| AIM: To investigate the effects of phosphatidylinositol -3 - kinase / protein kinaseB(PI3K/Akt)signaling pathway on vascular endothelial function in rats with myocardial ischemic postconditioning (I-PostC) and interventional effects of erythropoietin by observing the effects of myocardial I-PoctC and recombinant human erythropoietin (rhEPO)on contraction and relaxation of isolated aortic strips,levels of nitric oxide (NO)and activities of nitric oxide enzyme (NOS)in peripheral blood , expressions of mRNA and protein of PI3K/Akt in rats with acute myocardial ischemia and reperfusion.Methods: Forty-two male SD rats were randomized into 7 groups:①Sham operation group (Sham group): The suture placed under the left coronary artery (LCA) was not tied,②Ischemia/Reperfusion group (I/R group): LCA was occluded for 30 min, and then reperfused by loosening the ligature for 3 hrs,③Ischemia-Postconditioning group (I-PostC group): Rats underwent 3 cycles of 10s ischemia/10s reperfusion immediately at the beginning of reperfusion,④Wortmannin+I-PostC group (Wort+I-PostC group) : Wortmannin ( Wort ) (15ug/kg) was given via jugular intravenous injection before 3 cycles of 10s of ischemia/10s reperfusion. The rest procedures were the same as those for I-postC group,⑤recombinant human erythropoietin (rhEPO)group (rhEPO group) : rhEPO was administered at a dose of 5000U/kg intraperitoneally before the surgical procedure of reperfusion,⑥Wort+rhEPO group: Wort and rhEPO were administered with the same methods and at the same doses as used previously before the surgical procedure of reperfusion ,⑦rhEPO+I-PostC group: rhEPO was administered at a dose of 5000U/kg intraperitoneally and then rats underwent 3 cycles of 10s ischemia/10s reperfusion before the surgical procedure of reperfusion. The serum levels of nitric oxide (NO) and the activities of nitric oxide synthase (NOS) were examined in each group , contractive reaction to phenylephrine (PE),dilatant reaction to acetylcholine (Ach) and sodium nitroprusside (SNP) of thoracic aortic strips in vitro were analyzed; Reverse transcriptase-polymerase chain reaction (RT-PCR) was applied for determining expression of Akt mRNA , and imunohistochemistry method was used for determining expression of Akt protein in each group.Results:⑴Serum levels of NO and activities of NOS: The serum levels of NO and the activities of NOS in I/R group,Wort+I-PostC group,Wort+rhEPO group were obviously lower than those in Sham group (P<0.05) . I-PostC group ,rhEPO group and rhEPO+I-PostC group had higher levels compared with I/R group(P<0.05), while Wort+I-PostC group and Wort+rhEPO group had lower levels than I-PostC group (P<0.05), Wort+rhEPO group had lower levels than rhEPO group. There is a tendency for the levels of NO and the activities of NOS in rhEPO+I-PostC group to be higher than those in rhEPO group; however, there was no statistical difference (P>0.05). There were no significant differences among I-PostC group, rhEPO group, rhEPO+I-PostC group and Sham group, the same as the comparation among Wort+I-PostC group,Wort+rhEPO group and I/R group.⑵Contraction and relaxation of isolated aortic strips:IC50 for Ach in I/R group, Wort+I-PostC group and Wort+rhEPO group were significantly larger than those in Sham group(P<0.05), while IC50 in I-PostC group, rhEPO group and rhEPO+I-PostC group were much less than I/R group (P<0.05). Wort+I-PostC group and Wort+rhEPO group had larger IC50 comparedwith I-PostC group (P<0.05). Wort+rhEPO group had larger IC50 than rhEPO group(P<0.05). And IC50 were not sifgnificantly different in I-PostC group,rhEPO group and rhEPO+I-PostC. At the same time, the contractive reaction to PE and the non-endothelium-dependent dilatant reaction to SNP of aortic strips were not obviously different in each group (P>0.05).⑶The expressions of Akt mRNA in aortic tissues:Akt mRNA expressed in aortas in each group, with the lowest expression in Sham group . I-PostC group,rhEPO group and rhEPO + I-PostC group had higher expression of Akt mRNA than I/R group(P<0.05); Wort+I-PostC group and Wort+rhEPO group had significantly lower expressions of Akt mRNA compared with I-PostC group (P<0.05);the expressions of Akt mRNA in rhEPO group and rhEPO+I-PostC group were obviously higher than those in Wort+I-PostC group ( P<0.05 );Wort+rhEPO group had much lower expressions of Akt mRNA comparedwith those in group rhEPO(P<0.05); however, rhEPO+I-PostC group had significantly higher expressions of Akt mRNA than Wort+rhEPO group(P<0.05). There were no significant differences in Akt mRNA expressions among I-PostC group, rhEPO group and I-PostC +rhEPO group, the same as those among I/R group, Wort+I-PostC group and Wort+rhEPO group.⑷The expressions of Akt protein in aortic tissues: Akt protein expressed in aortic tissues in each group, with the lowest expressions in Sham group . I-PostC group, rhEPO group and rhEPO + I-PostC group had higher expression of Akt protein than I/R group(P<0.05), while Wort+I-PostC group and Wort+rhEPO group had significantly lower expressions compared with I-PostC group (P<0.05);the expressions of Akt protein in rhEPO group and rhEPO+I-PostC group were obviously higher than those in Wort+I-PostC group(P<0.05);Wort+rhEPO group had much lower expressions of Akt protein than rhEPO group(P<0.05); however, rhEPO+I-PostC group had significantly higher expressions of Akt protein than Wort+rhEPO group ( P<0.05 ) . There were no significant differences in Akt protein expressions among I-PostC group,rhEPO group and I-PostC +rhEPO group, the same as those among I/R group, Wort+I-PostC group and Wort+rhEPO group.Conclusions:⑴Myocardial ischemia reperfusion injury(IRI) in rats can cause severe endothelium-dependent diastolic dysfunction.⑵I-PostC can significantly ameliorate the impaired endothelium-dependent diastolic functions caused by myocardial IRI in rats.⑶Wortmannin– a specific PI3K inhibitor -- can lessen the protective effects of I-PoctC on vascular endothelium-dependent diastolic function, and reduce the expressions of Akt mRNA and protein in aortic tissues, suggesting that the protective effects of I-PostC on endothelial function may be related with the activation of PI3/Akt signaling pathways and its downstream target eNOS.⑷rhEPO can significantly improve the impaired endothelium-dependent diastolic functions, and exert similar protective effects on vascular endothelial function to I-PostC.⑸Wortmannin– a specific PI3K inhibitor– can lessen the protective effects of I-PoctC and reduce the expressions of Akt mRNA and protein in aortic tissues, suggesting that the protective effects of rhEPO on endothelial dysfunction caused by IRI may be related with the activation of PI3/Akt signaling pathways and its downstream target eNOS. Its underlying mechanisms need to be further explored.⑹There is no significant damage to aortic endothelium-dependent diastolic function in rats with acute myocardial ischemia reperfusion injury.
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