THE ROLE OF ACETYLCHOLINE IN HYDROCARBON-EPINEPHRINE ARRHYTHMIAS

¹ Department of pharmacology, Hahnemann Hospital and Medical College, Philadelphia 2, Pennsylvania

Petroleum ether causes a loss of sinoatrial dominance in the cat. This is in contrast to diethyl ether where even large doses ordinarily do not disturb sinus rhythm. Chloroform disturbs the sinus pacemaker only in a small percentage of trials.

Acetylcholine is capable of inhibiting or preventing the loss of sinus node dominance caused by petroleum ether or chlorform.

During diethyl ether administration the action of acetylcholine on the heart is enhanced in proportion to the dose of ether used. Conversely both petroleum ether and chloroform inhibit acetylcholine cardiac effects.

Acetylcholine inhibits the sinus node depressant effect of epinephrine.

The ventricular arrhythmias precipitated by epinephrine during the inhalation of petroleum ether or chloroform may be prevented or restored to sinus rhythm by acetylcholine. Further, atropine does not prevent this action of acetylcholine.

The results indicate that acetylcholine plays a major role in hydrocarbon epinephrine arrhythmias. The mechanism of the so called sensitization of the heart to epinephrine may be explained by the fact that its natural antagonist acetylcholine is inhibited by hydrocarbons.