Enhanced alpha-2 adrenergic controls and spinal morphine potency in inflammation.
The antinociceptive potency of spinal morphine is enhanced in rats after carrageenan-induced inflammation. This electrophysiological study examines whether changes in alpha-2 adrenergic systems are responsible. Dorsal horn nociceptive neurones were recorded under halothane anaesthesia in normal animals and animals with carrageenan inflammation. There was a mild increase in potency of the selective alpha-2 adrenoceptor agonist dexmedetomidine following carrageenan (ED50 = 1 microgram). Intrathecal idazoxan (100 micrograms), an alpha-2 antagonist, produced a significant facilitation of the C-fibre evoked response in carrageenan-treated but not normal animals. However since neither idazoxan (100 micrograms) or atipamezole (50 micrograms, another antagonist) influenced the potency of spinal morphine, the increased alpha-2 adrenergic activity in inflammation does not contribute to the enhanced potency of spinal morphine.
Stanfa
L C
LC
Department of Pharmacology, University College, London, UK.
Dickenson
A H
AH
D058669:Adrenergic alpha-2 Receptor Antagonists; D000818:Animals; D002351:Carrageenan; D004146:Dioxanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005071:Evoked Potentials / Q000187:drug effects; D019329:Idazoxan; D007093:Imidazoles / Q000494:pharmacology*; D007249:Inflammation / Q000139:chemically induced*; D007278:Injections, Spinal; D008297:Male; D020926:Medetomidine; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects*
D058669:Adrenergic alpha-2 Receptor Antagonists; D004146:Dioxanes; D007093:Imidazoles; D018341:Receptors, Adrenergic, alpha-2; C050701:atipamezole; D009020:Morphine; D002351:Carrageenan; D020926:Medetomidine; D019329:Idazoxan