title: Progesterone receptor isoform (A/B) ratio of human fetal membranes increases during term parturition.
abstract: OBJECTIVE
  The role of progesterone in the control of human parturition remains unsettled. Because there is no systemic progesterone withdrawal before the onset of labor, a 'functional progesterone withdrawal' has been proposed to be operative before human parturition. This may be accomplished by a change in the density of the progesterone receptor (PR) isoforms in myometrium and fetal membranes. The purpose of our study was to determine if spontaneous term labor is associated with changes of PR isoforms (PR-A and PR-B) in the fetal membranes.
  
  
  METHODS
  Fetal membranes were obtained from women undergoing elective cesarean delivery at term (not in labor group), and from women with a vaginal delivery (labor group). The expression of PR isoforms was assessed by Western blot analysis of amnion and chorio-decidua. Densitometric analysis of PR-A/PR-B ratio was performed. Immunohistochemistry with specific antibodies to PR-A and PR-B was done. Nonparametric statistics were used for analysis.
  
  
  RESULTS
  1) The predominant isoform of PR in women not in labor was PR-B, and PR-A in patients in labor. The ratio of PR-A/PR-B in fetal membranes was significantly higher in women in labor than in those not in labor (for amnion, median 4.3, range [0.9-8.4] vs median 0.4, range [0.3-2.6], P < .001; for chorio-decidua, median 2.0, range [1.1-19.2] vs median 1.2, range [0.1-2.0], P < .05). 2) Fetal membranes expressed both types of PR. 3) Immunohistochemistry showed the presence of PR-A and PR-B in the cytoplasm of amnion epithelial cells, chorion trophoblast, and decidual cells.
  
  
  CONCLUSIONS
  Human parturition at term is associated with changes in PR isoforms in the fetal membranes and, thus, a local 'functional progesterone withdrawal' may operate in human parturition through this mechanism.
authors.affiliation: Department of Obstetrics and Gynecology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Korea.
authors.forename: Soo-Young
authors.initials: SY
authors.lastname: Oh
authors.forename: Chong Jai
authors.initials: CJ
authors.lastname: Kim
authors.forename: Insuk
authors.initials: I
authors.lastname: Park
authors.forename: Roberto
authors.initials: R
authors.lastname: Romero
authors.forename: Yoo-Kyung
authors.initials: YK
authors.lastname: Sohn
authors.forename: Kyung Chul
authors.initials: KC
authors.lastname: Moon
authors.forename: Bo Hyun
authors.initials: BH
authors.lastname: Yoon
mesh_terms: D015153:Blotting, Western; D005321:Extraembryonic Membranes / Q000378:metabolism*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007743:Labor, Obstetric / Q000378:metabolism*; D011247:Pregnancy; D020033:Protein Isoforms; D011980:Receptors, Progesterone / Q000378:metabolism*
chemical_list: D020033:Protein Isoforms; D011980:Receptors, Progesterone; C101118:progesterone receptor A; C097314:progesterone receptor B