Oxytocin and vasopressin receptors in human and uterine myomas during menstrual cycle and early pregnancy

The purpose of this study was to determine the specificity and concentratio n of oxytocin (OT) and arginine vasopressin (AVP) binding sites in non-preg nant (NP) human and rhesus monkey endometrium, myometrium and fibromyomas, and to determine the cellular localization of OT receptor (OTR), Besides [H -3]AVP, [I-125]LVA, a specific VP1 receptor subtype antagonist, was used to determine vasopressin receptor (VPR) concentrations. Samples were obtained from 42 pre-menopausal and three pregnant women (5, 13 and 35 weeks gestat ion), and several NP and pregnant monkeys. Specificity of binding was asses sed in competition experiments with; unlabelled agonists and antagonists of known pharmacological potency. Cellular localization of OTR was determined by immunohistochemistry: In NP human uterine tissues, [H-3]AVP was bound w ith higher affinity and greater binding capacity than [H-3]OT, whereas in p regnant women and in NP and pregnant rhesus monkeys, uterine OT binding cap acity was greater, OT and AVP binding sites discriminated very poorly betwe en OT and AVP; [I-125]LVA blinding sites were more selective than [H-3]AVP. Their ligand specificity and binding kinetics indicated the presence of tw o distinct populations of binding sites for OT and AVP in primate uterus, E ndometrium of NP women and monkeys had low OTR and VPR concentrations. Myom etrial and endometrial OTR and VPR were down-regulated in midcycle and in e arly human pregnancy, they were up-regulated in the secretory phase and sec ond half of pregnancy. Immunoreactive OTR in NP uterus was localized in pat ches of myometrial muscle cells and small numbers of endometrial epithelial cells.