METHODS:Totally 40 healthy male SD rats were choose and randomly divided into 4 groups, normal control group, diabetid group, low dose melatonin group and high dose melatonin group. The changes of retinal structure were observed by hematoxylin-eosin staining(HE staining), ultrastructure of retinal ganglion cells were observed by electron microscopy, superoxide dismutase(SOD)and malondialdehyde(MDA)level in the retina tissue were detected by xanthine oxidase method, and protein expression levels of B cell lymphoma/lewkmia-2(Bcl-2), Bcl-2 associated X protein(Bax)and P53 were detected by Western Blot.

RESULTS: HE staining results showed that the rat retina tissue structure of the normal control group was clear, the retinal tissue of diabetes group rats were not clear, the nerve fiber layer was edema, the retina cells of low dose melatonin group were probably distinct, the interlayer cells were arranged neatly, and the inner and outer nuclear layers were slightly disordered, rats retinal structure in high dose melatonin group were further improved than that in low dose melatonin group; Electron microscope results showed that compared with diabetes group, retinal ganglion cells form in melatonin group were improved in different extent; Xanthine oxidase method detected that SOD level in retinal tissue of melatonin group rats were higher than that in diabetic group, the MDA level were lower than that in diabetic group, compared with diabetes group the differences both have statistically significant(P<0.05); Western blot results showed that the protein expression of Bcl-2 in low dose and high dose melatonin group gradually decreased, Bax and P53 protein expressions increased significantly, compared with diabetic group the differences were statistically significant(P<0.05).

CONCLUSION: Melatonin could improve the morphological changes of retina in diabetic rats and inhibit diabetic retinopathy to some extent.