Erythropoietin affords additional cardioprotection to preconditioned hearts by enhanced phosphorylation of glycogen synthase kinase-3β

The aim of this study was to determine whether erythropoietin (EPO) affords additional cardioprotection to the preconditioned myocardium by enhanced phosphorylation of Akt, STAT3, or glycogen synthase kinase-3β (GSK-3β). Preconditioning (PC) with 5-min ischemia/5-min reperfusion and EPO (5,000 U/kg iv) reduced infarct size (as % of area at risk, %IS/AR) after 20-min ischemia in rat hearts in situ from 56.5 ± 1.8% to 25.2 ± 2.1% and to 36.2 ± 2.8%, respectively. PC-induced protection was significantly inhibited by a protein kinase C inhibitor, chelerythrine (5 mg/kg), and slightly blunted by a phosphatidylinositol-3-kinase inhibitor, wortmannin (15 μg/kg). The opposite pattern of inhibition was observed for EPO-induced protection. The combination of PC and EPO further reduced %IS/AR to 8.9 ± 1.9%, and this protection was inhibited by chelerythrine and wortmannin. The additive effects of PC and EPO on infarct size were mirrored by their effects on the level of phosphorylated GSK-3β at 5 min after reperfusio...