title: Pregnancy increases ET-1-induced contraction and changes receptor subtypes in uterine smooth muscle in humans.
abstract: The purpose of the present study was to investigate whether pregnancy affects endothelin (ET)-1-induced contraction, the density ofET receptors, and the ratio of receptor subtypes (ET(A) and ET(B)) in uterine smooth muscle in humans. We also investigated which ET receptor subtypes mediate ET-1-induced contraction in the human uterus. In uterine membrane preparations, (125)I-labeled ET-1 ((125)I-ET-1) binding sites (Bmax) in pregnant women did not differ from those in age-matched nonpregnant women (596.2 +/- 107.1 vs. 512.1 +/- 167.7 fmol/mg protein). The dissociation constant (Kd) in pregnant women did not differ from that in nonpregnant women. Competitive displacement experiments with (125)I-ET-1 binding to the membranes using BQ-123 (ET(A) receptor antagonist) showed that the percentage of ET(A) receptors in uterine muscle was significantly higher in pregnant women than in nonpregnant women (P < 0.01). The calculated ratios of ET(A) to ET(B) receptors in pregnant and nonpregnant uteri were 92:8 and 68:32, respectively. Combination treatment with BQ-788 (ET(B) receptor antagonist) completely inhibited the BQ-123-resistant component of (125)I-ET-1 specific binding. ET-1 caused dose-dependent contractions in isolated human uteri from both pregnant and nonpregnant women. The maximum response was markedly greater in pregnant women than in nonpregnant women, whereas pD2 (-log[EC50]) values did not differ between pregnant and nonpregnant uteri. In pregnant human uterus, BQ-123 (10(-6) M) significantly shifted the dose-dependent curve of ET-1 response to the right, whereas BQ-3020 (ET(B) receptor agonist) did not cause contraction. These results suggested that ET-1-induced contraction of the human uterus is mediated through only ET(A) receptors and that ET-1-induced uterine contraction in humans is markedly increased during pregnancy. In addition, the present study suggests that, although (125)I-ET-1 Bmax are not altered during pregnancy, the proportion of ET(A) receptors is increased and that of ET(B) receptors is decreased in the pregnant human uterus.
authors.affiliation: Department of Obstetrics and Gynecology, Institutes of Medical Sciences, University of Tsukuba, Ibaraki, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Osada
authors.forename: H
authors.initials: H
authors.lastname: Tsunoda
authors.forename: T
authors.initials: T
authors.lastname: Miyauchi
authors.forename: Y
authors.initials: Y
authors.lastname: Sugishita
authors.forename: T
authors.initials: T
authors.lastname: Kubo
authors.forename: K
authors.initials: K
authors.lastname: Goto
mesh_terms: D000328:Adult; D001667:Binding, Competitive; D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology*; D016232:Endothelins / Q000378:metabolism; D005260:Female; D006801:Humans; D009130:Muscle, Smooth / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D010456:Peptides, Cyclic / Q000378:metabolism; D011247:Pregnancy / Q000502:physiology*; D017466:Receptors, Endothelin / Q000187:drug effects / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects*; D014599:Uterus / Q000378:metabolism*
chemical_list: D065128:Endothelin Receptor Antagonists; D019332:Endothelin-1; D016232:Endothelins; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D017466:Receptors, Endothelin; C075771:BQ 3020; C072247:cyclo(Trp-Asp-Pro-Val-Leu)