The effect of vitamin E on the antioxidative defense mechanism in streptozotocin-induced diabetic rats

The effect of vitamin E on the antioxidative defense mechanism was investigated in streptozotocin (STZ)-induced diabetic rats. Sprague-Dawley male rats were randomly assigned either to one of three STZ-diabetic groups, classified as STZ-0 E (basal diet), STZ-40 E (40 mg vitamin E/kg of diet) and STZ-400 E (400 mg vitamin E/kg of diet), or to the control group. After 26 days on the experimental diets, STZ (55 mg/kg body weight) was administered intravenously to the diabetic groups. The blood glucose levels of the diabetic rats were three times higher than those of the controls. In groups STZ-0 E and STZ-40 E, the serum glutamic oxaloacetic transaminase (GOT), glutamic pyruvic transaminase (GPT) and liver xanthine oxidase activities were all higher than those of the controls. However, the activities of these enzymes in the STZ-400 E group did not differ from those of the controls. Compared to the controls, liver superoxide dismutase (SOD) activity was significantly increased in group STZ-0 E and STZ-40 E, while the activities of liver glutathione peroxidase (GSH-Px) and glutathione S-transferase (GST) were significantly reduced. The liver vitamin E contents in groups STZ-0 E and STZ-40 E significantly lower than those of the controls. In additions, the activity of reduced glutathione (GSH) was decreased in the livers of all diabetic rats by 59%, 51%, and 19% for groups STZ-0 E, STZ-40 E and STZ-400 E respectively, relative to the controls. Dietary supplementation with large amounts of vitamin E resulted in an increase of GSH/GSSG activity. In the livers of rats in groups STZ-0 E and STZ-40 E, the lipid peroxide levels were 5.6 and 2.5 times higher than those of the controls. These results suggest that STZ-induced diabetic rats are more sensitive to oxidative stress and have higher rates of lipid peroxidation. Dietary vitamin E may reduce this peroxidative tissue damage by promoting antioxidative mechanism