Trabecular bone turnover and bone marrow cell development after immobilization

目的：探讨甲状旁腺激素(PTH)对制动相关骨丢失的影响。方法：1)6周龄雄性ddy小鼠接受右侧坐骨神经切断术(NX)或左侧肢体假手术(Sham)。对胫骨近端干骺端进行了组织形态计量学研究。2)观察骨髓细胞发育情况；3)进行FACS分析。采用RT-PCR方法检测PTH/PTHrP基因的表达。结果：1)固定后14d骨小梁体积明显减少。制动后破骨细胞数量一过性增加，骨形成增加。2)固定后12d，贴壁细胞数一过性下降，恢复至假手术组水平。加入甲状旁腺素后，NX肢体骨髓细胞形成的破骨细胞样细胞数量增加。3)NX侧和Sham侧Mac-1阳性细胞数差异无统计学意义。4)甲状旁腺素治疗可预防制动相关的骨丢失。这些结果表明，制动引起的骨形成一过性减少，破骨细胞数量增加，导致骨丢失。PTH可增加骨髓贴壁细胞的数量，促进破骨细胞的终末分化过程，防止制动相关的骨丢失。甲状旁腺素/甲状旁腺素rP信号通路在制动肢体的骨髓细胞中被促进。

During the three years from 1996 to 1998, we clarified trabecular bone turnover and bone marrow cell development after immobilization and the effects of parathyroid hormone (PTH) on immobilization-related bone loss.Methods : 1)6 week-old ddY male mice were subjected to eitherright sciatic neurectomy (Nx) or sham operation for left limbs (Sham). Histomorphometrical study was perfonned on the proximal metaphysis of tibia. 2) Bone marrow cell development was evaluated 3) FACSanalysis was done. Using RT-PCR procedure, mRNA expression of PTH/PTHrP was studied. 4) Either of 4 or4O mug/kgBW of PTH was administered subcutaneously 5 times a week.Results : 1) Trabecular bone volume significantly decreased 14days after immobilization. The number of osteoclasts transiently increased and bone formation increased after immobilization. 2) Adherent cellnumber transiently decreased andreturned to the same values of the Sham group 12 days after immobilization. The number of osteoclast-like cell formed from the bone marrow cells obtained from the Nx limbs increased under PTH addition. 3) There was no differences in the number of Mac-1positive cells between the Nx and Sham limbs. PTH/PTHrP mRNA was elevated in the bone marrow cells obtained from the Nx limbs on day 7.4)4)PTH administration prevented immobilization-related bone loss.These results demonstrated that immbilization caused transient decrease in bone formation and increase in the number of osteoclasts, leading to significant bone loss. The number of adherentmarrow cells increased and the terminal differentiation process of osteoclasts was promoted by PTH.PTH administration prevented immobilization-related bone loss. PTH/PTHrP signaling pathway was promoted in the bone marrow cells of the immobilized limbs.