COMPETITIVE INHIBITION BETWEEN OXYTOCIN AND LUTEINIZING HORMONE-RELEASING FACTOR (LRF) FOR THE SAME ENZYME SYSTEM IN THE RAT HYPOTHALAMUS

Abstract

From the observation that hypothalamic peptidases inactivating oxytocin might be involved in luteinizing hormone-releasing factor (LRF) metabolism and that the hypothalamus contains enzymes which can inactivate LRF, competitive inhibition studies were performed to determine if the peptidases inactivating oxytocin could act on LRF. In mixed substrate incubations, LRF significantly decreased peptidase activity in a hypothalamic supernatant fraction whereas thyrotrophin-releasing factor (TRF) had no effect. From kinetic studies, it was found that there was competitive inhibition between the two polypeptides for the same enzymes and that LRF may be true enzyme substrate. The results confirm the previous proposals that the hypothalamic peptidases can inactivate LRF and the possibility of a role for the enzymes in the regulation of reproductive function is suggested.