Inhibitory effect of excess iodide on thyroid hormone release as measured by intracellular colloid droplets.

Abstract

In an attempt to elucidate an inhibitory action of iodide on thyroid hormone secretion, the effect of excess iodide on an increase of intracellular colloid droplets was studied in rats and mice fed a low or high iodine diet and injected with TSH or dibutyryl 3’,5’-cyclic AMP. Pretreatment with excess iodide markedly depressed the increase of intracellular colloid droplets produced by TSH in rats and mice fed a low iodine diet. However, excess iodide failed to depress an increase of colloid droplets in response to TSH either in mice fed a high iodine diet or in the thyroid incubated in vitro. Since excess iodide depressed an increase of intracellular colloid droplets produced by dibutyryl 3’,5’-cyclic AMP, it is suggested that excess iodide manifests its inhibitory effect on thyroid hormone secretion at a site subsequent to generation of cyclic AMP. (Endocrinology 90: 986, 1972)