The development of obesity in genetically diabetic-obese (db/db) mice pair-fed with lean siblings. The importance of thermoregulatory thermogenesis.

The importance of reduced thermoregulatory thermogenesis as a mechanism for the high metabolic efficiency of the diabetic-obese (db/db) mouse has been investigated. Young db/db mutants were pair-fed to the ad libitum food intake of lean siblings for two weeks at two different environmental temperatures, 23 and 33 degrees C. At 23 degrees C, a temperature at which there is a substantial demand for thermoregulatory thermogenesis, the diabetic-obese animals deposited 51% more total energy and 75% more fat than the lean mice. At 33 degrees C (thermoneutrality) where there is no requirement for thermoregulatory heat, the mutants deposited 25% more fat than lean animals, but there was no significant difference in the total energy gain of the two groups. Pair-feeding resulted in a reduced protein deposition at both temperatures in the diabetic-obese animals compared to the lean. It is concluded that the high metabolic efficiency of the diabetic-obese mutant, like that of the obese (ob/ob) mouse, is caused by a low energy expenditure on thermoregulatory thermogenesis.