The development of cold-induced thermogenesis and the structure of brown adipocyte mitochondria in genetically-obese (ob/ob) mice.

The onset of cold-induced thermogenesis was studied in a strain of mice which produced among their offspring genetically-obese (ob/ob) individuals. A thermogenic response was present in a majority by day 5 after birth. The thermogenic response to cold was measured on days 5, 10 or 15 after birth, and the animals reared and the onset of obesity noted. The correlation between the subsequent development of obesity and a poor thermogenic response in early life was low. A poor thermogenic response at day 15 was associated with the presence in brown adipocytes of mitochondria with disordered internal structures. At day 42 both non-obese and obviously-obese mice showed a similar thermogenic response to moderate cold exposure. It would seem that in this strain of mice disordered internal mitochondrial structure in brown adipose tissue is associated with a poor thermogenic response to cold, but not invariably with the subsequent onset of obesity.