Characterization of beta-adrenoceptors in the dog saphenous vein

Abstract

In vitro experiments were carried out on strips of the dog saphenous vein to characterize beta-adrenoceptors mediating relaxation. Four beta-adrenoceptor agonists, isoproterenol, salbutamol, procaterol and alpha-(3,4,5-trimethoxyphenethylaminomethyl)-3,4-dihydroxybenzylalcohol hydrochloride (T-1583), all produced concentration-dependent relaxation of venous strips contracted by 10(-6) M methoxamine. These four drugs behaved as full agonists. In producing venous relaxation, procaterol was about 2.5 times more potent, and salbutamol and T-1583 were 7 and 98 times less potent than isoproterenol, on a molar basis. The concentration-relaxation response curves to the four agonists were shifted in a parallel way to the right by (t-butyl-amino-3-ol-2-propyl)oximino-9 fluorene hydrochloride (IPS 339), a selective beta 2-adrenoceptor antagonist, and by practolol. However, pA2-values for IPS 339 against the four agonists were all nearly 11.0, whereas those for practolol were all nearly 5.7. We conclude that beta-adrenoceptors in the dog saphenous vein mediating relaxation are predominantly on the beta 2 type.