Effects of the H2 receptor antagonist cimetidine on pituitary hormones in man

The effects of the histamine (H2) receptor antagonist cimetidine on serum levels of prolactin (PRL), growth hormone (GH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), follicle stimulating hormone (FSH) and cortisol were studied in five normal males. Cimetidine, when given by infusion at the dose of 100 mg/h for 5 h, did not alter adenohypophyseal secretion either basally or after pituitary stimulation with LHRH and TRH. However, 400 mg cimetidine given intravenously as a bolus injection significantly stimulated PRL release in all subjects, without affecting any other measured hormone. A dose-reponse relationship existed, and 200 mg cimetidine seems to be the minimum PRL-releasing dose when given as an intravenous bolus injection. These results suggest that cimetidine releases PRL and that this effect is dose-related, but only when large intravenous injections are given.