Abstract

Reserpine in single doses of 0.03 mgm. and above, when given to the isolated dog heart-lung preparation, causes a heart-rate increasing effect. The effect has the appearance of a continuous infusion of epinephrine or norepinephrine and in the dosage range of 1 to 5 mgm. is similar to the effect of approximately 3 microgm./min. of either of the two catechol amines given over a period of about 50 minutes. Long lasting release of epinephrine and/or norepinephrine best explains the phenomenon. Reserpine, in doses of 5 mgm. or larger, given to the heart under the chronotropic influence of sympathomimetic amines, has a rate-decreasing action which resembles the antiaccelerator action of veratramine in that it is atropine-resistant and antagonizes the positive chronotropic effects of extraneously supplied sympathomimetic amines. Such doses also antagonize the rate-increasing effect of initial doses of reserpine. Measured against ephedrine, the antiaccelerator potency of reserpine in the dog heart-lung preparation is about [unknown] that of veratramine (on a molar basis). Doses of 20 mgm. of reserpine and above have a negative inotropic effect upon the isolated dog heart in the heart-lung preparation.