Proteoglycan alterations in rabbit knee articular cartilage following physical exercise and immobilization.

Rabbit knee articular cartilage was studied after the joint was submitted to immobilization, running or increased weight bearing for 24-27 days. Immobilization with a plastic splint reduced the fraction of proteoglycans not extractable with 4 M guanidinium chloride (GdnHCl). In the immobilized joints the chondroitin sulfate content was elevated as calculated from the galactosamine/glucosamine ratio. The ability of these proteoglycans to reform aggregates with endogenous hyaluronic acid in Sepharose CL-2B chromatography was reduced. Increased exercise was associated with an elevation of proteoglycans extractable with 4 M GdnHCl. The increased weight bearing occurring in the contralateral knee elevated the content of proteoglycans not extractable with 4 M GdnHCl. Other effects of weight bearing included increased glucosamine concentration, suggesting accumulation of keratan sulfate-rich proteoglycans, and an elevated hydroxyproline concentration.