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Mol Hum Reprod. 2019 Mar 2. pii: gaz013. doi: 10.1093/molehr/gaz013. [Epub ahead of print]

A single post-ovulatory dose of ulipristal acetate impairs post-fertilization events in mice.

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Instituto de Biología y Medicina Experimental (IBYME-CONICET), Buenos Aires, Argentina.
Instituto de Investigaciones Farmacológicas (ININFA-UBA-CONICET), Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
Laboratory of Reproductive Medicine, Biochemical Chemistry Area, School of Biochemical and Pharmaceutical Sciences, National University of Rosario, Rosario, Argentina.
Department of Obstetrics and Gynaecology, School of Medicine, University of Campinas (UNICAMP), Campinas, Brazil.


Ulipristal acetate (UPA) is a selective progesterone receptor modulator used for emergency contraception that has proven to be highly effective in preventing pregnancy when taken up to 120 h after unprotected sexual intercourse. Even though it may act mainly by delaying or inhibiting ovulation, additional effects of UPA on post-fertilization events cannot be excluded. Therefore, the aim of this study was to determine whether a single post-ovulatory dose of UPA could prevent pregnancy using the mouse as a pre-clinical model. Mated females received a single dose of UPA (40 mg/kg) on day E1.5 or E2.5 (E0.5: copulatory plug detection) and post-fertilization events were evaluated. Our studies revealed that UPA administration produced a significant decrease in the number of conceptuses compared to control. Moreover, UPA-treated females exhibited a lower number of early implantation sites on day E5.5, despite normal in vivo embryo development and transport to the uterus at E3.5. Administration of UPA produced histological and functional alterations in the uterine horns, i.e, a dyssynchronous growth between endometrial glands and stroma, with non-physiological combination of both fractions compared to controls, and a completely impaired ability to respond to an artificial decidualization stimulus. Altogether, our results show that the administration of a single post-ovulatory dose of UPA impairs mouse pregnancy probably due to an effect on embryo-uterine interaction, supporting additional effects of the drug on post-fertilization events. Although these studies cannot be performed with human samples, our results with the mouse model provide new insights into the mechanism of action of UPA as an emergency contraception method.


decidualization; embryo transport; emergency contraception; implantation; ulipristal acetate


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