Labelling of vasopressin and oxytocin receptors from the human uterus

Abstract

Four labelled ligands, [ 3H]arginine vasopressin ([ 3H]AVP), [ 3H]oxytocin ([ 3H]OT), [ 3H]d(CH 2) 5[Tyr(Me) 2]AVP ([ 3H]VPA), and [ 125I)d(CH 2) 5[Tyr(Me) 2-Thr 4-Orn 8-Tyr(NH 2) 9]OT([ 125I]OTA)) and nine unlabelled analogues exhibiting enhanced selectivity for rat oxytocin (OT) and vasopressin (VP) receptors were used to characterize OT and VP receptors on myometrial membranes from non-pregnant and pregnant human uteri. On membranes from non-pregnant uteri, [ 3H]AVP, [ 3H]VPA, and [ 125I]OTA labelled with high affinity (K d values: 3.2, 2 and 0.8 nM, respectively) a major and apparently homogeneous population of sites, the ligand selectivity of which resembled that of rat V 1a VP receptors. On membranes from pregnant and non-pregnant uteri, [ 3H]OT labelled a single population of high-affinity sites that could be distinguished from VP receptors on the basis of ligand selectivity. Several analogues (in particular [ 125I]OTA) that are highly selective for rat OT receptors exhibited a much less pronounced selectivity for human OT receptors. Experiments with [ 3H]VPA allowed detection of VP receptors on myometrical membranes from pregnant uteri and confirmed that only OT but not VP receptors increase during pregnancy in humans.