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. However, in older male rats fed either low- or high-fat diets, we found no effects 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 insulin metabolism for lean heterozygous female rats compared to their homozygous counterparts. In the present study, the effect of the "fa" gene on body 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 rats were obtained by mating homozygous obese male rats with heterozygous lean female rats. Following weaning, rats were maintained on a standard laboratory diet until 10 weeks of age when they were killed after an overnight fast. Results: Body weight (p<0.03) and inguinal (p = 0.01) and combined retroperitoneal+parametrial (p=0.06) fat pad weights were heavier in heterozygous lean compared to homozygous lean female rats. Combined fat pad-to-body weight ratio (p = 0.05) and fat cell sizes (p = 0.06) were also higher in the heterozygous lean compared to homozygous lean rats. No differences in serum triacylglycerol, 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 present during the postweaning period in lean female rats. Implications for increased body fat and leptin with respect to sexual maturation and fertility are discussed.