title: Expression of oxytocin receptors is greatly reduced in the placenta of heavy mares with retained fetal membranes due to secondary uterine atony.
abstract: BACKGROUND
  Fetal membrane retention can be a life-threatening condition and its incidence exceeds 50% in heavy draught mares. Although fetal membrane retention is commonly treated with repeated injections of oxytocin, based on the suggestion that it is caused mainly by secondary atony of the uterus, this treatment sometimes fails. This led us to ask if expression of oxytocin receptors differs in mares that retain fetal membranes due to secondary uterine atony.
  
  
  OBJECTIVE
  To determine whether expression of oxytocin receptors in equine placental tissues differs when heavy draught mares expel fetal membranes or retain them because of secondary uterine atony.
  
  
  METHODS
  Controlled study using archived tissues.
  
  
  METHODS
  Placental biopsies (containing the endometrium and allantochorion) were taken from 8 heavy draught mares during parturition. Four mares expelled fetal membranes shortly after foaling (control mares) and 4 mares retained them (expulsion time was >3 h from delivery). The 4 mares that retained fetal membranes had secondary atony of the uterus. The amount of oxytocin receptors was estimated by measuring the intensity of western blot bands. The presence and location of oxytocin receptors were determined by immunocytochemistry.
  
  
  RESULTS
  Oxytocin receptor expression was nearly 50 times less intense in mares with placenta retention due to secondary atony of the uterus and immunocytochemical staining was barely visible. In the control mares, oxytocin receptors were found in both epithelial and endothelial cells of the placenta and staining was most intense where the endometrium contacts the allantochorion.
  
  
  CONCLUSIONS
  Inadequate expression of oxytocin receptors may be a cause of uterine atony leading to fetal membrane retention.
authors: Department of Animal Reproduction with Clinic, Faculty of Veterinary Medicine, University of Warmia and Mazury, Olsztyn, Poland.
authors: A
authors: http://orcid.org/0000-0002-6595-5153
authors: A
authors: Rapacz-Leonard
authors: Department of Animal Reproduction with Clinic, Faculty of Veterinary Medicine, University of Warmia and Mazury, Olsztyn, Poland.
authors: A
authors: A
authors: Raś
authors: Department of Clinical Physiology, Faculty of Veterinary Medicine, University of Warmia and Mazury, Olsztyn, Poland.
authors: J
authors: J
authors: Całka
authors: Department of Animal Reproduction with Clinic, Faculty of Veterinary Medicine, University of Warmia and Mazury, Olsztyn, Poland.
authors: T E
authors: TE
authors: Janowski
mesh_terms: D000818:Animals; D016022:Case-Control Studies; D004420:Dystocia / Q000662:veterinary*; D005321:Extraembryonic Membranes / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation / Q000502:physiology*; D036801:Parturition / Q000502:physiology; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D018045:Receptors, Oxytocin / Q000235:genetics / Q000378:metabolism*; D014593:Uterine Inertia / Q000662:veterinary*
chemical_list: D018045:Receptors, Oxytocin
keywords: allantochorion; endometrium; horse; parturition; uterine inertia