SUPPRESSION OF THE LUTEINIZING-HORMONE RELEASING EFFECT OF LUTEINIZING-HORMONE RELEASING HORMONE BY ARGININE-VASOTOCIN

The concentrations of 17-oxosteroids in the spermatic venous blood of anaesthetized dogs were used as an index of LH release to assess the effects of arginine-vasotocin on the response of the canine pituitary gland to exogenous luteinizing hormone releasing hormone (LH-RH). When injected into the carotid artery, arginine-vasotocin (1.0 μg/kg body wt) caused no significant alterations in the testicular output of 17-oxosteroids. The administration of LH-RH (5 μg/kg body wt, a standard dose) into the carotid artery produced typical stimulation of testicular 17-oxosteroid secretion. Administration of arginine-vasotocin (0.01, 0.1 or 1.0 μg/kg body wt) into the carotid artery 3 h before the administration of a standard dose of LH-RH inhibited the testicular secretion of 17-oxosteroids normally induced by LH-RH. However, pretreatment with arginine-vasotocin (1.0 μg/kg body wt) did not affect the testicular response to i.v. administration of human chorionic gonadotrophin (5 i.u./kg body wt). These results indicate that in the dog, arginine-vasotocin inhibits the LH-RH-induced release of LH by acting directly on the anterior pituitary gland.