Effects of Metoprolol on Left Ventricular Remodeling after Acute Myocardial Infarction in Rats

Objective To investigate the effects and mechanism of metoprolol on left ventricular remodeling(LVR) after acute myocardial infarction(AMI) in rats. Methods The Wistar rats were randomly assigned to three groups: AMI control(n=9),metoprolol treatment(n=9) and sham-operated group(n=9).The rats of AMI control and metoprolol treatment were ligated in the left anterior descending coronary artery;the sham-operated rats were not ligated.The metoprolol group was given with metoprolol 10 mg·kg-1·d-1,and the other two groups with the same dose of 0.9% natrium chloride.Four weeks later,the left ventricular end-diastolic dimension(LVDD),left ventricular end-diastolic volume(LEDV),left ventricular mass index(LVMI),ejection fraction(EF) and fractional shortening(FS) of each rat was detected by echocardiogram.Myocardial cell and interstitial tissue were observed by HE stain. Results Compared with those in the sham-operated group,the LVDD,LEDV and LVMI in AMI group were all significantly increased(P0.05).The parameters in AMI including EF and FS were all significantly alleviated(P0.05).Meanwhile,cardiac myocyte hypertrophy was found by HE stain.However,in metoprolol group,the EF and FS were improved in comparison to those in AMI group. Conclusion Metoprolol had a therapeutic effect on LVR after AMI,the mechanism of which should be associated with inhibiting sympathetic nerve hyperplasia and reforming anomalies of neuroendocrine and hemodynamics.