title: Isobolographic analysis of interaction between spinal endomorphin-1, a newly isolated endogenous opioid peptide, and lidocaine in the rat formalin test.
abstract: Endomorphin-1, a newly isolated endogenous opioid ligand, has a potential affinity with mu-opioid receptor. We investigated antinociception of intrathecal endomorphin-1 and lidocaine in the rat formalin test and examined the interaction between the two agents using isobolographic analysis. Intrathecal endomorphin-1 caused dose-dependent suppression of the formalin-induced biphasic behavioral response. Intrathecal lidocaine produced dose-dependent inhibition of phase-2 behavioral response. Isobolographic analysis confirmed that combination of intrathecal endomorphin-1 and lidocaine, given at a fixed dose ratio, produced synergistic suppression of phase-2 behavioral response. These data demonstrate that spinal endomorphin-1 synergistically interacts with local anesthetic lidocaine in producing antinociception in the formalin test.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, Asahikawa Medical College, Japan. hao@asahikawa-med.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Hao
authors.forename: O
authors.initials: O
authors.lastname: Takahata
authors.forename: H
authors.initials: H
authors.lastname: Iwasaki
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000779:Anesthetics, Local / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004347:Drug Interactions; D004357:Drug Synergism; D005557:Formaldehyde; D007278:Injections, Spinal; D008012:Lidocaine / Q000494:pharmacology*; D008297:Male; D009619:Nociceptors / Q000187:drug effects*; D009842:Oligopeptides / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000701:Analgesics, Opioid; D000779:Anesthetics, Local; D004338:Drug Combinations; D009842:Oligopeptides; C105293:endomorphin 1; D005557:Formaldehyde; D008012:Lidocaine