Intra-articular morphine and saline injections induce release of large molecular weight proteoglycans into equine synovial fluid.

Both morphine and physiologic saline injected intra-articularly into healthy equine tarsocrural joints induced a release of large molecular size proteoglycan (PG) subunits into the synovial fluid (SF) analysed 24 h postinjection. High-performance liquid chromatography (HPLC) with a size-exclusion column was used to assess the high molecular weight proteoglycans in equine synovial fluid (SF). The PG peaks of SF samples eluated separately from SF hyaluronate and other molecular components of the SF in the HPLC chromatographies indicating no interaction between hyaluronate and PG in the SF. Individual elution profiles varied between joints and horses. The amount of PG release was measured by relative area index from the HPLC chromatograms. The synovial fluid PG content was significantly increased (P < 0.05) after morphine but not in saline injected joints compared with pretreatment but there were no significant differences between the two groups. It was concluded that intra-articular injections of both morphine and physiologic saline are able to elicit a marked PG release into the SF from articular cartilage within 24 h of injection.