Effects of fructose, levamisole and vanadate on insulin action in rat adipose tissue

The effects of dietary fructose, levamisole and vanadate on insulin-stimulated conversion of D-[U-14C]glucose to 14CO2 and to 14C-labeled lipid were examined in rat epididymal adipose tissue. Male weanling rats were fed isoenergetic diets containing either 27% (wt/wt) fructose or glucose for 11 wk. During the final 4 wk, rats in each group were either untreated (control) or treated orally with 20 mg/kg body wt levamisole or 0.5 ppm vanadate via their drinking water. Basal glucose oxidation to CO2 was 45% higher in the fructose-control than in the glucose-control group. Insulin-stimulated glucose oxidation in both control groups was not higher than the basal rate in fructose-fed rats. Basal lipogenesis was 31% lower in the fructose-control than in the glucose-control group. Insulin-stimulated lipogenesis was much higher than basal, but was not different between fructose- and glucose-control groups. Levamisole increased basal lipogenesis in fructose-fed rats. Vanadate acted synergistically with fructose in greatly diminishing insulin-stimulated glucose oxidation. Fasting plasma insulin levels were lower and fasting plasma glucose and triglycerides were higher in fructose- than in glucose-fed rats, irrespective of treatment. Results suggest that adaptation to dietary fructose enhances basal oxidative capacity in an insulin-like fashion and reduces the basal lipogenic capacity of adipose tissue. Treatment with levamisole and vanadate lowers the overall rate of glucose metabolism and alters the effects of fructose.