The action of adrenalin,pituitrin and acetyl-cholin on the coronary arteries of the rabbit.

Abstract

The present investigation is a preliminary study of the action of the sympathetic and vagus nerves on the coronary arteries of the rabbit. The effect of adrenalin and acetyl-cholin on the coronary flow of the perfused heart of the rabbit was studied because of the action that these drugs are said to have on the extrinsic cardiac nerves. Pituitrin was employed for the purpose of comparing smooth muscle stimulation with that of the sympathetic nerve action of adrenalin.

Adrenalin was introduced into the perfusate by injecting it with a hypodermic syringe directly into the tubing at its attachment leading into the aorta. The concentration of adrenalin used was 1-10,000,000, 0.2 cc. of this being injected at a rate which would produce a dilution of approximately 1-200,000,000 in the coronary arteries. The above low concentration was employed to avoid the complicating effects produced by the extreme cardiac stimulation resulting from the higher concentrations that are ordinarily introduced. Adrenalin in this dilution produced a definite decrease in the rate of coronary flow. The decrease in the rate of perfusion varied from 12 to 22.5 per cent. The diminished perfusion rate began immediately after the introduction of the drug, and persisted up to the point of maximum cardiac stimulation. At this point the rate of coronary flow was slightly augmented for a short time. Even with these low concentrations of adrenalin there was a very distinct stimulating effect on the heart, as indicated by the acceleration in heart rate and increase in amplitude of contraction.

Pituitrin, in concentrations of 1-50,000 regularly produced a striking decrease in the rate of perfusion. This change in the perfusion rate persisted for some time after the drug was discontinued.