Bilateral changes of substance P-, neurokinin A-, calcitonin gene-related peptide- and neuropeptide Y-like immunoreactivity in rat knee joint synovial fluid during acute monoarthritis.

It has been hypothesized that the nervous system contributes to the symmetrical response in rheumatoid arthritis. In order to elucidate this, the bilateral concentrations of substance P-like immunoreactivity (SP-LI), neurokinin A-LI (NKA-LI), calcitonin gene-related peptide-LI (CGRP-LI) and neuropeptide Y-LI (NPY-LI) in rat synovial fluid during acute monoarthritis were studied. Equal volumes (0.05 ml) of either Freund adjuvants, carrageenan 2%, substance P 10(-5) M or human recombinant interleukin-1 alpha were injected into the right and saline into the left knee joint. Control rats were given saline bilaterally. Perfusates were obtained from both knees simultaneously at 2, 6 and 24 h after injection and were analysed by specific radioimmunoassays. Increase of SP-, NKA-, CGRP- and NPY-LI in synovial fluid occurred in both knees after injections with the pro-inflammatory substances into the right joints as compared to controls, except for unchanged SP-LI in the right knee joint after 24 h following hrIL-1 alpha injection. There was, however, generally no significant difference in the peptide contents between the right knee (injected with pro-inflammatory substance) as compared to the left knee (given saline) at 2, 6 or 24 h after injection except at three occasions. The results show that experimentally induced monoarthritis induces bilateral changes in synovial fluid peptide content.