Effect of zinc administration on thyrotropin releasing hormone-stimulated prolactinemia in healthy men

Previous in vitro studies have demonstrated zinc (Zn++) inhibition of basal and of potassium (K+) or thyrotropin-releasing hormone (TRH)-stimulated pr olactin (PRL) secretion, in a selective, reversible, and dose-dependent man ner. Thus, Zn++ may regulate physiologically pituitary PRL secretion. Furth ermore, studies with patients with uremia, cirrhosis or prolactinoma, have shown the coexistence of hypozincemia and hyperprolactinemia and zinc suppl ementation did not correct hyperprolactinemia in these patients. In normal individuals Zn++ administration produced controversial results on PRL secre tion. Here, we investigated whether zinc administration affects TRH-stimula ted PRL in healthy men. We found that Zn++ administration does not change t he TRH-stimulated PRL. Therefore, in normal conditions, Zn++ does not inhib it TRH-stimulated prolactinemia. In addition, we found that acute increases of blood PRL and TRH do not alter blood Zn++ levels.