title: Endometrial prostaglandin synthases, ovarian steroids, and oxytocin receptors in mares with oxytocin-induced luteal maintenance.
abstract: Oxytocin (OXT) has been used to prolong the luteal phase in mares, but its mechanism of action is unknown. The aim of this study was to evaluate the effect of chronic exogenous OXT administration to mid-luteal phase mares on luteal maintenance. Also, endometrial expression of prostaglandin endoperoxide synthase 2 (PTGS2), prostaglandin F2α, E2and I2synthases (AKR1C3, PTGES, and PTGIS), oxytocin receptor (OXTR), progesterone receptor (PGR), and estrogen receptors 1 (ESR1) and 2 (ESR2) were assessed in mares experiencing luteal maintenance 2 weeks after chronic exogenous OXT administration. Control mares (n = 5; C group) received 6 mL of saline im, whereas OXT (60 units/mare) was administered im (n = 6; OXT group), every 12 hours, on days 7 to 14 postovulation. After endometrial biopsy in groups C (Day 10) and OXT (Day 24), luteolysis occurred within 3 or 6 days, respectively. Luteal maintenance took place in 4 of 6 (67%) of OXT-treated mares. Progesterone in C group was the highest on biopsy day (P < 0.05). In OXT mares, PTGS2, ESR1 (P < 0.05), PTGES, PTGIS, PGR, and ESR2 (P < 0.01) gene transcription decreased, whereas OXTR increased (P < 0.05) in comparison with the C group. In OXT-treated mares, endometrial ESR2 protein expression decreased (P < 0.05), but OXTR increased (P < 0.05) compared with control animals. In both experimental groups, PTGS2 was mainly immunolocalized in surface epithelium, whereas AKR1C3, PTGES, PTGIS, and PGR were in surface and glandular epithelia. ESR1 and ESR2 were found in glandular epithelium and OXTR in stromal cells. High immunolabeling for PTGES, PTGIS, PGR, and OXTR and low for ESR2 was detected in endometrium of OXT-group mares with extended diestrus. Prolonged luteal function associated with chronic OXT treatment may be related to different spatial expression of OXTR and PGR in the endometrium. The observed reduction of endometrial ESR2 may be responsible for the maintenance of PGR in luminal and glandular epithelium. Also, ESR2 may attenuate the transcriptional activity of ESR1 in mare endometrium. This study offers new knowledge on the endometrial expression of ovarian steroids and OXT receptors in OXT pharmacologically induced luteal maintenance in the mare.
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal; Department of Animal Science, Coimbra College of Agriculture, Coimbra, Portugal.
authors: Maria R
authors: MR
authors: Rebordão
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal; Department of Reproductive Immunology and Pathology, Institute of Animal Reproduction and Food Research of PAS, Olsztyn, Poland.
authors: António
authors: A
authors: Galvão
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal; Department of Animal Science, Coimbra College of Agriculture, Coimbra, Portugal.
authors: Pedro
authors: P
authors: Pinto-Bravo
authors: Department of Animal Science, Coimbra College of Agriculture, Coimbra, Portugal.
authors: Joana
authors: J
authors: Pinheiro
authors: Department of Animal Science, Coimbra College of Agriculture, Coimbra, Portugal.
authors: Sandra
authors: S
authors: Gamboa
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal.
authors: Elisabete
authors: E
authors: Silva
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal.
authors: Luísa
authors: L
authors: Mateus
authors: CIISA, Faculty of Veterinary Medicine, University of Lisbon, Lisbon, Portugal. Electronic address: gmlfdias@fmv.ulisboa.pt.
authors: Graça
authors: G
authors: Ferreira-Dias
mesh_terms: D000818:Animals; D003338:Corpus Luteum / Q000187:drug effects* / Q000502:physiology; D004967:Estrogens / Q000235:genetics / Q000378:metabolism; D005260:Female; D006736:Horses / Q000502:physiology*; D010053:Ovary / Q000502:physiology*; D010120:Oxytocics / Q000494:pharmacology; D010121:Oxytocin / Q000494:pharmacology*; D011372:Progestins / Q000235:genetics / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000235:genetics / Q000378:metabolism*; D011960:Receptors, Estrogen / Q000235:genetics / Q000378:metabolism; D018045:Receptors, Oxytocin / Q000235:genetics / Q000378:metabolism*; D011980:Receptors, Progesterone / Q000235:genetics / Q000378:metabolism
chemical_list: D004967:Estrogens; D010120:Oxytocics; D011372:Progestins; D011960:Receptors, Estrogen; D018045:Receptors, Oxytocin; D011980:Receptors, Progesterone; D010121:Oxytocin; D011451:Prostaglandin-Endoperoxide Synthases
keywords: Endometrium; Luteal phase; Mare; Oxytocin; Oxytocin receptor; Steroids receptors