Objective
The purpose of this study is to prove protective action of melatonin on the development of neuropathy in diabetic rat.

Method
The experimental rats (Sprague-Dawley) were divided into 3 groups: Group 1, streptozotocin-induced diabetic rats with trial of melatonin; Group 2, streptozotocin-induced diabetic rats without trial of melatonin; Group 3, normal control. Streptozotocin was injected intraperitoneally in group 1 and 2. Melatonin was administered per orally in group 1 from 1 week after the injection of streptozotocin. The melatonin effect on diabetic neuropathy was evaluated by the measurement of conduction velocities and amplitudes of rat tail mixed nerve action potentials. The electrophysiologic examinations were performed before and 2, 4, and 6 weeks after administration of streptozotocin.

Results
The rat tail mixed nerve conduction velocities were decreased at 4 weeks in group 1 and 2, and showed significant improvement at 6 weeks in group 1 as compared with those of group 2 (p＜0.05). The amplitudes of the compound nerve action potentials did not show difference before and after streptozotocin and melatonin trials, neither among groups.

Conclusion
In this experimental study, we observed the inhibitory effect of melatonin on the progression of polyneuropathy in early stage of diabetic rat. For the clinical application to human beings, further study is required.