Intracerebroventricular tryptophan increases heating and heat storage rate in exercising rats

The role of increased hypothalamic tryptophan (TRP) availability on thermoregulation and rates of core temperature increase and heat storage (HS) during exercise was studied in normal untrained rats running until fatigue. The rats were each anesthetized with 2.5% tribromoethanol (1.0 ml kg(-1) ip) and fitted with a chronic guiding cannula attached to the right lateral cerebral ventricle 1 week prior to the experiments. Immediately before exercise, they were randomly injected through these cannulae with 2.0 microl of 0.15 M NaCl (SAL; n=6) or 20.3 microM L-TRP solution (n=7). Exercise consisted of running on a treadmill at 18 m min(-1) and 5% inclination until fatigue. Body temperature was recorded before and during exercise with a thermistor probe implanted into the peritoneal area. Rates of core temperature increase (HR, degrees C min(-1)) and heat storage (HSR, cal min(-1)) were calculated. TRP-treated rats showed a rapid increase in body temperature which was faster than that observed in the saline-treated group during the exercise period. The TRP group also showed a higher rate of core temperature increase and HS. TRP-treated rats that presented higher HR and HSR also fatigued much earlier than saline-treated animals (16.8+/-1.1 min TRP vs. 40+/-3 min SAL). This suggests that the reduced running performance observed in TRP-treated rats is related to increased HR and HSR induced by intracerebroventricular injection of TRP in these animals.