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  • Title: Evidence for two subtypes of alpha adrenergic receptors in canine airway smooth muscle.
    Author: Leff AR, Munoz NM.
    Journal: J Pharmacol Exp Ther; 1981 May; 217(2):530-5. PubMed ID: 6262489.
    Abstract:
    The contractile response of canine tracheal muscle to i.a. phenylephrine, clonidine and norepinephrine was studied isometrically in situ in 32 dogs after beta adrenergic and ganglionic blockade. Intra-arterial phenylephrine caused dose-related tracheal contraction which was not altered by yohimbine (5 microgram/kg i.a.). Prazosin (4 mg/kg i.v.) caused a 77 +/- 3% decrease in tracheal response to i.a. phenylephrine. Clonidine also caused dose-related tracheal contraction, which was not altered by prazosin (4 mg/kg i.v.) but was 95 +/- 2% blocked by 5 microgram/kg i.a. of yohimbine. Norepinephrine caused tracheal muscle contraction which was greater than both phenylephrine (P less than .05) and yohimbine (P less than .001). Prazosin (4 mg/kg i.v.) caused 53 +/- 6% blockade and yohimbine (5 microgram/kg i.a.) caused 76 +/- 2% blockade of the response to i.a. norepinephrine; prazosin plus yohimbine caused greater than 98% blockade of the response to i.a. norepinephrine. The dose-response curve to i.a. acetylcholine was not altered by treatment with prazosin (4 mg/kg i.v.) plus yohimbine (5 microgram/kg i.a.). These results demonstrate that tracheal contraction induced by sympathomimetic amines is mediated by two subtypes of alpha adrenergic receptors on tracheal muscle, alpha-1 for phenylephrine, alpha-2 for clonidine and both alpha-1 and alpha-2 for norepinephrine.
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