THE PHYSIOLOGIC ROLE OF THE SYMPATHETIC NERVOUS SYSTEM IN EXERCISE

¹ Laboratory of Chemical Pharmacology, National Heart Institute, and Laboratories of Physical Biology and Experimental Pathology, National Institute of Arthritic and Metabolic Diseases, National Institutes of Health, Bethesda, Maryland

Studies were made on the influence of blockade of sympathetic function on the performance and sequential alterations of plasma glucose, free fatty acids (FFA), lactate and triglycerides of rats required to exercise in a revolving cage. Rats were deprived of sympathetic function (SX rats) by depleting catecholamines from peripheral tissues of adrenal demedullated (DM) rats with syrosingopine in nonsedative doses, or by blocking the release of catecholamines at nerve endings with the potent bretylium-like drug, BW 392C60 (N-o-chlorobenzyl-N¹, N²-dimethylguanidine). The effects of exercise were also studied in intact, adrenalectomized (ADX) and DM rats. During exercise, plasma glucose rose about 90% in intact rats, but fell gradually in DM, ADX and SX rats. The FFA increase of 0.20 to 0.35 µEq/ml in ADX and SX rats was only about one-half that in intact rats and one-third that in DM rats. During the first 30 min, lactate rose about 3-fold in intact rats, and 2-fold or less in the other groups. With sustained exercise, lactate quickly returned to and remained at preexercise levels. Most ADX and SX rats collapsed before 150 min of exercise. In contrast, all intact rats ran longer than 150 min. The poor performance of SX rats was correlated with a fall in glucose, a small rise in FFA, no rise in body temperature and elevated heart glycogen. Our observations indicate that sympathetic blockade during exercise impairs performance and reduces FFA mobilization, and may interfere with the utilization of heart glycogen.