Effect of Apomorphine on the Canine SA Node

Abstract

A constant pressure perfusion of the sinus node artery was performed in 10 in situ and in 3 isolated SA node preparations. The selective administration of apomorphine caused a negative chronotropic effect which was not blocked by treatment with atropine. The sinus deceleration was usually produced by apomorphine, 10-300μg, while sinus irregularity and finally atrioventricular nodal rhythm in the in situ preparation or sinus arrest in the isolated one resulted from doses above 1mg. In the in situ preparation at a higher dose from 300μg to 1mg, a slight sinus acceleration was occasionally induced following sinus deceleration. In this time, a fall in blood pressure was usually observed. This acceleration response to apomorphine was inhibited by propranolol.
From these results, it is concluded that apomorphine induces direct depressive action on the SA node and, in extremely high doses, a slight sinus acceleration may be induced by reflex mechanism.