Prolactin and gonadotrophin dynamics in response to antagonists of LHRH and dopamine in ovariectomized rhesus monkeys: a dissection of their common secretion.

This experiment was designed to study the prolactin (PRL) and gonadotrophin response to an inhibitory analogue of luteinizing hormone releasing hormone (LHRH-A; ORG 30276) and a dopamine antagonist, metoclopramide (MCP), in castrated female rhesus monkeys. The LHRH-A given as an i.v. bolus followed by an infusion 2 h later induced a significant decline in circulating PRL levels reaching a maximum suppression 1 h after initiation of the LHRH-A infusion. Intravenous administration of MCP, performed 1 h after beginning the LHRH-A infusion, resulted in a prompt and abrupt rise in PRL levels in the LHRH-A group as well as in the controls. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels showed a progressive decline during LHRH-A treatment. Injection of MCP did not affect the levels of LH and FSH in either of the groups. The data obtained demonstrate in primates that the prolactin inhibitory effect of LHRH-A is easily overcome by the dopamine antagonist, MCP, whereas the LHRH-A-induced gonadotrophin suppression remains unaffected by MCP.