Release of endogenous noradrenaline from ligated cat hypogastric nerve by veratridine

The effect of veratridine on in vitro release of noradrenaline (NA) from ligated cat hypogastric nerve was investigated. After in vivo ligation for 24-48 h, large amounts of NA and dopamine-beta-hydroxylase (DBH) accumulated in the nerve segment immediately proximal to the ligature (P1). In vitro incubation of ligated nerves (segments P1 and P2) in oxygenated Krebs solution at 37 degrees C in the presence of veratridine caused a marked and dose-dependent release of endogenously accumulated NA into the incubation medium. The release continued to occur for a considerable time, even after washout of the drug. Veratridine-induced depletion of tissue NA was accounted for by its release, as NA, into the incubating medium. The secretory response to veratridine was readily blocked by tetrodotoxin (TTX). Veratridine-induced release was dependent on calcium and abolished by high magnesium. On the basis of the similarity between the NA secretory response to veratridine in this preparation and in adrenergically innervated organs, the results favour the view that the in vivo-ligated cat hypogastric nerve may serve as a useful model of adrenergic nerve terminals free of effector cells.