Sinoaortic denervation prevents postexercise reductions in arterial pressure and cardiac sympathetic tonus

Arterial pressure, cardiac sympathetic tonus (ST), and heart rate (HR) are reduced after a single bout of dynamic exercise in spontaneously hypertensive rats (SHR). To test if the arterial baroreflex is required for these postexercise responses, intact (n = 9) and sinoaortic-denervated (SAD) rats (n = 5) were chronically instrumented with an arterial catheter for the measurement of arterial pressure and HR and for the infusion of cardiac autonomic antagonists. Five days after instrumentation, cardiac ST and parasympathetic tonus (PT) were determined under two experimental conditions (no exercise and postexercise). SAD rats did not alter no-exercise cardiac ST (intact 47 +/- 3 vs. SAD 50 +/- 3 beats/min); however, no-exercise PT was reduced (intact -24 +/- 2 vs. SAD -4 +/- 4 beats/min, P < 0.05). Acute exercise reduced arterial pressure (postexertional hypotension, -20 +/- 3 mmHg, P < 0.05), cardiac ST (no exercise 47 +/- 3 vs. postexercise 24 +/- 3 beats/min, P < 0.05), and PT (no exercise -24 +/- 2 vs. postexercise -11 +/- 2 beats/min, P < 0.05) in intact SHR. In contrast, SAD prevented postexercise reductions in arterial pressure and cardiac ST (no exercise 50 +/- 3 vs. postexercise 59 +/- 7 beats/min). Furthermore, SAD had no effect on postexercise PT (no exercise -4 +/- 4 vs. postexercise -7 +/- 4 beats/min). These results demonstrate that the arterial baroreflex is required for the reduction in arterial pressure and cardiac ST that occurs in SHR after a single bout of dynamic exercise.