title: [3H]N-propylapomorphine and [3H]spiperone binding in brain indicate two states of the D2-dopamine receptor.
abstract: [3H]N-propylapomorphine ([3H]NPA) a dopaminergic catecholamine derivative, labels a sub-set of D2-dopamine receptors in bovine caudate particulate preparation. [3H]Spiperone, a dopamine receptor antagonist, labels twice as many sites as [3H]NPA. Dopaminergic ergots and potent neuroleptics compete for both radioactive ligands with similar high affinities. Catecholamines and catecholamine derivatives compete more potently for [3H]NPA binding than for [3H]spiperone binding. Guanyl nucleotides reduce both [3H]NPA binding and the high affinity phase of catecholamine and catecholamine derivative competition for [3H]spiperone binding. These results are similar to binding results reported in studies of two-state receptors linked to adenylate cyclase such as the beta-adrenergic receptors. These observations indicate that the D2-dopamine receptor in the brain may exist in two states and may be inversely coupled to brain adenylate cyclase activity.
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology; D001058:Apomorphine / Q000031:analogs & derivatives* / Q000378:metabolism; D001921:Brain / Q000378:metabolism*; D002090:Butyrophenones / Q000378:metabolism*; D002395:Catecholamines / Q000494:pharmacology; D002417:Cattle; D002421:Caudate Nucleus / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004876:Ergot Alkaloids / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D011954:Receptors, Dopamine / Q000378:metabolism*; D013134:Spiperone / Q000378:metabolism*
chemical_list: D014150:Antipsychotic Agents; D002090:Butyrophenones; D002395:Catecholamines; D004876:Ergot Alkaloids; D011954:Receptors, Dopamine; D013134:Spiperone; C009074:N-n-propylnorapomorphine; D006160:Guanosine Triphosphate; D000242:Cyclic AMP; D001058:Apomorphine