Effect of metergoline on the diurnal prolactin responses to insulin-induced hypoglycemia in normal men

(1) Insulin tolerance tests were performed at 0900 and 1800 hr on six young healthy men, under basal conditions and after metergoline pretreatment. (2) The hypoglycemia induced by insulin during the two tests was not significantly different. (3) Both morning and evening basal prolactin (PRL) levels were significantly lowered by metergoline. (4) Insulin hypoglycemia-induced PRL release was significantly inhibited by metergoline, both in the morning and in the evening. (5) Although dopaminergic mechanisms may account for these effects of metergoline, serotonergic mechanisms cannot be ruled out.