Increased brain L-arginine availability facilitates cutaneous heat loss induced by running exercise

The effects of increased brain availability of L-arginine (L-arg), a precursor for nitric oxide synthesis, on core body temperature (Tcore ) and cutaneous heat loss were evaluated in running rats. One week prior to the experiments, adult male Wistar rats received the following implants: a chronic guide cannula in the lateral cerebral ventricle and a temperature sensor in the abdominal cavity. On the day of the experiments, the rats were assigned to receive a 2-μL intracerebroventricular injection of either NaCl (0.15 mol/L) or L-arg solution (0.825, 1.65 or 3.30 mol/L); Tcore and tail skin temperature were measured while the rats ran at a speed of 18 m/min until they were fatigued. L-arginine induced a dose-dependent reduction in the threshold Tcore required for cutaneous heat loss (38.09 ± 0.20°C for 3.30-mol/L L-arg vs 38.61 ± 0.10°C for saline; P < 0.05), which attenuated the exercise-induced hyperthermia. Although the rats treated with L-arg presented a lower Tcore at the end of exercise (~0.7°C lower after treatment with the highest dose), no changes in the time to fatigue were observed relative to the control trial. These results suggest that brain L-arg controls heat loss during exercise, most likely by modulating the sympathetic vasoconstrictor tonus to skin vessels. Furthermore, despite facilitating cutaneous heat loss mechanisms, increased brain L-arg availability did not enhance physical performance.