title: Brain alpha-adrenergic receptors: comparison of [3H]WB 4101 binding with norepinephrine-stimulated cyclic AMP accumulation in rat cerebral cortex.
abstract: The ability of a series of adrenergic agents to displace the binding to brain membranes of [3H]WB 4101, a potent alpha-adrenergic antagonist (WB 4101 = 2-[2-(2,6-dimethoxyphenoxy)ethylaminomethyl]-1,4-benzodioxane hydrochloride), has been compared with the potency of these agents in stimulating or inhibiting the alpha-adrenergic component of cyclic AMP accumulation in rat cerebral cortex slices. [3H]WB 4101 rapidly bound to a high affinity site (KD = 2.7 nM) in membranes from cerebral cortex. Binding came to equilibrium by 2 min at 37 degrees C and was rapidly reversed in the presence of phentolamine. The potencies of adrenergic agents (WB 4101 greater than phentolamine greater than naphazoline) in displacing binding of [3H]WB 4101 were comparable to the potencies of these agents as inhibitors of the alpha-adrenergic component of norepinephrine-stimulated cyclic AMP accumulations. Phenoxybenzamine, clonidine, chlorpromazine and haloperidol were about 10--30 times more potent in inhibiting cyclic AMP accumulation than in displacing [3H]WB 4101 binding. The potency of classical alpha-adrenergic agonists in displacing WB 4101 (epinephrine greater than norepinephrine greater than methoxamine) correlated with the ability of these agonists to increase cyclic AMP levels. Overall a significant correlation (r = 0.87, P less than 0.005) was found between WB 4101 binding and alpha-adrenergically mediated cyclic AMP accumulation in brain. Several ligands bind to specific sites in brain membranes with alpha-adrenergic receptor properties. The identification of these binding sites as receptors depends on a correlation of binding with a known alpha-adrenergic receptor-mediated response in brain. These data demonstrating that WB 4101 correlates with norepinephrine-stimulated cyclic AMP accumulation suggest that WB 4101 may bind to the membrane receptor sites mediating the alpha-adrenergic accumulation of cyclic AMP in rat cerebral cortex.
mesh_terms: D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004146:Dioxanes / Q000378:metabolism*; D004147:Dioxins / Q000378:metabolism*; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D010647:Phenyl Ethers / Q000378:metabolism; D051381:Rats; D011941:Receptors, Adrenergic / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
chemical_list: D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D004146:Dioxanes; D004147:Dioxins; D010647:Phenyl Ethers; D011941:Receptors, Adrenergic; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D000242:Cyclic AMP; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; D009638:Norepinephrine