O desempenho físico em ambientes temperado e quente é diminuído pela ausência das aferências provenientes dos barorreceptores arteriais

Abstract

In the present study, we investigated whether running performance in temperate or warm environments was dependent on intact arterial baroreceptors reflexes. Wistar rats were submitted to either a sinoaortic denervation (SAD) or sham surgery (SHAM) and submitted to both constant intensity (18m/min) and incremental treadmill exercises (starting at a velocity of 10 m/min, with increments of 1 m/min every 2 min until the rats were fatigued) in both temperate (25°C) and hot (35°C) conditions. In these experiments, SAD and SHAM animals had a catheter implanted into the ascending aorta, and a temperature sensor implanted into the peritoneal cavity. Two days following these procedures, cardiovascular and thermoregulatory responses were evaluated. During constant-speed exercise, total exercise time until the rats were fatigued was reduced by SAD in both temperate (29 ± 3 min vs 66 ± 11 min, P<0.01; n=8) and hot condition (14 ± 1 min vs 23 ± 2 min, P<0.001; n = 8). Running performance was also affected by SAD during incremental-speed exercise, with maximal speed being significantly reduced (p<0.01). During constant-speed exercise, denervated rats displayed a higher increase in blood pressure when compared to SHAM rats (temperate: 141 ± 3 mmHg vs, 123 ± 2 mmHg P<0.001, n=8; hot: 174 ± 13 mmHg vs 134 ± 5 mmHg, P<0.02, n=8), but the thermoregulatory responses were not significantly different between the groups. SAD also induced an increase in the spectral power density of the very low oscillations of arterial systolic pressure during exercise (temperate: 20.3 ± 4.1 mmHg2 vs, 2.7 ± 0.4 mmHg2 P < 0.05, n = 6; calor: 26.9 ± 6.2 mmHg2 vs 5.9 ± 0.8 mmHg2, P < 0.05, n = 6). Furthermore, the heart rate values at the end of incremental exercise test were exacerbated by SAD (temperate: 593 ± 5 bpm vs, 533 ± 13 bpm P<0.05, n=5; hot: 639 ± 6 bpm vs 553 ± 19 bpm, P<0.05, n=5) Thus, chronic absence of arterial baroafferents anticipates exercise fatigue in temperate and warm environments. We suggested that an augmented cardiovascular strain has accounted the early interruption of the exercise SAD rats.