CORONARY VASOCONSTRICTION BY LOCALLY ADMINISTERED ACETYLCHOLINE, CARBACHOL AND BETHANECHOL IN ISOLATED, DONOR‐PERFUSED, RAT HEARTS

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Abstract
1 Experiments were carried out on rat isolated heart preparations in which the coronary vasculature was perfused through the aorta at a constant flow rate with arterial blood from donor animals. Single doses of drugs were injected into the aortic cannula. 2 Small doses of acetylcholine, carbachol or bethanechol decreased perfusion pressure (PP) without markedly affecting left ventricular pressure (LVP) and heart rate (HR); larger doses of these drugs increased PP (vasoconstriction), and decreased LVP and HR in a dose‐dependent manner. 3 Acetylcholine, carbachol and bethanechol had almost no effects when perfused through the aorta in such a way as to exclude the coronary vessels. 4 Coronary vasoconstriction in response to acetylcholine, carbachol and bethanechol was not significantly affected by reserpine pretreatment, phentolamine or hexamethonium, but was antagonized by small doses of atropine. 5 From these results it is concluded that in the coronary vasculature of the rat, the receptors involved in the vasoconstrictor actions of acetylcholine, carbachol and bethanechol are muscarinic.