Objective   To investigate protective effect and mechanism of tetramethylpyrazine (TMP) on myocardium in rats with acute myocardial infarction (AMI).

  Methods   Totally 105 specific pathogen free Sprague-Dawley rats were assigned into a sham group, an model group (AMI), low, moderate, and high TMP dose groups (L-, M-, and H-TMP with intraperitoneal injection of TMP at doses of 120, 240, and 360 mg/kg 24 hours after the establishment of AMI model) and a positive control group (ACT with intraperitoneal injection of atorvastatin at the dose of 8 mg/kg). Left ventricular function was measured with ultrasonography; serum tumor necrosis factor (TNF-α) and monocyte chemotactic protein 1 (MCP-1) were detected with enzyme-linked immunosorbent assay (ELISA); hematoxylin-eosin (HE) staining was used to examine pathological changes of myocardial tissue in each group. Tunel staining was used to observe the apoptosis of myocardial cells; real-time fluorescence quantitative PCR (QRT-PCR) was used to detect the expression of microRNA-34a (miR-34a) in myocardium and expressions of sirtuin 1 (sirt1), p53, B-cellymphoma-2 (Bcl-2), Bcl-2associated X protein (Bax), and cleaved-caspase 3 in myocardium were detected with Western blot.

  Results   Compared with the rats of sham group, the rats of AMI exhibited following significant abnormalities: increased left ventricular end diastolic dimension (LVEDD) and left ventricular end systolic dimension (LVESD) but decreased left ventricular posterior wall diameter at systole (LVPWDs), left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS); declined serum TNF-α and MCP-1; deformation and necrosis of myocardial cells and inflammatory cell infiltration in myocardial tissues; higher score for myocardial histopathological damage and apoptotic rate; up-regulated expressions of miR-34a (1.27 ± 0.15 vs. 0.45 ± 0.16), p53 protein (1.05 ± 0.12 vs. 0.28 ± 0.04), Bax (1.54 ± 0.19 vs. 0.15 ± 0.04), and cleaved-caspase 3 protein (1.12 ± 0.14 vs. 0.14 ± 0.03) but down-regulated sirt1 protein (0.37 ± 0.06 vs. 0.85 ± 0.07) Bcl-2 protein (0.13 ± 0.03 vs. 1.12 ± 0.18) (P < 0.05 for all). In comparison with the AMI rats, the rats with L-, M-, and H-TMP had following significant disparities: decreased LVEDD and LVESD, increased LVPWDs, LVEF and LVFS, down-regulated serum TNF-α and MCP-1, and lower score for myocardial histopathological damage and apoptotic rate; decreased expressions of miR-34a (0.93 ± 0.08, 0.75 ± 0.09, and 0.62 ± 0.08) and p53 (0.93 ± 0.09, 0.64 ± 0.08, and 0.55 ± 0.09), Bax (1.17 ± 0.16, 0.78 ± 0.06, and 0.47 ± 0.04), cleaved-caspase 3 protein (0.89 ± 0.11, 0.73 ± 0.09, and 0.42 ± 0.10) but increased expressions of sirt1 (0.46 ± 0.05, 0.55 ± 0.07, and 0.68 ± 0.09) and Bcl-2 protein (0.25 ± 0.04, 0.37 ± 0.05, and 0.84 ± 0.09) in myocardial tissues (all P < 0.05).

  Conclusion   Tetramethylpyrazine has a protective effect on myocardial injury in rats with acute myocardial infarction and the effect may be correlated with down-regulating the expression of miR-34a, inhibiting sirt1/p53 pathway and reducing myocardial apoptosis.