Variations in mineral apposition rate of trabecular bone within the beagle skeleton

The mineral apposition rate of trabecular bone was determined in several skeletal sites of young adult beagles. Tetracycline derivatives were administered intravenously or orally on 2 separate occasions preceding the day of sacrifice in order to label actively mineralizing bone surfaces. The rate of mineral apposition was calculated by dividing the distance between the 2 tetracycline markers by the time interval between their administration. The lumbar vertebra, proximal humerus, and pelvis, each of which contains red marrow, were found to have a significantly higher (P less than 0.001) rate of mineral apposition in trabecular bone than the skeletal sites containing yellow marrow--the proximal ulna and distal humerus. The mean apposition rate in the former 3 sites was 1.3 +/- 0.3 micrometers/day, while that in the latter 2 was 0.9 +/- 0.2 micrometers/day (uncorrected for plane of sectioning). It is tempting to speculate that this finding may be a consequence of differences in vascularity between red and yellow marrow.