Objective By analyzing the changes of bone microstructure, biochemical metabolism and mechanical properties of male and female rats in a tail-suspending osteoporosis model simulating weightlessness, to provide experimental evidence for bone mass change of astronauts and aerospace medicine.Methods Twenty male and 20 female 3-month-old SD rats were selected and randomly divided into 2 groups, tail-suspending ( TS) model group and control group.After 4-week experiment, the rats were killed.Bone mineral density ( BMD) of L4 lumbar vertebrae and the femurs was measured using dual-energy X-ray absorptiometry ( DEXA) .The trabeculae were analyzed using micro-CT.Ponceau staining was used for the bone tissue slices.Bone biochemical markers were detected using ELISA method.The biomechanical indexes were tested using a biomechanical testing machine. Results The BMD of L4 and the femurs in the TS groups was obviously lower than that in control groups.The bone volume fraction (BV/TV), the thickness (Tb.Th) and number of the trabeculae (TB.N) of were also lower (P<0.05).However, the bone surface to bone volume ( BS/BV) and trabecular separation ( Tb.Sp) in TS group were significantly higher than those in control group (P<0.05).The bone metabolic biochemical markers BLAP and TRAP in the TS groups were remarkably higher than those in control groups, which were 4.1 and 2.7 times in male groups and 4.5 and 3.1 times in female groups, respectively. Biomechanical testing showed that the maximum compressive load ( N) , maximal compressive stress ( MPs) of lumbar vertebrae, flexural load of the femurs decreased in male TS group by 27.5%, 26.4%, and 24.8%, respectively, and in female TS group by 36.6%, 33%, and 34%, respectively, comparing to the control group.BMD of L4 and the femurs, BV/TV, Tb.Th, TB.N, N, and MPa in female TS groups decreased significantly comparing to those in male TS groups. BALP and TRAP increased significantly in male TS groups comparing to those in male TS groups ( P <0.05).Conclusion After 4 weeks, obvious osteoporosis, destruction of the 3-dimensional microstructure , decrease of the mechanical strength in the vertebrae and thigh , and imbalance of the bone metabolism have been found in both male and female TS groups .In theory it increases the fracture risk , and this is most obviously in female rats than in male rats in TS groups .The risk of bone loss and fracture in different gender of astronauts should be recognized , and the results can guide us in personal intervention in the aerospace medical work .%目的：模拟失重尾部悬吊雌、雌性大鼠模型松质骨骨密度、骨小梁结构、骨组织形态、骨代谢生化指标及力学性能的对比研究，为不同性别航天员飞行后骨量变化及航天医学提供实验依据。方法3个月龄雌、雄性SD大鼠各20只，每组分别随机再分为2组，尾部悬吊4周组和空白对照组。到期处死SD大鼠，双能X线吸收法（ dual－energy X－ray absorption DEXA ）测定L4椎体、股骨踝部骨密度，Micro－CT进行骨小梁分析，改良丽春红染色方法进行骨组织切片染色，ELISA法检测血清骨代谢生化标志物，生物力学测试机进行生物力学检测。结果不同性别悬吊组大鼠较对照组大鼠椎体、股骨髁部骨密度均显著下降，松质骨的骨体积分数（ BV／TV）、骨小梁厚度（ Tb．Th）、骨小梁数目（ TB．N）、表面积体积比（ BS／BV）较对照组显著降低（ P＜0．05），骨小梁间隙（TB、Sp）较对照组显著增加；骨代谢生化指标骨特异性碱性磷酸酶（BALP）、抗酒石酸酸性磷酸酶（ TRAP）悬吊组较对照组显著增加，雄性悬吊组分别为对照组的4．1和2．7倍，雌性悬吊组分别为对照组的4．5和3．1倍；生物力学测试表明悬吊组椎体的最大压缩载荷（N）、最大压缩压力（MPa）、股骨最大抗弯曲载荷（N）雄性悬吊组分别较对照组下降：27．5％、26．4％、24．8％；雌性悬吊组分别较对照组下降：36．6％、33％、34％，力学强度显著下降。通过雌、雄性悬吊大鼠对比研究发现，雌性大鼠L4椎体、股骨髁部BMD，松质骨BV／TV、Tb．Th、TB．N、TB．N以及椎体的最大压缩载荷（ N）、最大压缩压力（MPa）、股骨最大抗弯曲载荷（N）显著降低（P＜0．05），骨小梁间隙（TB、Sp）、BALP、TRAP雌性悬吊组较雄性悬吊组显著增加（ P＜0．05）。结论尾部悬吊雌、雄性大鼠4周后分别出现明显的骨质疏松、骨小梁三维结构破坏、椎体及股骨生物力学显著下降、骨代谢失平衡，理论上增加了骨折的风险。同时更值得注意的是雌性悬吊大鼠骨质疏松程度较雄性悬吊组更加明显。不同性别航天员骨量丢失及骨折的风险应得到充分的认识，并指导我们航天医疗工作方面进行个性化干预措施。
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