Beta-adrenergic receptors in rat myocardium: direct detection by a new fluorescent beta-blocker

A new fluorescent beta-blocker, 9-amino-acridin propranolol (9-AAP), was administered i.v. to rats. Multiple fluorescent 9-AAP binding sites were observed on cardiac muscle cells in frozen sections. Intensity and density of cardiac 9-AAP fluorescence were markedly reduced following pretreatment with (+/-)- and (-)-propranolol but not with (+)-propranolol. Our findings suggest that 9-AAP may label beta-adrenergic receptor sites in rat myocardium.