36
boundper mole TBG,the expected ratio is 777000
#g/57000 mg = 13.6. The results of these analyses
are summarized in Table 30 and Figure 40. There
was no significant difference in TBG between the
Rongelap and Utirik groups or between the exposed and unexposed Rongelap groups. Eight subjects had high TBG levels. These were all females,
and five were known to be pregnant, a condition
that can elevate the serum TBG.
The results of these analyses provide no explanation for the difference in serum Ts concentrations between the larger groups of Rongelap and
Utirik subjects; however, these results are based
on highly selected sampling and therefore are not
representative of the island groups as a whole. Examination of individual Utirik and Rongelap
plasmas suggested that low T4 concentrations
were associated with relatively low TBG values.
To study the interrelationship of T4 binding and
TBG levels in greater detail, the dialyzable frac-
tions of T, (DFT4) were determined in a number
of plasma samples with low, normal, or elevated
TBG-binding capacities. The results are presented
in Table 31. In subjects with low TBG, the mean
DFT, was greater than in subjects with normal or
elevated TBG. The absolute free T4 was not dif-
ferent in the three groups, which indicated that
the abnormal T, levels among these subjects reflect alterations in plasma hormonebinding rather
than in thyroxine production rates. Since virtually
all the subjects with low plasma T, concentrations
in the larger Utirik and Rongelap groups had normal plasma TSH, we would expect a moresystematic study of TBG levels by RIA to show a
higher frequency of low TBG levels in the Utirik
group. Sucha studyis currently in progress.
F. IODOPROTEIN STUDIES
Analyses for protein-bound iodine in sera of
Marshallese people revealed a level significantly
higher than that seen in North America.!8.29 Subsequentstudies showedthat this elevation could be
attributed to an increase in the iodoprotein fraction and indicated that this was responsible for incorrect evaluation of thyroid function during the
early years of the surveys. This unusualfinding
promptedusto determine serum iodoprotein levels
in several other Pacific Islands groups (see Table
32). Except for a group of Americans living on
Kwajalein Atoll, these groups also exhibited high
serum levels of iodoprotein. The Maui group was
comprised ofpersons of almost pure Hawaiian ancestry, some of whom ate seaweed in large quantty, but the iodoprotein level did not correlate
with this dietary intake. In the Rongelap population, it 1s of interest that the iodoprotein levelre-
mained high in two athyreotic boys; after subtotal
thyroidectomy; and during thyroid suppression by
thyroxine administration.?° This strongly implies
an extrathyroidal (endogenous) or a dietary (exogenous) source for the iodoprotein. The cause of
the elevation, however, has not been ascertained.
One possibility is that it is produced in polymorphonuclear leukocytes. These cells are known
to organify iodine during phagocytosis.9! Although
the Marshallese do not have unusually high leu-
kocyte counts, they do have a mild eosinophilia
Table 32
Serum Iodoprotein Levels (4g %) in Pacific Island Populations and in Americans
Group
Rongelap exposed
No thyroid nodules
Thyroid atrophy
Thyroid nodules, pre-op
After partial thyroidectomy
After total thyroidectomy
Ailingnae
Utirik
Rongelap unexposed
No. in group
10
Total I
7.22.4
Tal
Iodoprotein
4021.0
2541.1
2
7
3
2.80.4
8.33.6
S.I+1.1
1.2405
3.61.1
44-18
1.300
4.239
2.62.0
4
5
24
7.81.2
16.1+89
8.742.8
3.7+0.8
3.8408
4.01.0
3.341.7
3.3417
4.63.5
4121.1
2.2408
3
6041.1
2.6+0.1
Kapingamarangi
Pingalap
23
27
11.543.0
8.42.0
6.2%2.6
3.6--0.6
Americans: Kwajalein
12
6641.3
3.91.1
Hana(Maui)
US.
13
9
6.71.3
6.44%1.3
4.1205
2.9=1.2
3.00.6
3.3419
1.905
1.11.0