Adrenergic Modulation of Adrenocorticotropin Responses to Insulin-Induced Hypoglycemia and Corticotropin-Releasing Hormone

To study possible adrenergic modulation of pituitary- adrenal responses to insulin-induced hypoglycemia and CRH we examined the effect of nonselective β-blockade (phentolamine) and nonselective β-blockade (propranolol) on plasma ACTH, cortisol, and vasopressin (AVP) responses to hypoglycemia and CRH in five normal men. Infusion of propranolol or phentolamine did not alter basal plasma ACTH or cortisol levels. The propranolol infusion enhanced the stimulatory effect of hypoglycemia on ACTH, cortisol, and AVP secretion and also enhanced the stimulatory effect of CRH on ACTH and cortisol secretion. Infusion of phentolamine inhibited hypoglycemia-induced ACTH and AVP secretion, but had no effect on the stimulatory effect of CRH on ACTH and cortisol secretion. The increments of plasma ACTH and cortisol induced by an almost maximal dose of CRH (1 μg/kg) were smaller than those induced by hypoglycemia. The propranolol-induced enhancement of the ACTH response to hypoglycemia was almost the same as the ACTH respon...