Effects Of Different Exercise Intensities Interventions On Cardiac Function In Rats With Myocardial Infarction

Background:Cardiovascular disease（CVD）has become a major cause of death and a major global public health problem.The cardioprotective effect of exercise intervention been confirmed in many animal experiments and clinical trials.Exercise therapy has become an effective supplement to surgery and drug therapy.High intensity intermittent exercise（HIIT）and aerobic exercise training（AT）can improve cardiac function,but the effect and molecular mechanism of HIIT and AET on cardiac function of massive infarction are still unclear.The purpose of this study was to observe the effects of HIIT,moderate intensity aerobic exercise（AT）and sedentary state（SED）on cardiac function after massive infarction,and to explore the molecular mechanism in order to optimize exercise prescriptions.Methods:24 rats were randomly assigned to control group（CON）,myocardial infarction sedentary group（MI-SED）,myocardial infarction AT group（MI-AT）,myocardial infarction HIIT group（MI-HIIT）.The animals in CON group and MI-SED group were placed in cages after operation,keeping constant temperature and humidity,giving adequate rat food and water,12 hours of light/darkness each day,simulating normal living environment,without special exercise program intervention.The MI-AT group trained on a 50-60%VO₂ treadmill（Zhongshi Dichuang Company,Beijing,China）for 50 minutes per day for 5 days a week.In MI-HIIT group,the training time was alternately 4 min 85%-90%VO2 treadmill training and 3 min50%-60%VO2 treadmill training.The training time was repeated 7 times for 49min/day,5 days a week.Both MI-AT and MI-HIIT groups had 40%VO2 warm-up and Tidy-up exercises for 5 minutes before and after training.The changes of exercise tolerance,left ventricular ejection fraction（LVEF）,ultrastructure of myocardial fibers and AMPK content were observed at the end of the experiment.Results:1.In the comparison of exercise tolerance before and after intervention,CON, MI-SED,MI-AT and MI-HIIT groups had significantly higher exercise tolerance than those before intervention(P_CON=0.000;P_MI-AT=0.009;P_MI-AT=0.000; P_MI-HIIT=0.000).There was no significant difference among BASELINE,MI-SED, MI-AT and MI-HIIT groups（P>0.05）,and the three MI groups were significantly lower than CON group（P<0.001）.After 4 weeks of intervention, the exercise tolerance of rats in MI-SED group was significantly lower than that in MI-AT group（P<0.001）and MI-HIIT group（P<0.001）.There was no significant difference between MI-AT and MI-HIIT groups（P>0.05）.2.Compared with BASELKINE,LVEF in MI-AT and MI-HIIT groups increased significantly after four weeks of intervention(P_MI-AT=0.000,P_MI-HIIT=0.000). There was no significant difference in LVEF between CON group and MI-SED group before and after intervention.There was no significant difference in LVEF between MI-SED,MI-AT,MI-AT and MI-HIIT before intervention.Four weeks after intervention,the LVEF of MI-SED group was significantly lower than that of MI-AT group（P<0.05）and MI-HIIT group（P<0.01）,but there was no difference between MI-AT group and MI-HIIT group（P>0.05）.3.Comparison of AMPK protein expression before and after intervention: Compared with the CON group,only the myocardial AMPK protein in MI-SED group decreased significantly（P<0.01）,while the myocardial AMPK protein in MI-AT and MI-HIIT group had no significant difference.The expression of AMPK protein in MI-SED group was significantly lower than that in MI-AT group（P<0.01）and MI-HIIT group（P<0.01）.The AMPK protein in MI-HIIT group was lower than that in MI-AT group.4.Under electron microscopy,the cardiomyocytes in the CON,MI-AT and MI-HIIT groups were normal and well-arranged,and the intercalated disks were intact.In the MI-SED group,there was a considerable degree of myocardial fibre disorder, and sarcoplasmic dissolution and fibrous hyperplasia were present.In the 90000x field,the mitochondrial structure of the CON group was normal and closely arranged,the cristae were arranged neatly,and the mitochondrial membrane was intact.In the MI-SED group,mitochondria showed vacuoles,swelling,and disordered arrangement,and the mitochondrial membrane was incomplete.The number of mitochondria in the MI-AT group was reduced,the membrane remained intact,and the cristae were normal.In the MI-HIIT group,the mitochondria appeared swollen and vacuolated with disrupted cristae Conclusion: Four weeks of AT and HIIT exercise intervention can protect mitochondrial function,reduce myocardial fibrosis and improve cardiac function and motor ability by up-regulating the expression of AMPK.There is no significant difference between themConclusion:Our study demonstrated that 4 weeks of AT and HIIT intervention could protect myocardial cells and improve LVEF and exercise capacity,which may be related to AMPK up-regulation,and that the effects were similar.HIIT showed myocardial mitochondrial damage.We will observe the effects of AT and HIIT on MI rats with a longer intervention period.