Enhanced breakdown of bovine articular cartilage proteoglycans by conditioned synovial medium in vitro: a possible role for prostaglandins.

Addition of conditioned medium derived from fragment cultures of synovium dissected from bovine knee joints (SM) to cultures of articular cartilage derived from the same animal resulted in a significant increase in breakdown of cartilage proteoglycans, measured as the release of [35S]sulphate from pre-labelled cartilage pieces. Culturing the synovium in the presence of indomethacin (indo-SM) at a concentration of 1.4 x 10(-5) mol/l reduced the breakdown-enhancing effect of the SM in some but not in all of the experiments. Addition of prostaglandins E1 or E2 (PGE1 or PGE2) (2.8 x 10(-7)-1.4 x 10(-5) mol/l) together with indo-SM resulted in a significant enhancement of breakdown of cartilage proteoglycans. PGA1, PGB1 and PGF2 alpha(less than 1.5 x 10(-5) mol/l) had, however, no effect in this system. Neither PGE1, PGE2 nor indomethacin at the concentrations mentioned above had any direct effect on breakdown of cartilage proteoglycans. No difference was found between the breakdown enhancing capacity of SM derived from synovium cultured in the presence of indo plus PGE1 or PGE2 (less than 4 x 10(-5) mol/l) and indo-SM. These findings are discussed in terms of cellular interactions.