Anti-nicotinic and anti-muscarinic actions of eperisone in the isolated canine atrium.

The effects of eperisone, an antispastic agent, on the chronotropic and inotropic responses to acetylcholine, nicotine or stimulation of intracardiac autonomic nerves were evaluated in isolated, blood-perfused canine atrium. Eperisone (10-300 micrograms) injected into the sinus node artery of the isolated atrium produced dose-related negative chronotropic and inotropic effects, which were not affected by atropine. In the same doses, eperisone inhibited the negative chronotropic and inotropic responses to an injection of acetylcholine and intracardiac parasympathetic stimulation. Eperisone also suppressed the negative followed by positive cardiac responses to nicotine, but did not modify the positive responses to intracardiac sympathetic stimulation or norepinephrine. The inhibitory effect persisted much longer for the responses to nicotine or parasympathetic stimulation than for those to acetylcholine. These results suggest that eperisone at doses that induce direct cardiac depressant effects exerts its blocking action on nicotinic receptors at parasympathetic ganglia and sympathetic nerve terminals and on muscarinic receptors at the effector cells in the dog heart.