NITRIC OXIDE TRIGGERS DELAYED ANESTHETIC PRECONDITIONING-INDUCED CARDIAC PROTECTION VIA ACTIVATION OF NUCLEAR FACTOR-κB AND UPREGULATION OF INDUCIBLE NITRIC OXIDE SYNTHASE

Nitric oxide (NO) plays a pivotal role both in triggering and mediating delayed protection against myocardial I/R injury during anesthetic-induced preconditioning (APC). However, the signaling mechanisms that underlie this phenomenon remain unclear. Using isoflurane as a representative anesthetic, the present study tested the hypothesis that NO released after anesthetic-induced preconditioning initiates delayed cardioprotection via activation of nuclear transcription factor-kappaB (NF-kappaB), leading to myocardial adaptation by upregulation of iNOS and increase in production of NO. Sprague-Dawley rats that received open-chest surgery under pentobarbital anesthesia were subject to 30 min of left coronary artery occlusion, followed by 120 min of reperfusion. Exposure to 60 min of 2.1% isoflurane inhalation with oxygen 24 h before ischemia significantly reduced I/R-induced myocardial infarct size that was associated with overexpression of iNOS protein and increased NO content in the heart. These protective effects were abolished by pretreatment with a NOS inhibitor, N-nitro-L-arginine methyl ester, an NF-kappaB blocker, diethyldithiocarbamate, before isoflurane, or a selective iNOS inhibitor, S-methylisothiourea, before left coronary artery occlusion. Isoflurane exposure also evoked a robust increase in myocardial NO content, followed by nucleus-bound translocation of p65 or p50 subunit of NF-kappaB and increase in NF-kappaB DNA-binding activity in heart tissues. These molecular events after isoflurane exposure were blocked by pretreatment with N-nitro-L-arginine methyl ester. We conclude that NO generated immediately after isoflurane exposure triggers downstream activation of NF-kappaB, resulting in subsequent upregulation of iNOS expression and NO synthesis that mediate APC-induced delayed cardioprotection.