Trabecular Bone Turnover and Bone Marrow Capacity for Bone Cells in Immobilization-Related Bone Loss
Adequate physical exercise promotes bone formation and inhibits bone resorption. Immobilization, in contrast, reduces bone formation and enhances bone resorption. In the present study, it was found that the immobilized tibia of mice after neurectomy of the sciatic nerve showed a decrease in bone formation from 3 to 5 days after the treatment. The bone resorption increased from 7 days, reached a peak level from 14 to 21 days after the start of immobilization, and thereafter gradually decreased. The population of alkaline phosphatase-positive cells among colony-forming units-fibroblastic, which are considered the progenitor cells of osteoblasts, decreased. The formation of colony-forming units for granulocytes and macrophages was not different between the immobilized tibia and the sham-operated tibia; however, the tartrate-resistant acid phosphatase-positive multinucleated cells transiently increased in the immobilized tibial bone marrow under parathyroid hormone stimulation, from 10 to 14 days postsurgery. The terminal process in the osteoclast development was thus thought to be enhanced by immobilization.
KeywordsImmobilization Unloading Bone marrow Colony-forming unitsfibroblastic (CFU-f) Colony-forming units for granulocytes and macrophages (CFU-GM)
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