Loading-induced changes in synovial fluid affect cartilage metabolism

The purpose of this study was to determine whether changes in the synovialfluid (SF) induced by in vivo loading can induce an alteration in themetabolic activity of chondrocytes in vitro. Therefore, SF was collectedfrom ponies after a period of box rest and after they had exercise for aweek. Normal, unloaded articular cartilage explants were cultured in 20%solutions of these SFs for 4 days and chondrocyte activity was determinedby glycosaminoglycan (GAG) turnover. In explants cultured in post-exerciseSF, GAG synthesis was enhanced and GAG release was diminished when comparedto cultures in pre-exercise SF. SF analysis showed that levels ofinsulin-like growth factors (IGF- I and IGF-II) tended to be higher inpost-exercise SF, while no differences were found in metalloproteinaseactivity, hyaluronic acid and protein concentrations. This study showedthat anabolic effects of joint loading on cartilage are, at leastpartially, mediated by alterations in the SF.