NITRIC-OXIDE SYNTHASE IN THE RAT ANTERIOR-PITUITARY GLAND AND THE ROLE OF NITRIC-OXIDE IN REGULATION OF LUTEINIZING-HORMONE SECRETION

By using immunobistochemistry and in situ hybridization, we have demon strated that the nitric oxide (NO)-synthesizing enzyme NO synthase is present in gonadotrophs and in folliculo-stellate cells of the anterio r pituitary gland of male and female rats. A marked increase in levels of NO synthase protein and mRNA was observed after gonadectomy. In vi tro studies on dispersed anterior pituitary cells suggest that NO inhi bits gonadotropin-releasing-hormone-stimulated luteinizing hormone rel ease. An inhibitory effect of NO has also been shown on growth-hormone -releasing-hormone-stimulated release of growth hormone [Kato, M. (199 2) Endocrinology 131, 2133-2138]. Thus these findings support a dual m echanism for NO in the control of anterior pituitary hormone secretion , an autocrine mediation of luteinizing hormone release on gonadotroph s, and a paracrine effect on growth hormone secretion involving follic ulo-stellate cells closely related to somatotrophs. We speculate that NO may participate in producing the pulsatile secretion patterns of th ese two pituitary hormones.