Nitroglycerin-induced suppression of excitation of afferent cardiac sympathetic nerves during myocardial ischemia.

Abstract

The effect of nitroglycerin on excitation of afferent cardiac sympathetic nerve fibers has been examined. Using anesthetized dogs, action potentials of the fibers were derived from either the 2nd or 3rd thoracic communicating ramus of the left side.Occlusion of the anterior descending branch of the left coronary artery resulted in development of systolic bulge of the anterior wall of the left ventricle and in excitation of myelinated Aδ and unmyelinated fibers. Systemic administrations of nitroglycerin in a dose of over 30μg/Kg reduced or eliminated systolic bulge and suppressed excitation of the afferent nerve fibers. The maximum duration of its inhibitory effect on afferent discharge was 240sec and it was produced with 60μg/Kg. The inhibitory effect of nitroglycerin was not observed during hypotension produced by the injections of regitine. The systemic administrations of regitine in a dose of over 100μg/Kg and a fall in systemic blood pressure produced by occlusion of the caval veins also eliminated systolic bulge and suppressed the afferent discharge.It is concluded that the inhibitory action on excitation of afferent cardiac sympathetic nerve fibers during myocardial ischemia is not specific for nitroglycerin and that the inhibitory action of nitroglycerin is dependent on the level of systemic blood pressure.