title: Determination on functional basis of presynaptic alpha 2-adrenoceptor subtypes in guinea-pig duodenum.
abstract: The effects of several alpha 2-adrenoceptor agonists and antagonists were examined on the cholinergic twitch contractions evoked by electrical field stimulation of guinea-pig duodenum. Oxymetazoline, xylazine, noradrenaline, alpha-methyl-noradrenaline or medetomidine (0.01-30 microM) were nearly equieffective in inhibiting duodenal twitch responses. The effects of xylazine were competitively counteracted by antagonists tested (0.03-10 microM) with the following order of potency: RX 821002 = idazoxan > rauwolscine = yohimbine = BRL 44408 >> prazosin = ARC 239 = BRL 41992. According to the current classification, it is suggested that alpha 2-heteroadrenoceptors involved in the modulation of duodenal cholinergic neurotransmission belong to the alpha ZD subtype.
authors: Institute of Pharmacology, School of Medicine and Dentistry, University of Pisa, Italy.
authors: R
authors: R
authors: Colucci
authors: C
authors: C
authors: Blandizzi
authors: D
authors: D
authors: Carignani
authors: G
authors: G
authors: Lazzeri
authors: G
authors: G
authors: Natale
authors: F
authors: F
authors: Crema
authors: M
authors: M
authors: Del Tacca
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002799:Cholinergic Fibers / Q000737:chemistry / Q000187:drug effects; D004386:Duodenum / Q000294:innervation* / Q000502:physiology; D004558:Electric Stimulation; D005769:Gastrointestinal Motility / Q000502:physiology; D006168:Guinea Pigs; D019329:Idazoxan / Q000031:analogs & derivatives / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D054833:Isoindoles; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D020926:Medetomidine; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D008771:Nordefrin / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010109:Oxymetazoline / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology*; D013570:Synaptic Membranes / Q000737:chemistry*; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D007093:Imidazoles; D007211:Indoles; D054833:Isoindoles; D007546:Isoquinolines; D010879:Piperazines; D018341:Receptors, Adrenergic, alpha-2; D014662:Vasoconstrictor Agents; D014991:Xylazine; D015016:Yohimbine; D010109:Oxymetazoline; C058525:2-methoxyidazoxan; C032994:AR-C239; D020926:Medetomidine; D008771:Nordefrin; D009638:Norepinephrine; D011224:Prazosin; D019329:Idazoxan; C072125:BRL 44408