
0.020(NS)
0.027
7
0.013(NS)
0.0(NS)
0.014(NS)
O.O(NS)
8
0.036(NS)
0.0(NS)
0.11
0.19
9
0.28
0.096(NS)
0.70
0.31
Concentration, % of
Injected Dose/kg
1
0.0(NS)
0.26(NS)
0.0(NS)
0.0(NS)
2
5.14
9.61
4.59
6.98
3
19.8
16.3
23.7
76.8
5
39.7
19.3(NS)
12.9(NS)
44.4
6
34.0(NS)
0.0(NS)
41.9(NS)
56.0
7
27.3(NS)
0.0(NS)
29.1(NS)
O.O(NS)
8
66.4(NS)
0.0(NS)
238.0
409.0
9
574.0
199.0(NS)
1460.0
663.0
NS = Count Not Significantly different from background. '

APPENDIX D
Nal(Tl) CRYSTAL WHOLE-BODY COUNTER
RETENTION AND LOCALIZATION DATA

157
Patient
PA
Patient
PB
Subject
NH
Subject
NM
x*
R**
X*
R**
x*
R**
x*
R**
Whole-Body
Whole-Body
Whole-Body
Whole-Body
20.3
84.1
24.0
84.0
21.7
92.0
21.3
88.0
44.6
70.7
48.0
63.7
45.4
92.0
44.7
88.0
65.0
64.0
67.2
57.6
69.2
75.8
67.4
79.1
113.6
54.5
115.4
47.9
117.4
67.0
113.3
64.4
138.2
52.4
139.1
55.7
141.7
69.2
140.5
67.9
166.7
53.8
167.6
62.3
165.2
67.8
158.4
65.8
Head
Head
Head
Head
20.8
68.5
24.1
70.8
21.9
71.7
21.5
86.3
.45.1
50.8
48.0
56.9
45.5
79.7
44.7
95.1
65.6
50.2
67.2
59.9
69.3
65.7
67.4
77.8
114.1
60.3
115.6
70.7
117.6
79.7
113.2
72.5
141.7
57.4
139.1
69.0
141.8
83.3
140.2
68.8
158.4
53.8
167.9
75.0
165.2
69.2
158.4
61.5
Chest
Chest
Chest
Chest
20.8 100.3
24.2
96.3
21.9
91.5
21.3
86.0
45.1
98.4
48.1
93.9
45.4
80.1
44.8
75.1
65.6
71.3
67.3
80.3
69.3
67.1
67.5
70.0
114.3
51.2
115.8
38.7
117.7
47.1
113.0
49.3
141.5
53.3
139.1
47.3
141.9
46.4
139.9
47.4
167.5
53.9
167.2
53.7
165.6
52.1
158.0
44.7
Abdomen
Abdomen
Abdomen
Abdomen
20.8
70.9
24.3
78.1
22.0
91.5
21.4
115.1
45.2
69.0
48.1
87.4
45.4
80.1
44.8
111.4
65.6
70.0
67.3
84.0
69.3
67.1
67.5
98.4
114.6
78.4
115.7
149.0
117.7
68.3
113.0
97.1
142.1
63.7
139.9
148.9
141.9
62.2
140.3
85.5
167.7
64.3
167.5
161.0
165.6
66.4
158.2
69.4
Legs
Legs
Legs
Legs
20.9
77.8
24.3
71.6
22.0
89.5
21.4
77.1
45.2
91.1
48.1
74.0
45.6 110.0
44.8
77.9
65.6
83.3
67.4
76.7
69.5 103.0
67.7
88.4
114.6
54.7
115.9
41.3
118.5
97.8
113.2
69.2
142.5
61.6
138.9
56.8
142.7
95.6
140.5
70.2
167.9
42.2
167.5
56.3
165.6
84.3
158.4
63.6
*Time after injection in hours.
**Per cent of initial amount in region. Partial-body counts are
corrected for interference due to other regions.

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158

159
15. R. A. McCance and E. M. Widdowson, "The Fate of Calcium and
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185. S. Ginsburg, J. G. Smith, F. M. Ginsburg, J. Z. Reardon, and
J. K. Aikawa, "Magnesium of Human and Rabbit Erythrocytes,"
Blood, 20:722 (1962).

170
186.
187.
188.
189.
190.
191.
192.
193.
194.
195.
196.
197.
198.
199.
200.
L. V. Avioli, T. N. Lynch, and M. Berman, "Digital Computer
Compartmental Analysis of 28jqg Kinetics in Normal Subjects,
Paget's Disease, and Thyroid Disease," J, Clin. Invest., 42:
915 (1963).
V. P. Petersen, "Potassium and Magnesium Turnover in Magnesium
Deficiency," Acta Med. Scand., 174:595 (1963).
J. H. Mendelson, B. Barnes, C. Mayman, and M. Victor, "The
Determination of Exchangeable Magnesium in Alcoholic Patients,"
Metabolism,14:88 (1965).
S. Wallach, J. E. Rizek, and A. Dimich, "Radiomagnesium Kinetics
in Normal and Uremic Subjects," J. Clin. Invest., 44:1107 (1965).
J. K. Aikawa and J. Z. Reardon, "Effect of 2,4-Dinitrophenol on
Magnesium Metabolism," Proc. Soc. Expt. Biol. Med., 119:812
(1965).
J. K. Aikawa and J. Z. Reardon, "Effect of Sodium Salicylate on
Magnesium Metabolism in the Rabbit," Proc. Soc. Expt. Biol. Med.,
122:884 (1966).
J. K. Aikawa, The Role of Magnesium in Biologic Processes,
Charles C. Thomas, Publisher, Springfield, Ill. (1963).
D. Skyberg, J. H. Stromme, R. Nesbakken, and K. Harnaes, "Neo
natal Hypomagnesemia with Selective Malabsorption of Magnesium -
A Clinical Entity," Scand. J. Clin. Lab. Invest., 21:355 (1968).
C. Raynud and C.
ment Echangeables
ium a L'aide du 2
Strahlentherapie,
Kellershohn, "Mesure des Compartiments Radipe-
des Taux D'echange et de Transfer du Magnes-
Mg Chez L'adulte Normal et Pathologique,"
65:430 (1967).
J. K. Aikawa and A. P. David, "^Mg Studies in Magnesium-Defi
cient Animals," Ann. N. Y. Acad. Sci., 162:744 (1969).
S. Wallach and A. Dimich, "Radiomagnesium Turnover Studies in
Hypomagnesemia," Ann. N. Y. Acad. Sci.,162:963 (1969).
Powell Richards, Hot Laboratory, Brookhaven National Laboratory,
Upton, L. I., N. Y., Personal Communication.
Clinical Laboratories, J. Hillis Miller Health Center, University
of Florida, Personal Communication.
W. J. Walker, Jr., "The Nature and Control of External Sources
of Variation in Whole-Body Counting," Doctoral Dissertation,
University of Florida (1971).
I. Davidsohn and J. B. Henry, "Sweat Electrolytes by Pilocarpine
Iontophoresis." Clinical Diagnosis by Laboratory Methods, W. B.
Saunders Co., Philadelphia, Pa.> 758 (1969).

171
201. International Atomic Energy Agency, Directory of Whole-Body Radio
activity Monitors, IAEA, Vienna, Austria (1970).
202. H. Pickover, "A Performance Comparison of Equi-Volume 4-Pi Geome
try Liquid and Plastic Scintillation Counters," Master of Science
Thesis, University of Florida (1965).
203. C. R. Richmond, "Retention and Excretion of Radionuclides of
the Alkali Metals by Five Mammalian Species," LA-2207, Los Alamos
Scientific Laboratory of the University of California, 34 (1958).
204. W. J. Dixon, Editor, Biomedical Computer Programs, University of
California Press, Berkeley,Calif. 177 (1969).
205. M. Berman, "The Formulation and Testing of Models," Ann. N. Y.
Acad. Sci., 108:182 (1963).
206. J. Anderson, S. B. Osborn, R. W. S. Tomlinson, and M. E. Wise,
"Clearance Curves for Radioactive Tracers Sums of Exponentials
or Powers of Time?" Phys. Med. Biol., 14:498 (1969).
207. W. S. Snyder, B. R. Fish, S. R. Bernard, M. R. Ford, and J. R.
Muir, "Urinary Excretion of Tritium Following Exposure of Man
to HTO a Two Exponential Model," Phys. Med. Biol., 13:547
(1968).
208. H. C. Gonick and M. Brown, "Critique of Multicompartmental
Analysis of Calcium Kinetics in Man Based on Study of 27 Cases,"
Metabolism, 29:919 (1970).
209. S. R. Bernard, "A Metabolic Model for Magnesium in Man," Oak
Ridge National Laboratory, Annual Information Meeting, October,
1971.
210. W. J. Dixon, Editor, Biomedical Computer Programs, Supplement X>
University of California Press, Berkeley, California, 94 (1969).
211. E. Lebowitz and P. Richards, "BLIP Seen as Important Radionuclide
Source," Radioisotope Report, 8:65 (1971).
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Permissible Dose for Internal Radiation (1959)," Pergamon Press,
London (1960).
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in Clinical Practice, Lea and Febiger, Philadelphia, Pa., 104
(1958).
214. Medical Internal Radiation Dose Committee, J. Nuc. Med.,
Supplements, Feb. 1968, Mar. 1969, Aug. 1969, Mar. 1970.

17?
215. A. Donath, Bern, Switzerland, Personal Communication.
216. W. Noyes, Department of Medicine, University of Florida, Personal
Communication.
217. S. O'Reilly, T. Strickland, P. M. Weber, W. M. Beckner, and L.
Shipley, "Abnormalities of the Physiology of Copper in Wilson's
Disease," Arch. Neurol., 24:385 (1971).
218. T. Sargent, J. A. Linfoot, and E. L. Isaac, "Whole-Body Counting
of ^7ca and ^Sr in the Study of Bone Diseases," IAEA, Clinical
Uses of Whole-Body Counters, Proceedings of a 1965 Panel,
Vienna, Austria.

BIOGRAPHICAL SKETCH
Genevieve Schleret Roessler was bom April 13, 1935, in Owatonna,
Minnesota where she attended elementary and high schools. She. attended
Mankato State College from 1953 to l'J56. During this tine she also
worked as part-time proofreader and news writer for the Daily People's
Press and the Steele County Photo News in Owatonna, Minnesota, finally
serving as acting editor of the latter newspaper for three months. She
and Charles E. Roessler were married in 1956 and moved to Clearfield,
Pennsylvania, where she was news editor of radio station WCPA for one
year. She received a Bachelor of Arts degree with a major in mathematics
from Jacksonville University, Jacksonville, Florida, in 1962. She
began her graduate study under a Public Health Service Fellowship in
September, 1965, and received a Master of Science in Radiation Biophysics
in December, 1966. She was employed as an instructor and supervisor
of whole-body counter activities in the Department of Radiology,
University of Florida from January, 1967 to September, 1969. During
that time she pursued research and published articles on lean body mass/
total-body potassium measurements and on cesium-137 body burdens in
humans. In September, 1969, she returned to graduate work in
radiological health in environmental engineering at the University of
Florida under an Environmental Protection Agency fellowship.
She is a member of the Health Physics Society and the Florida
Chapter of the Health Physics Society. She is currently treasurer and
publicity chairman and newsletter editor of the latter organization.
She was elected to membership in the Society of Sigma Xi in 1968.
She is the mother of seven children ranging in age from 3 to 14.
173

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.
n
3
,lU
v
Filly G. Dunavant, Chairman
Professor1-of Environmental
Engineering Sciences
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.
W. Tsmmett Bolch
Associate Professor of
Environmental Engineering
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.
Nv-
Oh *
Clyde M. Williams
Professor and Chairman
of Radiology
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.
Engineering Sciences

This dissertation was submitted to the Dean of the College of Engineering
and to the Graduate Council, and was accepted as partial fulfillment of
the requirements for the degree of Doctor of Philosophy.
March, 1972
Dean, Graduate School

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AUTHOR: Roessler, Genevieve
TITLE: Whole-body retention and excretion of magnesium in humans: (record
number: 577531)
PUBLICATION DATE: 1972
, as copyright holder for the aforementioned
dissertation, hereby grant specific and limited archive and distribution rights to the Board of Trustees of the
University of Florida and its agents. I authorize the University of Florida to digitize and distribute the
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This is a non-exclusive grant of permissions for specific off-line and on-line uses for an indefinite term. Off
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This grant of permissions prohibits use of the digitized versions for commercial use or profit.
Signature of Copyright Holder
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Please print, sign and return to:
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152
SUBJECT: PK STUDY GROUP: 5
DATE, TIME OF INJECTION: 2-10-70, 9:45 DOSE: 9.389 pCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Dficit*
0.5
100
-
-
100
9.6
95
0
0
95
-5
21.6
90
0
1
91
-9
45.7
83
0
2
85
-15
69.8
88
0
3
91
-9
93.8
90
0
3
93
-7
141.7
89
0
4
93
-7
165.7
85
1
4
90
-10
189.7
76
1
5
82
-18
213.8
67
1
7
75
-25
*Expressed as per cent
, rounded off
to the
nearest
whole number.
- Means not measured.


141
SUBJECT: PA3 STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 11:53 DOSE: 9.637 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
'Urine Feces
Excess or
Balance*' Deficit*
1.7
100
-
-
100
6.0
90
-
-
90
-10
20.5
90
9
0
99
-1
44.0
86
15
0
101
+1
67.9
81
19
1
101
+1
116.0
75
24
1
100
140.5
71
27
2
100
164.0
65
30
2
97
-3
187.8
55
33
2
90
-10
211.9
38
37
4
79
-21
*Expressed as per cent, rounded off to the nearest whole number.
- Means not measured.


49
(See Figure 9) consists of a 4-inch by 9-inch Nal(Tl), stainless steel-
cased crystal and four 3-inch photomultiplier tubes. The assembly is
enclosed in a lead-filled steel container with a thickness equivalent
to 3.11 inches of lead. No other shielding is used in this counter.
The entire assembly is mounted on a rigid, but movable, steel frame,
which provides a means of gradual rotation of the detector face
through an angle of 90. The crystal shield assembly can also be
raised or lowered a distance of 13 inches. In addition, the crystal
can be moved from a position flat with the end of its shield to a
position 2 inches inside the shield.
The various configurations make it possible to achieve a
number of convenient counting geometries. The subject lies on an
adjustable bed as shown in Figure 9 (the position for a total-body
count). Figure 10 diagramatically summarizes the counting geometries
used in this study.
In addition to the whole-body count position shown in Figure
9, the four other positions used in this research (head, chest, abdo
men, and legs) are demonstrated by an actual subject in Figures 11 14.
The output system from this counting system consists of
essentially the same equipment as that diagrammed in Figure 8.
Large Volume Well Counter
Radioactivity in urine and feces collections was measured in
an organic scintillation detector with a large volume chamber (202).
(See Figure 15.) The sample is inserted into the center of a right
circular cylinder, 4.5 inches in diameter by 12 inches long. Surround
ing the sample chamber is a cylindrical tank containing the scintillator;


Figure 12. Nal(Tl) Crystal Whole-Body Counter: Position for Chest Count.


APPENDIX A
COMPUTATION OF RADIATION DOSE


Figure 4. 4-Pi Liquid Whole-Body Counter Laboratory


24
Even so, these researchers continued 28>fg studies of magnesium
metabolism in both rabbits (169,170) and in humans (4). In several
reports in 1960, they summarized work to date which included: (1) urin
ary excretion, tissue distribution, exchangeable magnesium, and the
effect of starvation on urinary magnesium excretion in rabbits and
(2) serum magnesium concentrations, plasma clearance, urinary excretion,
exchangeable magnesium, and urinary and fecal excretion of orally admin
istered 28Mg in humans.
Other animal studies where ^Mg was used included a number in
1958 and 1959 by Brandt, Glaser, and Jones (171), Langemann (172),
Rogers and Mahon (173), MacIntyre (174), and MacIntyre, Davidsson, and
Leong (175). All these investigators used rats and measured the exchange
able magnesium in major organs, plasma, bone, and urine. Uptake of 28^g
in frog muscle was reported in 1960 by Gilbert (176), who found three
turnover components which he attributed to surface absorption, entry
into extracellular water and connective tissue, and entry into the cell.
He found that 75 81 per cent of the magnesium in muscle was non-exchange
able and difficult to remove by diffusion.
Also in 1960, Graham, Caesar,, and Burgen (177) summarized
their work on gastrointestinal absorption and excretion of 28^g in man
using oral administration of the isotope in three control subjects. The
same year, Silver, Robertson, and Dahl (178) reported a study of magnesium
turnover in human adults. They followed 10 adults (all but one had
hypertension) who received intravenous or oral doses of 28jyjg ranging from
20 to 104 pCi. They had been maintained on a constant diet for five days
before and three days after the administration of the isotope. The


I
Figure 13. Nal(Tl) Crystal Whole-Body Counter: Position for Abdomen Count.


153
SUBJECT: PL STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:00 DOSE: 5.405 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.5
100
-
-
100
9.3
99
2
-
101
+1
24.1
102
3
1
106
+6
48.1
102
5
1
107
+8
72.0
104
6
3
113
+13
120.1
80
9
5
94
-6
144.5
94
10
6
110
+10
168.5
90
12
7
109
+9
192.2
89
12
8
109
+9
216.0
88
12
11
111
+11
240.5
88
- '
-
-
*Expressed as per cent
, rounded off
to the
nearest
whole number

- Means not measured


115
7. Sweat analyses, which were performed in an effort to
find the reason for this deficit, showed that this route of excretion
contains an insignificant amount of 28Mg.
8. Localization of the isotope as measured by Nal(Tl) crystal
whole-body counting showed consistent patterns between results cf the
normal subjects. An atypical build-up of the isotope was found in the
abdominal region for the ALS patient who previously exhibited an appar
ent precipitous whole-body loss of ^Mg.
Conclusions
1. Based on published investigations to date, it is con
cluded that this turnover study is currently the most accurate. The
use of a true tracer dose of 10 pCi or less of high specific activity
^Mg and the sensitive whole-body counting system allowed administra
tion of a dose which would not upset the physiochemical balance of the
body. Also, this procedure permitted measurements up to six times longer
than previously reported studies.
O O
2. The amount of Mg to be administered in future investi
gations with this isotope should be guided by the 2.0 mrad/yCi dose
calculated from the data obtained in this study.
3. Based on the consistent, significantly abnormal retention
and excretion patterns shown by certain disease state measurements in
this study, it is concluded that this turnover procedure could serve
as a valuable adjunct to other diagnostic techniques.
4. A review of the results and procedures in this study
shows that if there was sufficient need for continuing the turnover
measurements beyond 10 days a special double measurement technique


NORMAL SUBJECTS
Total-Measured fg for Normals
ijx ana NJf *
Figure 22
ana


162
63. J. M. Hammarsten, H. E. Ginn, and W. 0. Smith, "Normal and Abnormal
Potassium and Magnesium Metabolism," Clinical Metabolism of Body
Water and Electrolytes, W. B. Saunders Co., Philadelphia, Pa.,
569 (1963).
64. R. Whang,-"Some Aspects of the Interrelationship of Magnesium and
Potassium," J. Chron, Pis., 21:207 (1968).
65. R. D. Lindeman, "Influence of Various Nutrients and Hormones on
Urinary Divalent Cation Excretion," Ann. N, Y. Acad. Sci., 162:
802 (1969).
66. C. H. Wall, Four Thousand Years of Pharmacy: An Outline History of
Pharmacy and the Allied Sciences, Lippincott, Philadelphia, Pa.,
665 (1927).
67. J. K. Aikawa, The Role of Magnesium in Biologic Processes, Charles
C. Thomas,Springfield, Ill., 3 (1963).
68. Encyclopaedia Britannica, "Epsom and Ewell," William Benton, Publish
er, Chicago, Ill., 653 (1967).
69. N. H. Choksky, "On the External Application of Magnesium Sulfate in
Treatment of Erysipelas," Lancet, 1:300 (1911).
70. E. L. Holt, A. M. Courtney, and A. L. Fales, "Chemical Composition
of Diarrheal as Compared with Normal Stools in Infants," Am. J. Pis.
Child., 9:213 (1915).
71. J. P. Peters and D. D. Van Slyke, Quantative Clinical Chemistry:
I. Interpretations, Williams and Wilkins, Baltimore, Md., 48 (1931).
72. C. H. Peck and S. J. Meltzer, "Anesthesia in Human Beings After
Intravenous Injection of Magnesium Sulfate," JAMA, 67:1131 (1916).
73. G. Somjen, M. Hilmy, and C. R. Stephen, "Failure to Anesthetize
Human Subjects by Intravenous Administration of Magnesium," J. Phar
macol. and Exper. Therap., 154:652 (1966).
74. E. C. Wacker and A. F. Parisi, "Magnesium Metabolism," New Eng. J.
Med., 278:772 (1968).
75. H. D. Kruse, E. R. Orent, and E. V. McCollum, J. Biol. Chem., 96:519
(1932), as cited by Davis (2).
76. T. B. Osborne and L: B. Mendel, Biol. Chem., 34:131 (1918), as cited
by Davis (2).
77. M. J. Shear, "The Role of Sodium, Potassium, Calcium, and Magnesium
in Cancer: A Review," Am. J, Cancer, 18:924 (1933).
78.B. S. Walker and E. W. Walker, "Normal Magnesium Metabolism and
Its Significant Disturbances," J. Lab. Clin. Med., 21:713 (1935).


155
Days After Patient PA Patient PB Subject NH Subject NM
Injection
Quantity of Sweat Collected (mg)
1
458.4
468.0
454.6
458.7
2
525.2
395.4
1199.1
501.6
3
459.4
479.8
463.3
455.9
5
478.5
465.9
456.5
451.2
6
441.8
451.4
477.9
481.8
7
476.6
485.3
481.8
458.2
8
541.9
496.9
470.4
460.1
9
489.2
482.6
480.2
467.4
28Mg
in Sweat, %
of Injected Dose
1
O.O(NS)
0.0(NS)
0.0(NS)
0.0(NS)
2
0.003
0.004
0.005
0.004
3
0.009
0.008
0.011
0.035
5
0.019
0.009(NS)
0.006(NS)
0.020
6
0.015(NS)
0.009(NS)
0.020(NS)
0.027
7
0.013(NS)
0.0(NS)
0.014(NS)
O.O(NS)
8
0.036(NS)
0.0(NS)
0.11
0.19
9
0.28
0.096(NS)
0.70
0.31
Concentration, % of
Injected Dose/kg
1
0.0(NS)
0.26(NS)
0.0(NS)
0.0(NS)
2
5.14
9.61
4.59
6.98
3
19.8
16.3
23.7
76.8
5
39.7
19.3(NS)
12.9(NS)
44.4
6
34.0(NS)
0.0(NS)
41.9(NS)
56.0
7
27.3(NS)
0.0(NS)
29.1(NS)
O.O(NS)
8
66.4(NS)
0.0(NS)
238.0
409.0
9
574.0
199.0(NS)
1460.0
663.0
NS = Count Not Significantly different from background. '


Figure 16. Nal(TI) Crystal Counter.
j


161
48. R. A. McCance, E. M. Widdowson, and H. LeMann, "Effect of Protein
Intake on Absorption of Calcium and Magnesium," Biochem. J.,
36:686 (1942).
49. S. Hanna, M. Harrison, I. MacIntyre, and R. Fraser, "Effects of
Growth Hormone on Calcium and Magnesium Metabolism," Brit. Md. J.,
12:5243 (1961).
50. S. Hanna, "The Influence of Vitamin D on Magnesium Metabolism,"
Metabolism, 10:735 (1961).
51. F. W. Heggeness, "Effects of Antibiotics on the Gastrointestinal
Absorption of Calcium and Magnesium in the Rat," J. Nutr., 68:573
(1959).
52. R. B. Meintzer and H. Steenbock, "Vitamin D and Magnesium Absorp
tion," J. Nutr., 56:285 (1955).
53. M. E. Kahil, J. E. Parrish, E. L. Simons, and H. Brown, "Magnesium
Deficiency and Carbohydrate Metabolism," Diabetes, 15:734 (1966).
54. N. Alcock and I. MacIntyre, "Inter-relation of Calcium and Magnesium
Absorption," Clin. Sci., 22:185 (1962).
55. B. L. Ardill, J. A. Halliday, J. D. Morrison, H. C. Mulholland, and
R. A. Womersley, "Interrelations of Magnesium, Phosphate, and
Calcium Metabolism," Clin. Sci., 23:67 (1962).
56. A. Cantarow and M. Trumper, "Magnesium Metabolism," Clinical Bio-
Chemistry, Fifth Edition, W. B. Saunders Co., Philadelphia, Pa.,
255 (1956).
57. B. L. O'Dell, "Magnesium Requirement and Its Relation to Other
Dietary Constituents," Fed. Proc,, 19:648 (1960).
58. D. M. Hegsted, "Present Knowledge of Calcium, Phosphorus, and
Magnesium," Nutr. Rev., 26:70 (1968).
59. I. Clark, "Metabolic Interrelations of Calcium, Magnesium, and
Phosphate," Amer. J. Physiol., 217:871 (1969).
60. W. M. Keynes, B. A. Barnes, and 0. Cope, "Urinary Excretion of
Calcium and Magnesium in Man Using a Diet of These Minerals,"
Proc. Roy. Soc. Med., 64:152 (1971).
61. G. Steams, "Human Requirement of Calcium, Phosphorus, and Magnesium,"
JAMA, 142:478 (1950),
62. G. S. Roessler and B. G. Dunavant, "Comparative Evaluation of a
Whole-Body Counter Potassium-40 Method for Measuring Lean Body Mass,"
Am. J. Clin. Nutr., 20:1171 (1967).


59
time after "injection" on semi-logarithmic graph paper. The straight-
line portion of the plot (observed during the last week of measurements),
which corresponds to the portion of the curve where no resolving time
was necessary, was extrapolated back to t = 0. The ratio of difference
between the extrapolated line and the actual line at any time, t, was
used to correct the net subject count.
Further analysis of the retention and excretion data was
carried out according to the method reported by Richmond (203). The
following equation was used to determine whole-body retention:
WBtx/(Stx/St0)
WBRt = or
WBt0
WBtx/ Stx .
WBRtx = 5
WBt / St
o o
where
WBRtx = whole-body retention at time t in counts per
minute (cpm),
WBt = whole-body activity at time tY in cpm,
WBtQ = whole-body activity at time tQ in cpm,
Stx = standard activity at time tx in cpm, and
StQ = standard activity at time tQ in cpm.
The whole-body activity was determined directly by whole-
body counting. The standard activities at the various time, tx, were
calculated from a best-fit curve of the phantom measurements. A
computer linear least squares program, Biomedical Computer Program,
BMD02R (204) was used to obtain the phantom decay curve.


I
PATIENTS
O
Ln
Figure 29. Total-Measured ^Mg Patients PC, PE, PH, and PJ.


thanks is due Larry Fitzgerald for his motivation and assistance in my
graduate work.
I particularly wish to thank my husband, Chuck, for his assistance,
advice, and encouragement in every phase of my graduate studies and
research. I wish to recognize the assistance of my oldest daughter,
Teresa, with typing, filing, and library work. She and my other
children, Cynthia, Mary, Francis, Kay, Jean, and Anne, have been very
patient and understanding throughout my graduate studies and have assumed
many household duties in order to ease my domestic responsibilities. I
wish to express special appreciation to my father, Leo Schleret, for his
continuing interest in my academic career and, in particular, for his
contribution as a "normal" in this research.
Financial support by the Environmental Protection Agency, Training
Grant Number 2-T01-EP00046-11, is also acknowledged.
iii


22
12
Mg
Mg ZZ
3.9s
Mg 23
'2*
fr 3.0,-
24.312
y .074..59
y.44
F 4.06
Figure 1
Isotopes of Magnesium (160)


. Total-Measured
2%g
Patients PK, PF, PD,
and PL.
Figure 31


9
In 1926, Leroy demonstrated that magnesium is essential in
animal diets (34). This finding prompted numerous studies in the
latter 1920s and early 1930s on magnesium's role in animals and in
man. In 1929, Joachimoglu and Panopoulous (35) analyzed foods typical
of a normal diet and concluded that an adequate amount of magnesium is
obtained by normal intake to meet the body's requirements. In 1932,
the daily need was reported as 300 mg (36), a figure which is still
quoted by some as authoritative (37). A number of reviews of magnesium
metabolism followed including: Shohl, 1933 (25); Schmidt and Greenberg,
1935 (38); and Greenberg, 1939 (39).
A thorough reviey of magnesium in nutrition in 1939 by Duck
worth (40) included a summary of metabolism and magnesium deficiency in
addition to a comprehensive synopsis on methods of estimation, occurrence,
and distribution, on the relationship of magnesium to disease, and on
magnesium requirements in domestic animals and in man. In his review
of the literature, he found that estimates of the daily requirements of
magnesium range from 20 298 mEq (24 358 mg). More recent metabolic
balance studies propose an average adult requirement of at least six
mg per kg of body weight per day (420 mg for a 70-kg man) (6).
A summary of the sources of magnesium and an analysis of
the reported data on magnesium balance in normals in different parts
of the world were published in 1964 by Seelig (41). Foods which she
considers as rich in magnesium include cocoa and chocolate, nuts, some
seafoods, bean- and pea-typs vegetables, and grains. Green leafy
vegetables, some fruits, and certain meats are listed as foods with a
moderate amount of magnesium. Many foods regularly eaten in a normal


127
SUBJECT: NC2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:35 DOSE: 10.56 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.2
100
-
-
100
9.5
96
6
-
102
+2
21.2
91
8
-
99
-1
44.2
90
11
-
101
+1
69.5
82
15
-
97
-3
93.4
82
17
-
99
-1
141.4
77
23
-
100
169.5
75
24
-
99
-1
192.0
74
25
-
99
-1
215.7
73
30
103
+3
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


LIST OF TABLES
Table Page
1. SUMMARY OF STUDY GROUPS 37
2. SUMMARY OF DETECTION SYSTEMS 41
3. 28Mg TURNOVER RESULTS IN HUMANS 81
4. COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT
28Mg STUDIES 85
5. PLASMA AND RED BLOOD CELL STABLE MAGNESIUM ANALYSES 90
6. COMPARISON OF THE WHOLE-BODY RETENTION MEASUREMENTS BY THE
4-PI LIQUID SCINTILLATION AND THE Nal(Tl) CRYSTAL WHOLE-
BODY COUNTERS 106
vi


112
lower for the next three days; then increasing values were observed
for the fifth and sixth days (-5.5 6.5 and =8.0 10.0, respectively).
Ratios fluctuated considerably on the last day of measurements (seventh)s
but this can be attributed largely to the low count rates and consequent
poorer statistics.
The only difference between subjects is limited to an indica
tion of a lower ratio in the chest and a higher ratio in the abdomen and
legs of PB than that observed in the other subjects after the third day.
A decrease in the ratio is due to an increase in the relative number
of counts in the higher energy region, 28^1. This could be a result of:
(1) a biological factor which favors the aluminum element over magnesium
or (2) an increasing average thickness of tissue and thus increasing
attenuation of the photon. An increase in the ratio would be due to
an inverse of the above.
Any interpretations of the data will not be made at this time.
Many variables could contribute to the change in the ratios which have
nothing to do with biological factors. One of these could be spectrum
shifts from day to day or from time to time during the day. Because of
this and the fact that there is no significant and consistent pattern
in the ratios, it is concluded that the 28^g 28^j_ equilibrium remained
constant.
28ng in Sweat
A comparison of the results of sweat analyses between the two
normals and the two patients in study group 7 showed no significant
difference. Results of these measurements are included in Appendix D.
It was concluded that sweat was not the variable involved in the deficit
in total-measured 28p[g in several ALS patients.


Figure 28.
Whole-Body Retention of
28Mg
Gastrectomy Patients


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.
n
3
,lU
v
Filly G. Dunavant, Chairman
Professor1-of Environmental
Engineering Sciences
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.
W. Tsmmett Bolch
Associate Professor of
Environmental Engineering
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.
Nv-
Oh *
Clyde M. Williams
Professor and Chairman
of Radiology
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.
Engineering Sciences


NORMAL SUBJECTS
q
ND,
, and NG.
Figure 21
Total-Measured '28mg for Normal;
NE
NF


15
sometimes accompanied by behavioral disturbances." These disturbances,
which can be reversed by administration of magnesium, include tetany,
generalized tonic-clonic as well as focal seizures, ataxia, vertigo,
muscular weakness, tremors, depression, irritability, and psychotic
behavior.
Despite the indications of a relationship between disease
conditions and magnesium abnormalities, published articles manifesting
a clinical interest in this cation were few until the 1950s. About
that time, Martin and co-workers (85,86) and Flink and colleagues (87-90)
published results which revived the interest in magnesium abnormalities.
Both groups detected low plasma levels of magnesium in surgical patients
receiving fluids parenterally, in patients receiving diuretic therapy,
and in diabetics.
Then in 1954, a serendipitous occurrence led to the discovery
that patients with chronic alcoholism and delirium tremors are magnesium
deficient. This was discovered when magnesium, because of its sedative
effect, was used by Flink and associates to treat delirium tremors (91).
The manifestations "were promptly alleviated by the administration of
magnesium sulfate intramuscularly in amounts which are not hypnotic."
Flink e£ al. found the serum levels of all of these patients on admission
to the hospital significantly lower than normal. They reason that
magnesium deficiency in chronic alcoholism is similar to that induced
by a magnesium deficient diet. The caloric requirement, of these patients
is satisfied by alcohol almost exclusively for a long time and, thus,
their diet is low in magnesium.
More recently, other clinicians have reported that, in addition
to a magnesium deficient diet, an alcohol-induced renal excretion is an


65
U
oc
>*
a
o
CO
Figure 18. Replications in Measurements of Whole-Body Retention
in Two Normals.


17
in man is also in the same edition (138). In that study, magnesium
deficiency was induced in seven volunteer adult human subjects. All
of the subjects developed neurologic and/or gastrointestinal changes
of varying degrees. All clinical and biochemical changes produced
in the study were reversed by the administration of magnesium. In
another review, conditions associated with abnormalities of magnesium
was reported by Barker (139). Seelig (41), in her review of the
requirements of magnesium by the normal adult, also reviewed the
different aspects of magnesium deficiencies and the role of magnesium
in disease. Magnesium in human nutrition was published as a home econo
mics report by the U. S. Department of Agriculture in 1962 (140). The
scope of the report included the biological role of magnesium in humans
and a review of data on magnesium in tissues.
Techniques for Measuring Stable Magnesium
The difficulty of making accurate in vivo measurements of
magnesium has always been a limiting factor in its investigation (141).
It is almost entirely this measurement problem that has kept the knowledge
of magnesium years behind that of the other essential elements in the
human body.
This situation has not gone unrecognized. In 1939, an
editorial in the Journal of the American Medical Association (19)
summarized the status of the magnesium problem at that time:
So little is known of the function of magnesium in the
organism that clinically observable abnormalities in man
cannot at present be said with certainty to be due to mag
nesium deficiency or to a disorder of magnesium metabolism.
The systematic study of magnesium metabolism by accurate
analytical and experimental methods is little more than
begun. Future investigations may be expected to add consider
ably to our knowledge of this problem.


Figure 8. Signal Diagram of the 4-Pi Liquid Whole-Body Counting System


BIOGRAPHICAL SKETCH
Genevieve Schleret Roessler was bom April 13, 1935, in Owatonna,
Minnesota where she attended elementary and high schools. She. attended
Mankato State College from 1953 to l'J56. During this tine she also
worked as part-time proofreader and news writer for the Daily People's
Press and the Steele County Photo News in Owatonna, Minnesota, finally
serving as acting editor of the latter newspaper for three months. She
and Charles E. Roessler were married in 1956 and moved to Clearfield,
Pennsylvania, where she was news editor of radio station WCPA for one
year. She received a Bachelor of Arts degree with a major in mathematics
from Jacksonville University, Jacksonville, Florida, in 1962. She
began her graduate study under a Public Health Service Fellowship in
September, 1965, and received a Master of Science in Radiation Biophysics
in December, 1966. She was employed as an instructor and supervisor
of whole-body counter activities in the Department of Radiology,
University of Florida from January, 1967 to September, 1969. During
that time she pursued research and published articles on lean body mass/
total-body potassium measurements and on cesium-137 body burdens in
humans. In September, 1969, she returned to graduate work in
radiological health in environmental engineering at the University of
Florida under an Environmental Protection Agency fellowship.
She is a member of the Health Physics Society and the Florida
Chapter of the Health Physics Society. She is currently treasurer and
publicity chairman and newsletter editor of the latter organization.
She was elected to membership in the Society of Sigma Xi in 1968.
She is the mother of seven children ranging in age from 3 to 14.
173


139
SUBJECT: PA STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:20 DOSE: 1.295 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balanc*
Excess or
Deficit*
1.7
97
3
-
100
3.7
93
5
-
98
-2
8.3
90
6
-
96
-4
21.2
84
10
-
94
-6
23.4
85
11
-
96
-4
26.0
84
12
-
96
-4
28.4
82
13
-
95
-5
32.3
84
14
-
98
-2
46.6
83
15
-
98
-2
48.6
79
16
-
95
-5
52.5
78
17
-
95
-5
56.8
77
18
-
95
-5
71.3
75
19
-
94
-6
74.1
69
21
90
-10
93.9
69
23
-
92
-8
123.3
66
30
-
96
-4
142.1
61
33
-
94
-6
165.6
55
-
-
-
*Expressed as per cent
, rounded off
to the
nearest whole number.
- Means not measured


APPENDIX C
SWEAT ANALYSIS, STUDY GROUP 7


167
140. M. L. Hathaway, "Magnesium in Human Nutrition," Home Economics
Research Report No. 19, U. S. Dept. Agriculture, Washington, D. C.,
(1962).
141. J. R. Elkinton, "The Role of Magnesium in the Body Fluids,"
Clin. Med., 3:319 (1957).
142. V. G. Haury, "Blood Serum Magnesium in Bronchial Asthma and Its
Treatment by the Administration of Magnesium Sulfate," J. Lab.
Clin. Med., 26:340 (1940).
143. R. F. Dine and P. H. Lavietes, "Serum Magnesium in Thyroid
Disease," J. Lab. Invest., 21:781 (1942).
144. S. Dahl, "Serum Magnesium in Normal Men and Women," Acta Haematol.,
4:65 (1950).
145. P. M. Hald, "The Determination of the Bases of Serum and Whole
Blood," J. Biol. Chem., 103:471 (1933).
146. D. M. Greenberg and M. A. Mackey, "The Determination of Magnesium
in Blood with 8-Hydroxyquinoline," J. Biol, Chem., 96:419 (1932).
147. A. D. Hirshfelder and E. R. Series, "A Simple Adaptation of
Kolthoff's Colorimetric Method for the Determination of Magnesium
in Biological Fluids," J. Biol. Chem., 104:635 (1934).
148. V. G. Haury, "Modification of Titan Yellow Method for Determination
of Small Amounts of Magnesium in Biological Fluids," J. Lab. Clin.
Med., 23:1079 (1938).
149. M. Orange and H. C. Rhein, "Microestimation of Magnesium in Body
Fluids," J. Biol. Chem., 189:3079 (1951).
150. F. C. Heagy, "The Use of Polyvinyl Alcohol in the Colorimetric
Determination of Magnesium in Plasma or Serum by Means of Titan
Yellow," Caad. J. Res., 26:sectipn E (1948).
151. J. B. Hill, "An Automated Fluorimetric Method for the Determination
of Serum Magnesium," Ann. N. Y. Acad. Sci., 102:108 (1962).
152. N. Alcock, I. MacIntyre, and I. Raddle, "The Determination
of Magnesium in Biological Fluids and Tissues by Flame Spectropho
tometry," J_;_ jClin^ Pattu_, 13:506 (1960).
153. N. Alcock, "Development of Methods for the Determination of
Magnesium," Ann. N. Y. Acad. Sci., 162:707 (1969).
154. A. Walsh, "The Application of Atomic Absorption Spectrophotometry
to Chemical Analysis," Spectrochim., 7:108 (1955).
155. J. E. Allan, "Atomic Absorption Spectrophotometry with Special
Reference to the Determination of Magnesium," Analyst, 83:466 (1958).


CHAPTER III
MATERIALS AND METHODS
Magnesium-28
In the literature review, it was pointed out that in 1939 the
only known radioactive isotope of magnesium was ^Mg with a physical
half-life of less than 10 minutes (39). Although the possibility of
?7
using Mg was alluded to, there is no evidence that it was ever used as
a tracer in biological investigations. Its use in this manner is doubt
ful since it has such a short physical half-life. Normally, tracer
studies are best carried out with an isotope with a half-life on the
order of days, weeks, and sometimes, months.
Although 28Mg has a half-life of only 21.3 hours, it has been
used as a suitable isotope in biological work since shortly after it was
first produced in 1951 (9). Magnesium-28 and its radioactive daughter,
aluminum-28 (28ai), have a number of energetic gamma rays which can be
readily detected by most gamma-counting systems. (See Figure 2.) Alumi
num-28 with a half-life of 2.24 minutes; rapidly attains secular equili
brium with ^Mg.
In this study, Mg was obtained from Brookhaven National
Laboratory where it is produced in a Van de Graaff accelerator by the
triton proton reaction (2%g(t,p)2%g) (197). A 1/4-inch diameter
metallic rod target enriched to 99.77 per cent is bombarded with a
beam of 3.4 MeV tritons. After bombardment, a 0.001-inch thick layer
33


Page
B. 28Mg BALANCE CHARTS NORMALS AND PATIENTS ...... 123
C. SWEAT ANALYSIS, STUDY GROUP 7 154
D. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER RETENTION
AND LOCALIZATION DATA 156
LIST OF REFERENCES 158
BIOGRAPHICAL SKETCH 173
v


16
important factor in magnesium depletion (92,93). Other studies of
magnesium depletion in alcoholism and reviews of the subject have been
published since that time (94-103).
As a result of Flinks discovery of magnesium deficiency in
alcoholics, extensive research on magnesium metabolism has been
stimulated, not only in alcoholics, but in other disease conditions as
well. Other magnesium insufficiencies have been reported in cases of
malabsorption syndromes, prolonged or severe loss of fluids, lactation,
diuretic therapy, diabetic acidosis, hyperaldosteronism, hypercalcemia
(104), hyper- and hypothyroidism (105), parathyroid disease (106,107),
inflammatory bowel disease (108), celiac disease (109) Kwashiorkor and
protein calorie nutrition (110), Grave's disease (111), and cardiac
necrosis (112). Barnes has evaluated magnesium requirements and
deficiencies in surgical patients (113,114) and Wacker and associates
were the first to describe normocalcemic magnesium deficiency tetany (115).
The relationship of magnesium metabolism and other conditions such as
hyperparathyroidism and osteolytic disease (116), chronic renal disease
(117), hypokalemia (118), gastrointestinal disease (119), and malnutrition
(120) were reviewed in 1969.
Literature reviews of magnesium deficiency are plentiful
(30,87,88,121-131) and they cover studies from the 1930s to the present.
The most recent comprehensive reviews were published in 1965 by Aikawa (132),
and in 1968 by Wacker and Parisi (74,104), and in 1969 by Gitelman and
Welt (133). Reviews of deficiencies in both man and in animals appeared in
the August, 1969, edition of the Annals of the New York Academy of Sciences on
The Pathogenesis and Clinical Significance of Magnesium Deficiency (134-
137). A summary of the experimental production of magnesium deficiency


132
SUBJECT: NH STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:03 DOSE: 6.368 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.5
99
-
-
99
-1
6.5
94
2
-
96
-4
19.1
85
4
-
89
-1
43.4
84
6
-
90
-10
67.5
85
8
-
93
-7
91.4
86
10
-
96
-4
139.4
84
13
-
97
-3
163.4
78
14
-
92
-8
187.4
77
19
-
96
-4
211.5
78
20
-
98
-2
235.6
73
20
93
-7
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


123.
166
R. Whang and L. G. Welt, "Observations in Experimental Magnesium
Depletion," J. Clin. Invest., 42:305 (1963).
124. Wohl and Goodhart, Modern Nutrition in Health and Disease, Lea and
Febiger, Fourth Edition, Philadelphia, Pa., 335 (1965),
125. C. Suter and W. 0. Kligman, "Neurologic Manifestation of Magnesium
Depletion States," Neurology, 5:691 (1955).
126. J. F. Hasselman and E. J. Van Kampen, "Magnesium," Clin. Chem.
Acta, 3:305 (1958).
127. P. Fourman, "Magnesium Metabolism in Man," Scientific Basis of
Medicine: Annual Reviews, The Athlone Press, London, 270 (1961).
128. L. Engbaek, "The Pharmacological Actions of Magnesium Ions with
Particular Reference to the Neuromuscular and the Cardiovascular
System," Pharm. Rev., 4:396 (1952).
129. V. G. Haury, "Variation in Serum Magnesium in Health and Disease;
A Review," J. Lab. Clin. Med., 27:1361 (1942).
130. E. C. Wacker and B. L. Vallee, "Magnesium Metabolism," New Eng.
J. Med., 259:431 (1958).
131. H. E. Martin, J. Mehl, and M. Wertman, "Clinical Studies of
Magnesium Metabolism," Med. Clin. N. Amer,, 36:1157 (1952).
132. J. K. Aikawa, "The Role of Magnesium in Biologic Processes; A Review
of Recent Developments," Electrolytes and Cardiovascular Disease,
S. Karger Basel, New York, N. Y., 9 (1965).
133. H. J. Gitelman and L. G. Welt, "Magnesium Deficiency," Ann. N. Y.
Acad. Sci., 115:233 (1969).
134. J. A. F. Rook, "Spontaneous and Induced Magnesium Deficiency in
Ruminants," Ann. N. Y. Acad, Sci., 162:727 (1969).
135. H. A. Heggtveit, "Myopathy in Experimental Magnesium Deficiency,"
Ann. N. Y. Acad. Sci., 162:758 (1969).
136. R. Whang, J. Oliver, L. G. Welt, and M. MacDowell, "Renal Lesions
and Disturbance of Renal Function in Rats with Magnesium Deficiency,"
Ann, N. Y. Acad. Sci., 162:847 (1969).
137. H. E. Martin, "Clinical Magnesium Deficiency," Ann. N. Y. Acad.
Sci., 162:891 (1969).
138. M. E. Shils, "Experimental Production of Magnesium Deficiency in
Man," Ann. N. Y. Acad. Sci., 162:847 (1969).
139. E. S. Barker, "Physiologic and Clinical Aspects of Magnesium Meta
bolism," J_;_ Chroru_ Dis^, 11:278 (1960).


5
The significance of this work as a contribution to the more
complete understanding of the function and metabolism of magnesium in
humans can perhaps be stated in the same way that McCance and Widdowson
(15) evaluated their research in 1939. In regard to experiments they
conducted on the fate of stable magnesium after intravenous administra
tion to normal persons, these researchers said:
These experiments are only a small contribution toward the
solution of a very large and complicated problem, but they
raise interesting points which deserve consideration.


TABLE 3
28Mg TURNOVER RESULTS IN HUMANS
Half-lives of Compartments*
Investigator
Number of
Subjects
Dose
(yCi)
Specific
Activity
Total
Mg
Hours
28Mg in:
Observed
1 2
(Hours)
3
4
Avioli et al.
(186)
15
175
=11
16
144
plasma,
urine
1.1
7.7
187
(1000)**
Wallach et al.
(189)
6
70
=16
4.3
72
plasma
0.17
2.4
66
-
Yun et al.
(ID
2
155
=20
7.8
70
plasma,
urine
1.31
6.9

347.1
Raynaud,
Kellershohn(194)
8
225
10.6
20
96
plasma,
excreta
0.13
1.8
46
-
Chon et al.
(37)
11
6
?
?
120
body
sections
-13.7-
- 933
Roessler
15
10
300
0.3
220
whole-
body,
excreta,
body
sections
- 5.4-
- 540
*Compartments are put in columns according to interpretations by this author as to what
the half-life represents.
**Half-life of a long-term storage site, estimated but not actually measured in the study.


'
I
I
i
Figure 11. Nal(Ti) Crystal Whole-Body Counter: Position for Head Count.


LIST OF FIGURES
Figure Page
1. ISOTOPES OF MAGNESIUM 22
2. RADIOACTIVE DECAY SCHEME OF MAGNESIUM-28 AND ITS
RADIOACTIVE DAUGHTER, ALUMINUM-28 34
3. FLOOR PLAN OF THE RADIATION BIOPHYSICS GRADUATE
PROGRAM FACILITY 42
4. 4-PI LIQUID WHOLE-BODY COUNTER LABORATORY ... 43
5. SUBJECT PREPARING TO ENTER THE 4-PI LIQUID WHOLE-
BODY COUNTER 44
6. ONE SIDE OF THE 4-PI LIQUID WHOLE-BODY COUNTER SHOWING
SIX PHOTOMULTIPLIER TUBES AND STEEL SHIELD 46
7. 4-PI LIQUID WHOLE-BODY COUNTER INSTRUMENTATION 47
8. SIGNAL DIAGRAM OF THE 4-PI LIQUID WHOLE-BODY
COUNTING SYSTEM 48
9. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: WHOLE-BODY COUNT
POSITION 50
10. GEOMETRY OF SUBJECT COUNTED ON THE Nal(Tl) CRYSTAL
WHOLE-BODY COUNTER 51
11. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
HEAD COUNT 52
12. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
CHEST COUNT 53
13. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
ABDOMEN COUNT 54
14. Nal(Tl) CRYSTAL WHOLE-BODY COUNTER: POSITION FOR
LEGS COUNT 55
15. LARGE VOLUME WELL COUNTER 56
16. Nal(Tl) CRYSTAL COUNTER ......... 58
vii


157
Patient
PA
Patient
PB
Subject
NH
Subject
NM
x*
R**
X*
R**
x*
R**
x*
R**
Whole-Body
Whole-Body
Whole-Body
Whole-Body
20.3
84.1
24.0
84.0
21.7
92.0
21.3
88.0
44.6
70.7
48.0
63.7
45.4
92.0
44.7
88.0
65.0
64.0
67.2
57.6
69.2
75.8
67.4
79.1
113.6
54.5
115.4
47.9
117.4
67.0
113.3
64.4
138.2
52.4
139.1
55.7
141.7
69.2
140.5
67.9
166.7
53.8
167.6
62.3
165.2
67.8
158.4
65.8
Head
Head
Head
Head
20.8
68.5
24.1
70.8
21.9
71.7
21.5
86.3
.45.1
50.8
48.0
56.9
45.5
79.7
44.7
95.1
65.6
50.2
67.2
59.9
69.3
65.7
67.4
77.8
114.1
60.3
115.6
70.7
117.6
79.7
113.2
72.5
141.7
57.4
139.1
69.0
141.8
83.3
140.2
68.8
158.4
53.8
167.9
75.0
165.2
69.2
158.4
61.5
Chest
Chest
Chest
Chest
20.8 100.3
24.2
96.3
21.9
91.5
21.3
86.0
45.1
98.4
48.1
93.9
45.4
80.1
44.8
75.1
65.6
71.3
67.3
80.3
69.3
67.1
67.5
70.0
114.3
51.2
115.8
38.7
117.7
47.1
113.0
49.3
141.5
53.3
139.1
47.3
141.9
46.4
139.9
47.4
167.5
53.9
167.2
53.7
165.6
52.1
158.0
44.7
Abdomen
Abdomen
Abdomen
Abdomen
20.8
70.9
24.3
78.1
22.0
91.5
21.4
115.1
45.2
69.0
48.1
87.4
45.4
80.1
44.8
111.4
65.6
70.0
67.3
84.0
69.3
67.1
67.5
98.4
114.6
78.4
115.7
149.0
117.7
68.3
113.0
97.1
142.1
63.7
139.9
148.9
141.9
62.2
140.3
85.5
167.7
64.3
167.5
161.0
165.6
66.4
158.2
69.4
Legs
Legs
Legs
Legs
20.9
77.8
24.3
71.6
22.0
89.5
21.4
77.1
45.2
91.1
48.1
74.0
45.6 110.0
44.8
77.9
65.6
83.3
67.4
76.7
69.5 103.0
67.7
88.4
114.6
54.7
115.9
41.3
118.5
97.8
113.2
69.2
142.5
61.6
138.9
56.8
142.7
95.6
140.5
70.2
167.9
42.2
167.5
56.3
165.6
84.3
158.4
63.6
*Time after injection in hours.
**Per cent of initial amount in region. Partial-body counts are
corrected for interference due to other regions.


Figure 5. Subject Preparing to Enter the 4-Pi Liquid Whole-Body Counter.


32
with normoinagne.sernia, one hypomagnesemia subject with periostitis of
unknown etiology and hypercalcemia, and one normomagnesemic subject
with chronic, severe malabsorption who had hypomagnesemia prior to treat
ment with magnesium infusions.
Pertinent details of many of these recent 28pig studies will be
discussed later in the results chapter of this study.
*


149
SUBJECT: PH STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:01 DOSE: 5.336 yCi
Time After Injection
Cumulative
Excretion*
Balance*
Excess or
Deficit*
(Hours)
Retention*
Urine
Fces
0.7
100
-
-
100
6.5
99
-
-
99
-1
24.7
100
3
0
103
+3
48.3
100
5
0
105
+5
72.3
99
6
0
105
+5
120.4
94
7
0
101
+1
144.7
88
7
1
95
-5
168.3
80
8
3
91
-9
192.5
67
8
3
78
-22
216.4
45
10
4
59
-41
*Expressed as per cent
, rounded off
to the
nearest
whole number
- Means not measured


133
SUBJECT: NH2 STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 11:55 DOSE: 9.373 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
7.2
98
-
-
98
-2
21.5
94
5
1
100
45.2
93
7
2
102
+2
69.5
88
9
2
99
-1
117.3
84
11
4
99
-1
141.5
81
12
5
98
-2
165.3
78
14
5
97
-3
189.3
75
16
5
96
-4
213.8
75
19
6
100
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured.


Figure 7
4-Pi Liquid Whole-Body Counter Instrumentation


8
magnesium is present in bone; however, its precise location there is
not known (27).
The exchangeable body content of magnesium in humans is 2.6 -
5.3 mEq/kg of body weight, whereas the total-body content is about 30
mEq/kg. The labile pool is contained primarily in connective tissue,
skin, and the soft tissues of the abdominal cavity; the magnesium in
bone, muscle, and red blood cells exchanges slowly (28).
The most recent summaries of magnesium content in humans,
particularly with regard to its biochemistry and its homeostasis,
appeared in reviews by Wacker (29) and Heaton (30) in 1969.
Requirements of Magnesium by the Normal Adult
Although magnesium has always been a part of man's diet
because of its abundance in nature, interest in it as a dietary con
stituent didn't develop to any extent until the latter part of the
nineteenth century. Reports in 1894 that it was present in animal
tissue (31) led many investigators to believe that magnesium more than
likely was an essential nutrient (32). The report of Sherman and
co-workers (33) in 1910 that magnesium was retained by humans subsisting
on a wide variety of diets was proposed as suggestive evidence of man's
requirement for this element (32).
In 1910, the Office of Experiment Stations of the United
States Department of Agriculture published Bulletin 227 which included
a summary of balance studies on magnesium (33). It was reported in
this bulletin that magnesium is absorbed from the intestinal tract
and deposited in the tissues of the body, especially in bone. However,
the balance data did not show that it was a required nutrient, nor that
it had a definite function.


CHAPTER I
INTRODUCTION
Nothing but a cloud of elements organic,
C. 0. H. N. Ferrum, Chor. Flu. Sil. Potassa,
Calc. Sod. Phosph. Magn. Sulphur, Mang.(?) Alumin.(?) Cuprum(?)
Such as man is made of (1).
Oliver Wendell Holmes, in a poem called "DeSauty, an electro
chemical ecologue," included magnesium in a list of elements of which he
thought man to be composed. Holmes wrote the poem in 1859, almost a
century before an accurate measurement of the human body content of
magnesium was made (2). Although he gave no indication about his
source of information, his prophetical inclusion of magnesium in the
composition of the human body came many years before scientists were to
provide conclusive evidence that magnesium is a required nutrient.
It is now known that magnesium is one of the most biologically
important metallic ions. Magnesium is second only to potassium in
abundance as an intracellular cation in humans (20-30 milliequivalents
per kilogram) (3); the element is knox-m to activate many enzymatic
reactions, it is essential for neuromuscular function and protein
synthesis, and it is an important constituent of bone (A).
Much has been written about the contribution of magnesium to
biological functions and its importance in metabolic processes. Never
theless, little information is available on magnesium in man (5), although
interest in its metabolism and nutritional significance has increased
1


56
Figure 15. Large Volume Well Counter


NORMAL SUBJECTS
=¡J
Total-Measured -Mg for Normals NA, NB,
Figure 20
and NC


APPENDIX D
Nal(Tl) CRYSTAL WHOLE-BODY COUNTER
RETENTION AND LOCALIZATION DATA


12
its zenith a century later (68) More recently it was shox^n that the
"healing" effect found from drinking the water containing the then
mysterious ingredient apparently was related both to its purgative
action and to its sedative effect.
Magnesium was used in that manner until 1911 when its external
use as sulfate was reported in Lancet (69) Patients suffering from
erysipelas or cellulitis applied a saturated solution of the compound
to painful areas and found relief. Four years later magnesium meta
bolism was first clinically studied by Holt e_t al. (70) in infants with
diarrhea by measuring magnesium intake and fecal excretion. However,
as recently as 1931, no clinical significance had been attached to
changes of magnesium in metabolism, even though the manifestations of
magnesium excess in man had been known since 1913, according to the
classic work, Quantitative Clinical Chemistry by Peters and Van Slyke (71).
In 1916, pharmacologic studies of the properties of magnesium as a
potential anticonvulsant and anesthetic agent showed that an excess of
the ion led to impairment of neuromuscular transmission (72). Further
study has shown that even general anesthesia can be produced by infusions
of magnesium; however, concentrations necessary to do this are dangerously
close to those required to produce respiratory paralysis (73). Uninten
tional production of magnesium excess occurs most frequently in patients
with renal failure (74).
On the other hand, the "indispensibility of magnesium for the
animal organism rested insecurely on a teleological basis" until the
early 1930s when Kruse jit al. (75) published their observations on
magnesium deficiencies in the rat. Earlier workers apparently had
failed in attempts to produce clinical changes in animals because of


91
Figure 25.
Whole-Body Retention of
28jig
ALS Patients.


135
SUBJECT: NJ STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:08 DOSE: 6.599 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
0.6
98
-
-
98
-2
6.1
92
7
-
99
-1
18.0
81
10
-
91
-9
41.9
88
13
-
101
+1
65.1
81
16
-
97
-3
90.0
85
18
-
103
+3
137.9
76
23
-
99
-1
162.0
71
25
-
96
-4
185.7
70
32
-
102
+2
210.0
70
33
-
103
+3
233.8
64
33
97
-3
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured.


169
171. J. L. Brandt, W. Glaser, and A. Jones, "Soft Tissue Distribution
and Plasma Disappearance of Intravenously Administered Isotopic
Magnesium with Observations on Uptake in Bone," Metabolism,
7:355 (1958).
172. F. W. Langemann, "The Metabolism of Magnesium and Calcium by the
Rat," Biochem. and Biophys., 84:278 (1959).
173. T. A. Rogers and P. E. Mahon, "Exchange of Radioactive Magnesium
in the Rat," Soc. Expt. Biol, and Med. Proc., 100:235 (1959).
174. I. MacIntyre, "Some Aspects of Magnesium Metabolism and Magnesium
Deficiency," Roy. Soc. Med. Proc., 52:212 (1959).
175. I. MacIntyre, D. Davidsson, and P. C. Leong, "The Turnover Rate of
Magnesium in the Rat Studied with 28Mg," Int. Abs. Biol. Sci.,
10:161 (1959).
176. D. L. Gilbert, "Magnesium Equilibrium in Muscle," J. Gen. Physiol.,
43:1103 (1960).
177. L. A. Graham, J. J. Caesar, and A. S. V. Burgen, "Gastrointestinal
Absorption and Excretion of 28Mg in Man," Metabolism, 9:646 (1960).
178. R. S. Silver, J. S. Robertson, and S. K. Dahl, "Magnesium Turnover
in the Human Studied with Mg28," J. Clin. Invest., 39:420 (1960).
179. I. MacIntyre, S. Hanna, C. C. Booth, and A. E. Read, "Intracellular
Magnesium Deficiency in Man," Clin. Sci., 20:297 (1961).
180. D. M. McAleese, M. C. Bell, and R. M. Forbes, "Magnesium-28
Studies in Lambs," J. Nutr., 74:505 (1961).
181. J. K. Aikawa, J. Z. Reardon, and D. R. Harms, "Effect of a
Magnesium Deficient Diet on Magnesium Metabolism in Rabbits; A
Study with Mg28," J. Nutr., 76:90 (1962).
182. Editorial, "Magnesium Metabolism,-' Nutr. Rev., 20:250 (1962).
183. H. E. Martin and F. K. Bauer, "Magnesium-28 Studies with the
Cirrhotic and Alcoholic," Proc. Roy. Soc. Med., 55:912 (1962).
184. R. Lazzara, K. Hyatt, G. E. Burch, J. Cronvich, and W. D. Love,
"Tissue Distribution, Kinetics and Turnover of Mg28 in the Dog,"
J. Clin, Res., 10:252 (1962).
185. S. Ginsburg, J. G. Smith, F. M. Ginsburg, J. Z. Reardon, and
J. K. Aikawa, "Magnesium of Human and Rabbit Erythrocytes,"
Blood, 20:722 (1962).


131
SUBJECT: NG STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:05 DOSE: 9.218 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours)Retention*Urine Feces Balance* Deficit*
0.4
98
-
98
-2
11.9
99
3
102
+2
22.0
83
7
100
45.6
82
9
101
+1
69.6
80
12
92
-8
94.0
80
14
94
-6
142.0
72
18
90
-10
165.2
70
21
91
-9
189.0
70
22
92
-8
213.0
66
24
90
-10
*Expressed in per cent,
rounded off
to the
nearest whole
number.
- Means not measured


108
suggests a lower degree of confidence in the crystal counter results.
Another major difference in the results using the crystal
counter is that the retention curve turned upward for PR's determination
at the same time that the curve turned downward in earlier work using
the 4-pi system. (Compare Figures 25 and 32.) This suggests that the
28
Mg may be relocating within the body in such a way that it is measured
with a lower efficiency in the 4-pi counter and a higher efficiency in
the crystal counter.
Localization Measurements of
The necessity for using the crystal counter retention measure
ments on the group 7 subjects also provided an opportunity to evaluate
this crystal system for localization studies.
In its present configxiration, the crystal counter is not
sufficiently collimated to restrict the measurement field to well-defined
regions of the body. Therefore, only four general regions head, chest,
abdomen, and legs were selected for analysis. The chest and abdominal
regions included the upper and lower arms. Corrections were made for
contributions to counts of one region from activity in the others.
Figure 33 shows the regional retention of the isotope (fraction
or per cent of the initial amount in each body section) for the four sub
jects in group 7. The ratios of each of these body regions to the total
amount of 28j^g present in the body initially were calculated as:
head, 7 per cent; chest, 60; abdomen, 19; and legs, 16.
The results for the two normal subjects, NH and NM, show the
following:
(1) The most rapid loss was from the chest region (=45 per
cent regional retention at 165 hours). The curves are almost identical


138
SUBJECT: NM STUDY GROUP: 7
DATE, TIME OF INJECTION: 2-17-71, 12:00 DOSE: 9.745 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Exo.
Balance* Def:
6.5
96
-
-
96 -4
20.8
94
5
1
100
26.0
91
7
2
100
45.0
88
9
2
99 -1
68.3
85
12
3
100
116.8
83
13
4
100
140.5
79
14
4
97 -3
164.8
78
16
4
98 -2
187.8
74
19
5
98 -2
213.5
74
-
-
-
*Expressed in per cent,
rounded off
to the
nearest
whole number.
- Means not measured


119
PRELIMINARY CALCULATION OF RADIATION DOSE
-Using Geometric Factor Method (213) and ICRP Half-Life (212)-
To calculate the total dose per yCi with the activity distri
buted throughout the total body:
Beta Dose: D^ = 73. 8 C E Teff rads.
28Mg: Dg = 7.38 x 1.43 x 1.53 x 8.85 x 10-8 = 1.43 x 10~4 rads.
28A1: Dg = 7.38 x 1.43 x 9.52 x 8.85 x 10-6 = 8.89 x 104 rads,
Gamma Dose: Dy = 33.1 x
Tabulated Computation:
103 c
K g Teff
Total =
rads.
10.32 x
10-4 rads.
Isotope
E
n
ua
K
Dy(rads)
28Mg:
.032
.96
1.1
x 10"4
5.2 x 101
2.6
x 10-4
.40
.31
3.2
x 10-5
6.2 x 101
3.2
x lO"4
.95
.29
3.2
x lO-5
13.6 x 10l
7.1
x 104
1.35
.70
3.1
x 10-5
4.6 x 101
2.3
x 10~4
28A1:
1.78
1.00
2.9
x lO-5
8.0 x 101
0.8
x lO"4
Total
= 16.0
x 10-4
Total Dose:
Dq 1
3+y
= ZDg +
EDy.
Total
dose =(10.3 + i
L6.0)x ;
10-4 rads
= 2.6 x 10'
.O
rads =
= 2.6 mrads.
C = radionuclide concentration in organ =
1 yCi
7 x 104 g
= 1.43 x 105 yCi/g.
Eg = average beta energy, MeV.
Where:


Figure 14. Nal(TI) Crystal Whole-Body Counter: Position for Legs Count.


57
four 5-inch photomultiplier tubes face the end of the tank. The tanks
and photomultiplier tubes are mounted in a 3.37-inch steel plate shield.
Read-out equipment consists of a single-channel analyzer with wide
window capacity, a scaler, and a timer.
Nal(Tl) Crystal Counter
Magnesium-28 in urine samples in groups 1 through 4 and in
sweat samples in group 7 were counted with a 4-inch by 4-inch Nal(Tl)
crystal counter. (See Figure 16.) The crystal is housed in a cylindri
cal cast steel shield, 28 inches high by 36 inches in diameter. The
shield has a 6-inch thick steel equivalent shielding on all sides.
Again, the output system is essentially that shown in Figure 8.
Data Analysis Techniques
Data was recorded manually from the three-channel analyzer,
on paper tape from the 400-channel analyzers, and in group 7 only it
was punched on cards. The data punched on cards represented totals in
the 400-channel analyzer channels and was submitted for summing (inte
gral counts) of the 28^g and A1 energy regions on an IBM 1800
computer.
Subsequent calculations were performed both with a conven
tional desk calculator and with Fortran IV programs run on the IBM
360/65 computer by means of a remote 2741 computer terminal located
in the whole-body counter laboratory.
Routine reduction of all counts to net counts per minute
was made on all data. Resolving time corrections were made on the net
subject counts during the first several days in study groups 3-6.
These corrections were made by plotting the phantom measurements versus


WHOLE BODY RETENTION
62
Figure 17. Whole-Body Retention of 2%g; Normal Subjects.


101
than normal retention of the isotope (Figure 30). PL, had been under
treatment for many years for hypertension, but denied the use of diure
tics or any medication just prior to or during the study. His retention
curve has a typical sum of exponentials shape, but is consistently higher
than the average normal subject. PD, on the other hand, not only had a
higher than normal retention, but his retention curve increases with
time.
Discussion of 2£$Mg Turnover Results in Patients
Although a small number of patients were studied within the several
groups representing the different disease conditions and the results
are varied, it is possible to make some general observations and also
some suggestions for further study. It is important at this point to
consider not only the erratic pattern of some of the whole-body retention
curves, but also the deficits and excesses which appear in the total-
measured 28y[gt One might speculate at this point that the general-
patterns of abnormal retention and/or excretion of the isotope is
related in some way to clinical abnormalities in the patients.
The behavior of the retention curves can be correlated with the
type of analyzer used in the various study groups. It is obvious in
study groups 3 to 6 that even the normal retention curves (Figure 17)
do not follow as smooth a function as the curves in study groups 1, 2,
and 7. As it was discussed earlier in this chapter, one might conclude
that the erratic behavior of many of the retention curves is related to
the type of analyzer used rather than to a disease condition.
Nevertheless, the most unusual patient results occurred in study
groups 1, 2, and 7 the groups with the least analytical problems.


CHAPTER II
LITERATURE REVIEW
Occurrence of Magnesium in Nature
Magnesium forms about 2.1 per cent of the earth's crust and
is the third most abundant of the industrial metals. It is widely
distributed in nature in a variety of forms; those used most commonly
are carbonate, oxide, and chloride which occur as dolomite, brucite and
carnallite (16). Its name is derived from Magnesia, a Greek city in
Asia Minor, where a large deposit of carbonate is located.
Magnesium has an atomic number of 12 and is usually classi
fied with the alkaline earth metals calcium, strontium, and others -
although in many ways it has a closer resemblance to zinc and cadmium
(17). Like the other metals of the alkaline earths, it readily forms
divalent ions.
Importance of Magnesium to Man
Magnesium Content in Living Tissue
It is now known that magnesium is present in all living
things (18). However, it wasn't until 1906 that the belief that
magnesium is essential for growth in higher plants was confirmed by
Wills tatter, who discovered that it forms an integral part of the
chlorophyll molecule (19*). Since that time, it has been shown that
magnesium is present in chlorophyll in all green plants and that it is
a universal microconstituent of lower plants. Higher animals have
6


98
typical negative sura of exponentials. The first measurement on this
subject (study group 1) shows a striking departure from the normal curve
beginning at about 100 hours and drops to a 10.5 per cent retention
at 165 hours; normal retention is 70 80 per cent after this same period
of time. PB's retention curve in study group 2 followed essentially the
same pattern with the rapid drop starting at a later point in time.
PB's third whole-body retention measurement was not made on the 4-pi
liquid whole-body counter due to his advanced progression in the disease
and his inability to lie in a supine position.
PA, whose ALS syndrome was described by his physician as one not
progressing as rapidly as PB's, also has lower than normal retention in
all three of the measurements. The first two measurements (PA and PA2),
made two months apart, are nearly identical. The last measurement
(PA3), almost two years later, again shows a low 28^g retention; however,
the resultant curve is shaped similar to PB's and takes a precipitous
drop at 120 hours. Additional information on these patients can be
gained by examining the total-measured ^Mg results shown in Figures
26 and 27. It is interesting to note in Figure 27 that in neither of
the two measurements made on PB is there 100 per cent accountability
of the isotope. At 190 hours the second measurement (PB2) accounted
for only 50 per cent of the administered isotope.
In contrast, although PA's pattern is abnormal (Figure 26), there
is almost total-accountability of ^Mg the first two measurements,
but in the third where the whole-body retention curve departs from the
sum of exponentials model, a deficit similar to PB's exists. In the
first two measurements fecal 28^g was not analyzed; however, normal
excretion would essentially account for PA's administered magnesium.


Ill
fraction of the initial activity than PA. Patient PB (with the more
progressive stage of the disease) appears to lose activity more rapidly
from the leg region (or conversely, fails to retain circulating 2%g in
that region) and to deposit it in the abdominal region. The buildup in
the abdominal region helps account for the apparent increase with time
of the patient's whole-body retention measurement. It has subsequently
been shown that with the configuration used at the time, the counting
efficiency is relatively higher for the abdomen than for the other
regions.
Magnesium-28 retention in the legs appears to be related to
age or to the physical activity of the subjects. The normals had
greater retention than the patients; normal NH (age 41) had a greater
retention than NM(age 71) and patient PA (who was still able to walk)
had greater retention than PB (who was confined to a wheelchair).
2^Mg 28Ai Equilibrium
The high energy resolution capability of the Nal(Tl) system
was used as a means of examining the data in study group 7 for possible
changes in the equilibrium of the parent daughter pair. Initial analy
sis of the data included a summing of all counts in two regions, the
2^Mg region, 0.03 to 1.6 MeV (includes interference from the 28^.1 peak)
and the 2A1 region, 1.6 MeV to 2.0 MeV (which is free from 28Mg inter
ference) The ratios of these energy regions were tabulated and examined
for differences between regions of the body, differences between subjects
within the normal and patient groups, and differences with time.
In general, the head and legs showed the lowest ratios (-5.0 -
6.0) while the abdomen and whole-body shoed the highest (-5.5 9.0).
After the first day (ratio =6.1), ratios dropped (=5.0 5.5) and stayed


67
physical half-life of the isotope made it extremely difficult to
identify a component with a half-life greater than the total observation
time in the experiment (220 hours).
Berman recommends that for compartmental analysis, the model
with the smallest number of compartments compatible with the data
should be chosen. Therefore, a two compartment model was chosen. The
individual data points were then analyzed by computer using a non
linear least squares method (Biomedical Computer Program, BMDX851) (210).
The sum of exponentials model used to describe the quantita-
28
tive Mg turnover in normals is:
R = Ae-^lt + Bex2t.
The dependent variable,
R = the per cent retention at any time, t, and the independent
variable,
t = the post-injection time in hours.
Parameters A, B, Xj, and X2 are as follows:
A = the per cent of the administered dose being excreted
directly from the first compartment;
B = the per cent entering into and being excreted from the
second compartment;
X.i = the turnover rate for the first compartment (in hours);
1This program obtains a weighted least squares fit, R =
f(t-^, ... t^; pjl, .. Pj[) + e, of a specified function f to data
values t^, ... t^, R by means of s stepwise Gauss-Newton iterations
on the parameters p^, ... p^. Within each iteration, parameters are
selected at any given step depending on which one, differentially at
least, makes the greatest reduction in the error sum of squares.


89
this study. Table 5 summarizes the results of plasma and red blood
cell analyses. The plasma analyses show that all normals and most of
the patients fall within the normal range. Only patients PF and PK
have values which are lower than normal. The red blood cell measure
ments show that two normals and four patients have values outside the
normal range. Normals NG and NI have above normal values. Higher than
normal levels were also found in red blood cell measurements of patients
PD, PH, and PJ, while a lower than normal level was observed for patient
PK. Only patient PK has abnormal magnesium levels in both plasma and
red blood cell measurements.
Magnesium-28 retention and excretion results for all patients
are shown in Figures 25 31. Whole-body retention values, grouped by
disease conditions, are superimposed on the normal retention band (from
Figure 19) and shown in Figures 25, 28, and 30. The total-measured ^Mg
results for these patients are shown in Figures 26, 27, 29, and 31.
These can be compared both to the individual normal results (Figures
20 23) and to the average for all normals (Figure 24).
Neuromuscular Patients
The whole-body retention curves for four of the neuromuscular
patients PA, PB, PG, all ALS patients, and PI, who has infectious poly
neuropathy, are shown in Figure 25. A number of different, lower than
normal retention patterns are obvious; however, only one, PI, appears
entirely within the normal range. As can be seen from the figure, PB's
retention curve shows the most dramatic departure from normal. In the
first two measurements on this subject, the whole-body retention was
lower than normal and also the resultant curve does not follow the


TABLE 6
COMPARISON OF THE WHOLE-BODY RETENTION MEASUREMENTS BY THE 4-PI LIQUID SCINTILLATION
AND THE Nal(Tl) CRYSTAL WHOLE-BODY COUNTERS
Per Cent Retention
Time After
Subject NH
Subject NM
Patient PA
Injection
(Hours)
4-Pi
Crystal
4-Pi
Crystal
4-Pi
Crystal
Counter
Counter
Counter
Counter
Counter
Counter
30
93
92
90
88
87
78
70
87
76
85
79
82
63
115
84
69
83
75
75
54
165
79
69
78
66
65
54
90 C


11
Nutr.tion, advocates "the maintenance of an adequate, even ample,
intake of calcium, magnesium, and phosphorus throughout the entire
life span" (61). She comments that "calcium, phosphorus, and magnesium
are usually considered together from a nutritional point of view
because all three occur in bone, and, with carbonate, make up the major
part of the bone mineral." Stearns also points out that of the three
elements, magnesium has been studied far less thoroughly because chemical
methods for its determination have been less satisfactory.
Potassium is another element frequently studied with magnesium,
since the two make up the bulk of the intracellular cations. Like calcium
more is known about potassium, primarily because of the ease with which
it can be measured (62) Two recent reviews concentrating on the
interrelationship of magnesium and potassium were published by Hammarsten
et al, (63) and Whang (64) The influence of various nutrients and
hormones on urinary magnesium and other divalent cation excretion was
reviewed in 1969 by Lindeman (65).
Clinical Significance of Magnesium
The first recorded association of magnesium with medicine
dates back to the Renaissance in Italy when various salts of magnesia
were used as laxatives (66) Magnesium sulfate, or epsom salts as it
was known hundreds of years ago, did not actually become popular as a
treatment until 1618 when it was used to "improve gastrointestinal
function" (67). A mineral springs was discovered that year on the manor
of Epsom in a municipal borough of Surrey, England. Although the
mineral composition of the water was not analyzed, its "healing"
qualities became so well known that a spa grew up at Epsom which reached


1] 4
of two exponentials model resulted in the following equation:
R = 8.5e-0'125t + 91.5e_0-00128t.
The first and second coefficients of the retention equation, 8.5 and
91.5, represent the quantities involved in the turnover of the two
compartments. Biological half-lives of 5.4 2.2 hours for the first
compartment and 540 35 hours for the second compartment were calcula
ted from the rate constants in the exponents of the fitted equation.
2. The resulting radiation dose from this single administra
tion of 2^Mg was calculated to be 2.0 mrad/pCi.
3. In the normal subjects, excretion measurements on the
average accounted for the amount of the 28^g not retained in the body.
Cumulative urinary excretion averaged 3 per cent per day, while fecal
excretion was approximately 0.5 per cent per day.
4. Stable magnesium analyses, made on all subjects in con
junction with the 28Mg measurements, showed no consistent pattern bet
ween normals and patients or between the various disease conditions.
5. Whole-body retention values for ALS and sub-total gastrec
tomy patients were significantly lower than normal, while several sub
jects, one of whom was known to have been on diuretics, had higher than
normal retention of the isotope. Repaired gastrectomy patients had
retention patterns within the normal range.
6. In the majority of the patients studied, the abnormal
retention of 28Mg was accounted for by amounts in the excreta. However,
in several patients, excretion did not account for the total amount
of the isotope not retained in the body, resulting in a deficit in the
total-measured 28^g.


68
A2 = the turnover rate for the second compax'tment (in hours) .
Biological half-lives for the two compartments can be derived
from this expression and are equal to 0.693/A] and 0.693/1?.
Figure 19 shows the data points of all the normals. The
retention equation obtained in this study by the non-linear least
squares method is:
R = 8.5e_0,129t + 91.5e--00128t.
This average equation is plotted as the solid line in the
Figure. The broken lines represent the estimated 95 per cent range of
the data or what can be called the "normal retention band." The first
and second coefficients of the retention equation, 8.5 and 91.5, repre
sent the quantities involved in the turnover of the two compartments.
Turnover rates are 12.9 and 0.128 per cent per hour for the two compart
ments, respectively. The second turnover rate can also be expressed as
3.07 per cent per day.
Biological half-lives of 5.4 1 2.2 hours (Is. d.) for the
first compartment and 540 35 hours for the second compartment were
calculated from the rate constants in the exponents of the fitted
equation.
Excretion of ^Mg jn Normals
Magnesium-28 excretion measurements were made on all subjects
in this study in addition to whole-body retention measurements in order
to examine 28^g balance. One should be able to account for the entire
activity (100 per cent of the administered dose) at any time after
administration of the isotope if all excreta are measured and if both
the whole-body retention and the excreta measurement techniques are
accurate.


xml record header identifier oai:www.uflib.ufl.edu.ufdc:UF0008954300001datestamp 2009-02-09setSpec [UFDC_OAI_SET]metadata oai_dc:dc xmlns:oai_dc http:www.openarchives.orgOAI2.0oai_dc xmlns:dc http:purl.orgdcelements1.1 xmlns:xsi http:www.w3.org2001XMLSchema-instance xsi:schemaLocation http:www.openarchives.orgOAI2.0oai_dc.xsd dc:title Whole-body retention and excretion of magnesium in humansdc:creator Roessler, Genevieve Schleretdc:publisher Genevieve Schleret Roesslerdc:date 1972dc:type Bookdc:identifier http://www.uflib.ufl.edu/ufdc/?b=UF00089543&v=0000113987388 (oclc)000577531 (alephbibnum)dc:source University of Florida


86
data from the chronic intake of magnesium. The half-life used for such
calculations was obtained from the Report of the J.CRP Committee II on
Permissible Dose for Internal Radiation (212) and was estimated from the
biological elimination of the stable element in humans in the absence of
experimental data from radioisotopes. Such a calculation was made of the
anticipated dose to standard man prior to this study. Considering the
radioisotope to be uniformly distributed through the whole-body as a
critical organ, assuming a single exponential turnover with a biological
half-life of 4320 hours as listed by the ICRP (212) and using the classi
cal method of calculation (213), it was estimated that the radiation
dose per yCi of injected 28jqg WOuld be 2.7 mrad. (See Appendix A.)
In reviewing the results of this study, it can be seen that
the calculation based on a single 4320-hour biological half-life is
inconsistent with the conditions following a single injection. When
no
the source of the Mg is a single administration rather than a chronic
intake, very little of the administered quantity reaches the very
long-lived biological compartment. Because of the short physical half-
life of the isotope, this portion of the administered quantity contri
butes only a small fraction to the radiation absorbed dose. Accurate
radiation dose calculations for the one-time dose situation should be
based on the model best representative of the biological turnover
following such an administration.
This study represents the longest known determination of both
retention and excretion of ^Mg uncjer these conditions; therefore, the
parameters determined in the retention equatipn in Figure 19 should
provide the most accurate estimation of the radiation dose to humans


Figure 23. Total-Measured 28Mg for Normals NX, Nl, and NM.


28
of the two major intracellular cations, magnesium and potassium. He
studied the turnover of the two elements in magnesium deficiency and
found indications that the magnesium ion occurs in pools differing in
size and turnover rate. They used a two-compartment model to describe
the turnover of 28Mg in plasma. Petersen concluded that the "total
24-hour exchangeable magnesium was reduced by more than 50 per cent in
magnesium deficiency, due mainly to a decrease in size of a slow pool,
which is believed to include skeletal magnesium."
Mendelson et al. (188) like Martin and Bauer (183) were not
satisfied with the relationship betxjeen serum magnesium levels and the
onset of withdrawal symptoms in alcoholics. They suggested that "although
alcohol withdrawal symptoms may be associated with total-body deficit
of magnesium incurred through poor dietary intake, it is also possible
that changes in distribution of magnesium in the extra-cellular intra
cellular compartments of the body as well as in bone may occur without
concomitant total-body deficit." The authors used 28^g to determine
exchangeable magnesium in alcoholic patients and,in 1965, reported signi
ficantly lower exchangeable magnesium values for "tremulous patients" than
for control subjects.
In a report the same year, Wallach and co-workers (189)
discussed results of "radiomagnesium kinetics in normal and uremic
subjects." Using analog computer analyses, they fitted a three compartment
model to plasma specific activity data following intravenous doses of
Mg. They concluded that hypermagnesemia influences the mechanisms
responsible for cellular transport of magnesium so that fractional influx
of cell magnesium is reduced.
In 1965 and 1966, Aikawa and his group used 28Mg (=40 yCi per mg


143
SUBJECT: PB2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 13:06 DOSE: 10.01 pCi
Time After Injection
(Hours)
Rtntion*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.2
100
-
-
100
8.3
97
5
-
102
+2
21.2
92
10
-
102
+2
45.2
88
13
-
101
+1
69.5
84
16
-
100
93.5
78
20
-
98
-2
141.5
65
25
-
90
-10
166.1
52
28
-
80
-20
190.1
23
30
-
53
-47
*Expressed as per cent
:, rounded off
to the nearest
whole number.
- Means not measured


1
2
L
r
28'-
Mechanical Equipment
Office
Secretaries' Office
Water Closet
Office
Low-Level Counting Laboratory
Waiting Room, Calculation Area
Dressing Room
Shower
Dressing Room
Computing Room
Graduate Students' Desk Area
Storage
Sample Preparation
Whole-Body Counter Laboratory
Storage
Graduate Student Desk Area
Office
Figure 3. Floor Plan of the Radiation Biophysics Graduate Program
Facility.


2
greatly during the past decade (6). Consequently, as recently as 1969,
researchers deplored the fact that this essential element had not been
investigated to anywhere near the same extent as calcium, phosphorus,
potassium and other fundamental ions (7). Because of the interrelation
ships of these cations, any lack of information on magnesium limits
the amount of knowledge obtainable on the function of the others.
The study of magnesium metabolism in the. human has been
hampered by technological difficulties (4). In spite of recent refine
ments in classical procedures such as precipitation, fluorimetry,
and the titan yellow method, the element is difficult to measure in
biological materials (8). Over the past decade, routine procedures
have been developed using emission flame spectroscopy and atomic
absorption spectrophotometry for analyses of the metal in body fluids,
tissue, and excreta. These techniques are accurate, but the equipment
is expensive and complex and consequently not available to many clinical
laboratories.
Another more important factor has delayed progress in the study
of the function of magnesium in humans. Although a complete analysis
of stable magnesium can be made from cadaver studies, this "final
analysis" supplies information only on what the content of the living
body was. It can not provide information on the dynamics and function
of magnesium in the living subject. Thus, in vitro measurements of
stable magnesium are made in serum, plasma, urine, feces, and even in
red blood cells, in attempts to establish some means of delineating
normal and abnormal metabolism of the element. The general consensus
of many authors (4,5,7) is that the level of magnesium in the various


21
Up to that time six isotopes of magnesium were known. (See Figure 1.)
Naturally occurring magnesium is composed of three stable isotopes,
2%lg (78.80 per cent), 25>jg (10.13 per cent), and 26>ig (11.17 per cent).
The three radioactive magnesium isotopes known prior to Sheline and
Johnson?s discovery were 22^g with a 3.9-second half-life, 23Mg with a
12-second half-life, and 27>jg with a 9.5-minute half-life.
Normally, one finds that the half-lives of the isotopes of any
particular element get shorter the farther the isotope is away from the
stable isotopes of the element. (This is depicted as the horizontal
distance in Figure 1.) For example, 22^g has a shorter half-life than
23Mg because it is farther from stable magnesium on the chart of the
nuclides. Following this "rule," one would expect that 28>ig would have
a half-life shorter than that of ^Mg. if this were the case, efforts
to produce this isotope would be of interest only to nuclear chemists
and physicists and would not be biologically useful. However, nuclear
scientists have found that another rule governs the stability of the
nuclides. So-called "magic numbers" of combinations of neutrons and
protons produce exceptionally stable atomic nuclei (161). These numbers
are 2, 8, 20, 28, 50, 82, and 126. Since 28^s atomic mass of 28 is
one of these numbers, it was predicted prior to the production of the
new isotope that the magic number rule would predominate and that 28^g
would have a greater stability, i. e., a longer half-life, than
With this in mind, Sheline and Johnson went to the University of Chicago
where they used both a betatron and a cyclotron to produce 28jfg. The
nuclear reactions are: 30si(y,2p)28Mg or 26Mg(aj2p)28Mg. in their report
of the production of ^Mg, the authors expressed the hope that 28^g would


142
SUBJECT: PB STUDY GROUP: 1
DATE, TIME OF
INJECTION: 5-20-69,
12:50
DOSE:
1.265 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balanc*
Deficit*
1.8
99
2
-
101
+1
3.6
98
3
-
101
+1
8.2
92
4
-
96
-4
21.2
91
5
-
96
-4
23.4
88
5
-
93
-7
26.0
88
6
-
94
-6
28.3
89
6
-
95
-5
32.3
88
7
-
95
_5
44.3
85
8
-
93
-7
52.4
84
9
-
93
-7
56.6
84
10
-
94
-6
70.4
82
11
-
93
-7
75.7
77
12
-
89
-11
92.8
78
16
-
94
-6
122.4
65
21
-
86
-14
141.2
50
22
-
72
-28
164.6
11
-
-
-
*Expressed as
per cent, rounded off
to the
nearest
whole number.
- Means not measured


70
Total-measured 2%g diagrams are shown in Figures 20 23 for
the 13 normal subjects. Each diagram shows the subjects whole-body
retention curve; added to it is the cumulative percentage of 28^g j_n
urine and feces. The difference between the total-measured 28j,jg an
100 per cent is labelled as "deficit" on the Figures. Numerical values
from which these graphs are plotted are tabulated in balance sheets in
Appendix B.
Figures 20 and 21 include results of subjects in groups 1-3
in which urine was the only excreta measured. In general, the results
are near, but somewhat less than the total balance or the 100 per cent
line. Figures 22 and 23 include the subjects in study groups 4 and 7.
Again, for the majority of the subjects, urine i^as the only excreta
measured. Figure 22 shows the two replications on subject NH. The
first measurement (labelled NH) in study group 4 where urine was the
only excreta measured, shows a small 4-5 per cent deficit at 220 hours.
However, the second measurement on this subject (NH2) included measure
ment of feces. This graph shows almost 100 per cent accountability;
a very small deficit is present at 220 hours.
Total-measured 28^g for the second study group 7 subject, NM,
is shown in Figure 23. Again, there is nearly 100 per cent accounta
bility of the administered isotope.
Although sweat was also measured in study group 7, it is not
plotted in the Figures since it was determined that the amount of 28j^g
in sweat was not significant. (See Appendix C .)
Since statistical fluctuations are apparent in the total-
measured 28^ig for these 13 normal subjects, an average retention and


23
find considerable use as a tracer (9).
Shortly after this first production of 28Mg} Brookhaven National
Laboratory (162) began producing it in a nuclear reactor by irradiating
an alloy of ^Li 26]qg with slow neutrons. The two reactions are:
6Li(n,t)%e and 26Mg(t,p)28>ig.
One of the first groups to use ^S^g experimentally as a tracer
was Glicksman et al, (163), who administered it intravenously to six
dogs and two patients. They found that the total-exchangeable magnesium
is much less than the theoretically calculated total amount in the body.
"This," they concluded, "would indicate that during the time of experi
mental observation (24 hours), a large quantity of magnesium does not
enter into the metabolic pool and appears to be fixed."
In 1958, Zumoff and associates (164) used ^^gci^ to study
"the kinetic behavior of magnesium in intact human subjects." They gave
oral doses of the isotope to study excretion, exchangeable magnesium,
and turnover in plasma. Their results showed that "magnesium kinetics
in diabetes mellitus and myxedema reveal departures from the normal
pattern."
About the same time, Aikawa and his colleagues (165) began
an extensive study in both animals and man with 28y[g. Because of the
conflicting results reported in previous studies using stable magnesium,
Aikawa*s group expected that the administration of the radioactive magnes
ium would prove to be a better way of following the behavior of orally
administered magnesium. In 1959, Aikawa et al. (166-168) observed that
low specific activity 28jqg o.5 yCi per mg magnesium) with the short
21.3-hour half-life made "impossible the use of a truly tracer dose."


100
at about the same time as PB's. Patients PE and PJ sub-total gastrec
tomies were performed prior to this study. More recently they had
reparative surgery to correct a malabsorption problem which was thought
to be causing neuromuscular ALS-type symptoms. After surgery their
symptoms gradually disappeared. Although magnesium retention and
excretion measurements were not made on these individuals while they
manifested neuromuscular disorder, they were studied with ^Mg after
their return to a normal condition. The objective here was to determine
if, in addition to the remission of the neuromuscular condition, these
patients had a normal magnesium turnover. The results show that
although the retention curves are somewhat irregular in pattern, they do
not fall out of the normal retention band. Normal ^Mg urinary and
fecal excretion measurements were also observed.
Other Patient Studies
Patients PK and PF show erratic whole-body retention curves (Figure
30). PF's curve remains within the normal retention band while PK's
rises above the normal band at several points. PF had both kidneys
removed prior to this study and had received a single kidney transplant.
Examination of PFs excretion data in Figure 31 shows a normal amount of
the isotope in the urine. Assuming a normal fecal excretion, there was
essentially total accountability of the administered magnesium in the
study of this patient.
PK, a female patient with an extensive small bowel resection,
excreted almost no ^Mg by the urinary route, but lost a normal amount
in the feces. Throughout the period of study a deficit or imcomplete
accountability of the 2%g exists.
The other two patients in this group, PD and PL, both have higher


129
SUBJECT: NE STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:16 DOSE: 9.158 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
-
100
11.1
96
4
-
100
25.9
91
6
-
97
-3
50.0
92
9
-
101
+ 1
73.5
90
10
-
100
97.9
88
12
-
100
145.7
83
17
-
100
169.6
77
20
-
97
-3
193.8
72
21
-
93
-7
217.9
72
22
_
94
-6
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


83
240 hours in this study, the approach is similar enough so that an
almost direct comparison can be made of the two sets of results. The
following comments can be made:
(1) This is the only other study published in which whole-
body retention, although not the primary intent of the study, was
measured directly rather than being calculated from plasma turnover or
from excreta measurements. However, Chon, used a scanning-type counter
rather than the more sensitive 4-pi liquid counter.
(2) The authors chose a two compartment model for fitting
although they admit that at least one other compartment may exist. They
assume that if a third compartment is present that their first compart
ment is actually a measure of the first two rapidly exchanging compart
ments ; and
(3) Eleven normal subjects were measured.
Almost identical results are obtained by Chon ejt al. and by
the measurements in this study for two of the constants in the retention
equation the per cent of the administered magnesium being excreted
directly from the first compartment (Chon e_t al. 10 per cent -
Roessler, 8.5 per cent) and the per cent of the administered magnesium
entering into and then being excreted from the second compartment.
(Chon et al., 90 per cent Roessler, 91.5 per cent).
However, Chon and his group found half-lives of these two
compartments to be 13.7 and 933 hours, in contrast to the 5.4 and 540
hours found in this study.
An estimate of the degree of accuracy of the results of Chon
et al. is difficult to make since the report gave no indication of the
degree of reproducibility of their measurements. No confidence intervals


ACKNOWLEDGMENTS
Foremost appreciation is expressed to Billy G. Dunavant, Ph.D.,
my committee chairman, for his supervision, inspiration, and guidance,
not only in this phase of graduate work, but also in previous graduate
study and employment. My interest in the area of the use of radioactive
isotopes in the biological field has stemmed from and followed his
interests.
I also gratefully acknowledge the contributions to my research
by the other members of my committee: W. Emmett Bolch, Ph.D., for
guidance in graduate work, for review and critical analysis of manu
scripts, and for participation in this research as a "normal"; Clyde
Williams, M.D., for clinical advice and direction; and Hugh Putnam, Ph.D.,
for inspiration and advice.
I should also like to acknowledge the support by the College of
Medicine, University of Florida, and, in particular, the many hours
of cooperation by Jared C. Kniffen, M.D., gastroenterologist, and
Donald T. Quick, M.D., neurologist. Others without whose assistance
this research would not have been possible include the staff at the
Clinical Research Center; the staff at the Medical Center Library;
Thomas Bauer, Howard Kavanaugh, Jerry Sawyer, Pat Edgett, Phyllis Durre,
Ann Groves, Lois Fischler, Mike Hewson, James McVey, and Sharon Corbett
of the Radiation Biophysics Section of the Department of Radiology; and
John Thomby, Ph.D., of the Department of Statistics. A special note of
ii


3
body fluids has little relationship to total-body magnesium and probably
predicts very little that is reliable and consistent about its metabolism.
The use of radioactive tracers has provided keys to new know
ledge about the metabolism of many essential elements. However, it
wasn't until 1953 (9) that a suitable radioisotope of magnesium
28
(magnesium-28 ( Mg)) was discovered. The first article on the use of
this isotope for biological investigations did not appear until five
years later (10).
Although the use of as a tracer overcomes many limita
tions present in stable analysis, the isotope itself has a limitation;
its short physical half-life (21.3 hours) makes long-term measurements
impossible (3).
Nevertheless, during the past decade, a number of attempts
have been made to further the understanding of magnesium metabolism
by determining the biological half-life and by defining the metabolic
compartmentalization of the element in humans. However, a later discus
sion will show that results of these studies vary widely. Most of these
studies involve the measurement of excretion rates and/or clearance
from plasma or serum of 28j,jg following a single administration of the
isotope in the chloride form. The short physical half-life limited
measurement to only 40 144 hours after administration. In addition,
until recently, only low specific activity (<20 microcuries per
milligram (yCi per mg) of magnesium)was available. Investigators who
used this lower specific activity compound report that the dose that
could be administered was "limited by concern for upsetting the magnesium
balance of the system under study" (4) and because of the possibility


168
156. J. B. Willis, "The Determination of Metals in Blood Serum by
Atomic Absorption Spectroscopy," Spectrochim,, 16:273 (I960).
157. J. B. Dawson and F. W. Heaton, "The Determination of Magnesium
in.Biological Materials by Atomic Absorption Spectrophotometry,"
Bichem. J., 80:99 (1961).
158. Charles Glover, Clinical Laboratory, Alachua General Hospital,
Gainesville, Florida, Personal Communication.
159. Gainesville Clinical Laboratory, Gainesville, Florida, Personal
Communication.
160. Knolls Atomic Power Laboratory, United States Atomic Energy
Commission, "Chart of the Nuclides," Sixth Edition.
161. G. D. Chase and J. L. Rabinowitz, "Introduction to the Radio
isotope," Principles of Radioisotope Methodology, Second Edition,
Burgess Publishing Co., Minneapolis, Minn., 10 (1964).
162. D. E. Alburger and W. R. Harris, "Decay Scheme of 28^^" Phys.
Rev., 185:1495 (1969).
163. A. S. Glicksman, M. K. Schwartz, H. Bane, K. E. Roberts, and
II. T. Randall, "Physiologic Distribution and Excretion of 28yg in
Dogs and Man," Clin. Res. Proc,, 4:14 (1956).
164. B. Zumoff, E. H. Bernstein, J. J. Imarisio, and L. Heilman,
"Radioactive Magnesium (28Mg) Metabolism in Man," Clin. Res.,
6:260 (1958).
165. J. K. Aikawa, E. L. Rhoades, and G. S. Gordon, "The Urinary and
Fecal Excretion of Orally Administered 28Mg," Clin. Res.,
6:261 (1958).
166. J. K. Aikawa and E. L. Rhoades, "28^g Studies of the Molybdivanadate
Method for Magnesium," Am. J. Clin. Path., 31:314 (1959).
167. J. K. Aikawa, "Gastrointestinal Absorption of Mg28 in Rabbits,"
Proc. Soc. Expt. Biol. Med., 100:293 (1959).
168. J. K. Aikawa, E. L. Rhoades, D. R. Harms, and J. Z. Reardon,
"Magnesium Metabolism in Rabbits Using Mg28 as a Tracer," Am. J.
Physiol., 197:99 (1959).
169. J. K. Aikawa, D. R. Harms, and J. Z. Reardon, "Effect of Cortisone
on Magnesium Metabolism in the Rabbit," Am. J. Physiol., 199:229
(1960).
170. J. K. Aikawa, "Effect of Alloxan-induced Diabetes on Magnesium Meta
bolism on Rabbits," Am. J. Physiol., 199:1084 (1960).


99
Therefore, it might be concluded that PA's low whole-body retention is
due to a higher than normal urinary excretion of magnesium. At 220 hours
he had a cumulative urinary excretion of about 40 per cent compared
to an average normal excretion of 25 per cent.
The third ALS patient, PG, has a whole-body retention pattern
similar to that of PA's first and second measurements with a signifi
cantly higher than normal excretion of the isotope in both urine and
in feces. However, the total-measured 28Mg for this patient is somewhat
higher than 100 per cent, indicating an overestimation of at least one
of the measurements.
Pi's whole-body retention falls in the normal range and both
urinary and fecal excretion are normal. Again, as with PG, the total-
measured 28Mg
is somewhat over 100 per cent.
Gastrectomy Patients
The four gastrectomy patients' whole-body retention curves are
shown in Figure 28 and their total-measured 28j4g is in Figure 29.
Patients PC and PH had sub-total gastrectomies and manifested ALS-type
symptoms. They also have abnormal retention curves. PC's retention
pattern is similar to that of ALS patients PA and PG and is about 30
per cent lower than an average normal at 220 hours. Figure 29 shows
that PC has almost normal urinary excretion; consequently, the ^Mg
deficit is greater than that which can be attributed to a normal
fecal excretion.
PH's whole-body retention curve is similar in shape to that of
ALS patient PB, but it shows a consistently higher retention; it is
obvious that he had a lower than normal urinary excretion, but his fecal
excretion appears normal. PH's whole-body retention curve shows a drop


40
3.0 to 12 minutes. After removal of the iontophoresis electrode, a
pre-weighed 2.75-inch filter paper was transferred to the area, covered
with plastic film, and left in place to collect sx^eat for 45 minutes.
The filter paper was removed, weighed, and counted on a 4-inch by 4-inch
Nal(Tl) crystal counter. Counting times ranged from 5 to 15 minutes.
Sterile techniques were used throughout the procedure to prevent
possible contamination of the filters with 28j^g from sources other than
sweat.
Instrumentation
The four detection systems used in this research are described
in this chapter and summarized in Table 2.
4-Pi Liquid Scintillation Whole-Body Counter
The University of Florida whole-body counter (62,201) is a
scintillation counter with an approximately 4-pi geometry. It is
located on the ground floor of the J. Hillis Miller Health Center in the
Radiation Biophysics Graduate Program Facility. A floor plan of the
entire facility is shown in Figure 3. Room 17 houses the whole-body
counter and output equipment, while supporting laboratories, sample
preparation areas, and other counting facilities are located in the
adjacent rooms. Figure 4 is a picture of the whole-body counter as seen
from the entrance to the counting room.
Figure 5 shows a closer view of the counter with a subject
preparing to enter the counting chamber. Subjects are centered longi
tudinally in the counter in a supine position. The detector consists of
liquid scintillator in six tanks that make up an annular configuration
which essentially surrounds the reclining subject. Twelve 16-inch


90
TABLE 5
PLASMA AND RED BLOOD CELL STABLE MAGNESIUM ANALYSES
Subject
Disease Condition
Age
Sex
Magnesium
Plasma Red
(r %)*
oi. d Cell
Normals
NA
28
M
N.A.**
N.A.**
NB
33
M
2.2
6.0
NC
36
M
2.1
5.5
ND
52
M
2.0
5.9
NE
47
M
2.3
5.9
NF
52
F
1.8
5.0
NG
59
F
1.8
7.1
NH
41
M
2.0
5.8
NI
48
M
2.1
6.9
NJ
43
F
2.1
5.8
NK
47
F
2.0
5.4
NL
56
F
2.0
5.8
NM
71
M
N.A.**
N.A.**
Patients
PA
ALS
50
M
2.1
5.6
PB
ALS
51
M
2.1
6.2
PC
Gastrectomy
54
F
2.0
4.6
PD
"Diuretic"
61
M
2.2
6.6
PE
Repaired Gastrectomy
61
F
2.1
4.4
PF
Kidney
23
F
1.6
6.3
PG
ALS
60
M
2.0
5.8
PH
Gastrectomy
52
M
1.8
6.7
PI
Infectious Polyneuropathy
42
M
1.9
5.4
PJ
Repaired Gastrectomy
54
M
2.2
7.1
PK
Bowel Resection
43
F
0.7
3.6
PL
Hypertension
50
M
N.A.**
N.A.**
Established Normal Values:
Mean
Range
2.0
1.7 2.3 4.
5.4
4 6.5
^Results are routinely reported in this unit, mg %, which means
milligrams of magnesium per 100 milligrams.
**N.A. = not analyzed.


151
SUBJECT: PJ STUDY GROUP: 5
DATE, TIME OF INJECTION: 2-10-70, 9:27 DOSE: 9.269 yCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Dficit*
1.0
100
-
-
100
10.6
95
8
-
101
+1
25.2
84
12
-
96
-4
48.4
78
14
1
93
-7
72.9
78
16
1
95
-5
96.4
75
17
1
93
-7
148.5
83
18
1
102
+2
172.6
82
19
1
102
+2
195.6
70
21
2
93
-7
219.6
61
25
3
89
-11
243.5
57
-
-
-
*Expressed as per cent,
rounded off
to the
nearest
whole number.
Means not measured.


18
Within a few years, the development of newer and better
techniques for precipitating magnesium in fluids encouraged a few
researchers to examine magnesium levels in body fluids (142). In
1942, Haury (129) reviewed the variation in serum magnesium in health
and disease and concluded that there was not a good correlation between
abnormal serum levels and disease conditions. It was not known then
whether this was due to poor techniques in measuring magnesium, to the
inability of serum to predict accurately total-body magnesium or
disturbance of magnesium within the body, or to the fact that magnesium
levels actually remained unchanged in many diseases.
Nevertheless, during the next 10 years, investigators (143,
144) continued to measure serum and/or plasma magnesium levels. The
older methods of precipitating magnesium as ammonium phosphate or hydrox-
yquinoline (145,146) were replaced by magnesium determinations by the
titan yellow technique (147-150), which was used extensively for some
years. In 1962, an automated fluorimetric method was described by
Hill (151) as an accurate procedure for magnesium analysis. Emission
flame spectrophotometry was another method recommended by Alcock et al. (152)
as a suitable measurement procedure in a wide range of materials. A more
recent publication by Alcock (153) reviewed the development of methods
for the determination of magnesium. She suggests that the best method
for estimation of magnesium in biological specimens is the "atomic
absorption, atomic emission, or the magnesium ammonium phosphate
precipitation method."
In 1963, MacIntyre (8) recommended that the method of choice
for magnesium measurements is absorption flame spectrophotometry. Others
maintain that the most acceptable means for magnesium analysis is the use
of the atomic absorption spectrometer (154-157). Although the instruments


122
28 28.1
For Mg Al,
£ Vi can ke coniputed in tabular form:
i
Back Scatter
Radiation
Mean Energy
. ,A.
H
Factor
Ai$i
3i
0.1560
0.332
1.0
-
0.332
82
1.240
2.641
1.0
-
2.641
Auger e
0.0014
0.0002
1.0
__
0.0002
(k shell)
Conversion
0.0029
0.0031
1.0
0.0031
e
Character-
0.0015
=0
1.0
-
0
istic x-ray
y 1
0.0364
0.0620
0.753
1.08
0.0504
y2
0.3998
0.264
0.340
1.05
0.0942
Y3
0.9415
0.562
0.329
1.02
0.1886
Yy
1.342
1.97
0.311
1.02
0.6250
y5
1.779
3.79
0.290
1.02
1.1222
Thus the dose can be computed:
5.0538
a.
D = A J A.$. = 3.93 x 10~4 yCi hrs/g x 5.0538 g rads/yCi hrs
m 7 1 1
m i
= 1.99 mrads


4
of chemical toxicity (11). A number of researchers discontinued their
work with because of the restrictions placed on the accuracy of
the results by both the isotopic compound and the measurement techniques
and equipment (12-14).
An opportunity to reduce these technical problems came when
Brookhaven National Laboratory began production of a high specific
activity preparation of (200-300 ytCi per mg magnesium). This
compound, plus the use of a highly sensitive 4-pi whole-body counter
for measuring whole-body retention of small quantities of the isotope,
made it possible to overcome problems associated with overloading the
system with magnesium. More important, the use of the whole-body
counter permitted measurements with a relatively small dose of the
isotope up to six times as long as was previously possible.
Therefore, a prime objective of this study was to determine
the biological half-life (or half-lives) of by measuring whole-body
retention after a single intravenous dose. Excretion was measured in
addition to the whole-body retention as a means of completing total-
balance studies of 28Mg. Another major objective of this study was to
determine the total-body radiation dose from the isotope. This deter-
' mination is particularly important now due to the availability and
anticipated frequent use of the higher specific activity 28Mg.
A small number of persons with selected disease conditions
who were suspected of having abnormal magnesium metabolism were included
in the study to examine the possibilities of using this isotope technique
for determining disease state metabolism anomalies. The feasibility
of using either retention or excreta measurements as a part of a diag
nostic procedure was another facet of this research.


66
the first step in the formulation of a model is to choose the type or
class of model applicable. Quite often in tracer kinetics, the model
can be described by a set of linear differential equations, the solu
tion for which are sums of exponentials (205). Others state that
"clearance curves for radioactive tracers are fit more simply by one or
more negative powers of timeM(206).
The two models when used to express retention can be repre
sented by the following general forms:
Power function: R = At-a + Bt-^ + ... + Xt-x.
Sum of exponentials: R = Ae-at + Bekt + ... + Xe-xt.
A majority of researchers (186,194,196,203,207,208) prefer
the latter model for compartmental analysis. Furthermore, the semi-
logarithmic plot of the data in this research (Figure 17), produced
an exponential-type curve. Therefore, a sum of exponentials model was
selected as the initial approach.
The next step in the analysis was to determine the order
(i.e., the number of independent functions) of the model. Some resear
chers report a three compartment turnover of 28^g in serum during the
first 20 hours after injection (196). Others (5,209) predict as many
as ten compartments (with half-lives from 0.623 to 5197 hours) from
turnover of 28^g in serum.
Visual inspection of the data in this research showed that at
least two compartments were involved in the turnover. However, it is
difficult to resolve more than two components since: (1) the whole-
body retention technique is relatively insensitive to multiple changes
in slope during the first day or so of observation, and (2) the short


35
is etched from the end of the rod. This method produces a higher speci
fic activity than other production methods.
OO
The material was received as MgC^ in 0.01 to 0.1 normal
HC1. It was diluted in the laboratory to the desired concentrations
with normal saline, checked for radionuclide purity, and then auto
claved before administration. The administered material had specific
activity of 200 300 yCi per mg of magnesium.
Experimental Conditions and Techniques
Fourteen normal subjects between the ages of 28 and 71 and
11 subjects with various disease conditions were measured in seven
groups over a period of 21 months. Two to six subjects were followed
at a time. Each subject was measured by whole-body counting prior to
the injection of the 28Mg to determine the background level of
^^Cs, and any previously administered diagnostic radioisotopes.
Plasma and red blood cell stable magnesium analyses were made prior to
injection of the isotope according to routine procedures of the Clini
cal Laboratories, J. Hillis Miller Health Center (198). None of the
subjects received medications containing magnesium during the study; no
other restrictions were placed on the quantity and composition of
intake.
One milliliter (ml) of the tracer solution was administered
through the anticubital vein by the "butterfly" infusion method to
subjects in the first six groups. One yCi was given to each subject
in group 1, while 6 to 10 yCi was administered in groups 2 through 7.
In group 7, the isotope solution was injected directly into the vein
since with this method there is less loss of radioactivity.


36
Whole-Body Retention Measurements
Whole-body retention was followed in a 4-pi liquid scintil
lation whole-body counter for as long as there was measurable activity.
In group 1, whole-body counts were made five times during the first two
24-hour periods, three times during the next two 24-hour periods, and
then every 24 hours through the seventh day. In groups 2 through 7,
counts were made twice during the first 24 hours after injection and
then every 24 hours (except Sunday) through the tenth day. A summary
of the study parameters is shown in Table 1.
Before measurement in the whole-body counter, each subject
dressed in a cotton "scrub suit." Subject counting times ranged from
0.1 to 10 minutes. Prior to and just after counting each subject, both
a 5-minute background count and a 2-minute count of a reference source
were made. The reference source is a nominal line (or "rod") source
consisting of a 6-foot long plastic tube filled with KC1. It is used
to correct for any variation in overall counter efficiency.
A unit-density phantom-*- (199) containing an amount of
approximately equal to that given to the subjects, was counted under
the same conditions as the subjects. The phantom was used to measure
the physical decay of the isotope and to evaluate any resolving time
losses.
-^The phantom in groups 1 through 6 consisted of an aqueous
solution in a 50-liter polyethylene carboy. In group 7, a sealed
source of ^8j^g was placed in the center of a phantom (designated as
"Tuboy") consisting of a bundle of sealed, sugar-filled polyvinyl
chloride tubes. The phantoms provided similar internal self-absorp
tion and scattering of the radioactivity as a human subject and thus
gave comparable count rates and spectrum shape.


25
authors concluded that the results should be interpreted with caution
because of the "relatively low specific activity"! (0.07 to 0.12 pCi
per mg magnesium) of the 28Mg.
In 1961, Maclntyr et al. (179) reported on studies of
patients with clinical magnesium deficiency. They carried out balance
studies and bone and muscle biopsies using stable magnesium and used
28ng in plasma turnover studies. They described 28]^g turnover as a
three-component system. Based on "previous animal work" this suggested
to them that "the three associated compartments were extra-cellular
magnesium with the fastest turnover rate, the vital organs with an inter
mediate turnover, and muscle with the slowest turnovef. The concept that
bone magnesium can always act as a reservoir was refuted.
McAleese, Bell, and Forbes (180) reported on 28Mg experiments
in lambs in 1961. They used both oral and intravenous doses and followed
the distribution of the isotope in various tissues and excretory path
ways. They expressed concern for the two limitations of the isotopic
compound; (1) the relatively short half-life and (2) the low specific
activity (0.45 to 0.75 pCi per mg magnesium).
Another approach to the study of magnesium metabolism was
taken by Aikawa et al. (181) who fed adult rabbits a controlled, deficient
iThe dose of 104 yCi of the 0.07 yCi per mg preparation
resulted in the administration of -1500 mg of stable magnesium or
=4 x 10^3 stable atoms. (The number of atoms of 28j^g in this dose,
=4 x 10l2}is insignificant in comparison.) It is not known how many
atoms will upset the magnesium balance of the system being studied. It
is obvious,'however, that the fewer the number of atoms of magnesium
injected instantaneously-into any living system, the less the chances are
of producing chemical toxicity or of disturbing the ion balance.


PATIENTS
Figure 26. Total-Measured Patient FA


38
A shadow shielded Nal(Tl) crystal scintillation whole-body
counter was also used in several of the study groups. Although its
counting efficiency is lower than that of the 4-pi system, it provided
the following useful information:
(1) Because its energy resolution is greater than that of
the 4-pi counter, it was used as a means of identifying unusual back
ground levels in several patients2 ;
(2) Since measurements with it are made with the subject in
a sitting position, it was used as an additional means of calculating
whole-body retention on one patient who was unable to lie flat to enter
the 4-pi counter;
(3) Since the detector has some collimation, it was used
in group 7 in an attempt to see if localization of the isotope took
place in the body; and
(4) Also because of its high energy resolution capacities,
it was used in group 7 to determine if the 28\tg 28^1 parent daughter
pair remains in equilibrium throughout its retention in the body.
Five counting positions (to be discussed later) were used for
the group 7 measurements; counting times ranged from 1 to 10 minutes.
The "Tuboy" phantom, described previously, was also counted
each time a set of subjects was counted on the crystal counter. Another
phantom, designated as "Tubman" (199), was used in this study. This
phantom is constructed in seven segments with varying thicknesses to
2It was found that two patients had residual radioactivity due
to having received &0qo in a vitamin B-12 test several years earlier.


45
diameter photomultiplier tubes are positioned so that two are on each
tank of scintillation fluid. (See Figure 6.)
The entire detector is contained in a 6-inch thick shield of
low background steel with a 1/8-inch thick lead lining. Output signals
from the photomultiplier tubes are fed into one of two types of scintil
lation spectrometers, a Packard model 3003 three-channel scintillation
spectrometer and a Packard model 115 400-channel analyzer. In Figure
7, the three-channel analyzer is shown on the left and the 400-channel
analyzer is in the center.
In study groups 1 and 2, the 400-channel analyzer was used
because the three-channel system was inoperable. The three-channel
analyzer was operative for use in study group 3-6; however, it was
discovered that resolving time corrections which were necessary in
groups 3-6 could be attributed to the analyzer system rather than to
the counter itself. Therefore, the 400-channel analyzer was used again
for group 7.
Figure 8 shows the signal diagram of the counting system when
the 400-channel analyzer (MCA) is used. Digital output from the system
was obtained by means of a high speed parallel printer and also by inter
facing an IBM 526 printing summary punch through a Packard model 70
parallel serial converter.
The three-channel analyzer consists of three independent
single-channel analyzers each of which were calibrated to measure the
137Cs, 4C>k, and the ^Mg 28^ energy regions. Digital counts were
recorded manually from each scaler.
Nal(Tl) Crystal Whole-Body Counter
The shadow-shielded crystal whole-body counter assembly


171
201. International Atomic Energy Agency, Directory of Whole-Body Radio
activity Monitors, IAEA, Vienna, Austria (1970).
202. H. Pickover, "A Performance Comparison of Equi-Volume 4-Pi Geome
try Liquid and Plastic Scintillation Counters," Master of Science
Thesis, University of Florida (1965).
203. C. R. Richmond, "Retention and Excretion of Radionuclides of
the Alkali Metals by Five Mammalian Species," LA-2207, Los Alamos
Scientific Laboratory of the University of California, 34 (1958).
204. W. J. Dixon, Editor, Biomedical Computer Programs, University of
California Press, Berkeley,Calif. 177 (1969).
205. M. Berman, "The Formulation and Testing of Models," Ann. N. Y.
Acad. Sci., 108:182 (1963).
206. J. Anderson, S. B. Osborn, R. W. S. Tomlinson, and M. E. Wise,
"Clearance Curves for Radioactive Tracers Sums of Exponentials
or Powers of Time?" Phys. Med. Biol., 14:498 (1969).
207. W. S. Snyder, B. R. Fish, S. R. Bernard, M. R. Ford, and J. R.
Muir, "Urinary Excretion of Tritium Following Exposure of Man
to HTO a Two Exponential Model," Phys. Med. Biol., 13:547
(1968).
208. H. C. Gonick and M. Brown, "Critique of Multicompartmental
Analysis of Calcium Kinetics in Man Based on Study of 27 Cases,"
Metabolism, 29:919 (1970).
209. S. R. Bernard, "A Metabolic Model for Magnesium in Man," Oak
Ridge National Laboratory, Annual Information Meeting, October,
1971.
210. W. J. Dixon, Editor, Biomedical Computer Programs, Supplement X>
University of California Press, Berkeley, California, 94 (1969).
211. E. Lebowitz and P. Richards, "BLIP Seen as Important Radionuclide
Source," Radioisotope Report, 8:65 (1971).
212. ICRP Publication 2: "Recommendation of the International Com
mission on Radiological Protection Report of Committee II on
Permissible Dose for Internal Radiation (1959)," Pergamon Press,
London (1960).
213. E. Quimby, S. Feitelberg, and S. Silver, Radioactive Isotopes
in Clinical Practice, Lea and Febiger, Philadelphia, Pa., 104
(1958).
214. Medical Internal Radiation Dose Committee, J. Nuc. Med.,
Supplements, Feb. 1968, Mar. 1969, Aug. 1969, Mar. 1970.


120
28Mg: Eg = 0.459 MeV/3 = 0.153 MeV.
28A1: Eg = 2.856 MeV/3 = 0.952 MeV.
Teff = effective half-life, days = (Tp x Tb)/(Tp + Tb).
Tp = physical half-life = 21.3 hours.
Tb = biological half-life = 4320 hours.
Te££ =(21.3 x 4320)/(21.3 + 4320) hours x 1/24 days/hour
= 0.885 days.
K = specific gamma-ray constant, R cm^/mCi hr
= 1.56 x 10? n E ua.
Y a
n = number of photons per disintegration at energy E.
E-y gamma-ray energy, MeV.
ua= linear absorption coefficient in air for energy E.
g = average geometric factor.


34
Mg
21.3h
Radiation
Typa
Energy
(MeV)
Equilibrium
Intimity
(% per decay)
28Mg
a*
.459
.212
95.0%
5.0
y,
.031
95.0
v2
.401
35.9
>3
.941
35.9
v4
1.342
54.0
Ys
1.373
4.7
y6
1.569
4.7
28ai
B~
2.656
100.0
Y
1.779
100.0
1.779 MeV
2s¡
Stable
Figure 2. Radioactive Decay Scheme of Magnesium-28 and Its Radioactive
Daughter, Aluminum-28. (Based on the Report of Alburger and Harris
(162).)


160
32.G. K. Davis, "Magnesium," Nutrition, 1:463 (1964).
33. H. C. Sherman,- A. J. Mettler, and J. E. Sinclair, U.' S. Dpt.
Agr. OES Bull., 227 (1910).
34. J. Leroy, Cmp. Rnd. Sc. Biol., 94:431 (1926),as cited by Davis (2).
35. T. Joachimoglu and G. Panopoulous, "Magnesium Content of Certain
Foods," Med. Welt, 3:1538 (1929).
36. K. Lang, "Eine Mikromethode zur Bestimmung kleinster Mengen von
Magnesium in biologischem Material," Biochem. Z., 253:215 (1932).
37. B. Chon, E. Jahns,and H. Misri, "Experimentelle 28^g ~ Verteilungs-
studien im Ganzkorperzahler," Nuclearmedizin, 1:106 (1968).
38. C. Schmidt and D. M. Greenberg, "Occurrence, Transport, and
Regulation of Calcium, Magnesium, and Phosphorus in the Animal
Organism," Phys. Rev., 15:297 (1935).
39. D. M. Greenberg, "Mineral Metabolism Calcium, Magnesium, and
Phosphorus," Ann. Rev. Biochem., 8:269 (1939).
40. J. Duckworth, "Magnesium in Animal Nutrition," Nutr. Abs. and Rev.,
8:30 (1939).
41. M. S. Seelig, "The Requirement of Magnesium by the Normal Adult,"
Am. J. Clin. Nutr., 14:342 (1964).
42. L. B. Mendel and S. R. Benedict, "The Paths of Excretion for
Inorganic Compounds: IV. The Excretion of Magnesium; V. The
Excretion of Calcium," Amer. J, Physiol., 25:1 (1909).
43. R. A. Womersley, "Studies on the Renal Excretion of Magnesium and
Other Electrolytes," Clin. Sci., 15:465 (1956).
44. L. C. Chesley and I. Tepper, "Some Effects of Magnesium Loading
upon Renal Excretion of Magnesium and Certain Other Electrolytes,"
J. Clin. Invest., 37:1362 (1958).
45. E. V. Tufts and D. M. Greenberg, "Biochemistry of Magnesium
Deficiency; Chemical Changes Resulting from Magnesium Deprivation,"
J. Biol. Chem., 122:693 (1938).
46. E. Watchom and R. A. McCance, "Subacute Magnesium Deficiency in
Rats," Biochem. J., 31:1379 (1937).
47. I. MacIntyre and D. Davidsson, "The Production of Secondary
Potassium Depletion, Sodium Retention, Nephrocalcinosis, and
Hypercalcaemia by Magnesium Deficiency," Biochem., 70:456 (1958).


88
tracer to study magnesium turnover in neuromuscular patients. Whole-
body turnover of radioisotopes of other essential human elements such as
iron (216), copper (217), and calcium and strontium (218) has been used
successfully to identify abnormalities in other disease conditions.
Therefore, this study was initiated with the objective of determining
whether the measurement of 28Mg turnover could be correlated with select
ed disease conditions.
This pilot study involved 16 whole-body retention and excretion
determinations following intravenous administration of Another
major objective of the study was to use these determinations to examine
the feasibility and possible applications of this technique as a diag
nostic test. It was hoped that the ^%g turnover determination could be
simplified to a one- or two-time measurement that would provide greater
potential in diagnosis than the currently used methods. Of these 16
determinations in this patient study, 10 represent a single turnover
measurement and the others were triplicate measurements at three points
in time on each of two patients.
Patients in the study included three with amyotrophic lateral
sclerosis (ALS) of unknown origin, two who developed ALS symptoms fol
lowing sub-total gastrectomies, one with infectious polyneuropathy, two
with repaired sub-total gastrectomies, a patient on diuretics, one
renal patient, a patient who had undergone an extensive small bowel
resection, and a patient with a history of hypertension.
In order to correlate the results between the stable magnes
ium levels, the ^Mg measurements, and these selected disease states,
routine clinical stable magnesium anslyses were made on all subjects in


13
the difficulty in obtaining a low magnesium diet (76). Kruse described
the classical symptomology of magnesium deficiency and observed that
it resembled that of low-calcium tetany.
During the next few years, there were many attempts to associ
ate dietary inadequacy of magnesium with increased incidence of malignant
neoplasms. Shear (77), in 1933, reviewed these reports and found the
evidence contradictory and insufficient, A short time later, Walker and
Walker (78) published a work which included an extensive review of the
physiological importance of magnesium and the variations of magnesium
levels in abnormal states. In their study, they compared the range
of serum magnesium in 91 miscellaneous medical and surgical patients
and in a group of persons with hypertension both with and without renal
damage. They concluded that "contrary to certain statements in the
literature, serum magnesium may be elevated in moderate or severe renal
insufficiency, especially if associated with hypertension."
The first investigators to succeed in producing magnesium
deficiency experimentally were Orent and his co-workers (79). They
stated in their 1934 paper that rats in the study showed a depletion
of bone magnesium after being fed a diet containing only 1.8 parts per
million (ppm) of magnesium. After four days on the diet "all exposed
skin areas became vividly red from vasodilation; irritability and
hyperexcitability was exhibited in eight to 10 days; growth stopped
after a week; convulsions began to occur by the 18th day; and death
usually followed the first or subsequent convulsions." That same year,
Hirshfelder (80) described magnesium deficiency in man. However, it
was not until 1959 that the first cure of magnesium deficiency in man


75
excretion was calculated and is shown in Figure 24. In this Figure, the
whole-body retention curve is the. one calculated from the least squares
fit of the data (Figure 19). It was plotted in Figure 24 by substitut
ing various values of time after administration of the isotope into the
established retention equation, R = 8.5e*"^*^29t + 91.5e_00128t# The
curve representing whole-body retention plus total-urinary excretion las
determined by plotting the sum of the whole-body retention and averaged
urinary excretion values versus time. Fecal excretion values were aver
aged and plotted in the same way.
The most stiking feature of Figure 24 is that, on the average,
the total amount of ^Mg was accounted for at all times after admini
stration. There is a slight, 1-2 per cent deficit toward the end of
the study, which is probably due to a small accumulative loss and
consequently, non-measurement of excreta.
The total-accountability (i. e. perfect balance) of the
on the average in the normal subjects is most significant in that it
verifies the accuracy of the retention measurements. The excreta
measurements also can be assumed to be accurate. Cumulative urinary
excretion averaged 3 per cent per day and fecal excretion was approxi
mately 0.5 per cent per day.
Comparison of Results to Reports of Other Investigators
Prior to the use of ^Mg, non-isotopic techniques used for
studying magnesium turnover indicated that there are several relatively
small, rapidly equilibrating compartments and that one or more of them
have a slow turnover (178). Early data on magnesium in man suggest that
there are at least three compartments in the body pool of magnesium


was reported (81). Five patients being fed intravenously developed
severe muscle cramps and convulsions. The symptoms suggested calcium
deficiency, but investigations showed that the patients had been
receiving a sufficient amount of calcium in the liquid nutrient. However,
they had received no magnesium. After intravenous administration of
magnesium sulfate, all of the patients improved within hours and were
soon asymptomatic.
A number of additional attempts to induce magnesium deficiency
took place in the 1930s through the 1960s. Knoop et al. (82), while
studying magnesium and vitamin D relationships in calves fed mineralized
milk, found that the soft-tissue content of magnesium is not appreciably
altered even in severe deficiency. This may be the reason that when
Fitzgerald and Fourman (83) fed a diet containing essentially no
magnesium to normals for 27 days no symptoms of magnesium deficiency
were observed. In addition, they found no differences in the magnesium
blood levels in these subjects between normal and low-magnesium intake
periods. In another case, Barnes et al. (27) did not observe any hypo
magnesemia or deficiency symptoms in a patient maintained for 38 days
on gastrostomy feedings which contained little magnesium.
In contrast, Shils (84) reported that plasma and red blood
cell magnesium levels fell significantly below normal in two normal
volunteer subjects while they were on a deficient diet for 274 and 414
days. Signs and symptoms of magnesium deficiencies appeared in both
subjects and reversal occurred upon administration of magnesium. In
comparison to the deficiency symptoms first reported in 1934 by Orent
et al. (79), Wacker and Paris! (74) more recently described the syndrome in
man as one involving "neuromuscular dysfunction manifested by hyperexcitability,


140
SUBJECT: PA2 STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 13:00 DOSE: 10.03 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
0.3
100
-
-
100
8.3
94
9
-
103
+3
21.1
87
13
-
100
45.0
82
18
-
100
69.0
76
21
-
97
-3
93.3
72
24
-
96
-4
141.2
64
31
-
95
-5
165.5
63
34
-
97
-3
189.5
54
37
-
91
-8
213.9
57
42
-
99
-1
237.9
29
51
-
80
-20
* Expressed as per cent
:, rounded off
to the
nearest
whole number.
- Means not measured


CHAPTER V
SUMMARY AND CONCLUSIONS
Thirty-one whole-body retention and excretion measurements
were made on 13 normal subjects and on 10 patients with selected
disease conditions to determine as accurately as possible the biological
half-lives from a single intravenous administration of 28^g in the forra
of MgCl2- The prime objective of this research was to contribute
information to the currently sparce knowledge on magnesium metabolism
in humans. Calculation of radiation dose based on the determined
half-lives was an important aspect of the research since the experi
mental use of 2^Mg is increasing rapidly and no dose estimates have
been established. The feasibility of this measurement technique for
studying abnormalities in disease conditions was also explored.
A high specific activity (=200 300 yCi per mg magnesium)
preparation of the radioactive isotope ^Mg (21.3-hour physical half-
life) was used in conjunction with the sensitive 4-pi liquid scintil
lation whole-body counting technique for retention determinations.
A Nal(Tl) crystal whole-body counter was employed to measure locali
zation of the magnesium in the body and appropriate low-level counting
systems were used for measurement of the isotope in excreta.
The pertinent information gained from this work can be
summarized as follows:
1. The fitting of whole-body retention data from the 15
determinations on normal subjects (including two replications) to a sum
113


159
15. R. A. McCance and E. M. Widdowson, "The Fate of Calcium and
Magnesium After Intravenous Administration to Normal Persons,"
Biochem. J., 33:523 (1939).
16. Encyclopaedia Britannica, "Magnesium," William Benton, Publisher,
Chicago, Ill., 581 (1967).
17. I. MacIntyre, "Magnesium Metabolism," Advanc. Intern. Med., 13:143
(1967).
18. W. R. Fearon, An Introduction to Biochemistry, Heinemann, London,
74 (1948).
19. Editorial, "Magnesium in Nutrition," JAMA, 113:1418 (1939).
20. Moleschott, "Physiologie der Nahrungsmittel," Ferber'sche
Universitatsbuchhandlung, 224 (1859) as cited by Widdowson et al.
(2) .
21. Bischoff, Z. ration. Med., 20:75 (1863) as cited by Widdowson et al.
(2).
22. Volkmann (1874), Quoted by von Voit, Handbuch der Physiologie,
6:345 (1881) as cited by Widdowson et al. (2).
23. Mitchell, Hamilton, Steggerda, and Bean, J. Biol. Chem., 158:625
(1945) as cited by Widdowson e_t al. (2) .
24. J. Duckworth and G. M. Warnock, "The Magnesium Requirements of
Man in Relation to Calcium Requirements, with Observations on the
Adequacy of Diets in Common Use," Nutr. Abs. and Rev., 12:167 (1942).
25. A. T. Shohl, "Mineral Metabolism Calcium and Magnesium," Ann. Rev.
Biochem., 2:207 (1933).
26. H. C. Sherman, "Mineral Elements in Food and Nutrition," Chemistry
of Food and Nutrition, The Macmillan Co., New York, N. Y., 227 (1952).
27. B. A. Barnes, 0. Cope, E. B. Gorden, "Magnesium Requirements and
Deficits: An Evaluation in Two Surgical Patients," Ann. Surg.,
152:518 (1960).
28. J. K. Aikawa, "^^Mg Studies of Magnesium Metabolism," Radioisotopes
in Animal Nutrition and Physiology, International Atomic Energy Agency
Vienna, Austria, 705 (1965).
29. E. C. Wacker, "The Biochemistry of Magnesium," Ann. N. Y. Acad. Sci.,
162:717 (1969).
30. F. W. Heaton, "The Kidney and Magnesium Homeostasis," Ann. N. Y. Acad.
Sci., 162:775 (1969).
31.H. C. Sherman, A. J. Mettler, and J. E. Sinclair, Weiske, Z. Biol.,
31:437 (1894) as cited by Davis (32).


163
79. E. R. Orent, H. D. Kruse, and E. V. McCollum, "Studies on Magnesium
Deficiency in Animals; VI. Chemical Changes in the Bone with
Associated Blood Changes Resulting from Magnesium Deprivation,"
J. Biol. Chem., 106:573 (1934).
80. A. D. Hirshfelder, "Clinical Manifestations of High and Low Plasma
Magnesium: Dangers of Epsom Salt Purgation in Nephritis," JAMA,
10?:1138 (1934).
81. "Magnesium Deficiency," Sci. Arner., 201:71 (1959)*
82. C. E. Knoop, W. E. Krauss, and C. C. Hayden, "Magnesium and
Vitamin D Relations in Calves Fed Mineralized Milk," J. Dairy Sci.,
22:283 (1939).
83. M. C. Fitzgerald and P. Fourman, "An Experimental Study of Magnesium
Deficiency in Man," Clin, Sci., 15:635 (1956).
84. M. E. Shils, "Experimental Human Magnesium Depletion," Am. J. Clin.
Nutr., 15:133 (1964).
85. H. E. Martin, H. Edmonson, R. Homann, and C. F. Berne, "Electrolyte
Problems on the Surgical Patient with Particular Reference to
Serum Calcium, Magnesium and Potassium Levels," Am. J. Med., 8:529
(1950).
86. H. E. Martin and M. Wertman, "Serum Potassium Magnesium, and Calcium
Levels in Diabetic Acidosis," J. Clin. Invest., 26:217 (1947).
87. E. B. Flink, "Magnesium Deficiency Syndrome in Man," JAMA, 160:1406
(1956).
88. E. B. Flink, R. McCollister, and A. S. Prasad, "Evidences for
Clinical Magnesium Deficiency," Ann Int. Med., 47:956 (1957).
89. R. Fraser and E. B. Flink, "Magnesium, Potassium, Phosphorus,
Chloride, and Vitamin Deficiency as a Result of Prolonged Use of
Parental Fluids," J. Lab. Clin. Med., 38:809 (1951).
90. E. B. Flink, R. McCollister, A. S. Prasad, R. P. Doe, "Normal
Renal Magnesium Clearance and the Effect of Water Loading,
Chorothiazide and Ethanol on Magnesium Excretion," J. Lab. Clin. Med.
52:128 (1958).
91. E. B. Flink, F. L. Stutzman, A. R. Anderson, T. Konig, and R. Fraser,
"Magnesium Deficiency After Prolonged Parental Fluid Administration
and after Chronic Alcoholism Complicated by Delirium Tremens," J.
Lab. Clin. Med., 43:169 (1954).
92.F. W. Heaton, L. N. Pyrah, C. C. Beresford, R. W. Bryson, and D. F.
Martin, "Hypomagnesaemia in Chronic Alcoholism," Lancet, 2:802 (1962)


Whole-body retention data from the determinations on normal
subjects were fit to a sum of two exponentials model. The coefficients
of the resultant equation are 8.5 and 91.5 and represent the quantities
in per cent involved in the turnover of the two compartments. Biologi
cal half-lives of 5.4 2.2 hours for the first compartment and 540 1
35 hours for the second compartment were calculated from the rate
constants in the exponents of the fitted equation.
The radiation dose from this single administration of 28Mg
was calculated to be 2.0 mrad/microcurie.
In the normal subjects, excretion measurements on the average
accounted for the amount of the 28y¡g not retained in the body. Cumula
tive urinary excretion averaged 3 per cent per day while fecal excretion
was approximately 0.5 per cent per day.
Whole-body retention values for amyotrophic lateral sclerosis
and sub-total gastrectomy patients were significantly lower than
normal, while several subjects, one of whom was known to have been on
diuretics, had higher than normal retention of the isotope. Repaired
gastrectomy patients had retention patterns within the normal range.
In the majority of the patients studied, the abnormal
retention of 28pjg was accounted for by amounts in the excreta. However,
in several patients, excretion did not account for the total amount of
the isotope not retained in the body, resulting in a deficit in the
total-measured 28j^g,
Localization of the isotope in the body as measured by Nal(Tl)
crystal whole-body counting showed consistent patterns between results
of the normal subjects. An atypical build-up of the isotope was found
in the abdominal region of the amyotrophic lateral sclerosis patient
x


31
suffered from normocalcemic tetanys.
In 1968, Chond, Jahns, and Misri (37) used ^Mg an attempt
to define as precisely as possible the proportions of magnesium in
various parts of the human body. Eleven normal subjects received intra
venous doses of the isotope and were followed up to 120 hours. For the
purposes of localization of magnesium, the body was divided into five
parts; the head, the thorax, the upper abdomen, the lower abdomen, and
the lower extremities. A sodium iodide, thallium-activated (Nal(Tl))
crystal counter was used for the body counts. Whole-body retention was
calculated from these sequential measurements; the data indicated that at
least two compartments were involved in the turnover of ^Mg.
The most recent reports found in the literature on the use
of 2%g include two in the August, 1969, issue of the New York Academy of
Sciences. Aikawa and David (195) summarized their team's past and also
the most recent results of experiments using 28yig as a tracer in rabbits.
The investigators report that recent results with the isotope to study
segments of the small intestine from deficient and normal animals suggest
that the "magnesium-absorbing ability of both proximal and distal areas
of the small intestine is enhanced by magnesium deficiency and is not
energy dependent."
Wallach and Dimich (196) reported on turnover studies in hypo-
magnesemic states in which 50 100 yCi of 28^g with a specific activity
of =17 yCi per mg magnesium was given intravenously. They determined the
plasma specific activity and urinary excretion of the isotope and total
magnesium for 72 hours after injection. The experimental group consisted
of eight alcoholic subjects with hypomagnesemia, three alcoholic subjects


128
SUBJECT: ND STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:15 DOSE: 10.20 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.4
100
-
-
100
8.8
97
2
-
99
-1
23.2
95
4
-
99
-1
43.1
94
6
-
100
71.0
87
7
-
94
-6
95.3
84
9
-
93
-7
143.1
81
13
-
94
-6
168.1
78
14
-
92
-8
192.0
75
17
-
92
-8
215.5
79
21
100
^Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


19
used in this type of analysis are too complicated for routine work in
small laboratories, many large hospitals are set up to do magnesium
and calcium measurements with the atomic absorption spectrophotometer
(158). A number of smaller laboratories send serum and urine samples
out to larger laboratories for analysis (159). Results of the latter
may take up to six days. It appears that the atomic absorption spectro
meter is an accurate, although certainly not a simple,method for routine
analysis of magnesium in biological fluids.
However, as emphasized previously, most investigators are
uncertain as to what these fluid analyses mean. Thus, the question
which remains to be answered is whether there are ways other than analy
sis of extracellular magnesium or examination of intake and excreta that
will provide information about magnesiums role in the human body which
is not available with current techniques.
Studies with Magnesium-28
In 1939, Greenberg (39) reviewed calcium, magnesium, and
phosphorus metabolism. He paid particular attention to the development
up to that time in the study of mineral metabolism made possible by
radioactive isotopes. Because of the "revolutionary nature and potential
importance of this subject," Greenberg departed from his usual approach
in a review article to digress on the usefulness of radioactive tracers
in animal organisms. He pointed out the advantages of.this "new tool"
for studying "absorption, permeability, storage, distribution, chemical
transformation, and paths of excretion of the mineral elements." Another
important advantage, he commented,is that in general only very small
doses of the substance need be administered, "thus avoiding the criticism


137
SUBJECT: NL STUDY GROUP: 4
DATE
, TIME OF INJECTION: 1-6-70,
16:20 DOSE:
6.790 yCi
Time
After Injection
Cumulative
Excretion*
Excess or
(Hours) Retention*
Urine Feces
Balance* Deficit*
0.9
97
-
-
97
-3
6.4
95
4
-
99
-1
18.9
81
6
-
87
-13
42.7
82
10
-
92
-8
66.8
78
13
-
91
-9
89.7
80
14
-
94
-6
138.8
79
17
-
96
-4
162.8
72
17
-
89
-11
186.7
71
18
-
89
-11
210.8
75
18
-
93
-7
234.9
67
-
-
-
*Expressed in per cent,
rounded off
to the
nearest
whole number
- Means not measured


147
SUBJECT: PF STUDY GROUP: 2
DATE, TIME OF INJECTION: 9-23-69, 12:43 DOSE: 10.15 yCi
Time After Injection
Retention*
Cumulative
Excretion*
Balance*
Excess o
Deficit*
(Hours)
Urine
Feces
0.3
100
-
-
100
8.1
99
2
-
101
+1
20.7
98
4
-
102
+2
44.8
93
5
-
98
-2
69.0
87
7
-
94
-6
92.8
88
9
-
97
-3
140.8
83
15
-
98
-2
168.9
80
16
-
96
-4
189.0.
77
17
-
94
-6
213.2
67
21
-
88
-12
236.1
69
30
-
99
-1
*Expressed as per cent
, rounded off
to the
nearest
whole number,

Means not measured.


% OF INITIAL CONTENT IN REGION
109
POST-INJECTION TIME, HOURS
Figure 33. Regional Retention of ^Mg.


APPENDICES


WHOLE-BODY RETENTION (R), %
IOO
Figure 19. Model for 28^jg Retention in Normal Subjects


78
man based on measurements of blood, urine, and feces in 15 subjects who
* OO
had received 150 175 yCi of Mg (-11 yCi per mg magnesium). They
fitted a sum of three exponentials model to the plasma data to determine
half-lives of 1.1, 7.7, and 187 hours.
In the same paper, Avioli and Berman postulate a more complex
model describing 23Mg kinetics which was later used by Bernard (209) to
obtain the following whole-body retention equation where t is in days;
R = 0.738e_0'00320t + 0.216e_0-164t + 0.034e-4-54t + 0.0115e"26-7t.
This function is obtained as the sum of four separate retention
functions, one for each compartment. The half-lives of the four compart
ments in hours are: 5197, 101.4, 3.66, and 0.623. Bernard uses this
function to estimate internal dose due to a continuous exposure to 28Mg.
Another measure of magnesium turnover was reported by Petersen
(187) in 1963. He treated his experimental data with the assumption
that plasma activity is a function of immediate dilution in a central
compartment and further transport into two parallel compartments governed
by the rate constants k^ and k^. He expressed the concentration in the
central compartment as:
C = ae-k-^t + be^c2t + c>
where k^ and k^ as determined yield half-lives of about 1 hour and 4
hours.
Several years later, Wallach, Rizek, and Dimich (189) studied
magnesium kinetics in plasma after intravenous administration of 50 -
70 yCi of =16 yCi per mg magnesium. Although measurements were made only
to 72 hours after administration, the total magnesium given was far less
than that used by Avioli et al. (186); therefore, the resultant turnover


87
after a single intravenous administration of the isotope.
After the parameters in Figure 19 had been obtained, the
method of the Medical Internal Radiation Dose (MIRD) Committee of the
Society for Nuclear Medicine (214) was followed to recalculate the
radiation dose. (See detailed calculations in Appendix A.) The model
used two uncoupled compartments characterized by the relative activities
and the biological half-lives found in this study. The whole-body was
considered as the target organ and the source for both compartments.
From this data, the radiation dose was calculated as 2.0 mrad per yCi.
Retention and Excretion of ^Mg jn Selected Disease Conditions
Because of magnesiums role in neuromuscular function, serum
or plasma levels of this element are routinely examined in patients with
neuromuscular disease. As it was pointed out in the literature review,
this extracellular measurement of a primarily intracellular ion rarely
provides any information with regard to metabolic magnesium abnormali
ties. Consequently, the measurement of stable magnesium in red blood
cells has been accepted by some clinicians as the method of choice for
determining these abnormalities. Although this determination may be more
sensitive to a disorder in magnesium turnover, it is generally agreed
that red blood cells are "enucleated impotent and dying cells which are
not representative for intracellular metabolism"(215).
Because of these uncertainties in the relationship between
plasma and red blood cell analyses and actual magnesium metabolism,
many clinicians have sought a better means of determining magnesium ab
normalities. Among these were a gastroenterologist and a neurologist at
the University of Florida who sought help in the use of a radioactive


126
SUBJECT: NC STUDY GROUP: 1
DATE, TIME OF INJECTION: 5-20-69, 12:10 DOSE: 1.304 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Balance*
Excess or
Deficit*
1.1
96
4
100
2.6
100
5
105
+5
5.1
97
6
103
+3
21.0
89
7
96
-4
23.2
90
8
98
-2
25.3
89
8
97
-3
27.8
89
9
98
-2
31.8
88
9
97
-3
44.6
86
10
96
-4
47.9
84
11
' 95
-5
52.0
85
11
96
-4
56.0
86
12
98
-2
70.2
80
13
93
-7
74.3
79
14.
93
-7
79.4
78
14
92
-8
93.0
79
15
94
-6
143.9
71
18
89
-11
*Expressed in per cent, rounded
off to the nearest
whole number.
Means not measured


144
SUBJECT: PC STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:14 DOSE: 9.298 yCi
Cumulative
Time After Injection Excretion* Excess or
(Hours) Rtentiii* Urine Feces Balance* Deficit*
0.7
100
-

100
10.8
91
6
-
97
-3
25.5
82
10
-
92
-8
49.3
76
14
-
90
-10
73.4
71
18
-
89
-11
96.8
68
19
-
87
-13
145.8
58
23
-
81
-19
169.3
58
25
-
83
-17
193.7
55
27
-
82
-16
217.8
53
27
-
80
-20
241.5
54
27

81
-19
*Expressed as per cent, rounded off to the nearest whole number.
- Means not measured.


no
for the two subjects.
(2) An intermediate loss occurs from the head region (-65
per cent regional retention after 165 hours). The curves are very
similar for the two subjects.
(3) There is an intermediate loss rate in the abdominal
region and a low loss rate in the leg region (>90 per cent regional
retention at 100 hours, >70 per cent at 165 hours). A possible build-up
occurs in both regions in the first 24 48 hours.
In summary, the normal subjects exhibited a higher rate of
loss from the chest region, a less rapid loss from the other regions,
and possible relocation (early build-up) in the abdominal and/or leg
regions.
In comparison, the results for the two patients, PA and PB,
show that:
(1) As with the normals, the most rapid loss was from the
chest region.
(2) The initial loss from the head region is more rapid than
that shown by the normals. Patient PA shows the lowest retention in
the head region of all four subjects. The data for PB suggests a
progressive build-up in this region after 48 hours.
(3) Patterns of the abdominal-regional curves differ between
patients to a greater degree than those of the normals. Patient PA's
curve is not distinguishable from the normal subjects, PB shows a
striking build-up in this region beginning at 24 hours and at 165 hours
reaches a level 2 1/2 times that of the other subjects.
(4) Leg-region curves for the patients are similar to those
of the normals but show a more rapid loss. PB appears to lose a greater


4>
ON
Figure 6. One Side of the 4-Pi Liquid Whole-Body Counter Showing Six Photomultiplier Tubes
and Steel Shield.
Bl


SUBJECT: PE
STUDY GROUP: 3
DATE, TIME OF INJECTION: 10-28-69, 9:23 DOSE: 9.061 yCi
Time After Injection
Cumulative
Excretion*
Excess or
(Hours)
Retention*
Urine
Feces
Balance*
Deficit*
0.7
100
-
-
100
10.4
99
8
-
07
+7
23.9
95
12
-
107
+7
47.8
95
18
-
113
+13
71.8
89
22
-
111
+11
96.3
84
26
-
110
+10
143.8
76
34
-
110
+10
167.7
74
36
-
110
+10
191.8
78
40
-
118
+18
215.7
73
46
-
119
+19
*Expressed as per cent
, rounded off
to the
nearest
whole number

- Means not measured


84
were reported on the constants determined for their retention equation.
In addition, only seven points of per cent whole-body retention versus
hours after administration were used to calculate the retention equation.
This small number of points would give a lower degree of confidence for
prediction of any of the four constants in the retention than that in
this study.
In addition to comparisons of the 28Mg biological half-lives,
one can compare the excretion rates of the isotope in this study to
those determined by other investigators. Table 4 summarizes the excreta
results of this study and presents them for the comparison to other
published reports. The urinary excretion for all investigators is quite
consistent. Fecal excretion has only been measured by two other investi
gators; one of these, Yun et clL_, report a single value at 70 hours.
The results of this study are about 1 1/2 times those reported by the
two other investigators. Again, the measurement period in this study
was 220 hours compared to 134 hours by Avioli e_t al. and lesser times
by the other investigators.
Calculation of Radiation Dose
This study and those of others cited here demonstrate the
potential for using 28^jg studies of magnesium's function and behavior
in humans. Magnesium-28 is currently more available than it was previ
ously and soon will be produced in a carrier-free form (211). Conse
quently, it is expected,that its use in human experimentation will
increase significantly.
In all studies where a radionuclide is administered to humans,
one must precede the experimental work with an estimate of the radiation
dose. Radiation dose calculations for ^Mg have typically been based on


63
The retention results for study groups 1 and 2 define a
fairly smooth, continuous function and have little within-group varia
tion. In contrast, in groups 3 and 4 there is more within-group
variation and, particularly in group 4, there is a greater departure
from a smooth function. In study group 7, there is good agreement in
the results of the two individuals and it is significant that the data
again more closely resembles that of groups 1 and 2.
Some of the differences in the results of the study groups
can be attributed to differences in instrumentation. The 400-channel
analyzer was used for study groups 1, 2, and 7, while the three-channel
analyzer was used for groups 3 and 4. It appears that there is more
precision in results when the 400-channel analyzer is used. This
assumption is supported by the fact that while resolving losses were
evident for initial high count rate measurements with the three-channel
analyzer, this was not the case for the 400-channel analyzer even with
doses as high as 10 yCi. In addition, the computational steps required
to make resolving loss corrections automatically introduces another
component of variance in the data for groups 3 and 4. Finally, any
error introduced in applying the resolving time corrections would affect
the results in two ways. The magnitude of the high count rate obser
vations would be directly affected and also all of the observations
would be affected because the value at t = 0 (see page 59) is used as
a denominator in computing each retention value.
However, in spite of the greater variability in some of the
study groups, the average retention values are approximately the same
in all groups.


102
It was in these groups that patient deficits were observed in the total-
measured 2£*Mg determinations. One explanation for a deficit in the
measurements would be incomplete collection of excreta. Although this
cannot be discounted, it is unlikely that in a patient like PB that it
would happen in both study groups 1 and 2 in such a reproducible manner.
The deficit and excess patterns are shown primarily by the
neuromuscular patients in the first case and the patients on or suspected
of being on diuretics in the latter. It appears then that these anoma
lies may be related to clinical conditions. Abnormal relocation of
the 2^Mg isotope in the body has been produced experimentally in a
phantom which simulates an adult human. If this were to occur in a
patient, counting efficiency would be altered to an extent which will
produce the magnitude of excess or deficit seen in this study. It is
possible that the isotope is being routed in large, atypical amounts to
the peripheral blood stream, to fluid of the peritoneal cavity, or to
some internal structure such as bone.
In spite of some of the uncertainties associated with these
results, a pattern of atypical behavior evolves that has a striking
consistency within the disease conditions studied. Specifically, the
following observations can be made:
(1) The patients with ALS (both of unknown origin and due to
gastrectomies) have lower than normal whole-body retention of 28y¡g.
(2) Some of these patients have an unusual retention curve
that drops precipitously around 100 hours after injection. ALS patient
PA did not show this pattern until his last measurement this may be
associated with progression in the disease.


AVERAGE-ALL SUBJECTS
2
Mg Average of Ail Normals.
Figure 24. Total-Measured


29
magnesium) to study the effect of 2,4-dinitrophenol (190) and sodium
salicylate (191) on magnesium metabolism in the rabbit. About the same
time, Aikawa (192) published a review of "recent developments" in the study
of the role of magnesium in biologic processes. He emphasized that 28]*^
although expensive and in short supply, had already contributed substanti
ally to the knowledge concerning the dynamics of magnesium turnover. He
concluded that:
In the final analysis, the ultimate explanation of the fact
that the magnesium ion alone is operative in such diverse but
fundamental cellular processes must be based on the unique
atomic structure of this element. Just how it is unique remains
to be ascertained.
In 1966, Wallach et al.(13) expanded on their study of magnesium in
normal and uremic patients. They gave intravenous injections of 28Mg with
a specific activity of 16 yCi per mg of magnesium to six control subjects
and to six patients with chronic renal disease and moderate to severe
azotemia. The authors utilized conventional analog and digital computer
techniques to analyze plasma concentrations and urinary data. From the
results they proposed a three-compartment model for magnesium transport
in humans.
A similar approach for evaluating magnesium dynamics jLn vivo
was reported by Avioli and Berman (5) in 1966. Using a 28p[g preparation
with a specific activity of =11 yCi per mg magnesium, these workers
observed the levels of activity in the plasma and excreta in 15 normal
volunteers up to six days after injection. Plasma disappearance of 28^g
was fitted to a sum of three exponentials model.
In 1966, Yuri et al. (11) reported a study of turnover of
magnesium in controls and in patients with idiopathic cardiomyopathy
and congestive heart failure. They said that the reason that the daily


LIST OF REFERENCES
1. O. W. Holmes, The Professor at the Breakfast Table, Houghton
Mifilin and Co., New York, 27 (1891).
2. E. H. Widdowson, R. A. McCance, and C. M. Spray, "The Chemical
Composition of the Human Body," Clin. Sci., 10:113 (1951).
3. M. Mori, R. Chiba, A. Tani, H. Aikawa, and N. Kawai, "The Production
of Radioisotope 2Mg," Int. J. Appl. Rad, and Isotopes, 18:579 (1967).
4. J. K. Aikawa, G. S. Gordon, and E. L. Rhoades, "Magnesium Meta
bolism in Human Beings," J. Appl. Physiol., 15:503 (1960).
5. L. V. Avioli and M. Berman, "28Mg Kinetics in Man," J. Appl.
Physiol.,21:1688 (1966).
6. A. J. Steiner, "Medical View of Magnesium in Nutrition," J. Appl,
Nutr., 21:11 (1969).
7. I. Clark, "Metabolic Interrelations of Calcium, Magnesium, and
Phosphate," Amer. J. Physiol., 217:871 (1969).
8. I. MacIntyre, "An Outline of Magnesium Metabolism in Health and
Disease A Review," J. Chron. Pis., 16:201 (1963).
9. R. Sheline and N. Johnson, "New Long-Lived Magnesium-28 Isotope,"
Phys. Rev., 89:520 (1953).
10.J. K. Aikawa, E. L. Rhoades, and G. S. Gordon, "The Urinary and
Fecal Excretion of Orally Administered Magnesium-28," Soc. Expt.
Biol, and Med. Proc., 98:29 (1958).
11. T. K. Yun, R. Lazzara, W. C. Black, J. J. Walsh, and G. E. Burch,
"The Turnover of Magnesium in Control Subjects and in Patients
with Idiopathic Cardiomyopathy and Congestive Heart.Failure Studied
with Magnesium-28," J. Nuc. Med., 7:177 (1966).
12. J. K. Aikawa, University of Colorado, School of Medicine, Denver,
Colorado, Personal Communication.
13. S. Wallach, State University of New York, Downstate Medical Center,
Brooklyn, N. Y., Personal Communication.
14. E. C. Wacker and Bert Vallee, "Magnesium Metabolism," New Eng. J, Med.,
259:475 (1958).
158


TABLE 1
SUMMARY OF STUDY GROUPS
2^Mg Time
Group No.
Number of
Subjects
Administered
Excreta
Followed
(yci)
Measured
(days)
Normal Other
Total
1
2
2
4
1.27
Urine
7
2
3*
3**
6
10.00
Urine
10
3
3
3
6
9.30
Urine
10
4
5
0
5
6.60
Urine
10
5
0
2
2
9.70
Urine,feces
10
6
0
4
4
5.50
Urine,feces
10
7
2***
2 & >'<
4
10.00
Urine,feces,
10
sweat
Total
15
16
31
^Includes
replication of
one
normal subject
from
group 1.
**Inc.ludes
replication of
two
patients from ,
group
1.
***Includes
replication of
one
normal subject
from
group 4.


TABLE 4
COMPARISON OF CUMULATIVE EXCRETION RESULTS OF PERTINENT 28Mg STUDIES
Cumulative Excretion (Per Cent of Dose) in Hours After Injection
Investigator
44
48
70
Urine
72
120
134
220
48
70
Feces
72 96
134
220
Roessler
9.0
9.3
12.0
13.5
15.0
16.7
27.9
2.0
2.5
2.5
3.0
4.3
5.0
Avioli et al.
(186)
Yun et al. (11)
7.3
10.6
10.7
11.6
16.9
1.8
1.4
1.2
2.6
Wallach et al.
(189)
Raynaud,
Kellershohn (194)
10.4
16.0
1.7


136
SUBJECT: NK STUDY GROUP: 4
DATE, TIME OF INJECTION: 1-6-70, 16:04 DOSE: 6.630 pCi
Time After Injection
(Hours) Retention*
Cumulative
Excretion*
Urine Feces
Excess or
Balance* Deficit*
0.5
99
-
-
99
-1
6.0
94
6
-
100
17.9
81
11
-
92
-8
41.9
88
16
-
104
+4
65.1
81
19
-
100
90.0
84
24
-
108
+8
138.3
o
76
30
-
106
+6
161.8
71
33
-
104
+4
185.6
67
40
-
107
+7
209.7
62
42
-
104
+4
233.5
62
43
105
+5
*Expressed in per cent, rounded off to the nearest whole number.
- Means not measured


82
(a combination of total dose and the specific activity of the prepara
tion) the number of hours followed, the sample measured, and the
results.
The most obvious conclusion that can be made from Table 3 is
that there is no consistency in the results from one study to another.
This could be due to differences in the other parameters tabulated on
the various studies. It can be seen from the Table that in this study
all of these parameters were equal to or better than those of the other
investigators. Of particular importance is the very small amount of
magnesium (0.3 mg) administered. This is many times less than that
given by any other investigator. The total hours that one is able to
follow the activity after administration is also of prime importance
since the total measurement time greatly affects the accuracy of the
determination. This is important primarily in the determination of
turnover times of the longer half-life compartment(s).
Probably the most significant contribution of this study is
that whole-body retention measurements were made directly. The use of
the 4-pi whole-body counter made this possible. Other investigators,
who do not have access to this counting equipment, have to rely on
plasma turnover and/or excretion to estimate whole-body retention. Of
significance also is the fact that excreta measurements which were made
in this study essentially verified the whole-body turnover at all times
28
after administration of the Mg.
It is interesting at this point to examine in more detail
the study by Chon et_ al. (Table 3). Although measurements were made
by these investigators up to 120 hours after administration compared to


121
COMPUTATION OF RADIATION DOSE
-Using MIRD Method (214)
and Biological Half-Life Determined in this Study-
A. Given:
1. Isotope 28]yig,
2. Critical organ whole body.
3. Administered activity 1 pCi.
4. Physical half-life 21.3 hours.
Biological half-life two components:
a. Uptake of 8.5 per cent with 5.4-hour half-life.
b. Uptake of 91.5 per cent with 540-hour half-life.
Assumptions:
1. Mass of whole body is 70 kilograms.
2. Shape of body is ellipsoidal.
3. Activity is uniformly distributed.
B. Dose Equations average dose to self-irradiated organ (214).
D
y
m L
A 4>
i i
rad.
Where A = cumulated activity, pCi hrs.
m = mass of critical organ, g.
Ai= equilibrium dose constant, g rads/pCi hr.
absorbed fraction for ith radiation in organ.
0.085 x 4.3 =0.53 pCi hrs.
0.915 x 20.49 = 26.99 pCi hrs. '
pCi = 0.085 pCi,
pCi = 0.915 pCi,
half-life, defined previously.
Teff! = (21*3 x 5.4)/(21.3 + 5.4) hrs = 4.3 hrs.
Teff2 = (21.3 x 540)/(21.3 +540) hrs = 20.49 hrs.
In the case of a two-component model:
'Xi 'Xj 'Xj
A = A^ + A£
= 1.44(Aq)^ x 1.44 x
X2 = 1.44(Aq)2 x Teff2= 1.44 x
Where: (A0)^ = 0.085 x 1
(A0)2 = 0.915 x 1
Te££ = effective


150
SUBJECT: PI STUDY GROUP: 6
DATE, TIME OF INJECTION: 4-8-70, 10:02 DOSE: 5.307 yCi
Time After Injection
(Hours)
Retention*
Cumulative
Excretion*
Urine Feces
Blarice*
Excess or
Dficit*
0.9
100
-
100
24.3
96
10
0
106
+6
48.7
92
15
0
107
+7
72.7
89
18
2
109
+9
120.9
81
23
4
108
+8
145.4
77
25
4
106
+6
169.0
74
26
4
104
+4
193.4
74
26
6
106
+6
217.2
64
26
6
96
-4
241.6
64

-

^Expressed as per cent
:, rounded off
to the
nearest
whole number.
- Means not measured


26
diet containing stable magnesium and at weekly intervals made an esti
mate of total-exchangeable magnesium using 2S^g and an isotope dilution
method. At the end of the' experimental period, various tissues were
analyzed for magnesium. The deficient diet caused a slight loss in
body weight, a decrease in serum magnesium, a decrease in urinary magnes
ium excretion, and a progressive decline in total-exchangeable magnesium.
However, the magnesium content of muscle, skin, kidney, heart, and liver
did not change; that of the lung fell by 25 per cent and that of bone
by only 15 per cent.
This work by Aikawa and his group(181) prompted several perti
nent comments in an editorial on magnesium metabolism in 1962 in Nutri
tion Reviews (182). The editor commented that:
(1) It is unfortunate that carrier-free 28^g is not available
and
(2) . had a true magnesium balance been made (by Aikawa),
it would have been possible to interpret the data on
total-exchangeable magnesium in a more meaningful way.
Studies with ^Mg the cirrhotic and the alcoholic followed
naturally from the background information reported by Flink (88) and
others on the possibility of magnesium deficiency in these conditions.
Martin and Bauer (183), having found no clear-cut correlation of sympto-
malogy with serum levels of magnesium in these disease states, attempted
to assess exchangeable magnesium using ^Mg. The preparation used to
study seven controls, five cirrhotics, and four acute alcoholics was of a
much higher specific activity (-30 pCi per mg magnesium) than had been
used previously. Four of the five cirrhotics and all of the acute alco
holics had exchangeable magnesium values below normal.
The higher specific activity 28^g was also used by Lazzara's


who previously exhibited an apparent precipitous whole-body loss of
28Mg.
Based on published investigations to date, it is concluded
that this turnover study is currently the most accurate. The use of a
true tracer dose of 10 microcuries or less of high specific activity
o o
Mg and the sensitive whole-body counting system allowed administration
of a dose which would not upset the physiochemical balance of the body.
Also, this procedure permitted measurements up to six times longer than
previously reported studies.
The amount of 28Mg to be administered in future investigations
with this isotope should be guided by the 2.0 mrad/microcurie dose
calculated from the data obtained in this study.
Based on the consistent, significantly abnormal retention
and excretion patterns shown by certain disease-state measurements in
this study, it is concluded that this turnover procedure could serve
as a valuable adjunct to other diagnostic techniques.
xi


Abstract of Dissertation Presented to the Graduate
Council of the University of Florida in Partial Fulfillment
of the Requirements for the Degree of Doctor of Philosophy
WHOLE-BODY RETENTION AND EXCRETION OF MAGNESIUM IN HUMANS:
I. BIOLOGICAL HALF-LIFE IN NORMALS AND SELECTED DISEASE STATES;
II. RADIATION DOSIMETRY
by
Genevieve Schleret Roessler
March, 1972
Chairman: Billy G. Dunavant, Ph.D.
Co-Chairman: W. Emmett Bolch, Ph.D.
Major Department: Environmental Engineering
Thirty-one whole-body retention and excretion measurements
were made on 13 normal subjects and 12 patients with selected disease
conditions to determine as accurately as possible the biological half-
lives from a single intravenous administration of ^%ig in the form of
MgClg. The prime objective of this research was to contribute informa
tion to the currently sparce knowledge on magnesium metabolism in
humans. Calculation of radiation dose based on the determined half-
lives was an important aspect of the research since the experimental
use of 28pig is increasing rapidly and no dose estimates have been esta
blished. The feasibility of this measurement technique for studying
abnormalities in disease conditions was also explored.
A high specific activity (200-300 microcuries per milligram
magnesium) preparation of the radioactive isotope 28Mg (21.3-hour
physical half-life) was uped in conjunction with the sensitive 4-pi
liquid scintillation whole-body counting technique for retention
measurements. A Nal(Tl) crystal whole-body counter was employed to
measure localization of the magnesium in the body and appropriate low-
level counting systems were used for measurement of the isotope in
excreta.
ix


27
group (184) to evaluate magnesium tissue distribution, kinetics, and
turnover in dogs. In 1962, they reported that important tissues which
did not reach equilibrium after injection of the isotope were the brain
and spinal cord, cortical bone, and skeletal muscle.
Ginsburg, Smith, Ginsburg, Reardon, and Aikawa (185) continued
research of magnesium metabolism in humans and in rabbits and, in 1962,
reported on results of a study in which they attempted to: (1) devise
a reliable method for determining magnesium in erythrocytes; (2) relate
erythrocyte magnesium concentration to reticulocyte count; (3) study the
in vitro uptake of 28yjg by erythrocytes; and (4) study the 28>ig uptake of
various tissues in experimental animals with reticulocytosis induced by
phenylhydrazine. This approach was undertaken because these investi
gators felt that the "current paucity of information concerning magnesium
metabolism in erythrocytes is due in part to the lack of a reliable method
for determining magnesium in red cells and in part to the fact that a
radioactive isotope of magnesium suitable for tracer studies has only
recently become available."
In 1963, Avioli, Lynch, and Berman (186) reported the first
study in a series on 28^g kinetics in normals and selected disease states.
They gave intravenous doses of a relatively high specific activity ^Mg
(-17 yCi per mg magnesium) to 10 normal subjects, five patients with
Pagets disease, three hypothyroid, and five hyperthyroid patients. A
digital computer compartmental analysis technique was used to identify and
quantitate exchangeable magnesium in bone, in extracellular fluid, and in
muscle.
Also in 1963, Petersen (187) described the close relationship