| Objective:The purpose of this study is to investigate the effects of exhaustive swimming exercise on the ultrastructure of adult Spraque-Dawley(SD) rats skeletal muscle and to explore the expression of Aerobic oxidase's activity and myogenic regulatory factors MyoD and myogenin during recovery after exhaustive exercise.Method:36 SD adult rats that only 6 weeks old were randomly divided in to 6 groups, and each group had six rats. A, control group(C); B, Immediately after exhaustive exercise group(E0); C, 12 hours after exhaustive exercise group(E12); D, 24 hours after exhaustive exercise group(E24); E, 48 hours after exhaustive exercise group(E48); F, 72 hours after exhaustive exercise group(E72). All exhaustive exercise groups were carried on tail-loaded swimming with the weight of 3% of body weight for seven days. After the last exhaustive exercise at different time points, each rat was anesthetized intraperitoneally to Slaughter with Urethane, and the gastrocnemius,soleus,vastus lateralis,rectus femoris muscle were taken. Some were used for cryopreservation in Liquid nitrogen and the others were used to fix with 4% paraformaldehyde or 2.5% glutaraldehyde. Then the ultrastructural changes of rat rectus femoris was obeseved under electron microscopy. Succinate dehydrogenase kit was used to determine the activity of succinate dehydrogenase (SDH), and quantitative detection of protein with Coomassie brilliant blue. The Protein expression of myogenic regulatory factors MyoD and myogenin were detected by SABC in Rat soleus and vastus lateralis.Result:1)After a week of hevay load exercise, Compared with the control group, the activity of SDH in all exercise groups'gastrocnemius had a significant improvement(P﹤0.05); Compared with E0, the activity of SDH in E12 and E24 decreased significantly(P﹤0.05); Compared with E24, the activity of SDH in E72 increased significantly(P﹤0.05). In our study, the change trends of SDH's activity were increased immediately after exhaustive exercise, then decreased, but gradually increased again in recovery stages.2)Under an electron microscope, myofibril was complete and Closely arranged in control group. The transverse stripe was clear and myofilament regularly arranged with a clearly distinguish structure. After exhaustive exercise, muscle ultrastructures had different changes in E0 and E24. After swimming, Sarcomere's light and dark band, Z line, mitochondria and so on all changed in skeletal muscle. In our study, the most serious changes of skeletal muscle were in E24. It included the obvious Z line anomalies, sarcomere within a wide range of fracture, increased number of mitochondria, destructive changes in mitochondria and so on.3)There are no protein expression of MyoD and myogenin in control group. After a week of hevay load exercise, the MyoD in rat soleus muscle clearly expressed at 24 hours with a peak at 48 hour, and decreasd at 72 hour. The myogenin in rat soleus muscle had a small amount of expression at 24 hour, and increased at 48hour with a peak at 72 hour. On the other hand, the MyoD in rat vastus lateralis muscle clearly expressed at 24 hours with a peak at 48 hour, and decreasd at 72 hour even lower than 24 hour. The myogenin in rat vastus lateralis muscle had a small amount of expression at 24 hour, and increased at 48 hour with a peak at 72 hour. The protein expression of MyoD was higher at 48 hour and 72 hour in rat soleus muscle than in vastus lateralis muscle(fast muscle),and lower in 24 hour. But the protein expression of myogenin was always higher at 24 hour, 48 hour and 72 hour in vastus lateralis muscle (fast muscle) than in soleus muscle (slow muscle).Conclusion:1)After a week of hevay load exercise, SDH's activity of rat gastrocnemius muscle increased immediately, then decreased significantly and rised again during recovery period. As a whole, the changes of SDH's activity showed that a week of hevay load swiming exercise can improve the activity of aerobic oxidase SDH.2)Under an electron microscope, a week of hevay load swimming exercise can result a significant effect on ultrastructure in skeletal muscle such as A band stretched, myofibril disordered, Z line fractured, Z line flow and so on.This showed that the heavy load swimming exercise can be one of important models to observe the changes of skeletal muscle.3)The results of SABC immunohistochemistry showed that the expression of myogenic regulatory factors myoD and myogenin had regularly changed after heavy load exercise and during recovery of 24h,48h,and 72h in rat soleus and gastrocnemius muscle. MyoD had the highest expression in E48 and myogenin had the highest expression in E72. This study showed that MyoD and myogenin play a role in muscle regeneration after exercise-induced muscle injury and they may serve as the indexes which indenify muscle precursor cells and mark muscle regeneration process. At last the protein expression and gene expression of MyoD and myogenin and their effects on the changes of skeletal muscle fiber subtypes under different exercise and training patterns need the progressive researches.
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