Effects of dietary carbohydrate and phenotype on adipose cellularity in female SHR/N-cp rats

1. Adipose mass and cellularity were studied in congenic female SHR/N-cp rats fed iosenergetic diets containing 54% carbohydrate as sucrose (SU) or cooked cornstarch (CS), 20% protein, 16% mixed dietary fat plus vitamins, minerals, and non-nutritive fiber ad libitum from 5 weeks until 8.5 months of age. Measures of adipocyte lipid content, cell number per depot, and mass of principal white (WAT) and interscapular brown (IBAT) adipoe tissue depots were determined at the end of the study. 2. Final body weights (BW) of corpulent rats were more than twice those for their lean littermates, and were greater when fed the SU than the CS diet in both phenotypes. Phenotype effects (corpulent greater than lean) were present for fat pad weight, adipocyte number, and adipocyte lipid content in the dorsal (DOR) and retroperitoneal (RP) WAT depots. Diet effects were present for depot weight, adipocyte number, and adipocyte lipid content in both WAT depots, and were of qualitatively similar magnitude in both phenotypes. 3. IBAT weights, IBAT:BW ratios, and IBAT cell number of corpulent greater than lean, and were greater than with SU than CS diet in both phenotypes. 4. These results indicate that obesity in the corpulent phenotype of the SHR/N-cp rat occurs as the result of hypertrophy and hyperplasia of white adipose tissue, and that isoenergetic substitution of simple for complex carbohydrate resulted in greater fat accretion in both phenotypes. The greater diet and phenotype-associated adiposity occurred despite greater mass and cellularity of BAT. The results also indicate that sexual dimorphism occurs regarding effects of diet and phenotype on expression of adipose tissue development in this strain.