Catecholamine affects acetylcholine release in trachea: alpha 2-mediated inhibition and beta 2-mediated augmentation.
We investigated the effects of catecholamines on acetylcholine (ACh) release from equine airway parasympathetic nerves. Trachealis strips were suspended in 2-ml tissue baths with Krebs-Henseleit solution containing atropine (10(-7) M), neostigmine (10(-6) M), and guanethidine (10(-5) M). Electrical field stimulation (20 V, 0.5 ms, 0.5 Hz, for 15 min) was applied, and ACh was measured by high-performance liquid chromatography with electrochemical detection. Epinephrine (Epi) and norepinephrine (NE) inhibited ACh release in a concentration-dependent manner. Inhibition was attenuated by the alpha 2-adrenoceptor antagonist idazoxan (10(-6) M) but not by the alpha 1-antagonist prazosin (10(-6) M). After alpha 2-blockade with idazoxan (10(-5) to 10(-4) M), Epi but not NE augmented ACh release. Isoproterenol (10(-7) to 10(-5) M) increased ACh release, an effect that was reversed by the beta 2-adrenoceptor antagonist ICI-118,551 (10(-5) M) but not by the beta 1-adrenoceptor antagonist atenolol (10(-5) M). Our results indicate that horse airway cholinergic nerves are modulated by both alpha 2-inhibitory and beta 2-excitatory adrenoceptors, with the former being predominant.
Zhang
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XY
Department of Large Animal Clinical Sciences, Michigan State University, East Lansing 48824.
Robinson
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NE
Wang
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ZW
Lu
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MC
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004146:Dioxanes / Q000494:pharmacology; D004558:Electric Stimulation; D004837:Epinephrine / Q000494:pharmacology*; D006736:Horses / Q000502:physiology*; D019329:Idazoxan; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009638:Norepinephrine / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects / Q000378:metabolism*
D004146:Dioxanes; D011433:Propranolol; D007545:Isoproterenol; D000109:Acetylcholine; D009638:Norepinephrine; D019329:Idazoxan; D004837:Epinephrine