THE INFLUENCE OF "HEART STIMULANTS" ON THE CONTRACTION OF ISOLATED MAMMALIAN CARDIAC MUSCLE

¹ From the Department of Pharmacology, Cornell University Medical College, New York, N. Y.

The property of producing sustained augmentation of the "systolic" force of mammalian cardiac muscle which is characteristic of the digitalis glycosides is absent in camphor, pentamethylene tetrazol ("Metrazol," "Cardiazol"), nikethamide (pyridine--carboxylic acid diethylamide, "Coramine"), and barium chloride.

The xanthines (caffeine, theobromine and theophylline) are ineffectual except in concentrations considerably above those attainable therapeutically. Compared with digitalis glycosides, their action is rapid in onset and brief in duration.

Epinephrine augments the "systolic" force of mammalian heart muscle to a marked degree and in concentrations attainable with therapeutic doses. The effect is almost immediate in onset; its duration is a matter of only about 10 to 20 minutes rather than hours as in the case of the digitalis glycosides.

Therapeutically attainable concentrations of ephedrine may increase the force of cardiac muscle. The range between the concentration which stimulates and that which depresses the heart muscle is small. Under the conditions of the present experiments it did not "potentiate" epinephrine action, but rather reduced it.