After agonist stimulation of PI3K way has been reported to play a protective role in myocardial I/R. This membrane-activated form of Akt has been shown to phosphorylate human eNOS specifically at serine 1177, resulting in enhanced eNOS activity and increased NO release. Upregulation of eNOS has been reported to protect against myocardial I/R injury through suppression of vascular cell adhesion molecule expression thereby preventing excessive leukocytic tissue infiltration. However, activation of iNOS, induced by pro-inflammatory cytokines, has been associated with myocardial depression. Excessive generation of NO by iNOS is detrimental to cardiovascular function, as exemplified in septic shock where burst generation of iNOS-derived NO causes hypotension, cardiodepression and vascular hyporeactivity. Supplementation with L-arginine under conditions where iNOS is expressed during myocardial I/R has been shown to result in a significant surge in the production of NO and ONOO2, which aggravate postischemic myocardial apoptosis. A recent study has demonstrated that myocardial I/R stimulates polymorphonuclear leukocyte MG132 133407-82-6 accumulation, resulting in myocardial injury through an iNOS-mediated mechanism involving generation of NO and ONOO2, and that treatment with FeTMPyP, a peroxynitrite decomposition catalyst, reduces I/R-induced, L-arginine-enhanced nitrative stress and cardiomyocyte apoptosis. These studies indicate that inhibition of iNOS activity or scavenging of peroxynitrite reduces nitrative stress and thereby attenuates tissue injury during myocardial I/R In the present study, l-THP treatment resulted in eNOS ser1177 phosphorylation, via augmentation of Akt ser473 phosphorylation, during myocardial I/R. However, this effect is outweighed by inhibition of iNOS expression by l-THP during myocardial I/R, resulting in a net decrease in NO production and hence cardioprotection. Growing evidence has indicated that HIF plays a major role in myocardial I/R injury. HIF-1 is a transcription factor that is expressed following a decrease in cellular oxygen pressure. VEGF is a key modulator of vasculogenesis and angiogenesis in physiological and pathological conditions. VEGF is a HIF-dependent gene, which is important in I/R because of regulating collateral vessel development. In this study, we found that temporary ischaemia increased expression of HIF-1a and VEGF, and after a longer time of reperfusion, HIF-1a and VEGF mRNA decreased to basal level, but l-THP increased the expression of HIF-1a and VEGF mRNA levels. In murine macrophages, in the absence of activation, the production of the pro-inflammatory cytokine TNF-a is repressed both at the transcriptional and translational levels. However, during myocardial I/R, TNF-a and iNOS-derived NO are produced in large quantities by macrophages. Inhibition of the excessive production of TNF-a and/or iNOS-derived NO can give rise to cardioprotection in such circumstances. Our data supported one concept that suppression of iNOS-derived NO production may contribute, at least partially, to the suppression of TNF-a production during myocardial I/R.