Sinoaortic denervation prevents enhanced heat loss induced by central cholinergic stimulation during physical exercise.

The present study investigated whether the effects of central cholinergic stimulation on thermoregulation during exercise are modulated by arterial baroreceptors. Wistar rats were submitted to sinoaortic denervation (SAD) or sham denervation (SHAM) and then fitted with a chronic guide cannula into the lateral cerebral ventricle. After 2weeks, a catheter was implanted into the ascending aorta, and a temperature sensor was implanted into the peritoneal cavity. Two days later, the rats were submitted to exercise on a treadmill at 18m/min until fatigued. Thermoregulatory and cardiovascular responses were measured after injection of 2μL of 10mM physostigmine (Phy) or 0.15M NaCl solution (Sal) into the cerebral ventricle. In SHAM rats, Phy injection induced a greater exercise-induced increase in blood pressure and lower increase in heart rate than Sal treatment. In the SAD group, the attenuation of heart rate in response to Phy was blocked despite an exaggerated increase in blood pressure. SHAM rats treated with Phy had a higher increase in tail skin temperature compared to Sal injection (31.9±0.4°C Phy-SHAM vs. 30.1±0.6°C Sal-SHAM, 5min after injection; p<0.05), resulting in a lower exercise-induced increase in core temperature. In contrast, SAD blocked the Phy injection effects in thermoregulatory responses during exercise (tail temperature: 30.1±1.2°C Phy-SAD vs. 29.5±1.2°C Sal-SAD, 5min, p=0.65). Therefore, we conclude that the enhancement of cutaneous heat loss induced by central cholinergic stimulation during exercise is mediated primarily by arterial baroreceptors.