AbstractAim:To investigate the role of inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO) in the cardioprotection of intermittent hypoxia (IH) against ischemia/reperfusion (I/R) injury.Methods:Langendorff-perfused isolated rat hearts were used to measure variables of left ventricular function during baseline perfusion, ischemia, and reperfusion period. Nitrate plus nitrite (NOx) content in myocardium was measured using a biochemical method. iNOS mRNA and protein expression in rat left ventricles were detected using reverse transcription polymerase chain reaction (RT-PCR) and Western blot, respectively.Results:Myocardial function recovered better in IH rat hearts than in normoxic control hearts. The iNOS-selective inhibitor aminoguanidine (AG) (100 μmol/L) significantly inhibited the protective effects of IH, but had no influence on normoxic rat hearts. The baseline content of NOx in IH hearts was higher than that in normoxic hearts. After 30 min ischemia, the NOx level in normoxic hearts increased compared to the corresponding baseline level, whereas there was no significant change in IH hearts. However, the NOx level in IH hearts was still higher than that of normoxic hearts during ischemia and reperfusion period. AG 100 μmol/L significantly diminished the NOx content in IH and normoxic hearts during ischemia and reperfusion period. The baseline levels of iNOS mRNA and protein in IH hearts were higher than those of normoxic hearts. Compared to the corresponding baseline level, iNOS mRNA and protein levels in normoxic rat hearts increased and those in IH rat hearts decreased after reperfusion. The addition of AG 100 μmol/L significantly decreased iNOS mRNA and protein expression in IH rat hearts after I/R.Conclusion:IH upregulated the baseline level of iNOS mRNA and protein expression leading to an increase in NO production, which may play an important role in the cardiac protection of IH against I/R injury.