The presence of the "fa" gene in heterozygous (FA/fn) lean female rats: Effects on body weight, body fat and serum leptin

Objective: In previous studies, suckling lean heterozygous (FA/fa) pups had higher body fat levels in comparison to lean homozygous (FA/FA) pups. Howe ver, in older male rats fed either low- or high-fat diets, we found no effe cts of the "fa" gene in heterozygous lean rats compared to homozygous lean rats. Other studies have reported effects of the "fa" gene on aspects of in sulin metabolism for lean heterozygous female rats compared to their homozy gous counterparts. In the present study, the effect of the "fa" gene on bod y weight and body fat in lean female rats was investigated. Research Methods and Procedures: Homozygous lean female rats were obtained by mating homozygous lean male and female rats. Heterozygous lean female ra ts were obtained by mating homozygous obese male rats with heterozygous lea n female rats. Following weaning, rats were maintained on a standard labora tory diet until 10 weeks of age when they were killed after an overnight fa st. Results: Body weight (p<0.03) and inguinal (p = 0.01) and combined retroper itoneal+parametrial (p=0.06) fat pad weights were heavier in heterozygous l ean compared to homozygous lean female rats. Combined fat pad-to-body weigh t ratio (p = 0.05) and fat cell sizes (p = 0.06) were also higher in the he terozygous lean compared to homozygous lean rats. No differences in serum t riacylglycerol, cholesterol, glucose, or insulin concentrations were found between the two groups, but serum leptin levels were significantly higher ( p<0.004) in heterozygous lean rats. Discussion: These results indicate that effects of the "fa" gene are presen t during the postweaning period in lean female rats. Implications for incre ased body fat and leptin with respect to sexual maturation and fertility ar e discussed.