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trols from the Eastern United States, who showed
0.80 ug% iodoprotein iodine in their serum, suggest that it is a normal, albeit minor, constituent.
The method of chromatography employed is such
that well under 5% (or 0.2 ug%) of serum thy-
roxine iodine appears in the unretardedor iodoprotein fraction. Therefore, the finding of iodoprotein does not appear to be a methodologic
artifact.
Morerecently, with the developmentof thyroid
abnormalities in the exposed Marshallese (to be
described), it was possible to examine serum iodoprotein levels in cases with thyroid hypofunction.
These data are presented in Table 16. It seems
likely that the source of the iodoprotein waslargely
extrathyroidal, since the levels of iodoprotein were
Table 16
Serum lodoprotein Levels in Relation
to Thyroid Function
Subject
No.
Total
iodine,
gi
PBI,
gt
7, iodine,
ugZe
lodoprotein
iodine,”
ug
Hypothyroid
3
5
3.2
1.0
(2.2)
3.1
1.9
(1.2)
3.1
65
1.8
(1.3)
Thyroidectomized**
17
1.8
64
5.0
2]
69
<0.5
(>1.3}
1.3
<0.5
(>0.8)
5.7
17
(4.0)
2.0
2.9
L-Thyroxine Treatedt
34
59
68
10.8 {9.1]
8.6 [8.2]
11.8 [7.1]
6.5 [4.6]
4.8 (5.3}
5.8 [4.6]
3.2 [4.5]
3.8 [2.9]
6.0 [2.5]
*Iodoprotein Jevels in parentheses represent the difference between PBI and 7,levels. The others were mea-
sured directly by the column method.
**:-Thvroxine stopped several weeks before sampling.
tTreated with c-thyroxine, 0.2 mg per day, for 6
months. Values in brackets are determination made prior
to Starting thyroxine treatment (1965).
2008312
near the normally high Marshallese values (a) in
cases which had been on suppressive thyroxine
therapy, (b) in cases with atrophic glands due to
radiation (subjects No. 3 and No. 5), and (c) in
thyroidectomized cases. The source of the iodoprotein is not known. Thepreviously reported finding
of high plasma proteins,® particularly gamma
globulins, in the Marshallese is of interest but may
be an unrelated phenomenon. It wil] be important
to see in future studies whether the iodoprotein
can be labeled with radioiodine.
The data on urine iodine show values in the
normal range. In general, it had been expected
that individuals living close to the sea and eating
seafood and fish would show relatively higher
iodine intake. The inhabitants of the Marshall
Islands have fish as one of their main sourcesof
animal protein. Furthermore, these people are
constantly exposed to sea spray, since the island
at its widest is about 4 mile across, and its highest
point is 20 ft above high tide.
The data on urinary iodine were used with the
results obtained with '°°I studies to calculate the
amount of iodine secreted daily by the thyroid.
The value 76 wg/day is somewhathigher than the
57 ug/day found by Stanbury etal.** or 58 ug/day
found by Freinkel and Ingbar*® but closer to the
value 70 wg /day proposed by Riggs.*’ Unfortunately, nothing is known abouttherate of turnover of the serum iodoprotein. If it has roughly the
same rate of degradation and the same volume of
distribution as thyroxine andit is assumed to have
its origin in the thyroid gland, then one would expect the Marshallese thyroids to secrete organic
iodine proportional to the level of organic iodine
in their serum. Addition of iodothyroxine values
to iodoprotein iodine levels for both Marshallese
and Americans and multiplication of the ratio by
the best value for iodine secreted by normal
Americansresults in
2,92 +4.53
This agreesfairly well with the 76 pg/day calculated independently from urine and radioiodine
studies and is compatible with the clinical picture
of a euthyroid status in spite of an elevated PBI
and elevated thyroid iodinesecretion rate. How-
ever, as noted above, it seems somewhat morelike-
ly that the serum iodoprotein is not of thyroidal
origin.
ee MEPee ee ee SR ee
devoid of physiological activity. Hence an iodoprotein containing only these iodoamino acids1s
likely to be also physiologically inactive. The
reason these individuals have such an iodoprotein
in the blood is not clear. The data on normal con-
tg a,
28°