Metabolic comparisons of 10-week-old obese (fa/fa) Zucker rats with both heterozygous (FA/fa) and homozygous (FA/FA) lean rats

Previously we found that some metabolic comparisons made between obese (fa/fa) Zucker rats and lean rats during the suckling period were dependent upon the genotype of the lean rats. In the present study, we determined if similar results were obtained after weaning. Homozygous (fa/fa) obese and heterozygous (FA/fa) and homozygous (FA/FA) lean male rats were killed at 10 weeks of age. Body and liver weights were greater in obese compared to lean rats (FA/fa=FA/FA). Inguinal and combined epididymal/retroperitoneal fat pad weights and fat cell sizes were also greater in obese compared to lean rats. Fat cell numbers were similar in all three groups. Liver and inguinal and epididymal/retroperitoneal fat pad enzyme activities for malic enzyme, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and fatty acid synthetase were all higher in obese compared to lean rats. Adipose tissue lipoprotein lipase activity also followed this pattern as did measurements for serum insulin, cholesterol and triacylglycerol. In inguinal adipocytes conversion of glucose to CO₂, glyceride-glycerol and fatty acids was higher in adipocytes from obese compared to lean rats in both the presence and absence of insulin. In epididymal/retroperitoneal fat cells, obese rats had higher basal glucose conversion to products than did lean rats but in the presence of insulin values were similar among the three groups due to a lack of insulin stimulation in fat cells from obese rats. These results indicate that in young adult male Zucker rats there is little effect of the 'fa' gene in heterozygous (FA/fa) lean rats.