Comparison between dose-responses of prolactin, thyroid stimulating hormone and growth hormone to two different histamine H-2 receptor antagonists in normal men.

The effects of the histamine H2-receptor antagonists, ranitidine and cimetidine on prolactin (PRL), thyroid stimulating hormone (TSH), and growth hormone (GH) were studied in six normal males. Intravenous bolus injections of saline and of 50, 100, and 200 mg ranitidine and 300 mg cimetidine were tested. Ranitidine (100 and 200 mg) and cimetidine (300 mg) caused a significant increase in PRL secretion, whereas saline and ranitidine (50 mg) did not. TSH and GH secretion were unaffected by all doses. A dose-response relationship between ranitidine and PRL was established, and a dose of 65 mg ranitidine was found to be the minimal effective PRL-releasing dose. Plasma ranitidine concentration was measured by specific RIA. The results indicate an effect of H2-receptor antagonists on physiological functions in the control of PRL secretion. Histamine, therefore, may play a role in the regulation of PRL secretion.