title: Irreversible inactivation of the beta-adrenoreceptor by a partial agonist. Evidence for selective loss of the agonist high affinity binding sites.
abstract: The catecholamine derivatives aminomenthylnorepinephrine (compound 1) and bromoacetylaminomenthylnorepinephrine (compound 2) were synthesized and their interaction with the rat lung beta-adrenoreceptor was characterized. Compared to (-)-isoproterenol, compounds 1 and 2 were 10 and 280 times less potent, respectively, at inhibiting (-)-[3H]dihydroalprenolol binding. At pH 7.4, all 3 compounds induced a loss of receptors (40-60%) which could be recovered by treatment with guanyl-5'-yl imidodiphosphate (Gpp(NH)p). However, at pH 8.1 Gpp(NH)p treatment did not recover those receptors lost by compound 2 only. The compound 2-induced receptor loss at pH 8.1 was time-dependent, prevented by propranolol but unaffected by Gpp(NH)p or after membrane heating at 50 degrees C which prevented the formation of the agonist high affinity binding state. Although, the maximal receptor loss as measured by [3H]dihydroalprenolol was 40-60%, more than 80% of the receptors were lost when measured by direct agonist binding, and the receptors left showed little agonist high affinity binding state formation. In rat reticulocyte membranes, compounds 1 and 2 stimulated adenylate cyclase activity with intrinsic activities of 0.55 and 0.31, respectively. However, at pH 8.1, compound 2 initially stimulated the enzyme followed by a blockade. These data indicated that both compounds 1 and 2 were partial beta-adrenoreceptor agonists and, at pH 8.1, compound 2 appeared to bind irreversibly only to those lung receptors able to form the agonist high affinity binding state. Furthermore, after irreversible binding, compound 2 appeared to act as an antagonist.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D004082:Dihydroalprenolol / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006358:Hot Temperature; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D008168:Lung / Q000378:metabolism; D009638:Norepinephrine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*
chemical_list: D011943:Receptors, Adrenergic, beta; D006165:Guanylyl Imidodiphosphate; D004082:Dihydroalprenolol; C047506:aminomenthylnorepinephrine; C047507:bromoacetylaminomenthylnorepinephrine; D011433:Propranolol; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D009638:Norepinephrine