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Occurrence of Estrogen Receptor in Bovine Placentomes Throughout Mid and Late Gestation and at Parturition¹

^a Klinik für Geburtshilfe, Gynäkologie und Andrologie der Groß- und Kleintiere mit Tierärztlicher Ambulanz, ^b Institut für Veterinär-Physiologie, Arbeitsgruppe Biomathematik und Datenverarbeitung, ^c Institut für Veterinär-Anatomie, -Histologie und -Embryologie, Justus-Liebig-Universität, D-35392 Giessen, Germany ^d Max-Planck-Institut für experimentelle Endokrinologie, D-30625 Hannover, Germany

The bovine placenta produces estrogens from the first trimester until the end of its life span. However, with the exception of the immediate prepartal and intrapartal phases, in which an involvement of placental estrogens has been suggested for the preparation of parturition, their function has not been elucidated yet. To test for a role of placental estrogens as local factors regulating placental growth and differentiation, placentomes from cows that were pregnant for 150, 220, 240, and 270 days, and parturient cows (3 animals per group) were screened immunohistochemically for the expression of estrogen receptor (ER). Indirect immunoperoxidase staining methods were applied using primary monoclonal antibodies (pmAbs) directed against the C-terminus (AER311, HT277) or the N-terminus (AER314, 1D5) of the ER molecule. Both types of pmAbs identified ER in stromal cells and capillary pericytes of the maternal caruncular septae. Using pmAb 1D5, the mean percentage of ER-positive caruncular stromal cells decreased from 39.0% ± 5.9% in pregnant cows to 17.5% ± 8.3% at parturition (P = 0.011). Only pmAb recognizing the C-terminus identified ER in the caruncular epithelium, in which positive reactions were found in all cells, with the exception of areas adjacent to the chorionic plate and to major chorionic villi, where the specific signal gradually faded and occasionally disappeared. No positive reactions were observed in the fetal part of the placentomes. The expression of ER in bovine placentomes was further confirmed by the detection of ER-specific mRNA by reverse transcriptase-polymerase chain reaction and by Western blot analysis. The results suggest a role for placental estrogens as paracrine factors involved in the regulation of placental growth and differentiation.

First decision: 23 March 2001.

¹ Supported by the German Research Foundation (DFG) grant SCHU 1195/1–1 and the Ewald und Hilde Berge-Stiftung.

² Correspondence: Gerhard Schuler, Klinik für Geburtshilfe, Gynäkologie und Andrologie der Groß- und Kleintiere mit Tierärztlicher Ambulanz, Justus-Liebig-Universität Giessen, Frankfurter Strasse 106, D-35392 Giessen, Germany. FAX: 049 641 29328; gerhard.schuler{at}vetmed.uni-giessen.de

³ Current address: Solvay Pharmaceuticals Research Laboratories, Hans-Böckler-Allee 20, D-30173 Hannover, Germany

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