Abstract
The present study aimed to investigate whether running performance in different environments is dependent on intact arterial baroreceptor reflexes. We also assessed the exercise-induced cardiovascular and thermoregulatory responses in animals lacking arterial baroafferent signals. To accomplish these goals, male Wistar rats were subjected to sinoaortic denervation (SAD) or sham surgery (SHAM) and had a catheter implanted into the ascending aorta to record arterial pressure and a telemetry sensor implanted in the abdominal cavity to record core temperature. After recovering from these surgeries, the animals were subjected to constant- or incremental-speed exercises performed until the voluntary interruption of effort under temperate (25° C) and warm (35° C) conditions. During the constant-speed exercises, the running time until the rats were fatigued was shorter in SAD rats in both environments. Although the core temperature was not significantly different between the groups, tail skin temperature was higher in SAD rats under temperate conditions. The denervated rats also displayed exaggerated increases in blood pressure and double product compared with the SHAM rats; in particular, in the warm environment, these exaggerated cardiovascular responses in the SAD rats persisted until they were fatigued. These SAD-mediated changes occurred in parallel with increased variability in the very low and low components of the systolic arterial pressure power spectrum. The running performance was also affected by SAD during the incremental-speed exercises, with the maximal speed attained being decreased by approximately 20% in both environments. Furthermore, at the maximal power output tolerated during the incremental exercises, the mean arterial pressure, heart rate and double product were exaggerated in the SAD relative to SHAM rats. In conclusion, the chronic absence of the arterial baroafferents accelerates exercise fatigue in temperate and warm environments. Our findings also suggest that an augmented cardiovascular strain accounted for the early interruption of exercise in the SAD rats.
Highlights
The physical exercise-induced increase in the demand of contracting muscles for oxygen and energetic substrates is a major challenge to body homeostasis and encompasses coordinated responses from the cardiovascular, ventilatory, hormonal, and thermoregulatory systems
The blood pressure lability determined by calculating the standard deviation of the mean arterial pressure (MAP) during the 60 min of rest was three-fold higher in the sinoaortic denervation (SAD) compared with SHAM animals (15 ± 3 mmHg vs. 5 ± 1 mmHg; P < 0.05)
The heart rate (HR) was higher in the SAD compared with SHAM animals throughout the resting period (437 ± 12 bpm vs. 346 ± 17 bpm at the 60th min; P < 0.05; Figure 1B)
Summary
The physical exercise-induced increase in the demand of contracting muscles for oxygen and energetic substrates is a major challenge to body homeostasis and encompasses coordinated responses from the cardiovascular, ventilatory, hormonal, and thermoregulatory systems. Previous reports showed that the surgical removal of the arterial baroafferents of the rat (sinoaortic denervation procedure - SAD) produced exaggerated exercise-induced increases in blood pressure [6,7] and iliac vascular conductance [8], and an exaggerated reduction in mesenteric conductance [9] These investigations regarding the consequences of an impaired baroreflex sensitivity on the physiological responses to exercise are clinically relevant considering that the loss of sensitivity is an outcome common to many diseases, such as diabetes, obesity, metabolic syndrome, and hypertension [10,11,12], and considering that physical exercise is a nonpharmacological tool for the treatment of such diseases [13,14]
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