Sustained Decrease in Coronary Blood Flow and Excitation of Cardiac Sensory Fibers Following Sympathetic Stimulation

The effect of electrical stimulation of the efferent cardiac sympathetic nerves on activity of afferent cardiac fibers in the sympathetic nerves and coronary hemodynamics of anesthetized dogs has been examined. During partial constriction of the coronary artery, a brief stimulation of the efferent cardiac sympathetic nerves resulted in sustained excitation of the afferent fibers and a sustained decrease in blood flow of the constricted artery which were associated with systolic bulge of the left ventricle and elevation of the ST segment of electrocardiogram. These changes were not produced without constriction. Pretreatment with phentolamine suppressed excitation of the afferent fibers, development of systolic bulge and elevation of the ST segment. Also, the decrease in coronary blood flow induced by stimulation was replaced by an increase after the administration of the agent. Propranolol suppressed excitation of the fibers, systolic bulge and elevation of the ST segment, but could not eliminate the decrease in blood flow. The results indicate that sympathetic stimulation caused a decrease in coronary blood flow through excitation of the alpha-adrenergic receptors while increasing cardiac work load and energy requirements through excitation of the beta-adrenergic receptors, leading to more severe myocardial ischemia and excitation of the afferent fibers.