Turnover of the Organic Matrix of Cartilage and Bone as Visualized by Autoradiography

Tibiae and humeri were removed from suckling rats at intervals of time after intraperitoneal injection of C(14)-L-phenylalanine, C(14)-L-leucine, S(35)-sulfate, or Ca(45) Cl(2). Autoradiograms of sections of the bones were prepared. Ca(45) was removed from sections treated with dilute acetic acid; neither the concentration of S(35) nor that of C(14) was thereby markedly decreased. The S(35) was removed from the demineralized sections on incubation in a solution of testicular hyaluronidase; the C(14) was not. These results are interpreted as indicating that most of the S(35) was present in the bones as chondroitin sulfate and that most of the C(14) in the bones was present as protein. In the epiphyses, the C(14) was initially concentrated in the proliferaing and hypertrophic chondrocytes, as was the S(35). Secretion of S(35)- and C(14)-labeled materials into the matrix followed. Thereafter, however, although the S(35)-labeled material (chondroitin sulfate) persisted in the matrix, albeit at a diminished concentration, and was incorporated into metaphyseal bone, the C(14)-labeled material (protein) was almost completely removed from the matrix. When rats were given repeated doses of 17-beta-estradiol benzoate so as to inhibit resorption of their metaphyses, repeated doses of S(35)-sulfate were discerned as strata of S(35) in their metaphyses. This was not the case if the rats received repeated doses of C(14)-L-phenylalanine or C(14)-L-leucine. On the basis of the results in these experiments it is suggested that although a portion of the chondroitin sulfate produced by the chondrocytes of the epiphyseal plate is retained and becomes part of the cores of metaphyseal spicules of bone, the protein of the proteinpolysaccharide is somehow removed before calcification of the cartilage ensues.