| Objective: To investigate the effect of melatonin on oxidative stress, sciatic nerve function and ultrastructure changes in rats with diabetic peripheral neuropathy. Methods: The experiment was divided into two parts: part one, melatonin was given for eight weeks immediately after diabetic rats were induced and part two, melatonin was given for eight weeks eight weeks later after diabetic rats were induced. Blood glucose and body weights, plasma and sciatic nerve superoxide dismutase, glutathion peroxidase activities, lipid peroxide product malonaldehyde levels, sciatic nerve ultrastructure changes and nerve conduction velocities, tailflick threshold were evaluated. Results: Superoxide dismutase and glutathione peroxidase activities were lower and malonaldehyde levels were higher in plasma and sciatic nerves of diabetes mellitus group than those in normal control group. Sciatic nerve showed demyelination changes and axon atrophy in diabetes mellitus group. Melatonin increased superoxide dismutase and glutathione peroxidase activities and reduced malonaldehyde levels in sciatic nerves and plasma, meliorated tailflick threshold, sciatic nerves nerve conduction velocities and ultrastructure changes. Preventive treatment with melatonin in early phase of diabetic peripheral neuropathy had more significant effect. Conclusion: Melatonin may inhibit oxidative stress and meliorate sciatic nerve function and ultrastructure changes in rats with diabetic peripheral neuropathy. Overproduction of reactive oxygen species and insufficieny in antioxidant enzymes may contribute to the development of diabetic peripheral neuropathy.
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