THE PARADOXICAL EFFECTS OF THIOCYANATE AND OF THYROTROPIN ON THE ORGANIC BINDING OF IODINE BY THE THYROID IN THE PRESENCE OF LARGE AMOUNTS OF IODIDE

It has been demonstrated by Wolff and Chaikoff (1948) that the administration of a large dose of iodide to the intact rat inhibits the organic binding of iodine by the thyroid gland. In the experiments reported, the inhibition was correlated with the plasma iodide concentration, and the effective values were found to be above 20–35 μg. per 100 cc. The ability of thiocyanate and of thyrotropin to affect the iodide concentrating power of the thyroid offered a means for manipulating the iodide content of the gland without changing the plasma iodide concentration appreciably. Thiocyanate markedly inhibits the capacity of the thyroid to concentrate iodide ion (Franklin, Chaikoff, and Lerner, 1944; VanderLaan and VanderLaan, 1947), and, at physiological plasma iodide concentrations, slows the process of synthesis of organic iodine compounds (Wolff, Chaikoff, Taurog, and Rubin, 1946). Thyrotropin increases the iodide concentrating power (Stanley and Astwood, 1949) and has the effect, at ordinary iodide values,