Thermoregulation and non-shivering thermogenesis in the genetically obese (ob/ob) mouse

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Abstract
The capacity for thermoregulation and thermogenesis in lean and genetically obese (ob/ob) mice has been investigated. At 4°C ob/ob mice rapidly die of hypothermia, because of a reduced capacity for cold-induced thermogenesis, but the animals are able to survive if previously adapted to 12°C. At all environmental temperatures between 30°C and 10°C the body temperature of ob/ob mice is 2.0–2.5°C below that of lean animals. This may be due to a lower “setting” for body temperature. At 34°C the oxygen consumption of obese mice is greater than that of the lean animals while at 30°C it is similar. When the environmental temperature is below 30°C the oxygen consumption of the lean mice is greater. The obese animals therefore expend less energy on thermoregulatory thermogenesis. The capacity for non-shivering thermogenesis was measured in lean and obese mice by investigating the effect of an injection ofl-nor-adrenaline (1000 μg/kg body weight) on the metabolic rate at 31°C. Non-shivering thermogenesis was reduced by one-half in the obese animals. One cause of the obesity of the ob/ob mouse is its high metabolic efficiency. We suggest that this high metabolic efficiency is due, at least in part, to less energy being expended on thermoregulatory thermogenesis.