U50,488H postconditioning reduces apoptosis after myocardial ischemia and reperfusion

Evidence has indicated U50,488H, a selective κ-opioid receptor (κ-OR) agonist, administered before ischemia attenuates apoptosis and infarction during ischemia and reperfusion (I/R). However, it remains unclear whether U50,488H postconditioning reduces apoptosis during I/R. This study was designed, therefore, to test the hypothesis that U50,488H administered at the onset of reperfusion inhibits cardiomyocyte apoptosis and to investigate the underlying mechanisms.

Male Sprague-Dawley rats were subjected to myocardial ischemia and reperfusion(MI/R) and were randomized to receive either vehicle, U50,488H, U50,488H plus Nor-BNI, a selective κ-OR antagonist, U50,488H plus wortmannin, a specific inhibitor of phosphoinositide 3'-kinase (PI3K), or U50,488H plus L-NAME, a nitric oxide synthase inhibitor (NOS inhibitor), immediately prior to reperfusion. In vitro study was performed on cultured neonatal cardiomyocytes subjected to simulated ischemia/reperfusion.

Treatment with U50,488H resulted in increases in Akt and endothelial nitric oxide synthase (eNOS) phosphorylation with secondary NO production both in vivo and in vitro and these effect were completely blocked by wortmannin and specific Akt inhibitor(AI). L-NAME treatment had no effect on Akt and eNOS phosphorylation; but, significantly reduced NO production. Moreover, treatment with U50,488H markedly reduced myocardial apoptotic death. Treatment with wortmannin and specific Akt inhibitor abolished the anti-apoptotic effect of U50,488H. L-NAME also significantly attenuated the anti-apoptotic effect of U50,488H.

These results demonstrate that U50,488H administered immediately prior to reperfusion increases Akt phosphorylation through a PI3-kinase-dependent mechanism and reduces postischemic myocardial apoptosis. Phosphorylation of eNOS with secondary NO production contribute significantly to the anti-apoptotic effect of U50,488H postconditioning.