Antagonism of central vasopressin receptors blocks hypoglycemic stress induced inhibition of luteinizing hormone release in male rhesus macaques

The first objective of this study was to investigate whether the inhibitory effect of insulin-induced hypoglycemia (IIH) on luteinizing hormone (LH) s ecretion was the same in unrestrained adult male rhesus macaques as has bee n previously reported in restrained female macaques. Since IIH did inhibit pulsatile LH secretion in adult male macaques, and some previous studies ha ve implicated arginine vasopressin (AVP) as a central mediator of this inhi bition, the second objective was to investigate whether antagonism of AVP a ction could reverse the IIH-induced inhibition of LH release in males. Ten adult male rhesus macaques (Macaca mulatta) were studied during 15-h period s (07.00-22.00 h), with blood samples collected every 15-min. There were th ree experimental groups; controls (n =5), IIH (n = 6) and IIH plus vasopres sin antagonist (AVPa; n = 6), During the hypoglycemia studies, the first 5 h served as a control for that occasion and an insulin bolus of 1 U/kg was administered intravenously at 12.00 h, During the IIH plus AVPa, the vasopr essin antagonist was infused intravenously from 12.00 h to 17.00 h. LH and testosterone decreased progressively after the insulin bolus in the IIH gro up reaching a minimum value at 4 h after the infusion. However, compared to the preinfusion levels, secretion of LH and testosterone was not suppresse d by hypoglycemia in the group treated with the AVP antagonist. The present study shows that in male macaques not subjected to the psychological stres s of restraint, IIH suppresses LH and testosterone secretion. This inhibiti on of LH release can be blocked in some animals by antagonism of central va sopressin receptors, suggesting that vasopressin is involved in the suppres sion of gonadotropin releasing hormone/LH release induced by hypoglycemia.