Vagal Blocking Action of Phentolamine and Dibenzyline Studied by Direct Perfusion of the Sinus Node ∗

Abstract

Summary

In the canine sinus node the negative chronotropic effect of vagal stimulation or of directly administered acetylcholine or methacholine can be blocked with directly administered phentolamine or Dibenzyline. Both these classical alpha adrenergic blocking agents are approximately equally effective, but relatively high concentrations are required for the vagal blocking action. The onset of vagal blockade is prompt but is seldom complete, and can be overcome with sufficiently high concentrations of acetylcholine. Considering the concentrations of phentolamine and Dibenzyline required during direct perfusion of the sinus node to produce effective vagal blockade, it seems unlikely that this experimental pharmacologic effect is of much significance during the use of these substances for their more familiar alpha adrenergic blocking action.