Binding of a catechol derivative of denopamine (T-0509) and N-tert-butylnoradrenaline (Colterol) to beta 1- and beta 2-adrenoceptors

The affinities for beta-adrenoceptors, the subtype-selectivity and the agonistic effectiveness of T-0509 (a catechol derivative of denopamine) and colterol (N-tert-butylnoradrenaline; Col) were compared with those of Other beta-agonists using a binding assay method. Specific binding of [3H]dihydroalprenolol (3H-DHA) to guinea pig left ventricular and lung membranes was saturable, and Scatchard and Hill analyses suggested that 3H-DHA bound to both membranes with a single population of binding sites with no binding site cooperativity. Addition of 5'-guanylylimidodiphosphate (GppNHp, 30 microM) led to a rightward shift of the 3H-DHA binding displacement curves of T-0509 and Col in both membranes, and the degree of shift was similar to that of full agonists such as isoproterenol (Iso), adrenaline (Adr) and noradrenaline (NA). Both T-0509 and Col were thus considered to be full agonists at both beta 1- and beta 2-adrenoceptors, respectively, unlike denopamine and procaterol. T-0509 and Col showed considerably high affinity for both beta 1- and beta 2-adrenoceptors, and T-0509, like denopamine, was as selective for the beta 1-subtype as NA (4.5-fold compared with Iso as a non-selective agonist), whereas Col was more selective for the beta 2-subtype than Adr (4.5-fold compared with Iso).