| OBJECTIVE: To investigate the role of inducible nitric oxide synthase/nitric oxide (iNOS-NO) in the second window of protection (SWOP) of renal ischemic reconditioning(IPC) against ischemia/reperfusion (I/R) injury in rats. METHODS: Rats were preconditioned with 4 cycles of 5-min renal artery occlusion/5-min reperfusion and 24 h later underwent 45-min renal artery occlusion followed by 24 h reperfusion. Blood urea nitrogen and creatinine were examined to demonstrate the renal function and Paller's count to assess the changes in renal pathological morphology. Serum nitric oxide was assayed by Greiss reaction. Renal iNOS activity, mRNA and protein were assayed by enzymatic method, reverse transcriptase-polymerase chain reaction and western blot, respectively. RESULTS: 1. IPC significantly decreased the levels of blood urea nitrogen, creatinine and Paller's count compared with those in I/R group. 2. Aminoguanidin, an inducible nitric oxide synthase inhibitor, abolished the second window of protection of IPC against I/R injury. 3. Renal iNOS activity and serum nitric oxide level were significantly increased 24 h after IPC. 4. RT-PCR showed that iNOS mRNA expression in IPC group was higher than that in Sham group. 5. Western blot demonstrated that iNOS protein increased moderately in IPC group compared with that in Sham group. 6. Aminoguanidin suppressed iNOS mRNA and protein expression caused by IPC. Sham operation didn't influence iNOS mRNA and proteinexpression.CONCLUSIONS: 1. IPC alleviated I/R injury in rat kidneys. 2. The second window of protection was greatly attenuated by the co-administration of aminoguanidin, an iNOS inhibitor. 3. IPC moderately upregulated the expression of iNOS mRNA and protein. iNOS-NO system was activated by IPC and iNOS-NO pathway may be of great importance in the mechanism of SWOP.
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