Competitive antagonism of α1-adrenoceptor mediated pressor responses in the rat mesenteric artery

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Abstract
(-)-Noradrenaline-mediated pressor responses in the rat mesenteric artery preparation are blocked by α1-adrenoceptor antagonists, BE2254 and prazosin with pA2 values of 8·59 and 8·52 respectively. The α2-adrenoceptor selective antagonist rauwolscine, does not influence responses to (-)-noradrenaline in concentrations up to 10 μm. This rank order is consistent with an α1-adrenoceptor mediated effect. Shifts in the (-)-noradrenaline dose-response curve produced by BE2254 and prazosin were parallel and there was no significant effect on the observed maximal response. Slope values from Schild plots were not significantly different from unity indicating that these antagonists were behaving as classical competitive antagonists.