الفهرس 
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Abstract
Introduction: Irisin is a novel myokine, which is discovered in 2012. It is released from skeletal muscle after exercise. It is involved in the browning of white adipose tissue and regulating bone metabolism. The present work was designed to study the correlation between the serum irisin level which is produced from the skeletal muscle by exercise and the severity of osteoporosis 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:Containing sedentary rats. group II (Ex): These rats trained (5 days per week for 8 weeks in a gradual manner). group III (OS): Rats received methylprednisolone intramuscular at doses of 0.2 mg/kg. three time/ week for 5 weeks. group IV: (Ex + OS): Rats underwent swimming in the same previous protocol and after 3 weeks they received methylprednisolone in the same dose as previous. We measured bone mineral content and density using DEXA. Then the rats were scarified under anesthesia and the blood was collected. The sera were obtained and analyzed to determine serum irisin, calcium, and CTX level. At the end of this experiment, the tibia of rats was excised and fixed in 10% neutral buffered formaldehyde for 2 days and decalcified in EDTA solution during 4 weeks for histopathological examination of slides stained with Hematoxylin and Eosin and Masson’s Trichrome. The present result revealed the following: Our work revealed that, by comparing to the control group, the osteoporotic (OST) group They showed loss of normal bone architectures showed significant decrease in serum irisin level. However, there was significant increase in CTX level. But insignificant decrease in calcium level. the exercise-trained (EX) group showed improvement in different bone parameter as bone mineral content and density. They showed significant increase in serum irisin level and insignificant increase in calcium level. there was significant decrease in CTX level. In conclusion, it can be concluded that Irisin may be the link between the beneficial effect of exercise and the protection against osteoporosis. Swimming exercise promoted bone metabolism and improved BMD and microstructure of the tibia. It would be recommended to: We recommend regular exercise practicing or taking recombinant Irisin as a supplementation for protection against osteoporosis.