Proteoglycan and collagen alterations in canine knee articular cartilage following 20 km daily running exercise for 15 weeks.

The composition of extracellular matrix was studied at 11 different sites in the knee (stifle) articular cartilage of young beagle dogs after running exercise of 15 weeks, 20 km/day. Water content was significantly elevated by 5-17% in the patellofemoral groove and in anterior and intermediate sites on the lateral condyle of femur. Collagen content was decreased by 14 to 20% in the same sites of the lateral condyle. Proteoglycan (PG) content was not significantly changed except in the posterior edge of the medial condyle of femur with a 30% decrease. The proportion of PGs capable of reaggregation with hyaluronan was increased in tibial and femoral surfaces (mean of all sites +18%). Also, the aggregating PG monomers were larger at all sites, as studied by agarose gel electrophoresis. The chondroitin-6 to 4-sulphate ratio was reduced at the summits of femoral condyles and patella by 10 to 25%, but increased in the patellar surface of femur and tibial medial condyle, fitting to a previous finding that strenuous running depleted proteoglycans at the summits of femoral condyle from the superficial zone that is rich in chondroitin-6-sulphate. The increased water content, accompanied with a decreased concentration of collagen in the lateral femoral condyle, suggests loosening of the collagenous framework, an idea compatible with an earlier notion of superficial depletion of PGs in these sites, and possibly predisposing to degeneration. The size increase of the aggregating PGs probably indicate that a larger proportion of matrix PGs were newly synthesized and hence the turnover rate of the PGs was enhanced. It is concluded that the strenuous running program induced locally restricted changes resembling early degeneration of articular cartilage, while simultaneously caused alterations that suggest a general stimulation of proteoglycan metabolism.