Effects of exercise training on responses to central injection of CRF and noise stress

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The purpose of this study was to test the hypothesis that the cardiovascular and sympathoadrenal responses to acute environmental stress are attenuated by exercise training. Furthermore, we tested the hypothesis that the cardiovascular and sympathoadrenal responses to intracerebroventricular (ICV) administration of corticotropin-releasing factor (CRF) would be attenuated by training. Conscious, unrestrained, male Sprague-Dawley rats assigned to either a treadmill trained (16–26 m/min, 30–60 min/day, 5 days/week) or nontrained (16–26 m/min, 10 min/day, 1 day/week) group were studied. After 8–10 weeks of training, maximal oxygen uptake was significantly higher in the trained (108 ± 3 ml/kg/min) vs. the nontrained (94 ± 4 ml/min/kg) group. There were no significant differences in baseline mean arterial pressure, heart rate and plasma catecholamine levels associated with training. Trained rats exhibited significantly attenuated elevations in arterial pressure (20 ± 3 vs. 36 ± 2 mmHg for nontrained) and heart rate (−3 ± 3 vs. 12 ± 5 beats/min for nontrained) in response to acute noise stress. Twenty minutes after ICV administration of CRF, blood pressure (trained = 119 ± 2 mmHg, nontrained = 127 ± 2 mmHg), heart rate (trained = 408 ± 8 beats/min, nontrained = 424 ± 10 beats/min), plasma norepinephrine levels (trained = 757 ± 54 pg/ml, nontrained = 775 ± 100 pg/ml) and plasma epinephrine levels (trained = 266 ± 29 pg/ml, nontrained = 225 ± 42 pg/ml) were significantly elevated in both trained and nontrained groups. CRF-induced elevations of blood pressure, but not heart rate or plasma catecholamine levels, were significantly attenuated in the trained group. These data support the hypothesis that regularly performed exercise is associated with diminished cardiovascular responses to environmental stress. Furthermore, the results indicate that exercise training can alter the cardiovascular response to a central nervous system pharmacologic stimulus in the rat.