THE ACTION OF PEOCAINE ON THE HEART

Abstract

The effect of procaine on rhythmicity and on the autonomic nervous mechanisms was observed in the spontaneously beating auricle of the tortoise Pseudemys elegans. The effect of procaine on stimulation threshold and contractility was studied on ventricle strips of this species horizontally suspended in a bath and stimulated rhythmically by condenser discharges. Refractory period and fiber condution time were detd. by recording 2 simultaneous electrograms with small wick electrodes placed on a horizontally suspended ventricular strip, rhythmically stimulated by condenser discharges and permitted to contract isometrically. Procaine in concn. of 190,000 to 1:5,000 showed an inconsistent effect on rhythmicity; the rate sometimes increased and sometimes decreased. The increasing auricular rate was not accompanied by a decrease in the contractility of the auricles, indicating that procaine enhanced auricular contractility. It was assumed that the increased auricular contractility was due to the removal of the vagal tone. The ability of procaine to antagonize the effects of epinephrine could not be shown conclusively in these expts. However, a procaine concn. of 1:10,000 seemed to block the rate increase caused by epinephrine 1:30,000,000. Procaine antagonized the effects of acetylcholine. The effect of procaine on the. ventricle was manifested in the elevation of the stimulation threshold and the prolongation of the fiber conduction time. Procaine in concn. of 1:50,000 caused no change in the beat size, and had no effect on the refractory period. Di-ethyl-amino-ethanol produced no consistent effect on either the auricle or ventricle of the turtle heart. Similarly p-aminobenzoic acid in concn. up to 1000 had no definite effect. The effect of procaine on stimulation threshold and on conduction was found to be definitely greater than that of quinidine. Both drugs prolonged ventricular conduction time in 1:100,000 concn., but the effect of procaine was greater. When the bath containing either one of the drugs was replaced by fresh Ringer''s soln., recovery was more complete after procaine than after quinidine. While procaine had little influence on ventricular contractions, quinidine in concn. of 1:50,000 depressed contractility. In the course of the clinical application of procaine, the blood pressure levels were not found to be lower. Extrasystoles occurring during open chest operations ceased following the infusion of procaine. In 2 instances ventricular tachycardia was slowed but not terminated by the admn. of procaine. It is probable that procaine prevents cardiac arrhythmias during operations by raising the stimulation threshold.