Blood pressure regulation in pheochromocytoma.

Two sets of studies were performed in 13 patients with proved adrenal pheochromocytoma to test the hypothesis that the sympathetic nervous system (SNS) is active and might contribute to the hypertensive state. Similar studies were performed in 15 additional patients considered to have essential hypertension. In the first set, 13 patients with pheochromocytoma were subjected to head-up tilt to assess the activity of the SNS. This maneuver decreased diastolic blood pressure in only two; heart rate increased appropriately in all except one. Changes in plasma norepinephrine (NE) were variable and did not correlate with changes in blood pressure (BP) and heart rate (HR). In the second set, 10 patients with pheochromocytoma were given a single oral dose of clonidine (0.3 mg) to evaluate what role, if any, the SNS might contribute to the hypertensive state. Fifteen patients with essential hypertension were studied similarly for comparison. Clonidine produced significant decreases in BP and HR but left plasma renin activity unchanged in both groups. In essential hypertension, the cardiovascular responses were accompanied by significant reductions in plasma NE. By contrast, plasma NE was unchanged in patients with pheochromocytoma, despite similar reductions in BP and HR. These results suggest that the sympathetic reflexes are intact in pheochromocytoma, and that much of the hypertension associated with these tumors may be related to increased sympathetic activity.