Related and unrelated changes in response to exercise and cold in rats: a reevaluation.

Groups of rats were subjected to various treatments: continuous exposure to cold (5 degrees C); exercise by running; intermittent cold exposure, -20 degrees C daily for 60 min; and in some experiments combined influence of cold acclimation and exercise for at least 6 wk. The resulting adaptive changes can be grouped in three different categories. Cold-specific changes included increased food intake, an increase in both mass and metabolic activity of brown adipose tissue leading to an increased capacity for nonshivering thermogenesis, and maintenance of the stores of ascorbic acid and muscle glycogen during cold exposure. These changes were associated with an improved resistance to cold with which the rats were able to maintain their body temperature in both cold air and water were typical of rats previously exposed to cold. Training-specific changes typically included increased activities of aerobic muscle enzymes and decreased activity of lactate dehydrogenase and a higher O2 uptake and shivering activity during cold exposure as compared with sedentary control rats. These changes were observed for trained rats only and were not associated with an improved resistance to cold. Other adaptive changes were found, to a variable extent, for all treated rat groups. These included cardiac hypertrophy, reduced urinary catecholamine excretion during and after stress situations, increased tail skin temperature response to isoproterenol, and a higher tail skin temperature during exposure to cold. There were no systematic differences between groups in changes of blood glucose, glycerol, or lactate concentrations during cold exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Modification of training-induced responses by repeated norepinephrine injections in rats.

Rats were subjected to daily (5 times/wk) running exercises, norepinephrine injections (0.5 mg/kg sc), or both for 9 wk; one rat group served as the control. Norepinephrine injections were used to potentiate the effect of the endogenous amine, the release of which is known to be stimulated by exercise. Changes observable in all treated rat groups included reduced weight gain, reduced food intake, decreased amount of epididymal fat, hypertrophy of the heart and adrenals, and increased tail skin temperature response to isoproterenol (0.2 mg/kg sc). The training-specific changes (increased activity of oxidative muscle enzymes) were not potentiated by training under the influence of exogenous norepinephrine administration. The changes produced by repeated norepinephrine injections alone (hypertrophy of the brown adipose tissue and increased colonic temperature response to isoproterenol) failed to develop if the rats underwent physical training in addition to drug treatment. Lower tail skin temperature in a cool environment (15 degrees C) was associated with norepinephrine treatment, whether or not there was simultaneous training. These results suggest that the chronic norepinephrine treatment-physical training combination led to complex adaptive changes that could not be systematically associated with either norepinephrine treatment or physical training alone.

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.