PLASMA DOPAMINE-BETA-HYDROXYLASE ACTIVITY IN PHAEOCHROMOCYTOMA

Abstract

Plasma dopamine-.beta. hydroxylase (D.beta.H) activity, a marker of catecholamine secretion that occurs via exocytosis, was determined preoperatively in 8 patients with pheochromocytoma. Despite elevated urinary catecholamine concentrations, mean plasma D.beta.H activity was 32.6 .+-. 3 u/l and was not significantly different from apparently healthy subjects. Seven days after surgery, 1 subject exhibited a 60% postoperative decrease of enzyme activity. These results suggest that diffusion across plasma membranes is the predominant mechanism of catecholamine release from pheochromocytomas. The postoperative change in 1 patient suggests tumor heterogeneity and exocytosis may contribute to catecholamine release in some patients.