| Objective：In order to study the role of VEGF and estimate the mechanism during the development of diabetic retinopathy, the expression of the VEGF in Diabetic Rat rwas examined. Methods：use Streptozocin (STZ) to obtain diabetic rat models and test the expression of VEGF mRNA and VEGF protein in retinal paraffin slide during different periods of DR by immunohistochemistry and in situ hybridization . Results：(1) In control group (M) , recovered blood sugar group and 1 month diabetic group ( M1), the morphology of retinal paraffin slides were normal and there was no expression of VEGF protein and mRNA. (2) In 3 months diabetic group (M3), there was no expression of VEGF mRNA. But VEGF protein (34%) mainly expressed in inner nuclear layer and ganglion cell layer, where GFAP expressed also. (3) In 5 months diabetic group (M5), the expression rate of VEGF mRNA is 67%. Its expression appeared in every layer of retina and in inner limiting membrane the expression was similar to GFAP. Eighty-nine percent of sample showed strong positive expression of VEGF protein in M5 group. It mainly located in cells of inner nuclear layer, ganglionic layer and vessel, which was also similar to GFAP. Conclusion：There is expression of VEGF during the development of DR in STZ rats and the expression in retina are produced by autocrine and paracrine.
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