Temperature responses of rats to treadmill exercise, and the effect of thermoregulatory capacity.

The relationship between work intensity and body temperature was investigated in the rat in an attempt to clarify whether alterations in thermoregulatory capacity can modify the rte and extent of body warming during exercise. Repeated noradrenaline injections led to increased hyperthermic response to that amine. However, during exercise these animals did not attain higher colonic temperatures as did the animals avoiding noradrenaline treatment. If noradrenaline was injected 60 min prior to test-exercise the body temperature of the rats rose to a higher level without the drug. The extent of this rise was, however, independent of the previous noradrenaline-treatment history. Beta blockade abolished the noradrenaline-induced hyperthermia but not the exercise-induced hyperthermia. Despite increased capacity for heat production, cold-acclimated rats did not attain higher colonic temperatures during exercise than did the running-trained, cold-stressed or sedentary control rats. However, the higher tail skin temperature of the cold-acclimated rats indicate that their heat production was enhanced but they maintained lower colonic temperature by dissipating the excess heat through the elevated blood flow to the tail and probably to other extremities. These results indicate that the rise in deep body temperature of the rats during work is proportional to work intensity and that the enhanced heat production capacity can be compensated for by increasing the heat loss activities.