Hypoglycemic 'stress' and gonadotropin-releasing hormone pulse generator activity in the rhesus monkey: role of the ovary

Abstract

Observations of long standing have suggested that the 'stress' of chair restraint inhibits the GnRH pulse generator in normal female monkeys while this phenomenon is rarely observed in ovariectomized animals. The role of the ovary in the response of the GnRH pulse generator to the stress of insulin hypoglycemia was investigated in both intact and ovariectomized rhesus monkeys. Following an overnight fast the animals, previously habituated to restraint, were placed in primate chairs and GnRH pulse generator activity monitored electrophysiologically. Insulin-induced reductions in mean blood glucose concentrations of 10-40% of control values interrupted pulse generator activity in intact monkeys but were without effect in ovariectomized animals. With larger reductions in blood glucose, pulse generator activity was interrupted in both groups but the inhibition was twice as long in intact than in ovariectomized animals. The reduced responsiveness of ovariectomized animals to insulin hypoglycemia was significantly reversed by estradiol replacement. Naloxone administration did not prevent the hypoglycemia-induced inhibition of pulse generator activity in either intact or ovariectomized rhesus monkeys. It is concluded that hypoglycemic 'stress' inhibits the GnRH pulse generator by a nonopioidergic mechanism and that ovarian products, most probably estradiol, exacerbate this effect.