Abstract
The purpose of the study was to investigate the effects of dietary green tea catechin and vitamin E on the phospholipse {TEX}$A_{2}${/TEX} activity and th antioxidative defense system in streptozotocin (STZ)-induced diabetic rats. Sprague-Dawley male rats weighing 100$\pm$10 gm were randomly assigned to one normal and five STZ-induced diabetic groups. The diabetic groups were assigned either a catechin-free diet (DM group), 0.5% catechin diet (DM-0.5C group), 1% catechin diet (DM-1C group), vitamin E-free diet (DM-0E group), and 400 mg vitamin E per kg diet (DM-400E group) according to the levels of dietary catechin or vitamin E supplementation. The vitamin E levels of the normal, DM, DM-0.5C, and DM-1C groups were 40 mg per kg diet. Diabetes was experimentally induced by an intravenous injection of streptozotocin after 4 weeks of feeding the five experimental diets. The animals were sacrificed on the 6th day of he diabetic state. The body weight gains were lower in all five diabetic groups after the STZ injection. The platelet phospholipase {TEX}$A_{2}${/TEX}({TEX}$PLA_{2}${/TEX}) activity in the diabetic groups was higher than that in the normal group. However, the enzyme activity in the DM-0.5C, DM-1C, and DM-400E groups was lower than that in the DM and DM-0E groups. The cytochrome {TEX}$P_{450}${/TEX} and cytochrome {TEX}$b_{5}${/TEX} content and NADPH-cytochrome {TEX}$P_{450}${/TEX} reductase activity were about 50~110% higher in the DM and DM-0E groups than in the normal group, yet significantly reduced by either catechin or vitamin E supplementation. The superoxide dismutase (SOD) content in the liver did not differ significantly in any of the groups. However, the glutathione peroxidase (GSHpx) activity was generally lower in the diabetic groups, compared with the normal group, whereas that of the DM-0.5C, DM-1C, and DM-400E groups was significantly higher compared with that of the DM and DM-0E groups. The levels of thiobarbituric acid reactive substances (TBARS) in the liver tissue were 148% and 201% higher in the DM and DM-0E groups, respectively, compared with the normal group, however, these levels were reduced by either catechin or vitamin E supplementation (DM-0.5, DM-1C and DM-400E). Accordingly, the present results indicate that STZ-induced diabetic rats exhibited an imbalance between free radical generation and scavenger systems in the liver which led to the acceleration of lipid peroxidation. However, these abnormalities were reduced and the antioxidative defense system was restored by either dietary catechin or vitamin E supplementation. In conclusion, the effects of dietary catechin or vitamin E in streptozotocin-induced diabetic rats would appear to inhibit lipid peroxidation as an anti-oxidant by regulating the activity of {TEX}$PLA_{2}${/TEX}.