Possible presence of slow reacting substance (SRS) in the synovial fluid of rheumatoid arthritis was studied. 15 samples out of 30 (50%) of synovial fluids showed SRS-like smooth muscle contractile activity ranging from 1.4 to 143 units/ml. This SRS-like activity on the guinea pig ileum was reversed by the specific SRS-A antagonist FPL 55712, and was hydrolysed by both purified human placental arylsulfatase B and type IV limpet arylsulfatase. Elution profiles of SRS-like substance on silicic acid chromatography, Sephadex LH-20 and DEAE-Sephadex A (-) 25 column chromatography were compatible with those of SRS-A. These results suggested that SRS was released from some kind of cells, possibly polymorphonuclear leukocytes, which migrated and stimulated immunologically in the synovial fluid of rheumatoid arthritis patient, and it might play any pathophysiological roles in the disease.
