الفهرس 
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Abstract
Acute myocardial infarction is a major reason for death all over the world with a continuous increased incidence. It is an acute condition of myocardial necrosis which caused by imbalance between coronary blood supply and myocardial demands. Irisin is a novel myokine, which is discovered in 2012. It is released from humans and rats’ skeletal muscle after exercise. Irisin is a peroxisome proliferator-activated receptor-γ coactivator-α (PGC1-α) dependent myokine. This work aimed to study the correlation between the serum irisin level which is produced from the skeletal muscle by exercise and the severity of the acute myocardial infarction in the exercise-trained rats. This study was done by using 48 adult male rats having 200-250 grams body weight. Rats were classified into four groups (12 for each group). •group I: Control sedentary group (C): Rats were housed for 8 weeks. •group II: Exercise-trained group (Ex): Rats were subjected to swimming exercise (5 days per week for 8 weeks in a gradual manner).•group III: Infarct group (MI): In which induction of acute myocardial infarction was done by subcutaneous injection of isoprenaline (85mg/kg) for 2 consecutive days with twenty four hours interval. •group IV: Exercise-trained infarct group (Ex-MI): Rats were subjected to swimming exercise for 8 weeks followed by isoprenaline-induced myocardial infarction in the last 2 days in the same dose as in group III. We recorded basal ECG for each rat at start of the study, before 1st dose of isoprenaline, then 24 hours after 2nd dose of isoprenaline. The following ECG variables were measured: QRS duration, QRS amplitude, QTc interval, and ST segment elevation. The rats were sacrified under anathesia and the blood was collected. The sera were obtained and analyzed to determine the serum level of irisin, lipid peroxidation (MDA), total antioxidant status (TAS), CK-MB and troponin I. At the end of this experiment, the hearts were excised and put in 10% neutral formalin for histopathological examination of slides stained with Hematoxylin and Eosin and Masson’s Trichrome. Also, immunohistochemistry for caspase 3 was done. he present work revealed that: 1-By comparing to the control group, the infarct (MI) group showed disturbed ECG parameters presented as significant reduction in QRS duration and amplitude. Also, there is significant prolongation in QTc interval together with significant elevation in the ST segment. 2- Concerning the biochemical analysis, the infarct group showed significant elevation of serum CK-MB, troponin I and lipid peroxidation level (MDA) as compared to the control sedentary rats, while the total antioxidant capacity and serum irisin level significantly decreased. The histopathological examination by Hematoxylin and Eosin for heart tissues from infarct (MI) group showed interstitial edema with marked neutrophil granulocytes that characterize acute extensive myofibrillary degeneration. While Masson’s Trichrome revealed significant increase in percentage area of degeneration and necrosis which was represented by increased collagen deposition. Also, results revealed significant increase in caspase 3 expression percentage area by the immunohistochemistry 3-By comparing to the control group, the exercise-trained (EX) group showed significant increase in serum irisin level and total antioxidant status. However, there is significant decrease in lipid peroxidation (MDA) 4-In the exercise-trained infarct (EX-MI) group, it was noticed that exercise training that preceded the induction of myocardial infarction improved the ECG parameters, biochemical parameters, histopathology and immunohistochemistry when compared to the infarct group. The improved ECG parameters were represented as significant increase in QRS duration and amplitude. Also, there is significant reduction in QTc prolongation and ST elevation. 5-Concerning the biochemical analysis, exercise in EX-MI group significantly reduced the isoprenaline-induced elevation of serum CK-MB and cTnI. Also, there is significant decrease in the lipid peroxidation (MDA) and significant increase in the total anti-oxidant and serum irisin levels as compared to the infarct group. The histopathological examination by Hematoxylin and Eosin staining for heart tissues from the EX-MI group showed less interstitial edema with less inflammation. Also, the Masson’s Trichrome staining revealed significant decrease in percentage area of degeneration which was represented by decreased collagen deposition. In addition, there is significant reduction in the apoptosis percentage area which was represented by significant decrease in caspase 3 expression percentage area. 6-In this experiment, we observed high positive correlation between the serum irisin level and each of QRS duration, QRS amplitude and total antioxidant status. Also, results showed high negative correlation between the serum irisin level and the studied parameters: ST segment elevation, QTc interval, serum CK-MB, serum troponin, serum malondialdehyde (MDA). This was confirmed by the negative correlation between serum irisin and the percentage area of both collagen deposition and caspase 3 expression. Conclusions from this study, it can be concluded that irisin may be the link between the beneficial effect of chronic exercise and the protection against acute myocardial infarction. This conclusion is supported by the negative correlation between serum irisin and lipid peroxidation level (MDA), CK-MB, troponin, collagen deposition and caspase 3 expression percentage areas. It is also supported by the positive correlation between serum irisin and total antioxidant status.