Effect of Changes of Blood pH on Reaction of Heart to Cocaine.

Abstract

Changes in the concentration of hydrogen ions of the blood previously reported 1 produced well-marked effects in the reaction of the heart to caffeine. Other drugs under these conditions have since been studied, among them cocaine. Observations were made on the heart in situ, after removal of the anterior portion of the chest wall. The experiments were done on cats anesthetized with urethane, under artificial respiration. The contractions were recorded on smoked paper by means of levers attached with fine threads to the right auricle and right ventricle. 1

The results obtained were in several respects much more striking than in the experiments with caffeine or the other drugs. The resistance of the heart to cocaine was greatly increased by the intravenous injection of alkali, and very much diminished by acid. Small doses of the alkaloid administered after the intravenous injection of weak acid caused pronounced depression of the heart. While alkali did not necessarily nor always prevent the action of cocaine, its injurious effect was greatly decreased and often entirely suppressed.

Experiment No. 1. Sodium carbonate in a concentration of 2.5 per cent was injected intravenously in divided doses, into a cat weighing 2.5 kilos, until a total of 0.9 gm. was given. The subsequent injection of 1 cc. of 1 per cent cocaine hydrochloride, or 4 mg. per kilo, failed to produce any noticeable change in the action of the heart. The same amount of the alkaloid, administered 33 minutes after 0.75 gm. sodium acid phosphate, given in a dilution of 2.5 per cent, decreased the frequency of the heart about 60 per cent, and greatly weakened the force of the contractions.

Experiment No. 2. A dose of 3 mg. cocaine hydrochloride, injected one minute after administration of 3 cc. of 1 per cent HCl acid, reduced the strength of the contractions 60 to 70 per cent and considerably decreased their frequency.