title: Naloxone blocks the analgesic action of levorphanol but not of dextrorphan in the leopard frog.
abstract: Intraspinal injection of levorphanol (3 micrograms) at the lumbar area of the leopard frog, Rana pipiens, induced analgesia which was completely blocked by co-injection of naloxone (3 micrograms), whereas dextrorphan (3 micrograms) induced analgesia which was unaffected by naloxone. Subcutaneous levorphanol (20 or 80 mg/kg) induced a dose-dependent analgesia which was blocked by concurrent naloxone (2 mg/kg), while only the higher dose of dextrorphan (80 mg/kg) induced analgesia which was unaffected by concurrent naloxone at 8 or 80 mg/kg. These data are the first to indicate naloxone-insensitive, dextrorphan-induced analgesia.
mesh_terms: D000818:Animals; D003917:Dextrorphan / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D007981:Levorphanol / Q000494:pharmacology*; D009019:Morphinans / Q000494:pharmacology*; D009270:Naloxone / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects*; D011894:Rana pipiens; D011957:Receptors, Opioid / Q000187:drug effects; D012684:Sensory Thresholds; D013116:Spinal Cord / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects*
chemical_list: D009019:Morphinans; D011957:Receptors, Opioid; D003917:Dextrorphan; D007981:Levorphanol; D009270:Naloxone