The Role of TRPV1‐Expressing Neurons in the Control of Heart Rate During Dynamic Exercise in Rats

Abstract

Heart rate (HR) increases at the beginning of dynamic exercise, then remains constant or gradually increases in response to the exercise intensity. Both central command and the exercise pressor reflex (EPR) are thought to play an important role for this tachycardic response. Recently, the contribution of transient receptor potential vanilloid 1 (TRPV1) channel to the EPR has been reported (Smith SA et al, J Physiol 2010). However, the role of the TRPV1 channel on the exercise tachycardia during dynamic exercise remains largely unknown. We therefore examined the effect of systemic TRPV1 channel blockade or activation on the HR response to treadmill exercise in rats. Male Wistar rats were previously implanted with telemetry transmitters (TRM54P, Millar) to measure HR and arterial blood pressure (AP), and trained to run on a treadmill. Both HR and mean AP (MAP) responses to treadmill running (20 or 40 m/min, 60 s) were compared before and after administration of TRPV1 channel agonists or antagonists. Neither the TRPV1‐selective (SB366791; 3 mg/kg) nor the nonselective (ruthenium red; 5 mg/kg) antagonists affected the HR response to exercise. However, another TRPV1 selective antagonist 5′‐iodoresiniferatoxin (IRTX; 0.3 mg/kg) or a TRPV1 agonist capsaicin (20 mg/kg, sc under anesthesia) markedly attenuated the HR response to exercise. MAP responses to exercise were not affected by these drugs. Given the partial agonist‐like effect of IRTX, systemic desensitization of the TRPV1 channel‐expressing neurons attenuated the EPR‐mediated HR response during dynamic exercise in rats. In conclusion, TRPV1‐expressing neurons play an important role for the HR response during dynamic exercise.