Background Much research has been focused on ischemia/reperfusion injury (IRI) to the transplanted organs. As a free radical, nitric oxide (NO) plays an important role in IRI. In this study, the production of NO and its functions during IRI were monitored in rat models after allotransplantation of kidney grafts.Methods Of 75 male LEW rats, 30 served as donors, and the remaining 45 rats were divided into three groups (15 rats in each group): controls (group 1), kidney allotransplantation followed by bilateral nephrectomy during reperfusion (group 2), 2 hours before operation, donors and recipients were treated with NG-nitro L-arginine methyl ester (L-NAME), a NO synthase inhibitor, at a dose of 30 mg/kg (group 3). Bilateral nephrectomies were performed while kidney grafts were reperfused. The kidney grafts were hypothemically stored for 24 hours. The production of NO before and after reperfusion was measured by electron paramagnetic resonance (EPR). The creatinine level, the glomerular filtration rate (GFR) and the protein carbonyl content in tissue samples were recorded on the first and the fifth day after operation. The data were evaluated by one-way analysis of variance. Differences were considered to be statistically significant when a P value was less than 0.05.Results After reperfusion for 15 minutes, the production of NO increased remarkably and kept increasing till 120 minutes, after which the level returned to normal. In group 3, which was pretreated with L-NAME, creatinine levels were higher than those in group 2 at the 24th hour (4.10±0.50 mg/dl vs. 3.77±0.42 mg/dl, P<0.05) and the 120th hour (3.19±0.79 mg/dl vs. 2.22±0.53 mg/dl, P<0.05). GFR levels in group 3 were lower than those in group 2 at the 24th hour (0.50±0.12 ml/min vs. 0.71±0.19 ml/min, P<0.05) and the 120th hour (0.59±0.38 ml/min vs. 1.27±0.23 ml/min, P<0.01). The content of protein carbonyl in tissue samples of group 3 was lower than that in group 2 at the 24th hour (29.01±7.02 nmol/mg protein vs. 49.39±13.13 nmol/mg protein, P<0.05), but was higher than that at the 120th hour (75.71±16.74 nmol/mg protein vs. 57.93±15.32 nmol/mg protein, P<0.05).Conclusions After transplantation of hypothemically stored kidney grafts, the increased NO production in the early stage has protective effects on the transplanted kidney. Application of L-NAME to inhibit NO production is harmful to the recovery of the renal functions of kidney grafts. Background Much research has been focused on ischemia / reperfusion injury (IRI) to the transplanted organs. As a free radical, nitric oxide (NO) plays an important role in IRI. In this study, the production of NO and its functions during IRI were monitored in rat models after allotransplantation of kidney grafts. Methods Of 75 male LEW rats, 30 served as donors, and the remaining 45 rats were divided into three groups (15 rats in each group): controls (group 1), kidney allotransplantation followed by 2 nephrectomy during reperfusion (group 2), 2 hours before operation, donors and recipients were treated with NG-nitro L-arginine methyl ester (L-NAME), a NO synthase inhibitor, at a dose of 30 mg / kg The production of NO before and after reperfusion was measured by electron paramagnetic resonance (EPR). The creatinine level, the glomerula r filtration rate (GFR) and the protein carbonyl content in tissue samples were recorded on the first and the fifth day after operation. The data were evaluated by one-way analysis of variance. Differences were considered to be significant when a P value was less than 0.05. Results after reperfusion for 15 minutes, the production of NO increased remarkably and kept off for 120 minutes, after which the level returned to normal. In group 3, which was pretreated with L-NAME, creatinine levels were higher than those in group 2 at the 24th hour (4.10 ± 0.50 mg / dl vs. 3.77 ± 0.42 mg / dl, P <0.05) and the 120 th hour (3.19 ± 0.79 mg / dl vs. 2.22 ± 0.53 mg / dl, P <0.05 ) GFR levels in group 3 were lower than those in group 2 at the 24 th hour (0.50 ± 0.12 ml / min vs. 0.71 ± 0.19 ml / min, P <0.05) and the 120 th hour (0.59 ± 0.38 ml / min vs .1.27 ± 0.23 ml / min, P <0.01). The content of protein carbonyl in tissue samples of group 3 was lower than that in group 2 at the 24th hour (29.01 ± 7.02 nm ol / mg protein vs. 49.39 ± 13.13 nmol / mg protein, P <0.05), but was higher than that at the 120th hour (75.71 ± 16.74 nmol / mg protein vs. 57.93 ± 15.32 nmol / mg protein, P <0.05) transplantation of hypothemically stored kidney grafts, the increased NO production in the early stage has protective effects on the transplanted kidney. Application of L-NAME to inhibit NO production is harm to the recovery of the renal functions of kidney grafts.