title: Roles of opioid receptor subtype in the spinal antinociception of selective cyclooxygenase 2 inhibitor.
abstract: BACKGROUND
  Selective inhibitors of cyclooxygenase (COX)-2 are commonly used analgesics in various pain conditions. Although their actions are largely thought to be mediated by the blockade of prostaglandin (PG) biosynthesis, evidences suggesting endogenous opioid peptide link in spinal antinociception of COX inhibitor have been reported. We investigated the roles of opioid receptor subtypes in the spinal antinociception of selective COX-2 inhibitor.
  
  
  METHODS
  To examine the antinociception of a selective COX-2 inhibitor, DUP-697 was delivered through an intrathecal catheter, 10 minutes before the formalin test in male Sprague-Dawley rats. Then, the effect of intrathecal pretreatment with CTOP, naltrindole and GNTI, which are µ, δ and κ opioid receptor antagonist, respectively, on the analgesia induced by DUP-697 was assessed.
  
  
  RESULTS
  Intrathecal DUP-697 reduced the flinching response evoked by formalin injection during phase 1 and 2. Naltrindole and GNTI attenuated the antinociceptive effect of intrathecal DUP-697 during both phases of the formalin test. CTOP reversed the antinociception of DUP-697 during phase 2, but not during phase 1.
  
  
  CONCLUSIONS
  Intrathecal DUP-697, a selective COX-2 inhibitor, effectively relieved inflammatory pain in rats. The δ and κ opioid receptors are involved in the activity of COX-2 inhibitor on the facilitated state as well as acute pain at the spinal level, whereas the µ opioid receptor is related only to facilitated pain.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Chonnam National University Hospital, Gwangju, Korea.
authors.forename: Cheol Hun
authors.initials: CH
authors.lastname: Choi
authors.forename: Woong Mo
authors.initials: WM
authors.lastname: Kim
authors.forename: Hyung Gon
authors.initials: HG
authors.lastname: Lee
authors.forename: Cheol Won
authors.initials: CW
authors.lastname: Jeong
authors.forename: Chang Mo
authors.initials: CM
authors.lastname: Kim
authors.forename: Seong Heon
authors.initials: SH
authors.lastname: Lee
authors.forename: Myung Ha
authors.initials: MH
authors.lastname: Yoon