TURNOVER OF THE ORGANIC MATRIX OF CARTILAGE AND BONE AS VISUALIZED BY AUTORADIOGRAPHY

Abstract

Tibiae and humeri were removed from suckling rats at intervals of time after intraperitoneal injection of C¹⁴-L-phenylalanine, C¹⁴-L-leucine, S³⁵-sulfate, or Ca⁴⁵ Cl₂. Autoradiograms of sections of the bones were prepared. Ca⁴⁵ was removed from sections treated with dilute acetic acid; neither the concentration of S³⁵ nor that of C¹⁴ was thereby markedly decreased. The S³⁵ was removed from the demineralized sections on incubation in a solution of testicular hyaluronidase; the C¹⁴ was not. These results are interpreted as indicating that most of the S³⁵ was present in the bones as chondroitin sulfate and that most of the C¹⁴ in the bones was present as protein. In the epiphyses, the C¹⁴ was initially concentrated in the proliferaing and hypertrophic chondrocytes, as was the S³⁵. Secretion of S³⁵- and C¹⁴-labeled materials into the matrix followed. Thereafter, however, although the S³⁵-labeled material (chondroitin sulfate) persisted in the matrix, albeit at a diminished concentration, and was incorporated into metaphyseal bone, the C¹⁴-labeled material (protein) was almost completely removed from the matrix. When rats were given repeated doses of 17-β-estradiol benzoate so as to inhibit resorption of their metaphyses, repeated doses of S³⁵-sulfate were discerned as strata of S³⁵ in their metaphyses. This was not the case if the rats received repeated doses of C¹⁴-L-phenylalanine or C¹⁴-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.

Full Text

The Full Text of this article is available as a PDF (991.1 KB).