Increase by naloxone of arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia in obese men.

The present study was carried out to establish whether the low arginine vasopressin (AVP) and oxytocin (OT) responses to insulin-induced hypoglycemia observed in obese men was due to alteration of the opioid control of posterior pituitary function. For this purpose, the AVP and OT releasing effect of insulin (0.15 IU/kg bw)--induced hypoglycemia was tested in eight normal weight men and in 10 age-matched obese subjects, without and with the previous treatment with the specific opioid receptor antagonist naloxone (3 mg in an iv bolus). In a control study, naloxone was given alone to the same subjects. Obese men showed similar basal glucose, AVP and OT levels, which remained unmodified after treatment with naloxone alone. Insulin induced a similar decrement of blood glucose levels in all subjects, with a nadir at 30 min. Plasma levels of AVP and OT rose strikingly in normal and obese subjects with mean peak responses at 30 min for AVP and at 45 min for OT. However, both AVP and OT responses were significantly lower in obese than in control subjects. Pretreatment with naloxone did not modify the AVP and OT responses to hypoglycemia in normal weight subjects, whereas it significantly enhanced both hormonal responses in obese subjects. In the presence of naloxone normal controls and obese subjects showed similar responses of both AVP and OT to hypoglycemia. These data indicate that an abnormal activity of endogenous opioids might account for the hypothalamic posterior pituitary dysfunction, which is responsible for the low AVP and OT responses to insulin-induced hypoglycemia in obesity.