Increased hepatic lipid soluble antioxidant capacity as compared to other organs of streptozotocin-induced diabetic rats: A cyclic voltammetry study

It has been suggested that oxidative stress plays an important role in the chronic complications of diabetes. The experimental findings regarding the changes in tissue antioxidant enzymes and lipid peroxidation of diabetic ti ssues have been inconsistent. Previous studies in our laboratory demonstrat ed that the reducing power of a specific tissue correlates with its low mol ecular weight antioxidant (LMWA) capacity. In the present study, the overal l LMWA capacity (reducing equivalents) of plasma and tissues of streptozoto cin (STZ)-induced diabetic rats (1-4 weeks) and insulin treated diabetic ra ts were measured by cyclic voltammetry. Levels of water and lipid soluble L MWA capacity progressively decreased in the diabetic plasma, kidney, heart and brain, while the diabetic liver, at 2, 3 and 4 weeks after STZ injectio n, showed a significant increase in the overall lipid soluble LMWA capacity (p < 0.001). Subsequently, analysis of specific components by high pressur e liquid chromatography (electrochemical detection) showed decreased levels of ascorbic acid in plasma, kidney, heart and brain of diabetic animals. T he alpha-tocopherol level dropped in all tissues, except for the liver in w hich there was a significant increase (p < 0.01 and p < 0.001 at 2-4 weeks) . Lipid peroxidation was assessed by conjugated diene levels, which increas ed significantly in all diabetic tissues except the liver. Insulin treatmen t that was started after 3 weeks of diabetes and continued for 3 weeks show ed no change in the conjugated dienes and in the overall LMWA capacity in a ll organs. Our results suggest a unique behavior of the liver in the STZ-in duced diabetic rats to the stress and indicate its higher capacity to cope with oxidative stress as compared to other organs.