Avian tibial dyschondroplasia. II. Biochemical changes.

Biochemical parameters (dry matter, DNA, protein, cAMP, and calmodulin) were measured in tibial dyschondroplastic (TD) cartilage. This abnormal cartilage, which is a mass of unmineralized, unvascularized cartilage found in the proximal metaphysis of the tibiotarsus and tarsometatarsus, was compared with normal epiphyseal growth plate and hypertrophic cartilage obtained from day-old embryonic cone. The latter tissue is an example of cartilage which rapidly undergoes vascularization and mineralization. When compared with normal growth plate, tibial dyschondroplastic cartilage was found to contain lower amounts of dry matter, DNA, protein, cAMP, and calmodulin. This cartilage did not respond to factors in serum which stimulate 35S uptake. Although the above two types of cartilage contained similar amounts of ash, TD cartilage had less phosphorus and potassium and more sodium than the growth plate. The two types of cartilage had similar lysozyme activity and proteoglycan (hexosamine) content. In many of the parameters measured, day-old hypertrophic cartilage was similar to the normal growth plate. However, these tissues did differ in DNA, protein, ash, and lysozyme content. Substantially greater amounts of ash and lysozyme were found in the hypertrophic cartilage, which appeared to be related to events of mineralization and vascularization of this cartilage. These events did not occur in the abnormal cartilage cells found in the tibial dyschondroplastic lesion.