ENOS and nNOS Mediate Isoflurane Preconditioning

Abstract

Anesthetic preconditioning (APC) has been shown to protect the heart against ischemia and reperfusion injury via a nitric oxide‐dependent mechanism. However, the role of nitric oxide synthase (NOS) isoforms in the cardioprotective effect of APC remains elusive. We examined the role of endothelial (eNOS) and neuronal NOS (nNOS) isoforms in cardioprotection by isoflurane. Pentobarbital‐anesthetized C57BL/6 and eNOS−/− mice underwent APC or equivalent amounts of air/oxygen (control) prior to 30 min of coronary occlusion followed by 2 h of reperfusion. APC was produced with 1.0 minimum alveolar concentration of the volatile anesthetic isoflurane for 30 min followed by a 15 min washout period. Infarct area and area at risk were delineated by 2,3,5‐triphenyltetrazolium chloride and phthalo blue dye, respectively. There were no significant differences in area at risk between groups. APC decreased infarct size in C57BL/6 mice (41±3% vs. 54±3% in control, n=8 mice/group, P<0.05), which was partially blocked by 7‐nitroindazole (25 mg/kg), a selective inhibitor for nNOS, administered intraperitoneally 15 min prior to APC. Disruption of eNOS gene did not significantly increase infarct size compared with C57BL/6 mice and partially blocked the cardioprotective effect of APC. Furthermore, APC‐elicited decrease in infarct size in eNOS−/− mice was abolished by 7‐nitroindazole. Cardiomyocytes were co‐cultured with endothelial cells and subsequently exposed to isoflurane (0.5 mM) or air (control) for 60 min prior to 2 h of hypoxia and 2 h of reoxygenation. Isoflurane significantly increased phosphorylated eNOS compared with control. The results demonstrate that eNOS and nNOS synergistically mediate cardioprotection against ischemia and reperfusion injury by isoflurane.