Inhibition of Insulin Secretion by Catecholamines in Pheochromocytoma

Abnormal glucose tolerance tests and blunted plasma insulin responses returned to normal in three patients and improved in a fourth after removal of a pheochromocytoma. In two subjects phentolamine restored intravenous glucose tolerance curves to normal and improved the insulin secretion response to glucose. These findings suggest that alpha-receptor stimulation by catecholamines is important in causing glucose intolerance and blunted insulin secretion in patients with pheochromocytoma. Tumor removal was more effective than phentolamine in restoring plasma glucose and insulin levels to normal after glucose administration, suggesting that the inhibitory effects of phenochromocytoma on insulin secretion may not be mediated entirely through catecholamine stimulation of alpha-adrenergic receptors.