THE EFFECTS OF AUTONOMIC NERVOUS SYSTEM INHIBITION ON THE CIRCULATORY RESPONSE TO MUSCULAR EXERCISE*

Abstract

In order to assess the contribution of the autonomic nervous system to the circulatory response to exercise, six normal subjects were studied at rest and during steady-state leg exercise in a control period without drugs and after pharmacologic inhibition of the autonomic nervous system. The latter was accomplished by the intravenous administration of atropine, 2 mg. and the oral administration of guanethidine for 21 to 26 days, with the maximal daily dosage ranging from 50 to 85 mg. During the control study, exercise resulting in a four-to fivefold increase in oxygen consumption produced average increases above resting values of 68% in heart rate, 17% in stroke volume index, 96% in cardiac index and 129% in the left ventricular minute work. After combined administration of atropine and guanethidine, identical exercise resulted in average increases above resting values of 28% in heart rate, 1% in stroke volume, 30% in cardiac index, and 5% in left ventricular minute work. These studies demonstrate the important contribution made by the autonomic nervous system to the circulatory response to exercise in man and to indicate that the sympathetic division plays the major role in this regard.