In vivo Identification and Distribution of Alpha- and Beta-Adrenoceptors in Rat Heart and Lung

Abstract

Uptake of ³H-prazosin (³H-PZ), a potent alpha-adrenoceptor antagonist, and ³H-dihydroalprenolol (³H-DHA), a potent beta-antagonist, was measured in rat heart and lung after intravenous injection. ³H-PZ binding was inhibited in a dose-dependent manner by phentolamine with maximum displacement at 5 mg/kg which represented 50–70% of the total binding. ³H-DHA was inhibited by increasing doses of l-propranolol with maximum displacement at 1 mg/kg (30–70% of total binding), whereas d-propranolol was approximately 100 times less potent, confirming stereospecificity of binding. These radioligands appeared to label adrenoceptors in vivo. The distribution of both radioligands in heart, lung and blood vessels was investigated.