Thermoregulation in the diabetic-obese (db/db) mouse. The role of non-shivering thermogenesis in energy balance.

1. Thermoregulation and non-shivering thermogenesis have been studied in the genetically diabetic obese (db/db) mouse. 2. At all environmental temperatures between 33 and 10 degrees C the body temperature of the diabetic mice was lower than that of the normal littermates, the difference varying from 1.1 degrees C at 33 degrees C to 4.5 degrees C at 10 degrees C. 3. At 4 degrees C the diabetic mice rapidly died (3.2h) of hypothermia while the normal mice maintained their body temperature within the normal range. 4. At 23 degrees C the diabetic animals exhibited a diurnal rhythm in body temperature which was similar in both phase and amplitude to the controls, but at every point throughout the 24h cycle the temperature of the mutants was lower by 1--2 degrees C. 5. The resting metabolic rate at thermoneutrality (33 degrees C) was higher per whole animal for the diabetics than for the normals. However, at temperatures below thermoneutrality the converse was observed; between 30 and 4 degrees C the RMR of the mutants was lower than the controls by approximately 25%. 6. The capacity for non-shivering thermogenesis in diabetic mice was only one-half that found in normal animals. 7. The diabetic mouse has abnormalities in thermoregulation and non-shivering thermogenesis which are similar to those found in the genetically obese (ob/ob) mouse. It is concluded that the high metabolic efficiency of the diabetic mouse, like that of the ob/ob mouse, can be explained by a reduced energy expenditure on thermoregulatory thermogenesis; this may represent a primary mechanism for the operation of the "thirfty genotype" associated with obesity and diabetes.