INACTIVATION OF ANTITHROMBIN-III IN SYNOVIAL-FLUID FROM PATIENTS WITHRHEUMATOID-ARTHRITIS

Objective-To investigate the thrombin inhibitory capacity of antithrom bin III in the inflamed human joint. Methods-Thrombin inhibitory capac ity was measured, using a kinetic spectophotometric method, in matched plasma and synovial fluid samples of patients with rheumatoid arthrit is (n=22) and osteoarthritis (n=16), together with normal control plas ma samples (n=13). In the same samples, the concentration of antithrom bin III was also determined by the method of radial immunodiffusion. T he combination of these measurements allowed the calculation of the sp ecific thrombin inhibitory capacity of these samples. Results-An incre ased concentration of antithrombin III in rheumatoid compared with ost eoarthritic synovial fluid was noted (p<0.05), However, there was a si gnificant depression in the specific activity of antithrombin III in r heumatoid synovial fluid when compared with matched plasma samples (p< 0.001) or with osteoarthritic synovial fluid (p<0.05). Conclusion-In r heumatoid synovial fluid the thrombin inhibitory capacity of antithrom bin III is disproportionately depressed relative to the concentration of antithrombin III, indicating the inactivation of antithrombin III i n the rheumatoid joint.