Alterations in the composition of growth cartilage septa during calcification studied by microscopic X-ray elemental analysis

Abstract

1. 1. Distribution of total mass, S and P measured by X-ray elemental analysis in microscopic sites at the zone of provisional calcification and adjacent uncalcified cartilage septa permitted a quantitative estimation of changes in content of sulfated glycosaminoglycans, as well as organic and mineral phases. 2. 2. Onset of calcification within the cartilage septa was identified by a sharp increase in concentration of P and total mass per unit area of histologic sections in measurements progressing from the hypertrophic cell zone to the metaphysis. 3. 3. P concentration was >2 per cent within cells and 4 per cent at cell margins of the late proliferating cell zone. These levels were sufficiently high to be suggestive that some mineral phase or phosphate precursors were present in the cells of this region. Such results were consistent with a biochemical study of phosphate partition in these cartilages correlated with histologic zones. 4. 4. There was a slight decrease of S and a larger decrease of organic mass per unit area of intact histologic section in progression of measurements from uncalcified to calcified septal matrix. The abrupt changes in the organic composition at the boundary of the zone of provisional calcification and high content of P at the margins of proliferating cells are probably related to separate biochemical steps in endochondral calcification.