FLUCTUATION OF MINERAL APPOSITION RATE AT INDIVIDUAL BONE-REMODELING SITES IN HUMAN ILIAC CANCELLOUS BONE - INDEPENDENT CORRELATIONS WITH OSTEOID WIDTH AND OSTEOBLASTIC ALKALINE-PHOSPHATASE ACTIVITY

We investigated the determinants of bone formation at individual remod eling sites (BMUs) in cancellous bone from 8 osteologically normal, se x hormone-replete women with endometriosis. All were tetracycline doub le-labeled (2, 12, 2, and 4 day regime) before iliac bone biopsy. At e ach BMU the mineral apposition rate (MAR) was determined conventionall y from the distance between label midpoints (MAR 1) and also from the distance between the mineralization front and the trailing edge of the second label (MAR 2). MAR 1 and 2 were compared with within-BMU measu rements of osteoid width (O.Wi) and the activities of osteoblastic alk aline phosphatase (AP) and succinic dehydrogenase (SDH, an enzyme in t he Krebs cycle), both quantitated by microdensitometry. A total of 143 BMUs were evaluated, of which 88 were satisfactory for all measuremen ts and 132 were satisfactory for all but SDH. There was a weak correla tion (r = 0.34) between MAR 1 and 2 at individual sites, with a mean d ifference of 0.49 mu m/day (mean MAR 0.82 mu m/day). The mean MAR of i ndividual subjects tended to be either increasing or decreasing (F = 1 6.1, p < 0.01). In linear regressions, MAR 2 was statistically depende nt on O.Wi, AP, and SDH (73% of the variance accounted for). In contra st, MAR 1 was weakly correlated with O.Wi and only 30% of its variance was accounted for by AP, SDH, and O.Wi. The variance in the MAR 2 dat a was inversely increased (p < 0.01) compared with MAR 1 as the number of days of bone formation represented. The data are best explained by large within-BMU variations in MAR over periods of up to a few days a nd longer term trends affecting all BMUs. Correlations between fluctua tion in MAR and osteoblastic AP and SDH activity suggest that bone for mation depends partly on AP activity and osteoblast energy balance. Ra ndom obliquity of sectioning has considerable theoretical effects on s ome correlations (e.g., between O.Wi and MAR), but further investigati on emphasized the likely biologic importance of the correlations invol ving enzyme activities.