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1 Sao Judas Tadeu University, Sao Paulo, Sao Paulo, Brazil
2 Hypertension Unit, Heart Institute (INCOR), University of Sao Paulo, Medical School, Sao Paulo, Sao Paulo, Brazil; Nephrology Department, Federal University of Sao Paulo, Sao Paulo, Sao Paulo, Brazil
3 Hypertension Unit, Heart Institute (INCOR), University of Sao Paulo, Medical School, Sao Paulo, Sao Paulo, Brazil
4 Department of Pharmacology and Toxicilogy, Wright State University, Dayton, Ohio, USA
* To whom correspondence should be addressed. E-mail: hipirigoyen{at}incor.usp.br.
Experiments were performed to investigate the influence of exercise training on cardiovascular function in mice. Heart rate, arterial pressure, baroreflex sensitivity and autonomic control of heart rate were measured in conscious, unrestrained male C57/6J sedentary (n = 8) and trained mice (n = 8). The exercise training protocol used a treadmill (1h/d; 5d/wk for 4wk). Baroreflex sensitivity was evaluated by the tachycardic and bradycardic responses induced by sodium nitroprusside and phenylephrine, respectively. Autonomic control of heart rate and intrinsic heart rate were determined using methylatropine and propranolol. Resting bradycardia was observed in trained mice as compared to sedentary animals (485 ± 9 vs. 612 ± 5 bpm), while mean arterial pressure was not different between the groups (106 ± 2 vs. 108 ± 3 mmHg). Baroreflex-mediated tachycardia was significantly enhanced in the trained group (6.97 ± 0.97 vs. 1.6 ± 0.21 bpm/mmHg, trained vs. sedentary) while baroreflex-mediated bradycardia was not altered by training. The tachycardia induced by methylatropine was significantly increased in trained animals (139 ± 12 vs. 40 ± 9 bpm, trained vs. sedentary) while the propranolol effect was significantly reduced in the trained group (49 ± 11 vs. 97 ± 11 bpm, trained vs. sedentary). Intrinsic heart rate was similar between groups. In conclusion, dynamic exercise training in mice induced a resting bradycardia and an improvement in baroreflex mediated tachycardia. These changes are likely related to an increased vagal and decreased sympathetic tone, similar to the exercise response observed in humans.
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