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 (pA(2) = 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.