THE TEMPORARY NATURE OF THE INHIBITORY ACTION OF EXCESS IODIDE ON ORGANIC IODINE SYNTHESIS IN THE NORMAL THYROID¹

Abstract

In 1944, Morton et al. observed that when 300 mg. of sheep thyroid slices were incubated in 3 cc. of a bicarbonate-Ringer medium to which various amounts of I127 as inorganic iodide had been added, inhibition of thyroxine and diiodotryosine formation occurred when the added I127 exceeded 20 gamma. The resemblance of this in vitro effect to the action of excess iodide in Graves’ disease in man led us to investigate this phenomenon in the normal intact thyroid (Wolff and Chaikoff, 1948a). In addition to confirming the inhibitory action of excess iodide upon thyroxine synthesis in intact thyroids, the investigation showed that such inhibition by a single injection of iodide was related to the level of plasma iodine (Wolff and Chaikoff, 1948b). So long as the concentration of plasma iodine exceeded 20–35 gamma per cent, organic binding of iodine failed to occur in the gland,