The significant reduction of high molecular weight-kininogen in synovial fluid of patients with active rheumatoid arthritis.

It has been proposed that kinin system was implicated in inflammatory joint diseases such as rheumatoid arthritis. Our present work provides further support on the involvement of the kinin system. In osteoarthritis patients, the total, high molecular weight (HMW)-, and low molecular weight (LMW)-kininogen levels in synovial fluid were not different from those in plasma. On the contrary, in rheumatoid patients, HMW-kininogen level in synovial fluid was significantly lower than that in plasma, whereas LMW-kininogen level in synovial fluid was not different from that in plasma. The reduction of HMW-kininogen level in synovial fluid was much more marked in active cases of those who showed high blood sedimentation rate and high C-reactive protein value. Furthermore, the reduction was closely related to the clinical severity. In active rheumatoid patients, HMW-kininogen level was further reduced in the synovial fluid after withdrawal of indomethacin.