IRREVERSIBLE CHANGES IN GLYCOSAMINOGLYCAN COMPOSITION OF ANATOMICALLYINTACT BOVINE ARTICULAR-CARTILAGE INDUCED BY INTERMITTENT LOADING

The changes in matrix composition induced by 1 MPa intermittent (0.2 H z) loading of anatomically intact bovine articular cartilage in vitro are studied. The kinetics of chondrocyte response was determined in ex periments where sesamoid bones of adult cows were loaded for 0, 3, 5 a nd 7 days. The reversibility of the induced changes were studied in se samoid bones that were loaded for 5 days and subsequently cultured wit hout loading for another 1, 2 and 3 weeks. Water content was not affec ted by loading, nor by subsequent unloaded culture. Glycosaminoglycan content was not affected by loading. nor by subsequent unloaded cultur e for another 2 weeks. However, after 3 weeks of culture following 5 d ays of loading, a significant decrease in glycosaminoglycan content wa s found. Glycosaminoglycan synthesis was already increased after 3 day s of loading. Loading for longer periods (5 and 7 days) further increa sed the glycosaminoglycan synthesis rate. Glycosaminoglycan synthesis decreased during the first week of subsequent culture without loading. In the third week it dropped to a lower level than observed for the c ontrol. The amount of 3-B-3(-) epitope was increased and the length of newly synthesized glycosaminoglycans was decreased by intermittent lo ading. Subsequent unloaded culture did not further increase the amount of 3-B-3(-) epitope. However, after 3 weeks of unloaded culture the n ewly synthesized glycosaminoglycans were as long as those synthesized in the control. The results suggest that the changes in glycosaminogly can chain length were reversible. However, the overall chondrocyte res ponse to our loading regime seems to be detrimental to the tissue: exp ression of 3-B-3(-) epitope induced by loading together with the drop in glycosaminoglycan content and synthesis observed at the end of the total culture period indicate that the cartilage is irreversibly damag ed.