Exercise during intermittent cold exposure prevents acclimation to cold rats.

1. Energy balance and brown adipose tissue growth were examined in four groups of male Wistar rats: (i) sedentary, living at 24 degrees C (warm), (ii) exercise-trained, 2 h daily, living at 24 degrees C, (iii) living at 24 degrees C but exposed to -5 degrees C, 2 h daily and (iv) living at 24 degrees C but exercise-trained while being exposed to -5 degrees C, 2 h daily. 2. Cold exposure during exercise training appeared to have little additional influence on body composition following 28 days of treatment; body mass gain, in addition to protein and fat gains, of exercised cold-exposed rats were similar to the gains observed in exercised warm-exposed control animals. However, in sedentary cold-exposed rats protein, fat and body mass gains were significantly lower than the gains measured in sedentary rats not exposed to cold. 3. Metabolizable energy intake, expressed mass-independently, was similar in sedentary warm-exposed rats and both groups of animals that were exercise-trained. Metabolizable energy intake was increased almost 15% in sedentary cold-exposed rats. 4. Energy expenditure (mass independent), excluding the net cost of exercise training, was not different in sedentary warm-exposed and exercised rats; energy expenditure was almost 20% higher in sedentary cold-exposed rats. 5. Total protein and deoxyribonucleic acid (DNA) contents of brown adipose tissue were more than doubled in sedentary rats exposed to cold; protein and DNA levels were similar among the other three groups of rats. 6. Treadmill running during daily, 2 h exposure at -5 degrees C appears to prevent the cold acclimation responses that occur in sedentary rats receiving similar cold exposure.