title: Lack of differential inhibition by nifedipine of pressor responses induced by alpha 1- and alpha 2-adrenoceptor agonists and by angiotensin II in anaesthetized cats.
abstract: The effect of nifedipine on pressor dose-response curves to phenylephrine, alpha-methylnoradrenaline and angiotensin II was determined in anaesthetized cats pretreated with propranolol and atropine. The selectivity of phenylephrine and alpha-methylnoradrenaline for postjunctional alpha 1- and alpha 2-adrenoceptors respectively was demonstrated by using the selective alpha 1-adrenoceptor antagonist doxazosin and the relatively selective alpha 2-adrenoceptor antagonist rauwolscine. Nifedipine infused intravenously produced a degree of inhibition of rises in diastolic blood pressure similar to that induced by all three agonists. It is concluded that alpha 1- and alpha 2-adrenoceptor activation induced by phenylethanolamine derivatives is equally dependent on extracellular calcium for vascular smooth muscle contraction. Antagonism of sympathetically mediated or angiotensin-induced vasoconstriction could contribute to the vasodilator effects of nifedipine.
authors.forename: V A
authors.initials: VA
authors.lastname: Alabaster
authors.forename: A M
authors.initials: AM
authors.lastname: Solca
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002415:Cats; D017292:Doxazosin; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology*; D008771:Nordefrin / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000031:analogs & derivatives / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D000804:Angiotensin II; D010656:Phenylephrine; D015016:Yohimbine; D009543:Nifedipine; D017292:Doxazosin; D008771:Nordefrin; D011224:Prazosin