An increase of thyroid hormone secretion in response to excess iodide in rats treated with thyroxine.

Abstract

When more than 5 μg thyroxine was administered to rats with prelabeled thyroids, excess iodide increased blood PB131I for about 24 hr. This increase of blood P B m I was apparently due to an increase in labeled thyroid hormone. The increase was not due to a decrease of the thyroxine distribution space or to a decrease of fecal loss of labeled hormone. No increase of blood PB131I was found in thyroidectomized, 131I-injected and thyroxine-treated animals after administration of excess iodide. Since the number of intrathyroidal colloid droplets increased progressively with time after administration of excess iodide in thyroxine-treated rat thyroids, and since an increase of colloid droplets was preceded by a transitory increase of intrathyroidal cyclic AMP, it is suggested that excess iodide augments thyroid hormone release through an increase of thyroidal cyclic AMP in rats treated with thyroid hormone. (Endocrinology 93: S80, 1973)