Effects of Physical Stress on the Synthesis and Degradation of Cartilage Matrix

The effects of mechanical stress on the metabolism of dog femoral head cartilage have been investigated. The model involves exercising the dog on a treadmill for an 8-month period and isolating the cartilage proteoglycans from three different anatomical regions of the femoral head. These regions are 1) the articulating area, which shows degenerative changes, 2) the area surrounding the articulating area, and 3) the non-articulating area. The hexosamine analysis of cartilage from the exercised animals, indicates 43% and 21% decreases in regions 1 and 2, respectively, while in region 3 no significant change was observed. The size of the proteoglycan aggregates and monomers also decreased with exercise in regions 1 and 2, and the cartilage from these two regions also incorporated more radioactive sulfate, suggesting a possible attempt to repair the degenerative alterations. The proteoglycan monomer (D1) from the articulating region of exercised dogs failed to interact with hyaluronic acid, while the monomers from other regions in the same animal did interact. Glycosaminoglycan chains from region 1 were smaller than in the control tissue, and there was an increase in chondroitin-4-sulfate synthesis. The results of the present study indicate that the cartilage from the articulating area and the surrounding area resist mechanical deformation by increasing synthetic activity. These observations suggest that the exercised animal can be a valuable model and provide increased understanding of the mechanism of cartilage degeneration.