title: Increase of serotonin receptors in rat uterus induced by estradiol.
abstract: [3H]Spiroperidol was used to label uterine membrane-binding sites that have the characteristics expected of serotonergic receptors. The characteristics of specific [3H]spiroperidol binding to the uterine membrane of 17 beta-estradiol-3-benzoate-treated ovariectomized rats were studied. The specific [3H]spiroperidol binding was rapid and reversible, and the half-maximal saturation, taken as the apparent dissociation constant (KD) for [3H]spiroperidol, was 5.16 +/- 0.24 (n = 12) nM [3H]spiroperidol. Scatchard plots of saturation curves of the specific [3H]spiroperidol binding were convex and the Hill coefficient was 2.06 +/- 0.11 (n = 12). Cinanserin, mianserin, metergoline (which are serotonergic antagonists), and serotonin (5-HT) inhibited the [3H]spiroperidol binding with apparent Ki values of 21.2, 14.1, 14.1, and 176.5 microM, respectively. Concentrations of 1 mM sulpiride (a dopaminergic antagonist) and dopamine reduced [3H]spiroperidol binding only 26 and 23%, respectively. 1 mM GTP reduced the potency of 5-HT (10(-6) - 10(-3) M) to displace bound [3H]spiroperidol. The uterine membranes were treated with various enzymes and protein-modifying reagents, and binding studies on the treated uterine membranes showed that protein(s), phospholipids, and N-acetyl-neuraminic acid in uterine membranes were important as specific binding sites of [3H]spiroperidol. Measurement of the specific binding of [3H]spiroperidol to uterine membranes from untreated and estradiol-treated ovariectomized rats showed that estradiol significantly increased the number of specific binding sites of [3H]spiroperidol, but did not change the apparent affinity of specific [3H]spiroperidol binding. Estradiol also did not change the dissociation constant or the number of binding sites for [3H]3-quinuclidinyl benzilate, which binds to muscarinic acetylcholine receptors. These findings suggest that [3H]spiroperidol mainly binds to 5-HT receptors in the uterine membrane of estradiol-treated ovariectomized rats. The finding that administration of estradiol significantly increased the number of [3H]spiroperidol-binding sites is consistent with the specific increase in the contractile response to 5-HT observed in isolated uterus from ovariectomized rats treated with estradiol.
mesh_terms: D000818:Animals; D002090:Butyrophenones / Q000378:metabolism*; D002369:Castration; D002462:Cell Membrane / Q000378:metabolism; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007700:Kinetics; D051381:Rats; D011919:Rats, Inbred Strains; D011985:Receptors, Serotonin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D013134:Spiperone / Q000378:metabolism*; D014599:Uterus / Q000187:drug effects / Q000378:metabolism*
chemical_list: D002090:Butyrophenones; D011985:Receptors, Serotonin; D004958:Estradiol; D013134:Spiperone