56
bound per mole TBG, the expected ratio is 777000
ug/57000 mg = 13.6. The results of these analyses
are summarized in Table 30 and Figure 40. There
was nosignificant difference in TBG between the
Rongelap and Utirik groups or between the exposed and unexposed Rongelap groups. Eight subjects had high TBG levels. These wereall females,
and five were knownto be pregnant, a condition
that can elevate the serum TBG.
The results of these analyses provide no explanation for the difference in serum T,4 concentra-
tions between the larger groups of Rongelap and
Uutirik 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 T, binding and
TBGlevels in greater detail, the dialyzable frac-
uons 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
higher frequency of low TBG levels in the Utirik
group. Such a studyis currently in progress.
F. (ODOPROTEIN STUDIES
Analyses for protein-bound iodine in sera of
Marshallese people revealed a level significantly
higher than that seen in North America.!8.20 Sub-
sequent studies 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 unusual finding
promptedus to 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 of persons of almost pure Hawaiian an-
cestry, some of whom ate seaweed in large quantitv, but the iodoprotein level did not correlate
with this dietary intake. In the Rongelap population, it is of interest that the iodoprotein level remained high in two athyreotic boys; after subtotal
DFT, was greater than in subjects with normal or
thyroidectomy; and during thyroid suppression by
ferent in the three groups, which indicated that
the abnormal Ty levels among these subjects reflect alterations in plasma hormonebindingrather
than in thyroxine productionrates. Since virtually
enous) source for the todoprotein. The cause of
the elevation, however, has not been ascertained.
elevated TBG. The absolute free T4 was notdif-
all the subjects with low plasma T,4 concentrations
in the larger Utirik and Rongelap groups had normal plasma TSH, we would expect a moresyste-
matic study of TBG levels by RIA to show a
thyroxine administration.*° This strongly implies
an extrathyroidal (endogenous) or a dietary (exog-
One possibility is that it is produced in poly-
morphonuclear leukocytes. These cells are known
to organify iodine during phagocytosis.9! Although
the Marshallese do not have unusually high leukocyte counts, they do have a mild eosinophilia
Table 32
Serum Iodoprotein Levels (ug %) 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
Kapingamarangi
Pingalap
Hana ( Maui)
Americans: Kwajalein
US.
No.in group
10
TotalI
7.22.4
2
7
2.80.4
8.323.6
5
16.1289
9
3
4
24
23
27
13
12
9
Til
lodoprotein
4041.0
2.5211
1220.5
3.621.1
S.5241.1
6.0+1.1
7841.2
4.4418
2.60.1
3.7+0.8
8.7228
11.5+3.0
8442.0
6.7213
4.01.0
6.242.6
3.60.6
4121.1
6.6201.3
64=1.3
3.80.8
3.91.1
4.120.5
1.30.0
4.2239
2.62220
2.9=1.2
3.3217
3.3417
4.6253.5
3.0=0.6
3.3219
2.2+08
1.9205
1121.0