PHARMACOLOGICAL CHARACTERIZATION OF α‐ADRENORECEPTOR SUBTYPES IN RAT ISOLATED THORACIC AORTA

1 The subtype of α-adrenoreceptor mediating contraction in rat isolated thoracic aorta was classified pharmacologically using preferential agonists and antagonists, and by utilizing mixed agonist and antagonist interactions. 2 Noradrenaline was 8 to 10-times more potent at contracting the aorta than phenylephrine and both agonists were about 1000 and 10,000-fold respectively more potent than azepexole (a preferential α2,-agonist). 3 Prazosin (a preferential α1,-antagonist) inhibited the dose-response curves to noradrenaline and phenylephrine 100 and 1000-times respectively more effectively than either phentolamine or rauwolscine (a preferential α2-antagonist). Furthermore, prazosin (5 times 10-9M). completely abolished contractions elicited by a single concentration of azepexole (3 times 10-4M). 4 In mixed antagonist studies, rauwolscine (5 times 10-7M) failed to shift the dose-response curves to nor-adrenaline and phenylephrine obtained in the presence of prazosin (5 times 10-9M). 5 In mixed agonist experiments, azepexole (3 times 10-4M) acted as a partial antagonist toward phenylephrine-induced contractions. 6 The results suggest that the α-adrenoreceptor of the rat thoracic aorta is predominantly, if not exclusively, of the α1-subtype.