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Even Small Changes in Body Temperature Can Affect the Cardiac Function in Anesthetized Mice

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 were 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. Sciatic nerve‐selective desensitization of TRPV1 channel by resiniferatoxin (10 µg, under anesthesia) significantly attenuated the HR response to exercise. Systemic administration of potent TRPV1 channel antagonist iodoresiniferatoxin (0.3 mg/kg ip), which has a partial agonist‐like effect, also attenuated it. On the other hand, either the TRPV1‐selective (SB366791; 3 mg/kg) or a nonselective (ruthenium red; 5 mg/kg) antagonists did not affect the HR response to exercise. In conclusion, desensitization of the TRPV1 channel‐expressing neurons attenuated the EPR‐mediated HR response during dynamic exercise in rats, suggesting that TRPV1‐expressing neurons play an important role for the HR response during dynamic exercise.