Spinal phospholipase A2 in inflammatory hyperalgesia:: role of Group IVA cPLA2

1 Current work has shown the importance of spinal cyclooxygenase (COX) products in facilitatory processes leading to tissue injury induced hyperalgesia. This cascade must originate with free arachidonic acid ( AA) released by the activity of spinal phospholipase A(2)' s (PLA(2)). In the present work, we studied the role of PLA(2)'s in spinal sensitization. 2 We first demonstrate the presence of constitutive mRNA in the spinal cord for PLA(2) Groups IB, IIA, IIC, IVA, V and VI by reverse transcription - polymerase chain reaction (RT-PCR) and sequencing. Using quantitative-PCR, we found that Group IVA cPLA(2) and Group VI iPLA(2) are the predominant PLA(2) messages in the spinal cord. Western blotting and activity assays specific for Group IVA cPLA2 and Group VI iPLA(2) verified the presence of these enzymes. PLA(2) activity in spinal cord homogenates was suppressed by methyl arachidonyl fluorophosphonate (MAFP) and arachidonyl trifluoromethylketone (AACOCF(3)), mixed inhibitors of Group IVA cPLA(2) and Group VI iPLA(2) as well as by bromoenol lactone ( BEL), a Group VI iPLA(2) inhibitor. The spinal expression of PLA(2) mRNA or protein was not altered in the face of peripheral inflammation. Secondly, we showed that intrathecal (i.t.) administration of MAFP and AACOCF(3), but not BEL, dose-dependently prevented thermal hyperalgesia induced by intraplantar carrageenan as well as formalin-induced flinching. Finally, i.t. injection of AACOCF(3), at antihyperalgesic doses, decreased the release of prostaglandin E-2 (PGE(2)) into spinal dialysate evoked by i.t. NMDA, while i.t. injection of BEL had no effect. 3 Taken together, this work points to a role for constitutive Group IVA cPLA(2) in spinal nociceptive processing.