Possible expression of the obese gene in the brown adipose tissue of lean heterozygote littermates of the genetically obese (ob/ob) mouse.

Lean littermates of the genetically obese (ob/ob) mouse of confirmed genotype, +/+ wildtype or ob/+ heterozygous, were fed either stock diet or a high-energy 'cafeteria' diet. Body weights food consumption, and weights and metabolic parameters of the interscapular and dorso-cervical brown adipose tissue sites were examined. Both genotypes showed similar characteristics of food intake and body weight gain on the cafeteria diet. The ob/+ brown adipose tissue was, however, different from the +/+ in that the GDP binding to the mitochondria was lower and the cytoplasmic density of the mitochondria in the tissue was higher in both stock and cafeteria fed groups. It is suggested that the decreased GDP binding is partly compensated for by an increase in the mitochondrial content of the brown adipose tissue of the ob/+ mice, thus normalizing the total thermogenic capacity and allowing the maintenance of lean body weight despite a slight expression of the obese gene in the thermogenic pathway.