Objective To investigate the effects of transplantation of bone marrow mesenchymal stem cells (BMSCs) transfected with adrenomedullin (ADM) on cardiac function in heart failure rats and the mechanism.Methods BMSCs were isolated from femur and tibia marrow of 10 rats,20 days old,body weight 30-50 g,and in vitro cultured.The third passage of BMSCs were tuansfected with adenovirus containing ADM and labeled with green fluorescent protein(GFP).Before transplantation,BMSCs were labeled with 4',6-diamidino-2-phenylindole (DAPI).Eighty healthy male Wistar rats weighted 180-200 g were randomly divided into 2 groups according to body weight:control group (n =10) was injected with normal saline (NS); diffuse myocardial injury heart failure rat model(n =70) was established by subcutaneous injection of isoproterenol (ISO,170 mg/kg) every day for 4 consecutive days.Four weeks after administration of ISO,heart function was assessed by echocardiography,the 39 rats with left ventricle ejection fraction(LVEF) ＜ 70％ of global heart failure model were randomly divided into three groups in accordance with the level of heart function:untransfected group,transfected group and NS group.DAPI labeled untransfected BMSCs suspension,ADM gene transfected BMSC suspensions (3 × 106/150 μl) and equal volume of NS were injected into the left ventricular anterior wall in 4 places in each goup.Control group received thoracotomy only.Four weeks after transplantation,rats were examined by ultrasound echocardiography,then were sacrificed and left ventricular were dissected.The myocardium was stained with Massons trichrome to analyze myocardial tissue fibrosis.The transplanted cells were observed by fluorescence microscopy and matrix metalloproteinase-2 (MMP-2) expression of myocardial tissue was detected in each group by Western blotting.Results After in vitro culture for three days,the BMSCs began to grow adherently,tended to be fused about 10 days,in the fusiform shape.Four weeks after transplantation,ultrasound echocardiography results showed that rat cardiac left ventricular end systolic diameter (LVDs),LVEF,and left ventricular cardiac fractional shortening (LVFS) were different between groups,and the difference were statistically significant(F =5.838,32.983,51.714,P ＜ 0.05 or P ＜ 0.01).Compared with the control group[(86.50 ± 1.54)％,(50.66 ± 1.87)％],the LVEF and LVFS of NS groups[(56.67 ± 6.86)％,(26.27 ± 4.01)％],the transfected group[(79.40 ± 1.70)％,(43.48 ±2.15)％] and untransfected group[(69.24 ± 7.30)％,(34.59 ± 5.13)％] were significantly lower(all P ＜ 0.05);compared with the NS group,the LVEF and LVFS of the transfected groups and the untransfected group were significantly increased(all P ＜ 0.05) ; compared with the untransfected group,the LVEF and LVFS of the transfected group were increased (all P ＜ 0.05).Compared with the control group [(3.16 ± 0.22)mm],the LVDs of the NS group[(5.35 ± 1.57)mm] was significantly increased (P ＜ 0.01); compared with the NS group,the LVDs of the transfected group and the untransfected group[(3.95 ± 0.55),(4.24 ± 0.92)mm] were significantly decreased (all P ＜ 0.05).There was no statistically significant difference between the control group,the transfected group and the untransfected group in LVDs (P ＞ 0.05).It can clearly be seen that there was GFP and DAPI labeled transplanted cells under a fluorescence microscope in the myocardial tissue transplanted area.There was significant difference in myocardial fibrosis area and the myocardial tissue protein expression of MMP-2 between groups(F =533.75,32.777,all P ＜ 0.01).The area ratio of the NS group[(15.200 ± 0.356)％,0.584 ± 0.013],the transfected group[(8.530 ± 0.573)％,0.386 ± 0.017] and the untransfected group [(10.670 ± 0.369)％,0.438 ± 0.015] and the MMP-2 protein expression were significantly higher than that of the control group[(1.070 ± 0.113)％,0.319 ±0.013,all P ＜ 0.01)]; compared with the NS group,the two index of the transfected group and the untransfected group were decreased (all P ＜ 0.05).Compared with the untransfected group,the two index of the transfected group was decreased (all P ＜ 0.05).Conclusion Transplantation of ADM gene transfected BMSCs can improve heart function of rats with heart failure significantly and reduce myocardial fibrosis.