Effect of Propranolol on Excitation of Afferent Sympathetic Nerve Fibers during Myocardial Ischemia

The effect of propranolol on excitation of afferent cardiac sympathetic nerve fibers during myocardial ischemia has been examined. Using anesthetized dogs, the action potentials of the fibers were derived from either the 2nd or 3rd thoracic communicating ramus of the left side. Coronary artery occlusion resulted in excitation of the myelinated Aδfibers and unmyelinated C fibers, and in development of systolic bulge of the occluded area of the left ventricular wall. Eight to 16min after the systemic administrations of 0.5-5mg/Kg propranolol, development of systolic bulge was suppressed and the latency for excitation of the afferent nerve fibers became longer than that of the control occlusion experiments. The number of the action potentials per second during occlusion was significantly smaller than that of the control occlusion and percent change in number per second was close to that of heart rate. Resultantly, the num-ber of the action potentials per cardiac beat was not different from that of the control occlusion experiments. It is considered that propranolol suppressed excitation of the afferent cardiac sympathetic nerve fibers through reduction in heart rate.