Epidural Dexamethasone Decreased Inflammatory Hyperalgesia and Spinal cPLA(2) Expression in a Rat Formalin Test

PURPOSE: The aim of this study was to investigate the effect of epidural dexamethasone on analgesia and cytosolic phospholipase A(2) (cPLA(2)) expression in the spinal cord in a rat formalin test. MATERIALS AND METHODS: Epidural dexamethasone injection was performed to Sprague-Dawley rats with a 25 gauge needle under fluoroscopy. Following the epidural injection, a formalin induced pain behavior test was performed. Next, the spinal cords corresponding to L4 dorsal root ganglion was extracted to observe the cPLA(2) expression. RESULTS: There were no differences in pain response during phase I among the groups. The phase II pain response in 300 µg of epidural dexamethasone group decreased as compared to control, 30 µg of epidural dexamethasone, 100 µg of epidural dexamethasone, and 300 µg of systemic dexamethasone groups. The expression of cPLA(2) decreased in Rexed laminae I-II in 300 µg of the epidural dexamethasone group compared with the ones in the control group. CONCLUSION: Taken together, these results suggest that 300 µg of epidural dexamethasone has an attenuating effect on the peripheral inflammatory tissue injury induced hyperalgesia and this effect is mediated through the inhibition of intraspinal cPLA(2) expression and the primary site of action is the laminae I-II of the spinal cord.