Comparison of spontaneous and retinoic acid stimulated rabbit articular cartilage degradation in vitro.

: The in vitro degradation of rabbit articular cartilage explants was evaluated with and without the addition of retinoic acid under various experimental conditions. Retinoic acid at nontoxic concentrations ranging from 1 X 10(-7) to 1 X 10(-5) M significantly increased cartilage degradation. The addition of phenanthroline or cycloheximide, but not pepstatin, significantly inhibited spontaneous and retinoic-acid-stimulated cartilage degradation at pH 7. When the pH was reduced to 5, only pepstatin inhibited spontaneous and retinoic-acid-stimulated cartilage degradation. No chondroitin sulphate release was observed when the temperature was reduced to 4 degrees C. The different inhibitory profiles observed at pH 7 and pH 5 suggest that cartilage degradation at pH 7 is associated with the presence and synthesis of a neutral metalloproteinase.