Cardiovascular response to static exercise during selective autonomic blockade in the conscious cat

Selective autonomic blockade with propranolol, atropine, and combined atropine and propranolol was used to elucidate the role of the autonomic nervous system in the cardiovascular responses that occur during voluntary static exercise in conscious cats. Seven animals were operantly conditioned to hold a bar against a fixed resistance for a constant time of 15 seconds and were then placed on an exercise regimen which consisted of small weakly increments in resistance. With a resistance of 100 g, heart rate (HR) increased by 7%. With exercise at a resistance of 200 g, HR (10%), left ventricular systolic pressure (LVSP, 16%), and LV max dp/dt (18%) increased, and significant changes in these parameters persisted throughout the remainder of the training period. β-Adrenergic receptor blockade with propranolol abolished the increase in LV max dp/dt, whereas HR and LVSP increased. After atropine, the increase in HR was abolished at the early training stages, whereas LVSP and LV max dp/dt increased. Administration of atropine and propranolol blocked the increase in HR and LV max dp/dt responses, whereas LVSP increased. In this study, the increased HR in response to exercise was mediated primarily by the parasympathetic nervous system, whereas the increases in LV max dp/dt were mediated by the sympathetic nervous system. Furthermore, the bradycardia accompanying chronic performance of isometric exercise resulted from both an increase in vagal tone and a decrease in sympathetic tone.