Effect of Acetylcholine on Isolated Cat and Rabbit Heart Ventricle Preparation

Abstract

Abstract: The atria and the upper part of the intra‐ventricular septum were removed from rabbit and cat heart, and the ventricular preparations were perfused in vitro with Krebs's solution. Preparations from twenty cats and 15 rabbits were studied for their sensitivity to acetylcholine. In the isolated rabbit ventricular preparations, acetylcholine in doses of 0.01‐0.1 pg caused a very weak negative inotropic and a chronotropic effect. Higher doses caused a dose‐dependent standstill. The cat ventricle preparations were rather insensitive to acetylcholine. When studied against noradrenaline induced increases in heart rate and force of contraction, acetylcholine in these preparations, also, caused a negative inotropic and chronotropic effect. In both the cat and rabbit preparations, the effect of acetylcholine was blocked by atropine 0.1 μg/ml in the perfusing solution. After pretreatment with atropine, acetylcholine (50‐100 μg) caused a positive inotropic and chronotropic effect that was blocked with propranolol 0.1‐0.2 μg/ml. This effect of acetylcholine was not obtained in preparations from reserpine treated animals.It was concluded that the cat and rabbit ventricle myocardium contains receptors to acetylcholine, and that stimulation of these cause a negative inotropic and chronotropic effect. Moreover, acetylcholine may release noradrenaline from the adrenergic nerve fibres. The difference in sensitivity to acetylcholine between the two species may indicate a difference in the significance of parasympathetic nerve stimulation to the ventricular myocardium in the two species.