Background—The hypothesis of the present study was that molecular mechanisms differ markedly when mediating ischemic preconditioning induced by repetitive episodes of ischemia versus classic first- or second-window preconditioning.

Methods and Results—To test this, chronically instrumented conscious pigs were subjected to either repetitive coronary stenosis (RCS) or a traditional protocol of second-window ischemic preconditioning (SWIPC). Lethal ischemia, induced by 60 minutes of coronary artery occlusion followed by reperfusion, resulted in an infarct size/area at risk of 6±3% after RCS and 16±3% after SWIPC (both groups P<0.05, less than shams 42±4%). Two molecular signatures of SWIPC, the increased expression of the inducible isoform of nitric oxide synthase and the translocation of protein kinase C to the plasma membrane, were observed with SWIPC but not with RCS. Confirming this, pretreatment with a nitric oxide synthase inhibitor prevented the protection conferred by SWIPC but not by RCS. Microarray analysis revealed a qualitatively different genomic profile of cardioprotection between ischemic preconditioning induced by RCS and that induced by SWIPC. The number of genes significantly regulated was greater in RCS (5739) than in SWIPC (2394) animals. Of the 5739 genes regulated in RCS, only 31% were also regulated in SWIPC. Broad categories of genes induced by RCS but not SWIPC included those involved in autophagy, endoplasmic reticulum stress, and mitochondrial oxidative metabolism. The upregulation of these pathways was confirmed by Western blotting.

Conclusions—RCS induces cardioprotection against lethal myocardial ischemia that is at least as powerful as traditional ischemic preconditioning but is mediated through radically different mechanisms.