(Hypertension. 1997;30:714.)
© 1997 American Heart Association, Inc.
Articles |
Acute and Chronic Effects of Exercise on Baroreflexes in Spontaneously Hypertensive Rats
From the Hypertension Unit, Heart Institute, Faculty of Medicine (C.E.N., E.M.K.), and the Exercise Physiology Laboratory, Physical Education School (G.J.J.S., C.E.N., P.C.B.), University of São Paulo, Brazil.
Correspondence to Patricia Chakur Brum, PhD, Exercise Physiology Laboratory, Physical Education School, University of São Paulo, Av Prof Mello Moraes, 65, São Paulo, Brazil 05508-900. E-mail pcbrum{at}spider.usp.br
Abstract We studied the effects of acute and chronic
exercise on the arterial baroreflex and chemosensitive
cardiopulmonary baroreflex (CCB) in spontaneously hypertensive
rats (SHR). Arterial baroreflex and CCB were evaluated in
normotensive rats (NR, n=11) and SHR (n=5) at rest and after 30 minutes
of an acute bout of exercise (45 minutes at 50% of
VO2max). In addition, these baroreflexes were
evaluated in sedentary (n=5) and exercise-trained (n=9) SHR. Exercise
training was performed on a motor treadmill, 5 days/week, during 60
minutes, at 50% of VO2max. Baroreflex
bradycardia and tachycardia, analyzed by baroreflex
sensitivity index (
heart rate/ mean arterial
pressure), were significantly lower in SHR than in NR (0.7±0.1 versus
2.0±0.1 and 1.8±0.2 versus 3.4±0.1 beats per minute [bpm]/mm Hg,
respectively). During the recovery period from acute exercise,
baroreflex bradycardia was significantly higher than at rest only in
SHR (1.7±0.1 versus 0.7±0.1 bpm/mm Hg). Hypotension and bradycardia
induced by CCB stimulation (5-hydroxytryptamine, IV)
were similar between SHR and NR, and an acute exercise bout did not
change these responses. Exercise training markedly improved baroreflex
bradycardia and tachycardia in SHR (1.9±0.1 versus
0.7±0.1 and 2.9±0.1 versus 1.8±0.2 bpm/mm Hg,
respectively). Exercise-trained rats had greater bradycardiac (118±26
versus 14±2 and 209±30 versus 19±5 bpm to 1 and 2 µg/kg 5-HT,
respectively) and hypotensive (30±6 versus 15±3 and 45±7 versus
17±2 mm Hg to 1 and 2 µg/kg 5-hydroxytryptamine, respectively)
responses to CCB stimulation. In conclusion, an acute bout of exercise
increases baroreflex bradycardia in SHR, and exercise training
attenuates hypertension concomitant with improved arterial
baroreflex and CCB sensitivity in SHR.
Key Words: exercise, acute and chronic • arterial baroreflex • baroreflex
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