Different levels of COX-1 and COX-2 enzymes in synoviocytes and chondrocytes during joint contracture formation

Objective. To measure the levels of prostaglandin endoperoxide H synthase ( PGHS) isozymes (or cyclooxygenase, COX) in vivo during the development of j oint contractures secondary to immobilization in rats. Methods. Rats had one knee joint immobilized for up to 32 weeks. Three grou ps were compared: 47 rats had knee joints immobilized, 38 animals had sham surgery, and 13 unoperated animals served as controls. Levels of PGHS-1 and PGHS-2 enzymes were characterized in the chondrocytes and synoviocytes of the knee joint by immunohistochemistry. Immunostaining intensity was quanti fied by microscopy using conventional analysis. Results. PGHS-1 level was lower in synoviocytes of the anterior capsule com pared with shams (1.3 vs 2.0; p < 0.05). PGHS-2 level was also lower in syn oviocytes of the posterior capsule (1.8 vs 2.3; p < 0.05), but higher in ch ondrocytes at the anterior aspect of the tibia compared with shams (1.6 vs 0.8; p < 0.05). PGHS-2 staining was increased in chondrocytes at the poster ior, opposed, and anterior aspects of the tibia compared with controls (1.1 , 0.6, 0.8 vs 0.2, 0.1, 0.2, respectively; all p < 0.05). Conclusion. Immobility induced joint contractures are characterized by a co ntrasting cellular pattern of PGHS enzyme levels: decreased in the synovium and increased in the chondrocytes. These findings suggest that chondrocyti c PGHS isoenzymes are important in cartilage degradation of contractured jo ints.