The spinal analgesic role of alpha 2-adrenoceptor subtypes in rats after peripheral nerve section.
Two putative agonists of subtypes of alpha 2-adrenoceptors, guanfacine (alpha 2A) and ST-91 ([2,6-dicthylphenylamino]-2-imidazoline, alpha 2C), were applied intrathecally and their effects on autotomy behaviour and on the flexor reflex before and after sciatic nerve section were examined. Neither drug influenced autotomy during a 17-day observation period. Both drugs dose dependently depressed the flexor reflex in rats with intact sciatic nerves. After axotomy, the sensitivity of the flexor reflex to guanfacine and ST-91 was moderately increased compared to normals. ST-91 i.t. at high doses evoked motor discharges, an effect which was reversed by the alpha 1-adrenoceptor antagonist, WB4101 (2-[2,6-dimethyoxyphenoxyethyl]-aminomethyl-1,4-benzodioxane). Thus, the effect of i.t. clonidine on the flexor reflex and autotomy behaviour observed previously may not involve its action on alpha 2A- and alpha 2C-adrenoceptors. Furthermore, due to its motor effect which may involve activation of alpha 1-adrenoceptors, ST-91 may not be a suitable tool to study the physiological function of spinal alpha 2C-adrenoceptors.
Puke
M J
MJ
Department of Anaesthesiology and Intensive Care, Karolinska Hospital, Stockholm, Sweden.
Luo
L
L
Xu
X J
XJ
D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000698:Analgesia; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003000:Clonidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004146:Dioxanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D016316:Guanfacine / Q000008:administration & dosage / Q000494:pharmacology*; D007278:Injections, Spinal; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D012018:Reflex / Q000187:drug effects; D012584:Sciatic Nerve / Q000187:drug effects / Q000601:surgery
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D018341:Receptors, Adrenergic, alpha-2; D016316:Guanfacine; C011266:ST 91; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D003000:Clonidine