| Objective:Considerable evidence indicates that theβ2-adrenoceptor agonist clenbuterol could decrease apoptosis in a rodent model of ischemic cardiomyopathy. In this study, we investigated the effects of clenbuterol on infarct size caused by myocardial ischemia/reperfusion (I/R) in anesthetized rats.Methods:Rats were randomized to:1) sham group,2) I/R group,3) clenbuterol +I/R group,4) ICI 118551+clenbuterol+I/R group,5) metoprolol+clenbuterol+I/R group,6) metoprolol+I/R group,7) Pertussis toxin+clenbuterol+I/R group. Under anesthesia, left anterior descending (LAD) coronary artery was occluded for 30 min followed by reperfusion for 2 h.Results:Compared with the control I/R group, clenbuterol (0.5mg-kg-1, i.p) had reduced infarct size, improved diastolic function and sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA) activity, increased SOD activity, and decreased MDA level and LDH, CK release. Clenbuterol increased the phosphorylation of ERK1/2, which resulted in inhibition of myocardial apoptosis as evidenced by the reduction of TUNEL-positive staining, Bax/Bcl-2 mRNA and Caspase-3 protein expression. The G,-protein inhibitor pertussis toxin blocked the clenbuterol-induced improvement in cardiac function and infarct size. Pretreatment with ICI 118551 (a selectiveβ2-AR antagonist) inhibited the effects of clenbuterol mentioned above (P<0.05). Theβ1-AR agonist metoprolol had the similar effects compared with the clenbuterol-treated group but failed to reduce MDA and improve SERCA activity. As a combination therapy, there were no synergistic effects of metoprolol+clenbuterol treatment.Conclusions:Clenbuterol pretreatment provides a significant cardioprotection mediated by theβ2-AR-Gi-protein signaling against ischemia/reperfusion injury. There are no synergistic effects in the combined use of clenbuterol and metoprolol. Objective:To investigation the effect of clenbuterol on anoxia/reoxygenation (A/R) injury in neonatal rat cardiomyocytes. In addition, we have explored possible mechanisms for the effects.Methods:To establish the model of anoxia/reoxygenation injury in primary neonatal cardiomyocytes. Cell viability was determined by the conventional MTT reduction assay; cell injury by lactate dehydrogenase(LDH) leakage; and cardiomyocyte apoptosis by Hoechst33342 and Annexin-PI staining; Intracellular reactive species(ROS) was monitored by the fluorescent DCFH-DA; Expression of apoptosis related factor Bcl-2 and Bax, phosphorylated ERK,caspase-3 were determined by western blot.Results:Clenbuterol and metoprolol protected the cardiomyocytes from anoxia/reoxygenation injury, as evidenced by decreased LDH release and increased cell viability. This protective effect concomitantly decreased ROS production and apoptosis in cardiomyocytes. But selectiveβ2 receptor antagonist ICI 118,551 could abolish the effects of clenbuterol. There are no synergistic effects in the combined use of clenbuterol and metoprolol. In clenbuterol-pretreated cardiomyocytes, we observed a decrease in the expression of pro-apoptotic protein Bax and caspase-3.We also found that clenbuterol pretreatment enhanced expression of anti-apoptotic protein Bcl-2 and activation of ERK concerning survival. The effects of clenbuterol were reversed by PI3K inhibitor LY294002 and ERK inhibitor PD98059. Only in in phosphorylated ERK1/2, there was no obvious difference between LY294002+clen+A/R group and clen+A/R group.Conclusion:Clenbuterol exerts cardioprotective effect against Anoxia/reoxygenation injury by inhibiting oxidative stress and apoptosis. Clenbuterol pretreatment increase the Bcl-2/Bax ratio and phosphorylation of ERK, decrease caspase-3 express. The respective inhibitor of ERK and PI3K, PD98059 and LY294002, prevent the anti-apoptotic effect. But only PD98059 attenuated the increasing phosphorylation of ERK of clenbuterol. So the ERK and PI3K/Akt pathway may be involved in the cardioprotective effect of clenbuterol...
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