| Objective:The purpose of this paper was to study the changes of skeletal muscle ultrasructure and the related regulatory factors during heavy load exercise and recovery in rat.Methods:36healthy male SD rats of6-week-old were randomly divided into6groups, n=6:A, sedentary control group (control, C); B immediately after exhaustive exercise group (exhaustive, EO); C12H after exhaustive exercise group (E12); D24H after exhaustive exercise (E24); E48H after exhaustive exercise group (E48); F72H after exhaustive exercise group (E72). The exhaustive exercise groups were carried on tail-loaded swimming for seven days. All rats were anesthetized with urethane intraperitoneally and killed at different time points after the last exhaustive exercise. The gastrocnemius and the rectus femoris were taken. Some was reserved in liquid nitrogen and the other was fixed with2.5%glutaraldehyde. The protein expression of mechanical growth factor MGF was measured by ELISA, and myogenic regulatory factors MyoD and MYOG were detected by WESTERN-BLOT in rat gastrocnemius. The ultrastructure changes of rat rectus femoris were observed by electron microscopy.Results:1) First, the normal ultrastructure of rat rectus femoris in the quiet control group was found by electron microscopy with a integrated myofibril structure, clear stripes and band.After a week of heavy load swimming, the skeletal muscle ultrastructure in different group changed in different degrees, and the changes were more evident in the EO and E24with the edema and widened muscle gap. At same time, the endoplasmic reticulum and mitochondria were seen a slight deformation. But the nucleus and nuclear envelope were still well preserved. Otherwise, the myofibrils was loose and thin. H band and I band were ill-defined. M line and Z line blurred. Z lines were distorted and disappeared, and some interstitial was shallowed and confused with the deformed, distorted, enlarged mitochondrial in exhaustive exercise groups.2) ELISA results showed that compared with the control group, after a week of heavy load swimming, the mechanical growth factor MGF as a skeletal muscle index were significantly increased, especially the exhaustive E12group and E24group(P<0.05).Serum index had similar changes in the MGF. 3) WESTERN-BLOT results showed that after a week of large load swimming the myogenic regulatory factor MYOD of skeletal muscle started to express in E12group, and reached the peak in E48group, with a significant difference compared with the quiet control group (P<0.05). But MYOD of skeletal muscle started to express in E24group, and reached the peak in E72group (P<0.05).Conclusion:1) The results by electron microscopy showed that:After a week of heavy load swimming the ultrastructure of skeletal muscles changes significantly:the belt stretched, myofibril deranged, Z lines was irregular and flowed. Endoplasmic reticulum and mitochondria obscured, crest was disorder or even disappear. Cell interstitial occured edema, muscle gap widened and so on.2) ELISA results showed that the MGF in skeletal muscle increased significantly during the large load exercise recovery period. It indicated that MGF may speed up muscle’s repair.3) WESTERN-BLOT showed that the expression of MYOD and MYOG increased significantly after a week of large load swimming, and the peak of MYOD was in48hours. The peak of MYOG was in72hours. The experiments show that two kinds of factors played the important roles in the regeneration and repair of microdamage in skeletal muscle, and they may be used as the indicators of muscle regeneration. The further study is essential about their expression in different exercise modles and the relation with muscle fiber isoforms. |
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