Melatonin inhibits lipid peroxidation and stimulates the antioxidant status of diabetic rats

Although melatonin has been established as a free radical scavenger and ant ioxidant, its effects in diabetes have not been thoroughly investigated. Th e purpose of this study, therefore, was to investigate the effects of melat onin administration on lipid peroxidation and antioxidant status in strepto zotocin (STZ)-induced diabetes in rats. Concentrations of malondialdehyde ( MDA) and reduced glutathione (GSH) in erythrocytes and activities of supero xide dismutase (SOD) and glutathione peroxidase (GSH-Px) were compared in 3 groups of 10 rats each [control non-diabetic rats (group I), untreated dia betic rats (group II) and diabetic rats treated with melatonin (group III)] . In the study groups, diabetes developed 3 days after intraperitoneal (i.p .) administration of a single 60-mg/kg dose of STZ. Thereafter, while the r ats in group II received no treatment, the rats in group III began to recei ve a 10-mg/kg i.p. dose of melatonin per day. After 6 wk, the rats in group s II and III had significantly lower body weights and significantly higher blood glucose levels than the rats of group I (P < 0.001 and P < 0.001, res pectively). There were no significant differences in body weight or blood g lucose levels between groups II and III. MDA levels in untreated diabetic r ats were higher than those in control group rats and in diabetic rats treat ed with melatonin (P < 0.01 and P < 0.05, respectively). However, MDA level s in diabetic rats treated with melatonin were not different from those of the control group. The GSH, GSH-Px and SOD levels of untreated diabetic rat s were significantly lower than those of the control group (P < 0.02, P < 0 .002 and P < 0.05, respectively). In group III, however, melatonin prevente d decreases in the thiol antioxidant and the associated enzymes, and so the se levels were not significantly different from those in the control group. These results confirm the presence of oxidative stress in STZ-induced expe rimental diabetes and indicate the beneficial free radical-scavenging and a ntioxidant properties of melatonin.