Effects of melatonin on plasma oxidative stress in rats with streptozotocin induced diabetes

The aim of this study was to evaluate the effect of single melatonin injection on plasma oxidative stress in rats with streptozotocin induced diabetes. Diabetes was induced after a single intraperitoneal dose of streptozotocin (60 mg/kg), while hyperglycemia was determined 10 days upon injection. Diabetic rats were divided into two groups. In the first group the injection of melatonin was applied intraperitoneally (20 mg/kg), while the second group received physiological solution. Twenty-four hours later the rats were killed and their blood was centrifuged. In the rat plasma the following parameters were evaluated: the glucose level, superoxide radical, lipid peroxidation, reduced glutathione, total antioxidant capacity, antioxidant enzymes and the aldose reductase activity. The injected melatonin decreased the superoxide radical in the rat plasma. Moreover, melatonin increased the total antioxidative capacity and the activity of antioxidative enzymes superoxide dismutase and glutathione peroxidase. These results indicate that melatonin is a strong scavenger, which may diminish negative effects of oxidative stress in diabetic rats 24 hours after its application The findings suggest that melatonin is also a strong antioxidant. It increases the antioxidant enzymes activity, inhibiting the release of superoxide radicals. A high total antioxidative capacity and the lower activity of aldose reductase enlarge melatonin scavenger capacity against reactive oxygen species in diabetic rats.