ACID HUMORAL CONTROL OF HEART BEAT

Abstract

The phenomenon of "potentiation" of humoral intermediation by acid was studied on the heart of the turtle. It was found that CO2 added to an acetylcholine containing Ringer''s soln. augmented the inhibitory effects of this soln. This may be regarded as an example of potentiation of exogenous humoral intermediation by an exogenous acid. Pre-acidulation of the heart by immersion in carbonated Ringer''s soln. produced similar potentiation which indicates the significance of tissue acidity. Exposure of the intact heart to carbonated Ringer''s soln. increased the inhibition produced by faradic stimulation of the vagus. This finding is regarded as an example of potentiation of endogenous humoral intermediation by exogenous acid. Exposure of the heart to small cones, of cyanide in Ringer''s soln. also increased the effects of vagal stimulation. It is suggested that this result illustrates potentiation of endogenous humoral intermediation by an endogenous acid (i.e., lactic acid). Simultaneous exposure of the heart to CO2 and cyanide produced a much greater potentiation than exposure to either substance alone. This is thought to indicate an additive effect of 2 endogenous acids upon tissue pH and anti-cholinesterase activity. Reasons are briefly stated in support of the hypothesis that potentiation of humoral intermediation by acid may provide an automatic chemical adjustment of general biological interest.