CIRCULATORY RESPONSES TO ACETYLCHOLINE IN NORMAL DOGS AND IN DOGS WITH EXPERIMENTAL AORTIC REGURGITATION

¹ Departments of Medicine and of Physiology, George Washington University, School of Medicine, Washington, D. C.

In the unanesthetized normal dog 2 mgm. of acetyl-beta-methylcholine chloride produces a slight fall in blood pressure, a marked reflex cardio-acceleration, a decided quickening of the velocity of blood flow and a large increase in the volume flow.

In dogs with chronic experimental aortic regurgitation the cardio-acceleration does not usually occur and the increase volume flow is produced by an increased stroke volume.

The fact that the total circulation time is reduced to half or a third normal in the unanesthetized dog renders doubtful the applicability of the techniques previously used in studying the human cardiac output under acetylcholine, and explains why such work indicates that the drug produces no change in the cardiac output even while producing marked symptomatic changes.