title: Investigations into the nature of alpha 2-adrenoceptors in rat tail arteries.
abstract: In rat isolated perfused tail arteries, dose-response curves were established for the vasopressor effects of phenylephrine (alpha 1-adrenoceptor agonist), clonidine (alpha 1- and alpha 2-adrenoceptor agonist), clonidine in the presence of 10(-7) mol/l prazosin (alpha 2-agonist), and BHT-920 (alpha 2-agonist). The ED50 values were: phenylephrine 1.85 X 10(-10) mol; clonidine 6.3 X 10(-10) mol; clonidine + prazosin 3.2 X 10(-6) mol; BHT-920 6.1 X 10(-6) mol. The arterial reactivity to BHT-920 was stable only after 4-5 h of perfusion. Responses to BHT-920 were not antagonized by yohimbine (alpha 2-adrenoceptor antagonist) but were antagonized by low concentrations of prazosin (alpha 1-adrenoceptor antagonist). These data constitute conflicting evidence regarding the existence of alpha 2-adrenoceptors in rat tail arteries. The data are consistent with the proposal that there are two recognition sites on alpha 1-adrenoceptors; phenylephrine and BHT-920 may stimulate different sites on alpha 1-adrenoceptors.
authors.forename: J F
authors.initials: JF
authors.lastname: Marwood
authors.forename: K L
authors.initials: KL
authors.lastname: Chapman
authors.forename: S J
authors.initials: SJ
authors.lastname: Armsworth
authors.forename: G S
authors.initials: GS
authors.lastname: Stokes
mesh_terms: D000818:Animals; D001381:Azepines / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010477:Perfusion; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000032:analysis / Q000187:drug effects*; D013623:Tail / Q000098:blood supply; D014661:Vasoconstriction / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D001381:Azepines; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; C024763:talipexole