BACKGROUND: Some studies have presented that vascular endothelial growth factor and its receptor system may take part in onset and development of diabetic nephropathy (DN).OBJECTIVE: To further verify the interventional effects of irbesartan on vascular endothelial growth factor (VEGF) and its Flk-1 receptor expressions in kidney of diabetes mellitus (DM) rat, and the possible mechanism of irbesartan.DESIGN: Randomized control animal study.SETTING: West China Hospital of Sichuan University.MATERIALS: Eighteen male closed colony SD rats weighing 150-200 g were cared in standardization.METHODS: This study was performed at Laboratory of West China Hospital of Sichuan University from August 2006 to April 2007. All rats were randomly divided into a DN group, an irbesartan group and a normal control group, with 6 rats in each group. 10 g/L streptozotocin (55 mg/kg) was intraperitoneally injected to establish models; rats in the control group were administrated with the same dosage of citric acid buffer solution; rats in the irbesartan group were administrated with 3 mg/(kg·d) irbesartan after model establishment. VEGF and FIk-1 expressions were detected using reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry technique; while, urine protein level, area and volume of renal glomerulus were detected, and correlations of data were analyzed.MAIN OUTCOME MEASURES: ①Renal pathological indicators, urine protein level, area and volume of renal glomerulus; ②VEGF and Flk-1 expressions;③renal immunohistochemical examination;④ correlation analysis.RESULTS:① Renal pathological examination by HE staining indicated that renal glomerulus was remarkably enlarged in the DN group; mesangial matrix was increased; mesangial cells were also increased; renal tubule was expanded. The lesions in the irbesartan group were milder compared to the DN group. Urine protein level in the DN group was significantly higher compared to the control group (P ＜ 0.01); renal weight/body mass, area and volume of renal glomerulus were significantly higher compared to the control group (P ＜ 0.01); urine protein level, renal weight/body mass, area and volume of renal glomerulus in the irbesartan group were significantly lower compared to the DN group (P ＜ 0.01). ② By the 16th week,VEGF and Flk-1 expressions in the DN group were significantly up-regulated compared to control group (P ＜ 0.05); while,VEGF and Flk-1 expressions in the irbesartan group were also up-regulated compared to the control group by the 16th week (P ＜ 0.05) but down-regulated compared to the DN group (P ＜ 0.05). ③ VEGF staining in the DN group was darker compared to control group (P ＜ 0.01), while the staining in the irbesartan group was also darker compared to the control group (P ＜0.01), but the staining in the irbesartan group was lighter compared to the DN group (P ＜ 0.01). Flk-1 staining was similar to the VEGF. ④ VEGF and Flk-1 were positively correlated, with urine protein level, area and volume of renal glomerulus (P ＜0.05).CONCLUSION: VEGF and its Flk-1 receptor play important roles in DN pathogenesis. Over expressions may cause renal injury, but irbesartan (angiotensin Ⅱ receptor antagonist) has the protective effects on kidney through inhibiting abnormal expression of VEGF and Flk-1.