Abstract: \Abstract: Objective To investigate the effects of mechanical loading on inflammation and ventricular remodeling in myocardial infarction (MI) rats. Methods Thirty male Wistar rats (8-week old, body weitht about 200 g) were randomly divided into sham operation group (Sham group), myocardial infarction model group (MI group) and mechanical loading treatment group (MI+L group) with 10 rats in each group. One day after the establishment of MI model in MI+L group, the knee loading was applied for 2 weeks. After mechanical loading, ST segment of the standard 12-lead electrocardiogram (ECG) lead Ⅱ, heart mass index (HMI), left ventricular mass index (LVMI) and heart weight/tibial length were measured. Left ventricular end-diastolic diameter (LVEDD) and infarct size were evaluated by 2, 3, 5-triphenyl tetrazolium chloride (TTC) staining. The number of infl ammatory cells was evaluated by HE staining. The collagen volume fraction (CVF) was evaluated by Masson staining. The protein expressions of nuclear factor- κb p65 (NF-κB p65), interleukin-6 (IL-6) and matrix metalloproteinase-9 (MMP-9) were assessed by immunohistochemistry. Results Compared with Sham group, MI resulted in a significant increase in the lead Ⅱ ST-segment, HMI, LVMI, LVEDD, heart weight/tibial length and infarct size in MI group. After mechanical loading, there were significantly decrease in lead Ⅱ ST-segment, HMI, LVMI, LVEDD, heart weight/tibial length and infarct size in MI+L group than those in MI group (P＜0.05). Cardiac histology showed that MI caused inflammation and fibrosis in myocardial tissues. After loading therapy, the number of inflammatory cells and CVF were significantly improved (P＜0.05). Immunohistochemical analysis showed that MI resulted in the increased protein expressions of NF-κB p65, IL-6 and MMP-9. The mechanical loading obviously inhibited the expressions of NF-κB p65, IL-6 and MMP-9. There was a positive correlation between the expressions of NF-κB p65, IL-6 and MMP-9. There was a positive correlation between NF-κB p65, IL-6, MMP-9 and ventricular remodeling markers (LVEDD, HMI, LVMI and heart weight/tibial length). Conclusion Mechanical loading can significantly improve myocardial injury in MI rats, which may be related to alleviating inflammation and inhibiting ventricular remodeling after MI.

Key words: myocardial infarction, inflammation, ventricular remodeling, NF-kappa B, matrix metalloproteinase 9, interleukin-6, rats, Wistar, mechanical loading