Enhanced Release of Dopamine-β-Hydroxylase from Sympathetic Nerves by Calcium and Phenoxybenzamine and Its Reversal by Prostaglandins

Abstract

Dopamine-β-hydroxylase (EC 1.14.2.1), an enzyme localized in sympathetic synaptic vesicles, was released together with norepinephrine during in vitro stimulation of the hypogastric nerve that innervates the vas deferens of the guinea pig. Stimulation of the nerve in the presence of high concentrations of calcium (7.5 mM) or phenoxybenzamine caused a marked increase in the amounts of the enzyme and norepinephrine released into the bath. The augmentation of release of dopamine-β-hydroxylase by 7.5 mM calcium or phenoxybenzamine was reversed by prostaglandin E2. These findings suggest that the release of the sympathetic neurotransmitter, norepinephrine, occurs by a process of exocytosis in which the vesicular content of soluble dopamine-β-hydroxylase is also released. The depolarization-induced exocytosis, which is stimulated by calcium, may be affected by prostaglandin E2 or phenoxybenzamine through inhibition or enhancement of the actions of calcium in the release process.