Age-related trend for osteopenia in femurs of female C57BL/6 mice.

Age-related changes in femoral cortical bone were quantified in female C57BL/6 mice. Variables included in this study were cortical thickness; number of osteocytes and periosteal preosteoblasts; bone DNA, protein, calcium, and phosphorus content; and uptake of 3H-thymidine, 3H-proline, and 45CaCl2. Also, the activity of bone alkaline and acid phosphatase was measured as well as the hydroxyproline content of the tissue. Femurs of old mice 28 months old, compared to those of young mice 7 months old, showed significant decreases in cortical thickness, number of bone cells, bone mineral content, and enzyme activity. The latter were accompanied by a marked reduction in ability to incorporate radiolabeled precursors of DNA and collagen synthesis as well as of the mineralization process. Hence, aging female C57BL/6 mice reveal structural and biochemical features indicative of developing osteopenia.