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