THE PROCESS OF CALCIFICATION DURING DEVELOPMENT OF THE RAT TRACHEAL CARTILAGE CHARACTERIZED BY DISTRIBUTION OF ALKALINE-PHOSPHATASE ACTIVITY AND IMMUNOLOCALIZATION OF TYPE-1 AND TYPE-2 COLLAGENS AND GLYCOSAMINOGLYCANS OF PROTEOGLYCANS

The rat tracheal cartilage was shown to calcify during development. Th e process of calcification was characterized in terms of distribution of alkaline phosphatase (ALP) activity and alterations to immunolocali zation of types I and II collagens and glycosaminoglycans of proteogly cans during the development of the tracheal cartilage, in comparison w ith calcification of the epiphyseal growth plate cartilage. ALP activi ty was not identified in the tracheal cartilage in the course of calci fication, which therefore differed from that in the growth plate. The tracheal cartilage matrix was not resorbed or invaded by type I collag en during calcification. This suggests that no osteogenesis is involve d in calcification of the cartilage. Immunoreactivity for type II coll agen became weaker in the central region of the tracheal cartilage dur ing development. No net loss of proteoglycans was identified with Alci an blue staining after calcification of the tracheal cartilage. Immuno reactivity for chondroitin 4-sulphate increased in the calcified trach eal cartilage, while reactivity for chondroitin 6-sulphate was weaker in the calcified area than in the surrounding uncalcified region of th e tracheal cartilage. The alteration of the extracellular matrices dur ing development may be involved in the calcification of the rat trache al cartilage.