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 si tes in the knee (stifle) articular cartilage of young beagle dogs afte r running exercise of 15 weeks, 20 km/day. Water content was significa ntly elevated by 5-17% in the patellofemoral groove and in anterior an d 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 increa sed in tibial and femoral surfaces (mean of all sites +18%). Also, the aggregating PG monomers were larger at all sites, as studied by agaro se gel electrophoresis. The chondroitin-6 to 4-sulphate ratio was redu ced at the summits of femoral condyles and patella by 10 to 25%, but i ncreased in the patellar surface of femur and tibial medial condyle, f itting to a previous finding that strenuous running depleted proteogly cans at the summits of femoral condyle from the superficial zone that is rich in chondroitin-6-sulphate. The increased water content, accomp anied with a decreased concentration of collagen in the lateral femora l condyle, suggests loosening of the collagenous framework, an idea co mpatible with an earlier notion of superficial depletion of PGs in the se 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 P Gs was enhanced. It is concluded that the strenuous running program in duced locally restricted changes resembling early degeneration of arti cular cartilage, while simultaneously caused alterations that suggest a general stimulation of proteoglycan metabolism.