Brown fat thermogenesis in a rat model of dietary obesity

The effects of chronic feeding of a high-fat diet or a cafeteria-type diet on weight gain and thermogenesis in brown adipose tissue as measured by the binding of a purine nucleotide (guanosine 5'-diphosphate, GDP) to mitochondria of brown adipose tissue have been studied in two strains of rats that differ in their susceptibility to dietary obesity. S 5B/Pl rats, which are resistant to developing obesity when eating a high-fat diet or drinking sucrose solutions, have greater specific GDP binding in interscapular brown adipose tissue (IBAT) than do Osborne-Mendel rats, which are sensitive to fat-induced obesity. A high-fat diet, fed isoenergetically to the low-fat diet, did not increase the growth of IBAT and decreased specific GDP binding in both strains. Feeding a cafeteria diet resulted in obesity and increased mass and protein content of the IBAT in both strains of rats. However, specific GDP binding increased in response to cafeteria feeding only in the Osborne-Mendel rats. These studies show that thermogenesis, as measured by GDP binding to mitochondria in brown adipose tissue, is suppressed by both isoenergetic and ad libitum feeding of a high-fat diet. The higher basal GDP binding in the brown fat of the S 5B/Pl rats suggests that higher thermogenesis of this tissue contributes to the resistance of this strain to fat-induced obesity. The inability of S 5B/Pl rats to further increase thermogenesis when eating a cafeteria diet may contribute to their becoming obese.