37 1 | —= >| +0F oO (Rongeiap+ Utirik) 4 \ \ \ \ Noiesions (Rongelap) = al a a / so 5 U.S. normal ‘ 4 20F 35- 30+ 5} 10 Aw a - Thyroid lesions Oo 40 ; —_——_—§ TGby RUA (ug/inl) 1 nN 01 10 “Basal 8 hr 24 hr basal @hr 2¢hr Post TSH Figure 42, Effect of TSH administration on thyroglobulin <5 0 15 20 ng/mi 2 30 35 We Figure +1. Percentages of people in various groups having given levels of thyrogiobulin (by RIA), 1973. and a high incidenceof parasitic infections. A preliminary examination of North Americans with abnormal leukocyte counts, however, did not show a correlation between leukocytosis and iodoprotein level. Further studies on this are indicated. The chemical nature of this iodoproteinis also unknown. By analogy with findings in various thyroid diseases,9? the iodoprotein is likely to be comprised mainly of iodoaibumin arising from the iodination of serum proteins. It is now recognized, however, that thyroglob- ulin (TG) is a minor component of normal plasma. At a reported concenrration of 5.10.49 (S.E.M.} ng/ml (range <1.6 to 20.7) in normal North Americans,?3 and assuming an iodine content of 0.5%, this would be equivalent to an iodoprotein iodine level of 2.60.25 ng/dl. Althoughit seems unlikely, a pron, that circulating thyroglobulin in the Marshallese could be elevated enough to give an iodoprotein level of 3 to 4 ug/dl (i.¢., >500 ug TG/dl),the possibility was investigated by radioimmunoassay measurements (M. Izumi, J. Bauueu, AND J. Rossins, unpublished observations, 1974; see Figure 41). The assay could detect TG levels >3 ng/ml; levels >40 ng/ml were not quantitated. In the Rongelap and Utrik groups without thyroid lesions (+7 and 25 subjects respectively), 380% of the values were within the U.S. range, and no correlation was seen between elevated serum iodo- protein and abnormal TG levels. A few members V0Cb 134 levels, 1973. oO, Persons with thyroid lesions { Rongelap plus Utirik); @, withoutlesions (Rongeijap). of each group, including the U.S. normal group. had TG values > 30 ng/mi, but the significance of this is uncertain. Of 24 subjects with elevated serum iodoprotein, only 1 had serum TG >30 ng/dl. A striking finding (Figure 41) was that in the * Rongelap plus Utirik group with thyroid lesions (36 people) almost 50% of the levels were <5 ng/ml, a muchhigher percentage thanin the other groups. Most of these people had had prior thyroid surgery or were athyreotic, andit is presumed that they had insufficient thyroid tissue for normal TG production. Furthermore, T4 suppression therapy may have contributed to the low TG levels in the Rongeilap people. TG was also measured before and after TSH injection in 10 Rongelap plus Utirik subjects with thyroid lesions and in 20 Rongelapese with none (Figure +2). In every case, TSH resulted in a rise in TG level, and there was no apparentdifference between the two groups. The unusually high level of iodoprotein in the . Marshallese peopleis intriguing, and furtherstud- ies are in progress, with !291 used as the tracer, in an attempt to identify the protein.” G. CORRELATION OF THYROID ABNORMALITIES WITH RADIATION EXPOSURE Statistics on the incidence of thyroid abnormal- ities in people living on the Marshall Islands are *Miss R.F. Straub, BNL, is doing the chemical analvses.