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  • 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.
    Author: Alabaster VA, Solca AM.
    Journal: Clin Sci (Lond); 1985; 68 Suppl 10():73s-75s. PubMed ID: 2857622.
    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.
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