title: Additive antinociception between intrathecal sildenafil and morphine in the rat formalin test.
abstract: The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 microL of 5% formalin solution was applied to the hind-paw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Chonnam National University, Medical School, Gwangju, Korea. mhyoon@chonnam.ac.kr
authors.forename: Myung Ha
authors.initials: MH
authors.lastname: Yoon
authors.forename: Kyung Deok
authors.initials: KD
authors.lastname: Park
authors.forename: Hyung Gon
authors.initials: HG
authors.lastname: Lee
authors.forename: Woong Mo
authors.initials: WM
authors.lastname: Kim
authors.forename: Tae Hoon
authors.initials: TH
authors.lastname: An
authors.forename: Yeo Ok
authors.initials: YO
authors.lastname: Kim
authors.forename: Lan Ji
authors.initials: LJ
authors.lastname: Huang
authors.forename: Cui Jin
authors.initials: CJ
authors.lastname: Hua
mesh_terms: D000700:Analgesics / Q000008:administration & dosage*; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005557:Formaldehyde / Q000633:toxicity; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage; D010146:Pain / Q000139:chemically induced; D059408:Pain Management; D010147:Pain Measurement / Q000187:drug effects; D010726:Phosphodiesterase Inhibitors / Q000008:administration & dosage*; D010879:Piperazines / Q000008:administration & dosage*; D011687:Purines / Q000008:administration & dosage; D051381:Rats; D017207:Rats, Sprague-Dawley; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000008:administration & dosage*; D013997:Time Factors
chemical_list: D000700:Analgesics; D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D013450:Sulfones; D005557:Formaldehyde; D009270:Naloxone; D009020:Morphine; D000068677:Sildenafil Citrate