The role of carotid bodies in the generation of active inspiratory and expiratory responses to exercise in rats

Abstract

New findings: What is the central question of this study? What is the carotid bodies' contribution to active inspiratory and expiratory response to exercise? What is the main finding and its importance? Removal of the carotid bodies reduced the active inspiratory and expiratory responses of diaphragm and abdominal internal oblique muscles, respectively, to high-intensity, but not to low-intensity, exercise in rats. Removal of the carotid bodies increased $P_{\mathrm{aC}{O}_2}$ and decreased arterial pH in response to high-intensity exercise. The carotid bodies contribute to the inspiratory and expiratory adjustments to high-intensity exercise in rats.

Abstract: Exercise involves the interaction of several physiological processes, in which adjustments in pulmonary ventilation occur in response to increased O₂ consumption, CO₂ production and altered acid-base equilibrium. The peripheral chemoreceptors (carotid bodies; CBs) are sensitive to changes in the chemical composition of arterial blood, and their activation induces active inspiratory and expiratory responses. Herein, we tested the hypothesis that the CBs contribute to the active inspiratory and expiratory responses to exercise in rats. We performed electromyographic recordings of the diaphragm (Dia_EMG ) and abdominal internal oblique (Abd_EMG ) muscles in rats before and after bilateral removal of the CBs (CBX) during constant-load low-intensity and high-intensity progressive treadmill exercise. We also collected arterial blood samples for gaseous and pH analyses. Similar increases in Dia_EMG frequency in both experimental conditions (before and after CBX) during low-intensity exercise were observed, without significant changes in the Dia_EMG amplitude. During high-intensity exercise, lower responses of both Dia_EMG frequency and Dia_EMG amplitude were observed in rats after CBX. The Abd_EMG phasic active expiratory response was not significant either before or after CBX during low-intensity exercise. However, CBX reduced the phasic active expiratory responses during high-intensity exercise. The blunted responses of inspiratory and expiratory adjustments to high-intensity exercise after CBX were associated with higher $P_{\mathrm{aC}{O}_2}$ levels and lower arterial pH values. Our data show that in rats the CBs do not participate in the inspiratory and expiratory responses to low-intensity exercise, but are involved in the respiratory compensation against the metabolic acidosis induced by high-intensity exercise.

Keywords: acid-base equilibrium; carotid bodies; inspiration and active expiration; physical exercise.