Abstract
Cholinergic influence on atrioventricular (AV) junctional rhythm via its intervention in the intracardiac autonomic nerves was investigated in the canine, blood-perfused AV node preparation. Large amounts of acetylcholine (ACh) injected into the anterior septal artery (ASA) caused a rapid increase in the rate of automaticity superimposed on a slow increase. Nicotine given in the ASA caused to a rapid increased superimposed on a slow increase. Large amounts of ACh injected into the posterior septal artery (PSA) caused a slow increase, which was superimposed by a rapid icrease in the presence of l-hyoscyamine. The rapid and slow increases were abolished by dl-propranolol given in the PSA and ASA, respectively. Both types of increases were suppressed by tetrodotoxin (TTX). Nicotine given in the PSA caused a decrease superimposed by a rapid increase, both of which were abolished by TTX. These reslts indicate that cholinergic excitatory intervention induces AV junctional tachycardia via norepinephrine release from sympathetic nerve endings, distributing widely from the proximal to distal portion of the AV junctional area.
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