Concentration of substance P, neurokinin A, calcitonin gene-related peptide, neuropeptide Y and vasoactive intestinal polypeptide in synovial fluid from knee joints in patients suffering from rheumatoid arthritis.

We have studied the presence of five neuropeptides in knee joint synovial fluid from either patients suffering from rheumatoid arthritis and pain (n = 18) or being subjected to arthroscopy due to meniscal/cruciate ligament injuries (n = 13). Radioimmunoassay technique was used for peptide analysis using antisera SP2 against substance P (SP), K12 against neurokinin A (NKA), CGRPR8 against calcitonin gene-related peptide (CGRP), NPY1 against neuropeptide Y (NPY) and VIP2 against vasoactive intestinal polypeptide (VIP). No SP could be detected, and lower levels of NKA was found in arthritic joints vs controls. CGRP and NPY was found in higher concentrations in arthritic patients vs controls. VIP was found sporadically in both arthritis and control patients. Our data show some quantitative differences between patients suffering rheumatoid arthritis and pain, and patients with non-inflamed joints without pain; indicating an involvement of peptidergic fibers in arthritis in humans.