Serum and synovial fluid concentrations of endothelin-1 in patients with rheumatoid arthritis

To determine the endothelin-1 (ET-1) concentrations in synovial fluid and serum of rheumatoid arthritis (RA) patients, this study was designed to examine if serum ET-1 concentration of control subjects has any correlation either with the ET-1 concentration of synovial fluid or ET-1 concentration of serum from RA patients. Twenty-eight patients were studied of whom eight males and twenty females with confirmed rheumatoid arthritis. Twenty-eight healthy volunteers were also included as controls. The immunoreactive concentration of ET-1 was measured using commercially available radioimmunoassay (RIA) kits (Peninsula Laboratories, Belmont CA) specific for ET-1. All the samples were performed in duplicate and after plotting % B/Bo for each standard directly on Y axis and endothelin concentrations on the X axis, the "best fit" curve was drawn and the amount of ET-1 was calculated. Mean ET-1 level in synovial fluid was 15.53 +/- 2.82 pg/me. In serum samples from RA patients, the mean ET-1 level was detected as 16.42 +/- 3.07 pg/ml (n = 28). Sera from twenty-eight healthy volunteers were analyzed as controls and mean ET-1 concentration was 8.68 +/- 1.96 pg/ml. A significant difference (P < 0.001) was found between ET-1 level of sera from RA patients and ET-1 levels from control sera. Highly significant difference (P < 0.001) was also detected between synovial fluid ET-1 and control ET-1 levels. However, no significant difference was found between ET-1 levels of synovial fluid and serum ET-1 levels of RA patients. Results of this study confirmed the presence of elevated levels of ET-1 concentration in synovial fluid and serum samples of patients with RA. The clinical significance and physiological role of endothelin in synovial fluids and sera of patients suffering from a variety of pathophysiological conditions of arthritis deserves further studies.