Tonic and reflex cardiovascular autonomic control in trained-female rats

The effects of exercise training on cardiovascular and autonomic functions were investigated in female rats. After an aerobic exercise training period (treadmill: 5 days/week for 8 weeks), conscious female Wistar (2 to 3 months) sedentary (S, N = 7) or trained rats (T, N = 7) were cannulated for direct arterial pressure (AP) recording in the non-ovulatory phases. Vagal (VT) and sympathetic tonus (ST) were evaluated by vagal (atropine) and sympathetic (propranolol) blockade. Baroreflex sensitivity was evaluated by the heart rate responses induced by AP changes. Cardiopulmonary reflex was measured by the bradycardic and hypotensive responses to serotonin. Resting bradycardia was observed in T (332 +/- 7 bpm) compared with S animals (357 +/- 10 bpm), whereas AP did not differ between groups. T animals exhibited depressed VT and ST (32 +/- 7 and 15 +/- 4 bpm) compared to S animals (55 +/- 5 and 39 +/- 10 bpm). The baroreflex and cardiopulmonary bradycardic responses were lower in T (-1.01 +/- 0.27 bpm/mmHg and -17 +/- 6 bpm) than in the S group (-1.47 +/- 0.3 bpm/mmHg and -41 +/- 9 bpm). Significant correlations were observed between VT and baroreflex (r = -0.72) and cardiopulmonary (r = -0.76) bradycardic responses. These data show that exercise training in healthy female rats induced resting bradycardia that was probably due to a reduced cardiac ST. Additionally, trained female rats presented attenuated bradycardic responses to baro- and cardiopulmonary receptor stimulation that were associated, at least in part, with exercise training-induced cardiac vagal reduction.