EFFECTS OF NICOTINE INJECTED INTO THE ATRIOVENTRICULAR NODE ARTERY OF THE DOG

¹ Department of Physiology, Faculty of Medicine, University of Montreal, Montreal, Quebec, Canada

In dogs under chioralose anesthesia, the heart was exposed and the atrioventricular (A-V) node artery was cannulated. Nicotine solutions (0.1, 1 and 10 µg/ml) were injected into the A-V node artery. The response to nicotine, 1 and 10 µg, was characteristically biphasic, consisting of an immediate A-V block, followed shortly by an A-V nodal acceleration. This response was similar to that obtained from nicotine injections into the sinus node artery. The A-V blocking effect of nicotine was abolished by intranodal atropine and significantly decreased by hexametbonium. The accelerating effect of nicotine was inhibited by intranodal propranolol and intranodal hexamethonium. After nicotine injections into the A-V node artery, the inhibitory effect of vagus nerve stimulation was abolished for approximately 30 minutes, whereas the response to intranodally injected acetylcholine remained. The degree of A-V nodal acceleration in response to left stellate ganglion stimulation was not affected by nicotine. Reflex effects of nicotine on systemic blood pressure and sinus rate (Bezold-Jariach reflex) obtained after injection into the anterior descending artery were not observed with A-V node artery injections.