Decreased cerebrospinal fluid neuropeptide-converting enzyme activity in monoarthritic rats

The activity in rat cerebrospinal fluid (CSF) of dynorphin-converting enzyme (DCE) and substance P endopeptidase (SPE) was determined in control animals and in rats with monoarthritis. Enzymatic activities were measured with specific radioimmunoassays toward the N-terminal products Leu-enkephalin-Arg6 and substance P1-7, respectively. A monoarthritis stable during weeks 2-6 post-injection was induced by injection (0.05 ml) into one joint with Freund's adjuvant. Both SPE and DCE were significantly decreased 15 days after the intraarticular injection. Despite the degree of arthritis that was sustained equally at four weeks after inoculation, both DCE and SPE were back to control levels at that time. It can therefore be concluded that arthritis from a single joint is sufficient to elicit changes in CSF convertase activities, and that these effects disappear between 2 and 4 weeks after injection, although the arthritis persists.