36 bound per mole TBG,the expected ratio is 777000 ug/37000 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 sub- jects had high TBG levels. These wereall fernales, and five were knownto be pregnant, a condition that can elevate the serum TBG. The resuits of these analyses provide no explanation for the difference in serum T, concentra- tions 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 groupsas 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 TBG leveis in greater detail, the diaiyzable fractions of Ty (DFT4) were determined in a number of plasma samples with low, normal, or elevated TBG-binding capacities. The resuits are presented in Table 31. In subjects with low TBG, the mean DFT, was greater than in subjects with normalor elevated TBG. The absolute free Ty was not different in the three groups, which indicated that the abnormal T, levels among these subjects reflect alterations in plasma hormone binding rather than in thyroxine production rates. Since virtually ali the subjects with low plasma T, concentrations in the larger Utirik and Rongelap groups had normai plasma TSH, we would expect a more systematic study of TBG levels by RIA to show a higher frequencyof 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 Subsequent studies showed thatthis elevation could be attributed to an increase in the iodoprotein traction andindicated that this was responsible for in- correct evaluation of thyroid function during the early years of the surveys. This unusual finding promptedus to determine serum iodoproteinlevels 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 ancestry, some of whom ate seaweed in large quan- tity, but the iodoprotein level did not correlate with this dietary intake. In the Rongelap popuiation,it is of interest that the iodoprotein level re- mainedhigh in two athyreotic boys; after subtotal thyroidectomy; and during thyroid suppression by thyroxine administration.2° This strongly implies an extrathyroidal (endogenous) or a dietary (exog- enous) 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 leukocyte counts, they do have a mild eosinophilia Table 32 Serum [odoprotein Levels (ug %) in Pacific Island Populations and in Americans Group Rongelap exposed No thyroid nodules Thyroid acrophy Thyroid nodules, pre-op After partial thyroidectomy After total thyroidectomy Ailingnae Utirik Rongelap unexposed Kapingamarangi ' Pingalap Hana (Maui) Americans: Kwajalein US. 5006153 No. in group 10 Total I 251.1 8.33.6 3.61.1 4.2439 6.01.1 2,620.1 2.9201.2 9 3.51.1 4 5 24 23 27 13 12 9 Iodoprotein 4.01.0. 2.820.4 3 ° 7.22%2.4 2 7 Tal 7.81.2 16.1=8.9 8.72.8 1153.0 8.4-2.0 6.71.3 6.641.3 6.42 1.3 1.20.5 4.41.8 3.70.8 3.80.8 4.01.0 6.22.6 3.60.6 4121.1 3.91.1 4.10.5 1.3200 2.62.0 3.31.7 3.3217 4.63.5 3.0+0.6 3.3219 2.20.8 1.905 [.12=1.0