Two classes of [3H]spiperone binding sites in bovine neurohypophysis: D-2 receptors and putative 5-HT2 receptors.
Binding of [3H]spiperone was studied in membranes obtained from bovine neurohypophyses devoid of intermediate lobe tissue. Non-linear Scatchard plot suggested the presence of more than a single class of binding sites. Competition experiments using ketanserin, a ligand selective for 5-HT2 receptors, were carried out to ascertain whether serotonergic, in addition to dopaminergic receptors, might be responsible for the heterogeneity of [3H]spiperone binding. Computer-assisted modeling suggested the presence of two classes of binding sites for ketanserin (Kd = 1.6 +/- 0.2 and 366.7 +/- 20.5 nM, respectively). The Kd value for ketanserin binding to the high-affinity sites, as well as the Kd of [3H]spiperone for these sites suggested by the 2 sites model indicate that they represent serotonin 5-HT2 receptors. The [3H]spiperone Kd at the ketanserin low-affinity sites (65 +/- 7 pM) and the rank order of inhibitory potencies for several antagonists show that the low-affinity sites represent dopamine D-2 receptors.
Treiman
M
M
Institute of Medical Physiology C, University of Copenhagen, Panum Institute.
Andersen
P H
PH
D000818:Animals; D014150:Antipsychotic Agents / Q000378:metabolism; D001667:Binding, Competitive; D002417:Cattle; D007650:Ketanserin / Q000378:metabolism; D016018:Least-Squares Analysis; D010904:Pituitary Gland, Posterior / Q000378:metabolism*; D011869:Radioligand Assay; D011954:Receptors, Dopamine / Q000032:analysis*; D017448:Receptors, Dopamine D2; D011985:Receptors, Serotonin / Q000032:analysis*; D013134:Spiperone / Q000378:metabolism*
D014150:Antipsychotic Agents; D011954:Receptors, Dopamine; D017448:Receptors, Dopamine D2; D011985:Receptors, Serotonin; C031611:spiroperidol receptor; D013134:Spiperone; D007650:Ketanserin