Carrageenan-induced hyperalgesia is associated with increased cyclo-oxygenase-2 expression in spinal cord.

The discovery of the inducible form of cyclo-oxygenase, known as cyclo-oxygenase-2 (COX-2), has provided insight into the mechanisms involved in the inflammatory response. Peripheral inflammation induced by intraplantar injection of carrageenan is associated with a marked increase in COX-2 mRNA and prostaglandins in the surrounding tissue and the accompanying oedema is sensitive to COX-2-selective drugs. In this study, we investigated whether COX-2 in spinal cord was similarly induced by carrageenan and whether the associated development of altered pain sensitivity, hyperalgesia was affected by the COX-2 selective inhibitor DuP 697. Intraplantar injection of carrageenan caused a marked hyperalgesia at 4 h which was significantly attenuated by treatment with DuP 697 (10 mg kg-1). At the same time levels of COX-2 mRNA in lumbar spinal cord were significantly increased two-fold by carrageenan treatment. However, DuP 697 potentiated COX-2 mRNA induction, which indicates the existence of a potential regulatory mechanism to overcome COX-2 inhibition.