PLASMA INORGANIC IODIDE, A CHEMICAL REGULATOR OF NORMAL THYROID FUNCTION1

Abstract

In an earlier communication (Wolff and Chaikoff, 1948) it was shown that the administration of large amounts of iodine temporarily inhibits the capacity of the normal thyroid gland to bind iodine organically. This inhibition appeared to be related to the level of plasma iodine. So long as the concentration of plasma iodine exceeded 20–35γ per cent, no organic binding of iodine occurred in the gland, and only when the concentration fell below this critical range did the gland resume its function of depositing iodine in an organic form. On the basis of these findings it was postulated that the level of plasma iodine is part of a homeostatic mechanism governing hormone synthesis in the normal gland. Thus, when a large amount of iodine is ingested, the prevention of its deposition as organically bound compounds in the thyroid gland keeps the ingested iodine circulating as inorganic iodide, in which form it is readily excreted by the kidney.