Study Of Bone Metabolism And Its Modulative Factor On Exercise Induced Bone Fatigue In Rat

Objective: exercise induced bone fatigue is a common phenomenon and is one of the trobulesome problems for athletes.It is not completely known by us about the mechanism of sport bone fatigue.The study started establishing repeatable animal model of sport bone fatigue and investigated bone mineral density, bone biomechanics, serum biochemical markers of bone and modulative factors of bone to analyse characteristics of bone changes and discuss the mechanism on exercise induced bone fatigue.Methods: 66 female SD rats(8weeks old)were randomly assigned to three groups:animal model group of sport bone fatigue(36), quiet control group (20,10 of them captive for 8 weeks)and a bout of high-intensity exercise group (10);animal model groupof sport bone fatigue run high intensity treadmill exercise for 4 weeks. During the modeling, rats'bone 99mTc-MDP were monitored by SPECT; bone stiffness were measured;serum E2 level were measured by double-antibody sandwich enzyme immunoassay;blood serum ALP and TRAP level were measured by colorimetry; When they were diagnosed to achieve bone fatigue according to standards.So we complete the animal model of the exercise induced bone fatigue. animal model group of the exercise induced bone fatigue were randomly assigned to two groups:free recovery group and exercise intervention recovery group.All rats recover for 4 weeks.serum E2 level were measured by double-antibody sandwich enzyme immunoassay;blood serum ALP and TRAP level were measured by colorimetry tibiaes'parameters of BMD and BMC were measured by DXA method;bone biomechanics were measured by anuda microcomputer control electronic universal testing machine; protein expression of ER and TGF-?1 in bone tissue were measured through immunohistochemistry;gene expression of ER,TGF-?1,BMP,OPG and OPGL in bone tissue were examined RT-PCR.Results:(1) After heavy treadmill running of four weeks, bones'stiffness of rat decreases 33%; the technetium-99m-methylene diphosphonate has obviously rising(P<0.05); concentration of tartrate-resistant acid phosphatase in blood serum has obviously increased(P<0.01); the level of estrogen and alkaline phosphatase in blood serum has obvious decreased(P<0.05 or P<0.01).These has proved that the building up of the animal experimental mode is successful, A bout of high-intensity treadmill exercise did not give rise to changes on these indicators significantly. (2)Alkaline phosphatase of serum were significantly lower(P<0.01) and serum estrogen lower(P<0.05)in exercise induced bone fatigue;tartrate-resistant acid phosphatase of serum significantly higher in exercise induced bone fatigue than group(P<0.01); (3) bone mineral density,maximum load, stiffness, maximum stress and modulus were significantly lower(P<0.01);bone mass content and maximum energy absorption were significantly lower in exercise induced bone fatigue rats; (4) Protein expression of estrogen receptor and transforming growth factor ?1 was significantly lower in exercise induced bone fatigue group than in control group(P<0.01), gene expression of estrogen receptor, transforming growth factor ?1, bone morphogenetic protein-2 , osteoprotegerin were significantly lower in exercise induced bone fatigue group(P<0.05 or P<0.01);gene expression of osteoprotegerin ligand was significantly higher(P<0.05); (5)the above-mentioned indicators are all no statistically significant difference after free recovery and exercise recovery of four weeks.Conclusion: This study established rat model of exercise induced bone fatigue after 4 weeks of high-intensity treadmill exercise successfully; while one-time high-intensity treadmill exercise does not cause the occurrence of bone fatigue.rats of exercise induced bone fatigue decrease estrogen levels, decline in bone formation markers and increased bone resorption markers, leading to the occurrence of bone metabolism disorder finally; tibial bone mineral density decrease and biomechanical properties of tibia reduce, they are the basis of falling on bone mechanical properties in rat of exercised bone fatigue. Decreasing of ER expression is the key to exercise induced bone fatigue pathogenesis in rats. Decreasing of Expression on TGF-?1,BMP and OPG and increasing of OPGL expression in bone tissue was the important factor in molecular biology in rats of exercise induced bone fatigue; suppression of bone changes on exercise induced bone fatigue in female rats is reversible.