title: Characterization of adrenoceptor subtypes in cat cutaneous vasculature.
abstract: Experiments were undertaken to characterize the relative contribution of adrenoceptor subtypes in mediating vasoconstriction to exogenous agonists in the digital cutaneous vascular bed of the anesthetized cat using laser-Doppler flowmetry. Intra-arterial administration of (-)-epinephrine and (-)-norepinephrine into the brachial artery caused a dose-related vasoconstriction (decreased flow) with ED50 values of 7 and 21 ng, respectively. Blockade of beta adrenoceptors with propranolol did not alter the response to (-)-epinephrine nor did i.a. isoproterenol produce a significant vasodilation. Vasoconstrictor responses elicited by (-)-epinephrine and (-)-norepinephrine were antagonized by treatment with phentolamine (2.5 mg/kg i.v.) and by yohimbine (0.5 mg/kg i.v.) but were only marginally blocked by prazosin (0.1 mg/kg i.v.). A dose-related depression of cutaneous blood flow was also caused by clonidine at doses virtually identical to those of (-)-norepinephrine. Clonidine-induced vasoconstriction was antagonized by rauwolscine (0.5 mg/kg i.v.) but not by prazosin (0.1 mg/kg i.v.). Dose-response curves to a variety of additional adrenoceptor stimulants were constructed with the potency rank order for all agonists being: (-)-epinephrine greater than B-HT 920 = (-)-norepinephrine = clonidine much greater than (-)-phenylephrine much greater than B-HT 933 greater than methoxamine. Treatment with prazosin (0.1 mg/kg i.v.) antagonized methoxamine induced cutaneous vasoconstriction but not the decreased blood flow caused by B-HT 933. In contrast, rauwolscine (0.5 mg/kg i.v.) blocked the responses to B-HT 933 but not methoxamine.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pharmacology, University of Oklahoma Health Sciences Center, Oklahoma City.
authors.forename: M C
authors.initials: MC
authors.lastname: Koss
mesh_terms: D000818:Animals; D001381:Azepines / Q000494:pharmacology; D002415:Cats; D003000:Clonidine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000032:analysis* / Q000187:drug effects; D012039:Regional Blood Flow / Q000187:drug effects; D012867:Skin / Q000098:blood supply*; D014661:Vasoconstriction / Q000187:drug effects
chemical_list: D001381:Azepines; D011941:Receptors, Adrenergic; C015603:azepexole; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin; D004837:Epinephrine