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Department of Physiology, Northeastern Ohio Universities College of Medicine, Rootstown, Ohio 44272
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.
sympathetic tonus; parasympathetic tonus; spontaneously hypertensive rats; arterial baroreflex; postexertional hypotension
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