ELECTROPHYSIOLOGICAL-ANATOMIC CORRELATES OF ATP-TRIGGERED VAGAL REFLEX IN DOGS

To test the hypothesis that afferent traffic of the ATP-triggered vagal reflex travels mainly in the right vagus nerve, we quantitated the response of the sinus node pacemaker activity and atrioventricular (AV) nodal conduction to increasing doses of intra-atrial ATP under baseline conditions, in the presence of aminophylline, and subsequently after either right followed by left cervical vagotomy or vice versa. In addition, the effect of right vagal C-fiber afferent blockade on the action of ATP in the sinus node was also determined. Because vagal efferent traffic to the sinus and AV nodes travels mainly via the right and left vagus nerves, respectively, the working hypothesis predicted that left vagotomy would have a much smaller effect than right vagotomy on the negative chronotropic action of ATP in the sinus node and predicted similar effects of left vs. right vagotomy on the negative dromotropic action of ATP on AV nodal conduction. ATP suppressed sinus node automaticity and AV nodal conduction in a dose-dependent manner. The attenuation of the action of ATP on the sinus node by right vagotomy was much more pronounced than that caused by left vagotomy, while the negative dromotropic action of ATP in the AV node was similarly attenuated by right vs. left vagotomy. In addition, sinus node automaticity, which was only mildly attenuated by left vagotomy, was markedly suppressed by right vagal C-fiber afferent blockade. It was concluded that in the dog, afferent vagal traffic triggered by intra-right atrial ATP travels under these experimental conditions mainly via the right vagus nerve.