[Chondroclastic properties of the cartilaginous tissue macrophages of developing bone]

By the electron microscopic and cytochemical studies, in the vascular canals of cartilaginous epiphyses and in the zones of endochondral process of the rabbit and rat femoral bones, there were revealed monocytes, macrophages, the cells of the intermediate differentiation stages among the perivascularly located forms. In the lysosomes as well as on the surface of cytoplasmic membrane of mature macrophages the activity of acid phosphatase and non-specific esterase was demonstrable. Phagolysosomes showed accumulation of 35S-sulphate label 2 hours after its injection into an organism. Macrophages cause degradation of non-mineralized cartilaginous matrix by secreting hydrolases and other enzymes and then phagocytize the preformed substrate. In the zones of endochondral process, macrophages also penetrate into the "capsules" of hypertrophic chondrocytes and are involved in their destruction. The cells are regarded as tissue--specific macrophages--chondroclasts.