[ ABSTRACT] AIM:To investigate the cardiac AMP-activated protein kinase ( AMPK) activity and the effects of AMPK activator on cardiac structure and function in the mice with different β-adrenoceptor (β-AR) stimulation patterns . METHODS:Male BALB/c mice were subcutaneously injected with AMPK activator ( AICAR, 250 mg· kg -1 · d-1 ) or saline, and infused with β-AR agonist isoproterenol (ISO, 5 mg· kg-1· d-1) for 14 d.The cardiac functions were evalu-ated by echocardiography or hemodynamic method , and the hearts were harvested after infusion cessation immediately or 3 d later.Phosphorylated AMPK ( p-AMPK) was measured by Western blot .RESULTS:Sustained ISO infusion increased p-AMPK level.AICAR did not further increase p-AMPK but attenuated ISO-induced increase in heart weight .Sustained ISO infusion increased cardiac systolic function as indicated by left ventricular fractional shortening ( FS) and maximum rate of pressure rise (+dp/dtmax).The cardiac systolic function was not further increased by AICAR .The cardiac diastolic func-tion as indicated by left ventricular end-diastolic pressure (LVEDP) was not different in each group .In contrast, cardiac p-AMPK level was similar between the control mice and the mice with sustained ISO infusion and ceased infusion for 3 d. In this model, AICAR improved the cardiac systolic and diastolic functions , which were impaired by ISO.Moreover, the increased pattern of p-AMPK level was similar with that of heart rate upon ISO stimulation .CONCLUSION: Sustained ISO infusion increases p-AMPK.After ISO infusion cessation for 3 d, p-AMPK is decreased to the basal level .β-AR-in-duced inotropic effects should be avoided to investigate the cardioprotective role of AMPK activation in the β-AR stimulation models.

Objective: To observe the regulatory effects of miRNA-31 (miR-31) on LATS2 and cardiomyocyte hypertrophy via down-regulating miR-31 expression in rat's cardiomyocytesin vitro. Methods: Rat's cardiomyocytes were isolated and cultured for 10 daysin vitro, according to different intervention methods, the cells were divided into 4 groups:①Blank control group,②AngII intervention group,③Lentivirus with miR-31 inhibitor infection group,④Negative lentivirus infection group. On day-8, gene expressions of MiR-31, LATS2, cardiac hypertrophy ANP and β-MHC were examined by qRT-PCR; on day-10, cell morphology was observed by fluorescence staining. LATS2 protein expression was examined by Western blot analysis. Dual luciferase reporter plasmids were transfected into 293T cells, then luciferase activity was detected to identify the targeting effect of miR-31 on LATS2. Results: Compared with Blank control group, AngII intervention group showed increased gene expressions of miR31, cardiac hypertrophy ANP and β-MHC,P<0.05, enlarged cardiomyocyte surface,P<0.05; while decreased gene and proteinexpressions of LATS2,P<0.05. Compared with AngII intervention group, Lentivirus with miR-31 inhibitor infection group had down-regulated expressions of miR31, cardiac hypertrophy ANP and β-MHC,P<0.05, reduced cardiomyocyte surface, P<0.05; while slightly increased LATS2 gene expression and obviously increased protein expression,P<0.05. Dual luciferase reporter assay presented that relative luciferase activity of TRAF6-3' UTR+miR-146b was significantly decreased than TRAF6-3' UTR+miR-NC,P<0.01 and relative luciferase activity of LATS2-3' UTR+ miR-31 was signiifcantly reduced than LATS2-3' UTR-NC+miR-31,P<0.01. Conclusion: Cardiomyocytes hypertrophy could be reversed at certain degree by down-regulating miR-31; the targeting effect of miR-31 on LATS2 was involved in cardiomyocyte hypertrophyregulation.