Insulin and Glucagon Responses in Subjects with Pheochromocytoma: Effect of Alpha Adrenergic Blockade

Impaired immunoreactive insulin (TRI) release was demonstrated in 3 of 5 subjects with pheochromocytoma. Chronic alpha adrenergic blockade with phenoxybenzamine or phentolamine corrected the insulin-releasing defect in 2 subjects but had no effect in the third. Surgical removal of the tumor resulted in complete amelioration of the impaired insulin release and improved glucose tolerance in all 3 subjects who were abnormal preoperatively. Fasting immunoreactive glucagon levels were normal in the 2 subjects in whom they were measured and neither alpha adrenergic blockage nor removal of the pheochromocytoma altered these levels. Thus, when chronic hypercatecholamine secretion in subjects with pheochromocytoma results in glucose intolerance, it is associated with inhibition of insulin release. Alpha adrenergic blockade or removal of the tumor reverses both abnormalities.