Nitric oxide modulates autonomic effects on spontaneous sinus discharge rate and atrioventricular nodal conduction in open chest anesthetized dogs. Elvan, Arif, Michael Rubart, Douglas P. Zipes. Krannert Institute of Cardiology, Department of Medicine, Indiana University School of Medicine, Roudebush VA Medical Center, Indianapolis, Indiana
APStracts 3:0284H, 1996.
The purpose of this study was to investigate the role of nitric oxide (NO) in mediating vagal and sympathetic modulation of spontaneous sinus cycle length (SCL) and atrioventricular (AV) nodal conduction time (AH-interval) in 62 open chest mongrel dogs anesthetized with a -chloralose. Infusion of an inhibitor of NO synthase (NOS), NG -monomethyl-L-arginine (L-NMMA, 4mg/ml), into the sinus and AV nodal arteries attenuated significantly (p<0.01) the negative chronotropic and dromotropic response to vagal nerve stimulation (VS) and VS during ansae subclaviae stimulation (SS) or isoproterenol (ISO) infusion. Intravenous administration of L-arginine (100 mg/kg) reversed these responses toward control values while D-arginine did not have a significant effect. L-NMMA significantly (p<0.01) enhanced the effects of SS and ISO on SCL and AH-interval; L-arginine reversed these changes toward baseline. L-NMMA increased the minimum concentration of acetylcholine needed to induce 50% or 100% prolongation of SCL or induction of second degree or complete AV block during concomitant isoproterenol infusion. L-arginine reversed these effects. NOS inhibition did not affect the direct cholinergic actions of ACh on SCL and AH-interval but enhanced -adrenergic positive chronotropic and dromotropic effects. We conclude that NO plays a stimulatory role in mediating vagal neurotransmission and vagal modulation of sympathetic effects, and an inhibitory role in the mediating sympathetic neurotransmission. 

Received 6 December 1995; accepted in final form 19 June 1996.
APS Manuscript Number H1131-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996