title: Roles of opioid receptor subtypes on the antinociceptive effect of intrathecal sildenafil in the formalin test of rats.
abstract: Recently, it has been known that the antinociception of sildenafil, a phosphodiesterase 5 inhibitor, is mediated through the opioid receptors. There are common three types of opioid receptors mu, delta, and kappa. We characterized the role of subtypes of opioid receptor for the antinociception of sildenafil at the spinal level. Intrathecal catheters were placed for drug delivery and formalin solution (5%, 50 microl) was injected for induction of nociception within male SD rats. The effect of mu opioid receptor antagonist (CTOP), delta opioid receptor antagonist (naltrindole), and kappa opioid receptor antagonist (GNTI) on the activity of sildenafil was examined. Intrathecal sildenafil decreased the flinching responses during phases 1 and 2 in the formalin test. Intrathecal CTOP and naltrindole reversed the antinociception of sildenafil during both phases in the formalin test. Intrathecal GNTI reversed the effect of sildenafil during phase 2, but not phase 1. These results suggest that sildenafil is effective to acute pain and the facilitated pain state at the spinal level. Both mu and delta opioid receptors are involved. However, it seems that kappa opioid receptors play in the effect of sildenafil.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Republic of Korea. mhyoon@chonnam.ac.kr <mhyoon@chonnam.ac.kr>
authors.forename: Myung Ha
authors.initials: MH
authors.lastname: Yoon
authors.forename: Woong Mo
authors.initials: WM
authors.lastname: Kim
authors.forename: Hyung Gon
authors.initials: HG
authors.lastname: Lee
authors.forename: Yeo Ok
authors.initials: YO
authors.lastname: Kim
authors.forename: Lan Ji
authors.initials: LJ
authors.lastname: Huang
authors.forename: Tae Hoon
authors.initials: TH
authors.lastname: An
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D004347:Drug Interactions; D006146:Guanidines; D008297:Male; D009019:Morphinans; D009271:Naltrexone / Q000031:analogs & derivatives / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects*; D017288:Pain Threshold / Q000187:drug effects; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000145:classification / Q000502:physiology*; D000068677:Sildenafil Citrate; D013004:Somatostatin / Q000031:analogs & derivatives / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology*; D013997:Time Factors
chemical_list: C411465:17-cyclopropylmethyl-6,7-didehydro-4,5-epoxy-5'-guanidinyl-3,14-dihydroxyindolo(2',3'-6,7)morphinan; D006146:Guanidines; D009019:Morphinans; D009292:Narcotic Antagonists; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D011957:Receptors, Opioid; D013450:Sulfones; C049352:phenylalanyl-cyclo(cysteinyltyrosyl-tryptophyl-ornithyl-threonyl-penicillamine)threoninamide; D013004:Somatostatin; D009271:Naltrexone; D000068677:Sildenafil Citrate; C055382:naltrindole