The β2-adrenoceptor agonist bronchodilators terbutaline and orciprenaline are also weak α1-adrenoceptor antagonists

Abstract

Recently, the β2-adrenoceptor agonist terbutaline was shown to have α1-adrenolytic activity in mouse isolated pulmonary arteries in vitro and to lower pulmonary artery pressure in anaesthetised mice. The aim of our study was to determine the α1-adrenoceptor antagonist activity of terbutaline and its structurally close resorcinol, orciprenaline, in rat isolated small mesenteric arteries set up for myography. Their α1-adrenoceptor antagonist potency was then compared with their potency as β2-adrenoceptor agonists. Concentration-response curves to methoxamine were competitively antagonised by terbutaline (30–300 μM) or orciprenaline (30–300 μM) with a pKB of 4.70 ± 0.09 or 4.79 ± 0.17, respecti..