Objective To investigate the role of endothelial nitric oxide synthase(eNOS)in the pathogenesis and development of diabetic cystopathy.Methods Diabetic model was established by a single intra-peritoneal injection of 60 mg/kg STZ in male Sprague-Dawley rats.Thirty-six rats were randomly divided into 3 groups:normal control,diuresis control and diabetes groups each(n=12).Examinations were performed at 6W and 12W after injection of STZ.Cystometry was taken to evaluate the bladder function.Expression levels of eNOS mRNA and protein were assessed with RT-PCR and Western blot assays respectively and their correlations with bladder function index were analyzed.Results The bladder capacity,single voiding volume and post-voiding volume at 6W were(0.75±0.04),(0.70±0.02)and(0.06±0.00)ml in normal group,(1.62±0.15),(1.52±0.30)and (0.11±0.01)ml in diuresis group,and(2.29±0.16),(2.06±0.25)and(0.23±0.01)ml in diabetic group.Compared with normal and diuresis groups,they were significantly increased in diabetic group(P＜0.01).At 12W,they were(0.86±0.06),(0.80±0.04)and(0.07±0.00)ml in normal group,(1.93±0.10),(1.77±0.11)and(0.13±0.02)ml in diuresis group,and(2.65±0.26),(2.09±0.21)and(0.56±0.06)ml in diabetic group.Post-voiding volume increased significantly compared with that at 6W in diabetic group(P＜0.01).At 6W,voiding efficiencies of each group were(93.3±2.1)%,(93.2±2.7)%and(90.0±2.5)0A,with no significant difference.While at 12W they were(93.1±2.2),(93.8±3.2)and(78.1±2.6)%.Voiding efficiency was significantly reduced in diabetic group compared with other 2 groups.No significant difference was observed among bladder pressures of each group.Expression levels of eNOS mRNA from each group at 6W were 0.81±0.12,0.90±0.12,and 1.98±0.16.Compared with normal and diuresis groups,eNOS mRNA expression level significantly increased in diabetic group(P＜0.01).while at 12W they were 0.87±0.17,1.05±0.11,and 2.89±0.23 respectively.Compared with that at 6W,expression level of eNOS mRNA significantly increased at 12W in diabetic group(P＜0.01).Expression levels of eNOS protein were 0.98±0.12,0.93±0.14,and 2.28±0.16.eNOS protein expression level significantly increased in diabetic group,compared with normal and diuresis groups(P＜0.01).At 12 W they were 1.03±0.13,1.14±0.11,and 3.12±0.20,respectively.Compared with that at 6W,expression level of eNOS protein significantly increased at 12W in diabetic group(P＜0.01).The expression level of eNOS mRNA was negatively correlated with voiding efficiency in diabetic group(r=-0.669,P＜0.01).Conclusion The up-regulated expression levels of both eNOS mRNA and protein may participate in the pathogenesis and development of diabetic cystopathy.