title: Dopamine D2 receptor binding in adrenal medulla: characterization using [3H]spiperone.
abstract: The possibility that dopamine may function as a neuromodulator or neurotransmitter in the adrenal gland, and not merely serve as a precursor to the catecholamines, has been suggested. If this hypothesis is correct, receptors for dopamine should be identifiable in the adrenal. The present work demonstrates the existence of a high-affinity receptor in adrenal medulla using [3H]spiperone as the radioligand to label the receptors. [3H]Spiperone bound rapidly, reversibly, and with high affinity to bovine adrenal medullary membranes. Scatchard analysis yielded a Kd of 0.09 nM and a Bmax of 51 fmol/mg protein. In competition binding experiments, dopaminergic antagonists were at least 100 times more potent in displacing [3H]spiperone from its binding sites than adrenergic or serotonergic receptor antagonists. Similarly, agonists at the dopamine receptor more readily competed for [3H]spiperone binding than other receptor agonist drugs tested. Furthermore, D2 selective antagonists and agonists were much more potent than D1 receptor ligands. These results suggest that [3H]spiperone may bind to a high-affinity D2 dopamine receptor in adrenal medulla.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D001667:Binding, Competitive; D002021:Buffers; D002417:Cattle; D066298:In Vitro Techniques; D007700:Kinetics; D010741:Phospholipases A / Q000494:pharmacology; D011954:Receptors, Dopamine / Q000032:analysis / Q000378:metabolism*; D017448:Receptors, Dopamine D2; D013134:Spiperone / Q000378:metabolism*; D014316:Tritium
chemical_list: D002021:Buffers; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D014316:Tritium; D013134:Spiperone; D010741:Phospholipases A