i ~J Table {5 t2 1 Kinetic Studies With '!-I NO, OF CASES | | 6: Zz foi | a a - 1 iG aon jo LE r— 4 . ad 6 PROTEIN -~ BOUND ‘GO iODINE, ug % l2 Figure 21. creased the backgroundslightly. Mathematical analysis* of these data was done on an IBM 7094 computer with the program of Berman etal.** No experimental correction was madefor extrathyroidal radioactivity “seen” by the counter, since the computer program adjusted the readings over the neck for this factor. A least-squares best fit, assuming exponential thvroid uptake and renal excretion of iodide, produced a “best” value for this factor, termed 03,. The results of the studies with '**I are shown in Table 15, where they are compared with values obtained from normal individuals residing in the United States. It can be seen that the rate of thyroid uptake andthe rate of urinary excretion are both decreased. Since they are decreased more or less proportionately, the calculated asymptotic up- take is normalorslightly elevated. One may use these data plus the urine iodide values to calculate the average daily secretion of thyroid hormone, assuming steady state conditions, using the formula EU °=T=U where S = amount ofiodine secreted by the thyroid (ug/day), U’ = fractional thyroid uptake of iodine, and & = urinary iodine (g/day). With E = 105 pg/day and U=0.42, the value for § is calculated to be 76 pg iodine/day. This valueis *We are indebted to Dr. Mones Berman, National Institutes of Health, Bethesda, for this analysis. Group As* Ay,** Marshallese U.S. normals 0.72 1.0 0,97 2.0 Theoretical No. uptake a;,,+ cases 42% 33% 0.08 ~ 2] - *Fraction of extrathyroidal iodide transferred to the thyroid per day. **Fraction of extrathyroidal iodide excreted in the urine per day. tValue derived by the computer for the fraction of extrathyroidal iodide “seen” by the counter. somewhathigher than similar ones calculated for other groups but is not extraordinarily high.** ° Serum Cholesterol. Serum cholesterol determinations on most of the exposed and an equal num- ber of the unexposed population were carried out in 1957 and 1959. Theresults are tabulated in Appendix 5. Although the cholesterol levels in the exposed group are about 17% below the levels in the unexposed group, the difference is not quite significant at the 5% level. Individual values were not indicative of thyroid disease. Discussion of Previous Thyroid Studies. Until the recent developmentof hypothyroidism in two boys, it had been the concensus ofail physicians who examined these people that they were euthy roid. A conceivable explanation for the high PBI could be an elevation of thyroxine-binding proteins in serum which, as in the congenital elevation of thyroxine-binding globulin described hy Beierwaltes and Robbins,** causes an increasein the serum PBI without hyperthyroidism. The levels of the TBG in the Marshallese serum meuasured by Robbins, however, were within normai limits. The discrepancy between PBI and BEI suggested the presence of an iodoprotein in serum The chromatographyof serum iodine showing an iodoprotein level in the Rongelap people of 2 ue% (and higher in the Utirik people} seems t» implicate the iodoprotein as the cause for the ¢lrvated PBI. No adequate data are available on the calorgenic potency of serum iodoproteins, but there are someresults which show that mostof the iodinated aminoacidsin this protein are monolodotyresine and diiodotyrosine.*’:*° These iodoamino acids are