Tonic and reflex cardiovascular autonomic control in trained-female rats

Abstract

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

Dynamic resistance training decreases sympathetic tone in hypertensive ovariectomized rats

“…In male SHR rats, moderate-intensity treadmill exercise training reduced AP, HR, and sympathetic tone. Moreover, the reduced resting HR correlated with the reduced sympathetic tone observed in female Wistar rats after moderate-intensity aerobic treadmill training (5). In another study, we previously reported that resting bradycardia may be the candidate mechanism for AP reduction in OVX rats undertaking aerobic treadmill training (6).…”

“…Sympathetic tone was determined as the difference between maximum HR after methylatropine injection and IHR. Vagal tone was measured as the difference between the lowest HR after propranolol injection and IHR (3,5). …”

“…Studies have demonstrated resting bradycardia in young (3) and old (4) normotensive male rats, in young normotensive females rats (5), in female ovariectomized rats (6,7), in male and female hypertensive rats (8,9), and in humans (10). The mechanisms underlying the cardiac adaptive response to exercise training differ between species and genders (3,5,10). A recent report from our laboratory demonstrated that changes in the cardiac autonomic control in trained female rats were correlated with reduced basal heart rate (HR), which suggests that autonomic control of HR plays a role in the resting bradycardia observed in trained female rats (5).…”

“…The mechanisms underlying the cardiac adaptive response to exercise training differ between species and genders (3,5,10). A recent report from our laboratory demonstrated that changes in the cardiac autonomic control in trained female rats were correlated with reduced basal heart rate (HR), which suggests that autonomic control of HR plays a role in the resting bradycardia observed in trained female rats (5). …”

“…Thus, it has been well established that aerobic exercise training causes decreases in basal AP and HR, which are associated with improvements in cardiovascular autonomic control (5,9) and baroreflex sensitivity (6,8,11). Recently, there has been growing clinical evidence showing the positive effects of resistance exercise training on the body composition and metabolic profile of both normal and diseased populations.…”