THE NATURE OF THE SERUM IODINE AFTER LARGE DOSES OF I¹³¹*†

Abstract

THE administration of a large dose of radioiodine to man (1, 2) and to the rat (3) is sometimes followed by a temporary rise in the level of serum protein-bound iodine. The present study was undertaken to elucidate the nature of the serum iodine after large doses of radioiodine in man. Recent studies have indicated that the blood iodine normally present in man and in the rat is almost entirely thyroxine, loosely attached to the serum proteins. In support of this view is the demonstration of the identity between the serum iodine and thyroxine added to serum in terms of: precipitability with the serum proteins (4–9), solubility in n-butanol (4, 5, 9), inability to dialyze (4, 6, 9), recrystallization to constant specific activity (9), and development in various chromatographic systems (10, 11, 12). The latter method has demonstrated that small amounts of other iodine-containing compounds may also be present. Similar studies have shown that the serum iodine in Graves' disease appears to be identical with thyroxine (13), although there is some evidence which does not support this view (14).