Phenylethanolamine-N-methyltransferase activity determines the epinephrine concentration of pheochromocytomas

We evaluated the activity of phenylethanolamine-N-methyltransferase (PNMT) and dopamine-beta-hydroxylase (DBH) in 16 pheochromocytomas. Ten of the tumors were from patients with Multiple Endocrine Neoplasia and six of the tumors were from patients with sporadic pheochromocytomas. All of the pheochromocytomas contained PNMT and DBH activity. There was a significant correlation between PNMT activity and epinephrine concentration in the pheochromocytomas (r=0.61); there was no significant correlation between PNMT activity and norepinephrine concentration (r=0.38) or DBH activity and norepinephrine (r=0.06) or dopamine (r=0.31) concentration. In general, the patients with the highest PNMT activity in their pheochromocytomas tended to have paroxysmal (rather than sustained) hypertension and to excrete more E than NE in their urine.