title: Characterization and localization of oxytocin receptors in the uterus and oviduct of the non-pregnant ewe using an iodinated receptor antagonist.
abstract: Some of the binding characteristics of a novel oxytocin receptor ligand 125I-labelled [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(ortho-methyl)-Tyr2,Thr4,Orn8,Tyr9-NH2]-vasotocin ([125I]OTA) have been determined in the sheep uterus. The compound was subsequently used for the autoradiographic localization of oxytocin receptors in the uterus and oviduct of the ewe. Specific binding of [125I]OTA to crude membrane fractions of ovine endometrium was time-dependent and was unaffected by the addition of cations to incubation media. Endometrial membranes contained a single population of saturable, high-affinity binding sites for the iodinated ligand (dissociation constant (Kd) 0.23 +/- 0.08 nmol/l) and unlabelled oxytocin competed with [125I]OTA for binding sites with high affinity (Kd 1.29 +/- 0.4 nmol/l) in the presence of Mg2+ In contrast, unlabelled OTA was able to compete with high affinity (Kd 1.13 +/- 0.16 nmol/l) in the absence of cation. Competition studies with a number of oxytocin analogues and related peptides and the tissue distribution of [125I]OTA binding sites also indicated that [125I]OTA bound to the ovine oxytocin receptor. This was further validated by autoradiographic studies which showed specific labelling with [125I]OTA to be greater to uterus and oviduct obtained from ewes which had been killed within 2 days of oestrus than to similar tissue from ewes killed during the luteal phase. In both the ampullary and isthmic regions of the oviduct and the myometrium, [125I]OTA binding sites were confined to smooth muscle. Endometrial binding sites for [125I]OTA were consistently located on the luminal epithelium and epithelial cells lining secretory glands.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Anatomy, School of Medical Sciences, University of Bristol.
authors.forename: V J
authors.initials: VJ
authors.lastname: Ayad
authors.forename: S E
authors.initials: SE
authors.lastname: Guldenaar
authors.forename: D C
authors.initials: DC
authors.lastname: Wathes
mesh_terms: D057911:Angiotensin Receptor Antagonists; D000818:Animals; D001345:Autoradiography; D004717:Endometrium / Q000737:chemistry; D005187:Fallopian Tubes / Q000737:chemistry*; D005260:Female; D010121:Oxytocin / Q000032:analysis* / Q000037:antagonists & inhibitors / Q000378:metabolism; D011485:Protein Binding; D011945:Receptors, Angiotensin / Q000032:analysis* / Q000378:metabolism; D018045:Receptors, Oxytocin; D012756:Sheep / Q000378:metabolism*; D013997:Time Factors; D014599:Uterus / Q000737:chemistry*
chemical_list: D057911:Angiotensin Receptor Antagonists; D011945:Receptors, Angiotensin; D018045:Receptors, Oxytocin; D010121:Oxytocin