Summary of iodine physiology and metabolic studies using radioactive isotopes of iodine

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Title:
Summary of iodine physiology and metabolic studies using radioactive isotopes of iodine
Series Title:
United States. Atomic Energy Commission. MDDC ;
Physical Description:
3 p. : ill. ; 27 cm.
Language:
English
Creator:
Hamilton, J. G
University of California
U.S. Atomic Energy Commission
Publisher:
Technical Information Division, Oak Ridge Directed Operations
Place of Publication:
Oak Ridge, Tenn
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Subjects

Subjects / Keywords:
Iodine in the body   ( lcsh )
Iodine -- Isotopes -- Metabolism   ( lcsh )
Iodine -- Metabolism   ( lcsh )
Iodine -- Physiological effect   ( lcsh )
Iodine Radioisotopes   ( lcsh )
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federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Bibliography:
Bibliography: p. 3.
Restriction:
"Date Declassified: June 25, 1947"
Statement of Responsibility:
by J.G. Hamilton.
General Note:
Manhattan District Declassified Code
General Note:
"Date of Manuscript: October 18, 1944"

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University of Florida
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 005023955
oclc - 277770361
System ID:
AA00009280:00001


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MDDC 1060



UNITED STATES ATOMIC ENERGY COMMISSION


' '


SUMMARY OF IODINE PHYSIOLOGY AND METABOLIC STUDIES

USING RADIOACTIVE ISOTOPES OF IODINE



by
J.G. Hamilton


University of California


,'E PF CL L:B





\ DEPOSITORYR


This document consists of 3 pages.
Date of Manuscript: October 18, 1944
Date Declassified: June 25, 1947


This document is for official use.
Its issuance does not constitute authority
for declassification of classified copies
of the same or similar content and title
and by the same authorss.




Technical Information Division, Oak Ridge Directed Operations
Oak Ridge, Tennessee


















SUMMARY OF IODINE PHYSIOLOGY AND METABOLIC STUDIES


USING RADIOACTIVE ISOTOPES OF IODINE


By J. G. Hamilton


INTRODUCTION

An excellent summary of the overall picture of iodine physiology has been compiled by Salter.'
The total body content of iodine in adult humans over most regions of the world ranges from 20 to 50
milligrams of which approximately 1 5th is present in the thyroid whose weight will average 25 g.
Iodine in blood and tissue fluids is said to be somewhat less than 0.1 milligram per kilo. The value
for muscle is stated to be of the order of J milligrams per kilo and comparable levels are indicated
for the endocrine organs such as the pituitary, ovaries, adrenal cortex, and parathyroid glands.

The intake of iodine per day is, of course. extremely varied and may range from less than 10
micrograms per day to almost a milligram per day. It is stated that in geographical regions of rela-
tively low iodine content that approximately 25''i of the eliminated iodine is excreted by way of the
lungs, 50'19 via kidneys, and the remaining by way of the skin and hair. In the fasting state the fecal
excretion is negligible. These values are conjectural to a certain degree and are only indicative of
the endogenous metabolism of individuals who can be said to be in a state of iodine balance


TRACER STUDIES WITH RADIOIODINE

A study of the absorption and excretion in normal human subjects indicates that this element ia
rapidly absorbed and rapidly eliminated.' When from 50 to 100 milligrams of iodine are given orally
to normal adult human subjects in the fasting state, approximately 50"C, is absorbed within the first 15
minutes from the digestive tract and within I 1. 2 hours over 90, has been absorbed When a labeled
dose of 14 milligrams is given to normal human adult subjects the iodine is almost exclusively ex-
creted by way of the kidneys at an exponential rate, the half time being approximately 18 hours.3 The
uptake by the thyroid under these conditions for normal adult subjects averages 4'. These values
have been confirmed by Chaikoff and his colleaguess in rats using radiolodine with inert carrier in
comparable quantities. They made a careful analysis of the concentration of iodine in the soft tissues
of the body, notably the small intestine, liver, and kidney and found that the disappearance of iodine
from these tissues was closely paralleled by the fall f[ labeled iodine in the blood. At the end of eight
days the ratio of concentration of the iodine taken up by the thyroid to that in the soft tissues was the
order of I(P, when the radioiodine employed had no added carrier. In these experiments the iodine
concentrated in the endocrine organs was also investigated and lound in .ll instances to be comparable
to the iodine content of the blood and soft tissues noted previously. His group also made a detailed
study of the uptake of iodine by the thyroid in rats, rabbits, sheep, and guinea pigs With the exception
of the rat. the average uptake by the thyroid gland of radiolodine without inert carrier at the end of 24
hours was approximately 20'-. In the case of the rat the uptake was considerably greater and frequent
levels in excess of 657'. were encountered. Comparable studies with human subjects have given a value
of 20% uptake for normal adults when iodine without carrier was used.'

It is of considerable interest to note that at the end of 26 hours in both the thyroid and in the blood
plasma approximately 90'. of the radioiodine, when administered without carrier, has been converted
into di-iodotyrosine and thyroxine.' It will be remembLered that these two organic iodine compounds


MDDC 1060










MDDC 1060


.00001 .0001 .001 .01 .1 1 40 100


MG IODINE PER KG OF BODY WEIGHT


Figure 1.








MDDC 1060


are amino acids, and are incorporated into thyroid protein, thyroglobulin, which, of course, comprises
the principal protein in the thyroid colloid. This must, at least in part, explain the tenacity with which
the thyroid holds its accumulated iodine and the difficulty with which the iodine thus stored can be
washed out with the administration of inert iodine.
In normal human subjects, when iodine without carrier was administered by mouth, the 200,:, which
accumulated in the thyroid was retained for many weeks without significant loss.
The very important relation of the thyroid uptake of iodine to the total quantity of iodine given in
test doses is summarized in chart form (Figure 1). The values are taken from Chaikoff's work with
rats,'s, the experience of the author with human subjects at U. C. Hospital,2'3"1 the experiments of
Hertz7 and his assistants using rabbits, and the studies with rats reported by LeBlond." The very
rapid increase of iodine uptake by the thyroid with the decrease of weight of administered iodine is
clearly apparent.
It has been the experience of the author that the prior administration of iodine in man almost
completely blocks the ability of the thyroid to accumulate radioiodine even when given in a total of
less than 10-7 grams of iodine. The time relationship between the administration of inert iodine and
the subsequent tracer dose of radioiodine was never carefully studied with respect to the blocking ef-
fect of the inert iodine upon the thyroid. However, it was apparent that this action of iodine lasts for
a period of at least several weeks.
The destructive effect of carrier-free iodine upon the thyroid tissue of rabbits and dogs without
perceptible radiation effects upon any other tissues has been demonstrated.' Complete destruction of
the entire gland without either physiological or histological changes to the parathyroids in rabbits and
dogs has been observed. The quantity of radioiodine required was 300 microcuries of I'S per kilogram
which produced a thyroid irradiation of over 25,000 r. Smaller amounts of radioiodine without inert
carrier have been employed in the treatment of a few cases of hyperthyroidism with complete and pro-
longed remission of all of the clinical evidences of this type of thyroid disorder. The dose required
ranged from 1 to 1.5 millicuries of I'1 (20 to 30 microcuries per kg of body weight). The internal
thyroid irradiation was estimated to have been from 1000 to 3000 r.


PROTECTION ASPECTS

In order to protect personnel from absorbing radioiodine from the atmosphere it is estimated
that 100 milligrams of potassium iodide should be taken each day. This amount should thoroughly
block absorption by the gland of any significant amount of radioiodine.


REFERENCES

1. Salter, W. T., The Endocrine Function of Iodine, Harvard University Press, p 113, 1940.
2. Hamilton. J. G., Amer. Jour. of Physiol. 124:667 (1938).
3. Hamilton, J. G. and M. H. Soley, Amer. Jour. of Physiol. 127:557 (1939).

4. Hamilton, J.G., Radiology 39:541 (1942).

5. Perlman, J., 1. L. Chaikoff. and M. E. Morton. J. Bioi. Chem. 139:443 (1941).
6. Morton, M. E., J. Perlman, and I. L Chaikoff, J. Biol. Chemistry 140:603 (1941).

7. Hertz, S., A. Roberts. J. H. Means, and R. D. Evans, Amer. Jour. of Physiol. 128:565 0.940).
8. LeBlond, C. P., Revue Canadienne de Biol. 1:402 (1942).




UNIVERSITY OF FLORIDA
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