Calcium-channel inhibition in pheochromocytoma.

Nifedipine, a calcium-antagonist and potent vasodilator, was tested in three patients with pheochromocytoma. In two patients who were normotensive, nifedipine prevented a rise in blood pressure but not in plasma epinephrine and norepinephrine following the iv injection of the dopamine-antagonist metoclopramide. In another patient who was hypertensive, nifedipine was as effective in lowering blood pressure as labetalol or phenoxybenzamine, and did not modify the elevated plasma and urinary catecholamines. Nifedipine appears to control hypertension in pheochromocytoma, without altering catecholamine levels, suggesting that calcium-channel blockade interferes with catecholamine vascular action but not with tumoural catecholamine release. Calcium-antagonists may be helpful in preventing the pressor complications of provocative tests used in the screening of pheochromocytoma.