Lack of effect of morphine-3-glucuronide on the spinal antinociceptive actions of morphine in the rat: an electrophysiological study.
Previous studies have shown that morphine-3-glucuronide (M3G), a metabolite of morphine, may functionally antagonize the antinociceptive action of morphine. The interaction between morphine and M3G was therefore investigated in the halothane-anaesthetised rat. Extracellular unit recordings were made of the innocuous A-beta fibre and noxious C-fibre evoked responses of convergent dorsal horn neurones. Intrathecal M3G (5 micrograms, 100 micrograms and 500 micrograms) alone did not show any antinociceptive effect. There was a slight, but not statistically significant, decrease in the antinociceptive effect of 5 micrograms morphine in the M3G-pretreated groups. However, M3G pretreatment (5 micrograms, 100 micrograms and 500 micrograms) had no effect on the higher dose of morphine (50 micrograms) used. We conclude that M3G has, at most, a minor effect on the spinal antinociceptive effects of morphine.
Hewett
Karen
K
Department of Pharmacology, University College London, LondonUK Nuffield Department of Anaesthetics, University of Oxford, OxfordUK.
Dickenson
Anthony H
AH
McQuay
Henry J
HJ
D000700:Analgesics / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D004594:Electrophysiology; D007278:Injections, Spinal; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009022:Morphine Derivatives / Q000494:pharmacology*; D009412:Nerve Fibers / Q000187:drug effects; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D009474:Neurons / Q000187:drug effects; D009619:Nociceptors / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects*
D000700:Analgesics; D009022:Morphine Derivatives; D009020:Morphine; C018108:morphine-3-glucuronide