NITRIC-OXIDE STIMULATES BOTH THE BASAL AND REFLEX RELEASE OF VASOPRESSIN IN ANESTHETIZED RATS

In view of the fact of the high concentration of neuronal nitric oxide synthase (NOS) in the supraoptic and paraventricular nuclei as well a s the posterior pituitary, it has been supposed that nitric oxide (NO) may be involved in the regulation of hormone secretion from these sit es. In the present study, L-arginine, the precursor of NO, and N-omega -nitro-L-arginine methyl ester (L-NAME), the NOS inhibitor, were intra cerebroventricularly (i.c.v.) administered into the pentobarbital anes thetized rats. The results showed that plasma arginine vasopressin (AV P) concentration increased after the injection of L-arginine (1.0 mg i n 10 mu l, i.c.v.) and decreased after the L-NAME (270 mu g in 5 mu l, i.c.v.). The elevated plasma AVP level in response to short-term hypo tension induced by intravenous infusion of sodium nitroprusside was al so significantly reduced by i.c.v. administration of L-NAME. The resul ts indicate that NO acts as a stimulating factor to both the basal and reflex release of AVP, opposing the view that NO plays an inhibitory role in the regulation of AVP secretion. (C) 1996 Elsevier Science Ire land Ltd.