Effect of cold rearing on metabolic rate and growth rate of obese (ob/ob) mice.

Oxygen consumption, total body mass, and body fat content were measured in lean and obese animals housed from birth at either 17 +/- 2 or 28 +/- 2 degrees C. Results for each of the three parameters were recorded at three time points 26, 35, and 56 days of age. The experiments demonstrate that at both ambient temperatures oxygen consumption expressed per kilogram body mass is consistently greater in lean animals. In all animals oxygen consumption (ml/kg/min) falls between 26 and 56 days, but significantly so in obese mice at 17 degrees C. There is no difference in age-related reduction of oxygen consumption between the genotypes at 28 degrees C; cold environment also significantly impairs growth of obese animals but not of lean ones. Contrary to those at 28 degrees C obese mice at 17 degrees C do not differ significantly in body weight from lean controls by 56 days of age. Carcass fat is consequently reduced in cold-reared obese mice compared to warm-reared obese, when expressed as grams of fat. When expressed as percentage fat, cold-reared lean and obese mice have less fat at 56 days.