الفهرس 
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Abstract
The present work studied the effect of PRP on skeletal muscle repair in senile male albino rats.
Fifty- four senile male albino rats were used in this study. Rats were divided equally into three groups. group I was further equally subdivided into; subgroup IA: rats were left without intervention, subgroup IB: rats were sham operated where a 5 mm long incision was done in the skin of the right hind limb in each rat. Three rats of both subgroups were sacrificed on the 1st, 7th day and 21st days post injury respectively.
group II consisted of eighteen rats where muscle injury was induced in the right hind limb and rats were left for spontaneous healing and further equally subdivided into subgroup IIA; rats were sacrificed on the first day post-injury, subgroup IIB; rats were sacrificed on the seventh day and subgroup IIC; rats were sacrificed on the twenty first day.
group III: consisted of eighteen rats, muscle injury was induced as group II, but rats were treated with PRP on days 0, 3, 5 and 7. Rats were also equally subdivided into subgroups IIIA, IIIB and IIIC where sacrifice was done on the first, seventh and twenty first days, respectively.
At the end of the experiment, rats were sacrificed, and the injured muscles were excised and processed for light and electron microscopic examination.
Our results showed that aging had deleterious effect on the healing of skeletal muscles including; early weakened inflammatory cellular infiltration which increased afterwards and became persistent. The number of SCs cells was decreased with fewer regenerating myotubes. On the 21st day after injury myofibers showed findings of an inadequate healing including; new blood vessels, regenerating myofibers and inflammatory cellular infiltration. Some myofibers had an uneven distribution, and unclear striations. Fibroblasts, blood vessels and inflammatory cells were seen accumulating among myofibers. Semithin sections revealed varying maturation stages of myofibers; some appeared with peripherally nuclei while others with centrally located one. Others showed multinucleated and mononucleated myotube with few vacuolation. Blood vessel, inflammatory cells, lipid droplets and nerve trunk were detected in the spaces between parallel myofibers.
Ultrathin sections revealed sarcomere with numerous vacuolations, disrupted Z lines and irregular nucleus. Widely separated myofibers with interfiber macrophages were aso noticed.
On the other hand, the skeletal muscle injury of PRP treated senile rats revealed early strong inflammatory cellular infiltration which subsides afterwards and numerous regenerating myofibers. On the 21st day, the normal architecture of myofibers was restored. The fibers appeared parallel with peripherally situated flattened nuclei. Fine collagen fibers and numerous blood vessels were seen in between myofibers.
Semithin sections demonstrated almost regularly aligned myofibers with visible striations. Most of the myofibers had peripheral flattened vesicular nuclei.
Ultrathin sections showed myofibers with almost regular sarcomeres with alternating light and dark bands between successive Z lines. Heterochromatic nuclei some of which had prominent nucleolus were also detected under the sarcolemma.
CONCLUSION
The present work revealed that aging had deleterious effect on the healing of skeletal muscle. On the other hand, PRP application to injured muscles in senile rats led to stronger post injury acute inflammatory response and prevented the persistence of age-related delayed inflammatory state. Moreover, it markedly enhanced myogenesis and decreased fibrous tissue formation.
PRP treatment accelerated the rate and improved the quality of skeletal muscle recovery from injury in senile rats.
Therefore, PRP application is strongly advised for skeletal muscle injury in elderly. Further studies are recommended to evaluate role of gender in healing of elderly muscles by using PRP.