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

Abstract

Exercise involves the interaction of several physiological processes, in which adjustments in pulmonary ventilation occur in response to increased O 2 consumption, CO 2 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 aCO 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.

Peripheral chemoreflex activation induces expiratory but not inspiratory excitation of C1 pre‐sympathetic neurones of rats

“…This is relatively short which is important as it prevents large changes in PP which causes mechanical instability and loss of whole cell neuronal recordings. Several previous studies demonstrated that bilateral denervation of carotid body chemoreceptors abolished the respiratory, sympathetic, and cardiovascular responses to KCN at this concentration in vivo and in situ 33–35 …”

The carotid bodies exercise control over active expiration but not peak performance during high‐intensity treadmill running

“…If similar synergistic interaction applies to respiratory motor control during intense whole body exercise, the selective carotid body contribution to exercise hyperpnoea may be less than that evident in the study by Spiller et al. (2020). Nevertheless, whatever the nature of that potential interaction, there is a substantive role for carotid body feedback in the manifestation of the full hyperpnoeic response to exercise, at least in rats.…”

“…Synergistic interaction between the muscle metaboreflex and the central chemoreflex has been shown in humans using post-exercise cuff occlusion to activate muscle afferents (Alghaith, Balanos, Eves, & White, 2019). If similar synergistic interaction applies to respiratory motor control during intense whole body exercise, the selective carotid body contribution to exercise hyperpnoea may be less than that evident in the study by Spiller et al (2020). Nevertheless, whatever the nature of that potential interaction, there is a substantive role for carotid body feedback in the manifestation of the full hyperpnoeic response to exercise, at least in rats.…”

“…It is established that peripheral chemoreceptor inputs modulate active expiration (Malheiros‐Lima, Silva, Souza, Takakura, & Moreira, 2020). In this issue of Experimental Physiology , Spiller, da Silva, Francescato, and Moraes (2020) explore whether the carotid bodies are necessary for the recruitment of active inspiration and expiration during low‐ and high‐intensity exercise in rats.…”

“…On the long‐standing issue of the role of the carotid bodies in the ventilatory response to exercise, Spiller et al. (2020) reveal that the principal arterial chemoreceptors are an important component in the integrative feedback system that drives active inspiration and expiration, which appears especially important in the defence of acid–base homeostasis. Removal of the carotid body's contribution to the exercise hyperpnoea results in a greater systemic acidosis during high intensity exercise, with potential implications for muscular performance depending upon the nature of the exercise that is performed.…”