VASOPRESSIN MEDIATES HYPOGLYCEMIA-INDUCED INHIBITION OF LUTEINIZING-HORMONE SECRETION IN THE OVARIECTOMIZED RHESUS-MONKEY

The objective of the present study was to examine the role of vasopres sin in the regulation of LH secretion in the rhesus monkey. The effect of vasopressin administration on basal LH secretion and vasopressin a ntagonism on stress-induced inhibition of LH secretion were examined. Intracerebroventricular (i.c.v.) infusion of vasopressin (20 mu g/h) t o chair restrained ovariectomized rhesus monkeys (n = 5) decreased the area under the LH curve by -51.61 +/- 13.73 ng/ml/h compared to -8.35 +/- 7.11 ng/ml/h following infusion of artificial CSF (aCSF; p = 0.02 1). This effect was independent of any change in mean arterial pressur e. Subsequently, the role of vasopressin in hypoglycemia-induced suppr ession of LH was examined. Administration of insulin (1 U/kg BW) to ch air-restrained ovariectomized rhesus monkeys decreased the area under the LH curve by -60.88 +/- 19.77 ng/ml/h. The decrease in LH was signi ficantly different from that observed in aCSF-infused euglycemic contr ols which exhibited a slight decrease in LH (-8.35 +/- 7.11 ng/ml/h; p 0.036). In contrast, the area under the LH curve was increased slight ly (1.42 +/- 11.93 ng/ml/h) when insulin administration was combined w ith i.c.v. infusion of the vasopressin antagonist [deaminopenicillamin e(1), O-methyl-tyrosine(2), arginine(8)]-vasopressin (120 mu g/h; p = 0.013 vs. insulin only). The demonstration that vasopressin administra tion inhibits LH secretion whereas vasopressin antagonism prevents hyp oglycemia-induced LH suppression suggests that vasopressin is a physio logical inhibitor of LH secretion in the rhesus monkey.