The action of aspirin on plasma kininogen and other plasma proteins in rheumatoid patients: relationship to disease activity.

1. When six female seropositive rheumatoid patients were given placebo therapy for 48 h, their plasma kininogen level, 9.2 +/- 0.7 microgram bradykinin equivalents (bk eq) per ml, was found to be 59% greater than that of a group of eight healthy female volunteers (5.8 +/- 0.5 microgram/ml). 2. When the rheumatoid patients received aspirin therapy for 1 week, their mean plasma kininogen concentration fell by 31% to 6.3 +/- 0.8 microgram Bk eq/ml. This was accompanied by a 20.4% fall in mean plasma alpha 2-globulin level. Haematocrit and total plasma protein were not significantly altered (P > 0.05). 3. The fall in kininogen was very rapid, the main reduction occurring within the first hour. 4. Aspirin therapy greatly reduced the pain assessments but had no effect on plasma concentrations of IgG, IgA, IgM, complement component C3, nor on ESR, haemoglobin, leucocyte count, nor ring size. Left hand grip strength was increased while right hand grip strength was unchanged. 5. The action of aspirin on plasma kininogen and alpha 2-globulin was similar to that of indomethacin. Plasma kininogen has been considered to be an acute phase reactant. The possible diagnostic value of plasma kininogen estimation is discussed.