| [Objective]1. To establish a tail-suspended rat model for the study of bone metabolism and growth under the simulated microgravity or long-term bed condition;2. Study on the effects of simulated micogravity on bone metabolism;3. Study on the effects of simulated micogravity on biomechanical behavior of weight loading bone;4. Study on the effects of simulated micogravity on fracture healing of weight loading bone.The ultimate purpose of this study is to understand the effects and mechanism of microgravity on bone metabolism, and to provide a good way for prevention and cure of osteoporosis induced by long-term weightlessness flight or long-term bed condition. [Methods]1. To make model: 2-month-old male SD rats were divided randomly into tail-suspended group and control group, 8 for each group. The tails of tail-suspended rats were pasted by ventilated adhesive tape on two sides. The other end of the adhesive tape was suspended by a plastic circle which can move freely along a rod. The head of rat was kept on low position, and hindlimb unloaded without constraint moving. The control rats were untreated. All the rats were fed equivalence of food without limited drinking hi the same cages for 4-wk;2. Observation on rat model: To observe the activities, diet, body weight, colour and luster of hair and tail of rats during tail-suspension;3. Measurement of hormone and gland: To measure corticosterone by radio-immunity, and to measure the relative weight of adrenal gland and thymus with scale;4. Measurement of biochemical markers of bone metabolism: Serum Ca, P, ALP and TRAP was measured by automatic biochemistry analyzer, BGPmeasured by radioimmunoassay;5. Basic physical items of right tibiae: Mass of fresh and dried bone, bone volume, mineral content and calcium were measured respectively.6. Biomechanical test: Structural and material mechanical properties of right femur were measured by three-point bend test;7. Micro vessel density of bone: After abdomial aorta was filling with gelatin-ink, the left proximal tibia was chiped and microvessel density was measured with stereological method;8. Observation on structure of bone: Structure and ultrastructure of bone was observed under microscope and transmission electron microscopy(TEM) respectively; and the expression of TGF- β1 in bone was observed under microscope by immunohistochemical method;9. Fracture model of rat weight-bearing bone: After the middle of left tibia was fractured and fixed with 0.8mm Kirschner wire, 40 two-month-old male SD rats were divided randomly into tail-suspended group and control group and fed for 4-wk;10. Observation on fracture healing: Fracture was observed through X-ray and callus observed by microscope, TEM every week;11. The expression of VEGF and TGF- β1 in callus was observed under microscope by immunohistochemical method;12. Torsion tests of the left tibiae were undertaken after fracture 4-wk. [Results]1. During 4-wk tail-suspension, the rats moved, ate freely and did not bite tails. All rats were alive without ischemia and necrosis of tail. And body weight of tail-suspended rats didn't decreased significantly(P > 0.05);2. After 4-wk tail-suspension, serum corticosterone, relative weight of adrenal gland and thymus weren't different compared with the control (P > 0.05);3. Compared with the control, ALP and BGP of tail-suspended rats dropped significantly(P < 0.01 and P < 0.05 respectively),and serum Ca, P and TRAP didn't changed notably(P > 0.05);4. Compared with the control, length and calcium content of tibia were not affected(P > 0.05),but bone volume and mass of fresh bone decreased notably (P < 0.01), and mass of dried bone and mineral content also did (P < 0.05);5. Structural and material mechanical properties of right femur were affected significantly (P < 0.01 or P < 0.05);6. Microvessel density of proximal tibia decreased strikingly (P < 0.05) after 4-wk tail-suspension;7. Plasm, organell and the number of osteoblasts reduced, observed under micro...
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