Grant-in Aid for Scientific Research(C)(2)

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The microgravity will induce bone loss. With young healthy males (n=13, 26.6±3.5) we have executed the 6-degree head down tilting bed rest immobilization for 20 days. We have revealed 2-mechanisms for the bone loss, the coupled metabolic high turnover of osteoclast and osteoblast and another osteolysis without hyperactivity of osteoclast and osteoblast, and over-expression of calcium sensing receptor and cytokine mRNAs in macrophage/peripheral mononuclear cell. In the coupled high turnover group, both activity of osteoclast and osteoblast had increased. Another group did not show any increase of metabolic markers of osteoclast and osteoblast. Comparing the 2 group with pQCT, only the BMD of the cancellous bone decreased in the coupled high turnover group. In another, the BMD of both bones decreased. Theses 2-typed bone loss reaction induced by immobilization should be determined hereditally. When this polymorphism is determined, high and low risk persons in space flight would be clearly divided, and the protective methods for each group for bone loss will be created most effectively.