BIOCHEMICAL EVIDENCE FOR THE DUAL ACTION OF LABETALOL ON α‐ AND β‐ADRENOCEPTORS

Open Access
Publisher Website
Google Scholar
Abstract
1 Labetalol (AH 5158A) inhibited the adrenaline-stimulated adenylate cyclase activity of rat liver and heart. This drug had no effect on basal or guanosine triphosphate (GTP)-activated adenylate cyclase activities. 2 Labetalol displaced the binding of the specific ligands [3H]-dihydroergocryptine and (—)-[3H]-dihydroalprenolol from their respective α and β-adrenoceptors in rat heart and liver. The affinity of labetalol was 10 fold higher for the β- than for the α-adrenoceptor. It appeared to be 10 to 100 times less potent than phentolamine in blocking α-adrenoceptors and 5 to 10 times less potent than propranolol in blocking β-receptors. 3 It is concluded that labetalol exerts its dual α- and β-antagonism by acting directly on the plasma membranes, where it binds competitively to α- and β-adrenoceptors.