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.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adrenergic alpha-2 Receptor Agonists
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Adrenergic alpha-2 Receptor Antagonists
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Adrenergic alpha-Agonists / pharmacology
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Adrenergic alpha-Antagonists / pharmacology
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Animals
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Cholinergic Fibers / chemistry
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Cholinergic Fibers / drug effects
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Duodenum / innervation*
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Duodenum / physiology
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Electric Stimulation
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Gastrointestinal Motility / physiology
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Guinea Pigs
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Idazoxan / analogs & derivatives
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Idazoxan / pharmacology
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Imidazoles / pharmacology
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Indoles / pharmacology
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Isoindoles
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Isoquinolines / pharmacology
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Male
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Medetomidine
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Muscle Contraction / drug effects
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Muscle Contraction / physiology
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Nordefrin / pharmacology
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Norepinephrine / pharmacology
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Oxymetazoline / pharmacology
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Piperazines / pharmacology
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Prazosin / pharmacology
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Receptors, Adrenergic, alpha-2 / physiology*
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Synaptic Membranes / chemistry*
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Vasoconstrictor Agents / pharmacology
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Xylazine / pharmacology
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Yohimbine / pharmacology
Substances
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Adrenergic alpha-2 Receptor Agonists
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Adrenergic alpha-2 Receptor Antagonists
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Adrenergic alpha-Agonists
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Adrenergic alpha-Antagonists
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Imidazoles
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Indoles
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Isoindoles
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Isoquinolines
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Piperazines
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Receptors, Adrenergic, alpha-2
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Vasoconstrictor Agents
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Xylazine
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Yohimbine
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Oxymetazoline
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2-methoxyidazoxan
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AR-C239
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Medetomidine
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Nordefrin
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Norepinephrine
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Prazosin
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Idazoxan
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BRL 44408