Competitive antagonism of alpha 1-adrenoceptor mediated pressor responses in the rat mesenteric artery.

(-)-Noradrenaline-mediated pressor responses in the rat mesenteric artery preparation are blocked by alpha 1-adrenoceptor antagonists, BE2254 and prazosin with pA2 values of 8.59 and 8.52 respectively. The alpha 2-adrenoceptor selective antagonist rauwolscine, does not influence responses to (-)-noradrenaline in concentrations up to 10 microM. This rank order is consistent with an alpha 1-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.