Plasma and synovial fluid cAMP in patients with rheumatoid arthritis.

cAMP was measured in plasma and synovial fluid from 11 patients suffering from rheumatoid arthritis with a specific protein-binding assay. Plasma and synovial fluid values were 17.0 +/- 6.8 pmol/ml and 8.3 +/- 3.7 pmol/ml, range 5-28 pmol/ml and 5-16 pmol/ml, respectively. No correlation could be established between plasma and synovial fluid levels, plasma and disease activity, or synovial fluid and disease activity, as judged by Lansbury's index. It is concluded that it seems unlikely that synovial fluid cAMP is derived solely from plasma and that no simple relation exists between cAMP in plasma and synovial fluid and total disease activity.