BONE-MARROW CELL-DEVELOPMENT AND TRABECULAR BONE DYNAMICS AFTER OVARIECTOMY IN DDY MICE

To clarify the relationship between the sequential changes of trabecul ar bone turnover and bone marrow cell development in ovariectomized (o vx) mice, bilateral tibiae of 8-week-old ddy mice were obtained. Histo morphometric analyses of the trabecular bone of the proximal tibia of ovx mice revealed increases in the bone formation rate and the osteocl ast surface for the first 28 days postovariectomy, The trabecular bone volume showed a rapid decrease for the first 28 days and a steady sta te for the subsequent 14 days, In bone marrow cell culture experiments , the numbers of total and nonadherent bone marrow cells per tibia obt ained from the ovx mice increased. The formation of osteogenic nodules and osteoclast-like multinucleated cells in the marrow cultures obtai ned from ovx limbs showed a significant increase on days 14 and 28 and returned to the sham-operated level by day 42, The numbers of colony forming units (fibroblastic) and colony forming units (granulocytes an d macrophages) that developed from the marrow cells did not differ bet ween the ovx and sham limbs at any time during the study period. Fluor escence-activated cell-sorter analysis revealed no population changes in the cell development of macrophages. These results demonstrate that there are two stages in the development of osteopenia after ovx. Duri ng the first 28 days after ovx, the ovariectomy enhances the developme ntal process from bone marrow stromal cells to osteoblasts and the ter minal differentiation from osteoclast precursors to mature osteoclasts , The trabecular bone turnover also increases, In the subsequent 14 da ys, the changes in the osteogenic and osteoclastogenic potentials of t he bone marrow cells are alleviated and the trabecular bone dynamics a re in a steady state, The changes in bone marrow cell development are closely associated with those at the trabecular bone surface. (C) 1998 by Elsevier Science Inc. All rights reserved.