INHIBITORY CONTROL OF NITRIC-OXIDE ON THE ARGININE-VASOPRESSIN AND OXYTOCIN RESPONSE TO HYPOGLYCEMIA IN NORMAL MEN

IN order to establish whether nitric oxide (NO) participates in the re gulation of arginine-vasopressin (AVP) and/or oxytocin (OT) secretion in humans, six normal men were treated with placebo (normal saline) or the NO synthase inhibitor N,G-nitro-L-arginine methyl ester (L-NAME), given at doses (40 mu kg(-1) injected plus 50 mu g kg(-1) infused i.v .) previously found to be unable to change blood pressure. Experiments were carried out both in basal conditions and during stimulation of p osterior pituitary secretion with insulin (0.15 IU kg(-1))-induced hyp oglycaemia. The administration of saline or L-NAME alone was unable to change basal AVP or OT levels. Insulin-induced hypoglycaemia, however , enhanced plasma AVP and OT levels by two-fold in the absence of L-NA ME and by fourfold in the presence of the NO synthase inhibitor (NOS). Blood glucose levels decreased in a similar manner during the insulin tolerance tests, regardless of L-NAME administration. In all experime nts, AVP and OT responses to hypoglycaemia followed a similar pattern, with mean peak levels at 45 min. These data suggest that in normal me n NO is not involved in regulation of basal AVP and OT secretions, whe reas it exerts an inhibitory role in the control of the posterior pitu itary hormone responses to hypoglycaemia.