The Effects Of Different Intensities Of Long Time Exercises On The Downstream Signals Of MTOR In Cardiac Muscle

Aim:In the current study, the changing characteristics of p70S6K,4EBP1 and eIF2B were focused on after various intensities exercise trainings of long period to explore the influences of long time exercise training on myocardial hypertrophy and hope to provide more evidences for the cellular mechanisms of protein synthesis in myocardium.Methods:54 male SD rats aged 7 weeks were randomly divided into nine groups,6 for each:group control (C), moderate intensities (28 m/min,60 min treadmill) group with myocardium being isolated at time point of immediately (MO),6 (M1),12(M2) and 24(M3) hours after the last exercise training, high intensities (38 m/min,60 min treadmill) group at time point of immediately (HO),6 (H1),12(H2) and 24(H3) hours after the last exercise training. The training lasted for 7 weeks and there were two days break a week. Body weights were recorded on every Monday and we also noted the weight of body and the heart by the time getting the samples. The protein levels of both endogenesour and phosphorylated forms of p70S6K and 4EBP1 and the phosphorylatoin of eIF2B were determined by Western blot analysis.Results:1) The tendency of body weight were all increasing as the time went on, while the body weight of high intensities group decrease on the third and froth week slightly and came back to normal after that. The body weight appeared to be significantly different when the moderate intensity group compared to the control group and the high intensity group compared the moderate one.2) Significant difference of body weight was not observed between the groups, however, when it comes to the ratio of weight of heart to body, both training groups differs much from the control group significantly, and so as the high intensity group from the moderate group.3) The total amount of p70S6K of exercise training group almost remains the same level as the control group. The phosphorylation of p70S6K (Thr389) and its ration to total p70S6K in the moderate group raise after the exercise and reached the peak value 12 hours after the last training.4) The total 4EBP1 at every time point of exercise training group shows no difference from the control group while in the moderate group the amount of phosphorylated 4EBP1(Thr37/46) and the ratio of 4EBP1(Thr37/46)/4EBP1 reached its climax immediately after the last training and then diminished below the basal level.5) The amount of phosphorylation of eIF2B e (Ser535) increase with the time after the last exercise both in the moderate and high intensity group and peak at the time point of 24 hours.Conclusions:1) Both moderate and high intensity of long time exercise trainings induced myocardial hypertrophy.2) P70S6K and 4EBP1 play important roles in the protein synthesis during moderate exercise training related to physiological cardiac hypertrophy.3) eIF2B may be responsible for both physiological and pathological myocardial hypertrophy.