Alpha 1-adrenoceptor subtype(s) mediating noradrenaline-induced contractions of the guinea-pig aorta

The effect of alpha 1-adrenoceptor subtype selective antagonists, WB 4101, SZL-49 and chloroethylclonidine on noradrenaline-induced contractions of the guinea-pig aorta has been studied in an attempt to identify the alpha 1-adrenoceptor subtype(s) involved in the response. Noradrenaline and SDZ NVI 085 induced contractions of the aorta. Noradrenaline-induced contractions were competitively antagonised by WB 4101 (pA2 = 8.92, slope = 1.05). The contractions were significantly reduced by SZL-49 but not by chloroethylclonidine, indicating an action on alpha 1A-adrenoceptor subtype. Noradrenaline-induced contractions of the aorta were not inhibited by nifedipine (10(-6) M). The results are interpreted to suggest that alpha 1A-adrenoceptor subtype mediates noradrenaline-induced contractions of the guinea-pig aorta and that activation of alpha 1A-adrenoceptor subtype in the guinea-pig aorta is probably linked to intracellular Ca++ release.