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)