Neurohypophysial secretion to insulin-induced hypoglycemia and its regulation by endogenous opioids in women

In animals, there is sexual dimorphism of both neurohypophysial peptide secretion in response to stressful stimuli and to the inhibitory effects of opioids. In men, endogenous opioids inhibit the release of oxytocin when AVP secretion is stimulated by insulin-induced hypoglycemia. We have now investigated the role of endogenous opioids in the AVP and oxytocin response to insulin-induced hypoglycemia in women. Twelve subjects, 6 in the follicular and 6 in the luteal phase of the menstrual cycle, were infused on 2 occasions with naloxone (4 mg bolus and 6 mg/h) or saline. Soluble insulin (Human Actrapid, 0.15 mu/kg, iv) was given and serial blood samples taken. Blood sugar fell significantly (p less than 0.05) and similarly in all groups. In the follicular phase hypoglycemia led to a rise in plasma AVP from 1.3 +/- 0.2 to 1.8 +/- 0.2 pmol/l in the saline-infused subjects (NS), and from 1.0 +/- 0.1 to 2.0 +/- 0.2 pmol/l in the naloxone-infused (p less than 0.05). AVP rose similarly from 0.6 +/- 0.1 to 1.6 +/- 0.5 pmol/l (p less than 0.05) in the luteal phase controls and from 0.8 +/- 0.1 to 1.5 +/- 0.3 pmol/l (p less than 0.05) in naloxone-infused subjects in the luteal phase. There were no significant differences between any of these groups. There were no significant changes in plasma oxytocin in any group. We therefore conclude that in women, unlike men, endogenous opioids do not modulate oxytocin or vasopressin release during insulin-induced hypoglycemia.