Probing of β-adrenergic receptors by novel fluorescent β-adrenergic blockers

Abstract

The synthesis of 2 high-affinity fluorescent .beta.-adrenergic blockers was described: dl-N1-[2-hydroxy-3-(1-naphthyloxy)propyl]-N2-(9-acridyl)-1,2-propanediamine (9-aminoacridylpropanolol, 9-AAP) and dl-N-[2-hydroxy-3-(1-naphthyloxy)propyl]-N''-dansylethylenediamine (dansyl analogue of propranolol, DAPN). 9-AAP and DAPN competitively inhibited the l-epinephrine-dependent adenylate cyclase activity [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1] in turkey erythrocyte membranes without affecting the F-stimulated adenylate cyclase activity. Similarly, 9-AAP and DAPN inhibited in a competitive manner the binding of [125I]-iodohydroxybenzylpindolol to these .beta.-adrenergic receptors. The 2 fluorescent .beta.-adrenergic blockers 9-AAP and DAPN probed specifically .beta.-adrenergic receptors in the CNS and other organs when injected into rats. The fluorescence pattern was monitored by fluorescence microscopy performed on cryostat slices of these organs. The appearance of the characteristic fluorescence pattern was blocked in a stereospecific fashion by a prior injection of l-propranolol and not by a prior injection of d-propranolol. These compounds offer a powerful means to map .beta.-adrenergic receptors in vivo. The stereospecific displacement of 9-AAP from the .beta.-adrenergic receptors of turkey erythrocyte membranes by l-propranolol and l-epinephrine could be detected in vitro using front-face fluorescence. The potential use of these compounds to probe .beta.-receptors in vitro and in vivo was discussed.