Effects of Serotonin on Iodide and Intermediary Metabolism in Isolated Thyroid Cells1

Abstract

Serotonin in concentrations of 1 and 10 μg/ml greatly stimulated the organification of iodine and the formation of iodothyronines in suspensions of isolated thyroid cells. Iproniazid enhanced the stimulatory action of low, but not of high, concentrations of serotonin. The effects of serotonin on the iodine metabolism of isolated cells were blocked by phentolamine, but not by either propranolol or reducing agents (ascorbate, sodium bisulfite). Serotonin also stimulated the conversion of glucose-l-14C to 14CO2, the incorporation of 14C-labeled amino acids into TCA-precipitable proteins by isolated cells. In addition, adenyl cyclase activity was stimulated by serotonin in both intact and sonicated preparations of isolated cells. The precursors of serotonin, L-tryptophan and 5-hydroxytryptophan, as well as its metabolite, 5-hydroxyindolacetic acid, did not stimulate either iodine metabolism or adenyl cyclase activity, while tryptamine did. These findings suggest that the stimulatory effect of serotonin depends upon the amine, rather than the 5-hydroxyl, group. (Endocrinology88: 620, 1971)