Abstract: Objective To explore the expression and role of microRNAs-221 (miR-221) in rats with acute myocardial infarction (AMI).Methods A total of 35 male Sprague-Dawley (SD) rats were randomly selected from 45 rats to establish an AMI model by ligation of left anterior descending branch of coronary artery;then 30 of the model rats with AMI successfully established were randomly divided into an AMI,a control and an inhibition group (10 in each group);another 10 rats of non-model group were regarded as a sham operation group without the ligation.The rats of control group were transfected with miR-221 negative non-carrier lentiviral vector marked by green fluorescent protein (GFP) at the dosage of 4 x 107 viruses via injection into myocardial tissues.The rats of inhibition group were treated the same as those of control group but with miR-221 inhibitor positive lentiviral vector.The rats of AMI and sham operation group were injected with normal saline.All the treatments were performed once the every other day consecutively for two weeks.T cardiac function of all the rats was recorded during the treatment period.The expression of miR-221 in myocardial was detected with reverse transcription-PCR (RT-PCR).Apoptosis index (AI) of myocardium was calculated based on the results of TdT-mediated dUTP-biotin nick end-labeling (TUNEL) assay.The expression of Bcl-2 (B-cellymphoma-2),Bax (B-cell lymphoma 2-associated X protein),PI3K (phosphoinositide 3-OH kinase),and p-AKT (phosphorylated protein kinase B) were determined with Western blot.Results Compared with that of sham operation group (0.18±0.02),the expression of miR-221 in AMI group (1.16±0.12) and control group (1.16±0.12) increased significantly (both P<0.01).The expression of miR-221 (0.30±0.03) in the inhibition group was lower than that in AMI group and control group (both P<0.01).Compared with the expression of Bax (0.13±0.01),Bcl-2 (0.53±0.05),PI3K (0.45±0.04),and p-AKT (0.87±0.09) in sham operation group,the expression of Bax increased;the expression of Bcl-2,PI3K,and p-AKT decreased in AMI group and control group (P<0.01 for all).The expression of Bax decreased;while the expression of Bcl-2,PI3K and p-AKT increased significantly in the inhibition group (all P<0.01).Conclusion The expression of miR-221 is high in the myocardium of rats with AMI and down-regulated miR-221 expression could inhibit the apoptosis of myocardium in rats with AMI by activating PI3K/AKT signaling pathway to regulate the expression of the downstream protein of Bax and Bcl-2.