Glycosaminoglycans and endochondral calcification.

Present controversy about endochondral calcification and ossification is concerned with changes in glycosaminoglycans. Some authors report a rise in amounts of glycosaminoglycans while others a fall. Cartilage was carefully sliced under microscopic control to provide samples of material from different functional zones of the developing tissues. The following zones were studied histochemically and analyzed for their content of total nitrogen, hydroxyproline, total hexosamines, uronic acid and phosphorus: the resting zone; the zone of proliferating and maturing cells; the calcifying zone, characterized by degenerating hypertrophic cells and early mineral deposition; the ossifying region, where early bone formation takes place. Serial analyses provided evidence that glycosaminoglycans increases before calcification starts. Afterwards, part of the glycosaminoglycan content is removed. This biphasic process appears to occur during the calcification of other tissues too, such as secondary bone and dentine.