Zone Electrophoresis in Filter Paper of Serum I131 After Radioiodide Administration.

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Abstract
Serum from 6 patients who had received radioiodide (oral) or I131-labeled 1-thyroxine (intraven.) was studied by zone electrophoresis in filter paper at pH 8.6 (barbital buffer, ionic strength 0.1). Most of the I131 (approx. 85%) had a mobility intermediate between the alpha1-and alpha2-globulins, and the remainder had the mobility of albumin. No differences were detected between thyroxine added to serum (in vivo) and the thyroid hormone secreted by a normal thyroid gland, by a Graves'' disease thyroid gland, and by a functioning thyroid carcinoma. Two patients had received very large doses of radioiodide, and their serum contained large amts. of butanol-insoluble I131, whereas in the other patients the serum I131 was largely butanol-soluble, and behaved like thyroxine on paper chromatography. These 2 forms of serum I131 had similar mobilities on zone electrophoresis, but could be differentiated by fractional precipitation of the serum proteins with phosphate buffer (pH 6.5). The radioiodine, therefore, was attached, in each instance, to a different protein, and the identity in their mobilities was fortuitous. Zone electrophoresis of purified hog thyroglobulin, and of I131-labeled rat thyroglobulin in a crude thyroid extract, revealed that these substances also had a mobility in the range of the alpha globulins of human serum. This finding is compatible with the previous suggestion that the butanol insoluble I131 which is sometimes present in the serum after large doses of radioiodide, may be thyroglobulin, released into the circulation from damaged thyroid tissue.

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