NO produced by endothelial NO synthase is a mediator of delayed preconditioning-induced endothelial protection.

Preconditioning with brief periods of ischemia-reperfusion (I/R) induces a delayed protection of coronary endothelial cells against reperfusion injury. We assessed the possible role of nitric oxide (NO) produced during prolonged I/R as a mediator of this endothelial protection. Anesthetized rats were subjected to 20-min cardiac ischemia/60-min reperfusion, 24 h after sham surgery or cardiac preconditioning (1 x 2-min ischemia/5-min reperfusion and 2 x 5-min ischemia/5-min reperfusion). The nonselective NO synthase (NOS) inhibitor l-NAME, the selective inhibitors of neuronal (7-nitroindazole) or inducible (1400W) NOS, or the peroxynitrite scavenger seleno-l-methionine were administered 10 min before prolonged ischemia. Preconditioning prevented the reperfusion-induced impairment of coronary endothelium-dependent relaxations to acetylcholine (maximal relaxation: sham 77 +/- 3; I/R 44 +/- 6; PC 74 +/- 5%). This protective effect was abolished by l-NAME (41 +/- 7%), whereas 7-NI, 1400W or seleno-l-methionine had no effect. The abolition of preconditioning by l-NAME, but not by selective nNOS or iNOS inhibition, suggests that NO produced by eNOS is a mediator of delayed endothelial preconditioning.