i
~J
Table {5
t2
1
Kinetic Studies With '!-I
NO, OF CASES
|
|
6:
Zz
foi
|
a
a
- 1
iG
aon
jo
LE
r—
4
.
ad
6
PROTEIN -~ BOUND
‘GO
iODINE, ug %
l2
Figure 21.
creased the backgroundslightly. Mathematical
analysis* of these data was done on an IBM 7094
computer with the program of Berman etal.** No
experimental correction was madefor extrathyroidal radioactivity “seen” by the counter, since
the computer program adjusted the readings over
the neck for this factor. A least-squares best fit, assuming exponential thvroid uptake and renal excretion of iodide, produced a “best” value for this
factor, termed 03,.
The results of the studies with '**I are shown in
Table 15, where they are compared with values
obtained from normal individuals residing in the
United States. It can be seen that the rate of thyroid uptake andthe rate of urinary excretion are
both decreased. Since they are decreased more or
less proportionately, the calculated asymptotic up-
take is normalorslightly elevated. One may use
these data plus the urine iodide values to calculate
the average daily secretion of thyroid hormone,
assuming steady state conditions, using the formula
EU
°=T=U
where
S = amount ofiodine secreted by the thyroid
(ug/day),
U’ = fractional thyroid uptake of iodine, and
& = urinary iodine (g/day).
With E = 105 pg/day and U=0.42, the value for §
is calculated to be 76 pg iodine/day. This valueis
*We are indebted to Dr. Mones Berman, National Institutes
of Health, Bethesda, for this analysis.
Group
As*
Ay,**
Marshallese
U.S. normals
0.72
1.0
0,97
2.0
Theoretical
No.
uptake
a;,,+
cases
42%
33%
0.08
~
2]
-
*Fraction of extrathyroidal iodide transferred to the
thyroid per day.
**Fraction of extrathyroidal iodide excreted in the urine
per day.
tValue derived by the computer for the fraction of
extrathyroidal iodide “seen” by the counter.
somewhathigher than similar ones calculated for
other groups but is not extraordinarily high.** °
Serum Cholesterol. Serum cholesterol determinations on most of the exposed and an equal num-
ber of the unexposed population were carried out
in 1957 and 1959. Theresults are tabulated in Appendix 5. Although the cholesterol levels in the
exposed group are about 17% below the levels in
the unexposed group, the difference is not quite
significant at the 5% level. Individual values were
not indicative of thyroid disease.
Discussion of Previous Thyroid Studies.
Until
the recent developmentof hypothyroidism in two
boys, it had been the concensus ofail physicians
who examined these people that they were euthy roid. A conceivable explanation for the high PBI
could be an elevation of thyroxine-binding proteins in serum which, as in the congenital elevation of thyroxine-binding globulin described hy
Beierwaltes and Robbins,** causes an increasein
the serum PBI without hyperthyroidism. The
levels of the TBG in the Marshallese serum meuasured by Robbins, however, were within normai
limits. The discrepancy between PBI and BEI suggested the presence of an iodoprotein in serum
The chromatographyof serum iodine showing an
iodoprotein level in the Rongelap people of 2 ue% (and higher in the Utirik people} seems t»
implicate the iodoprotein as the cause for the ¢lrvated PBI.
No adequate data are available on the calorgenic potency of serum iodoproteins, but there are
someresults which show that mostof the iodinated
aminoacidsin this protein are monolodotyresine
and diiodotyrosine.*’:*° These iodoamino acids are