RESUMEN
RU486 is a partial progesterone and estrogen receptor antagonist, functioning to actively silence progesterone receptor gene-associated transcription. For this reason, it has been used as both a contraceptive and an abortive agent. In the present study, cellular and gene specific effects of RU486 were investigated in a rat model of early pregnancy, including key phases of the window of receptivity and early implantation. As these stages are hormonally regulated by progesterone and estrogens, the focus here was to elucidate the mechanism of action of a single dose of RU486, used as a postcoital contraceptive, to successfully prevent implantation of a viable blastocyst. Immunofluorescent techniques were used to examine the change in protein levels of PR in RU486-treated endometria at days 4.5, 5.5 and 6.5 of pregnancy. Changes in the Pgr gene expression level as a consequence of RU486 administration was evaluated using quantitative real-time reverse transcription polymerase chain reaction. The progesterone receptor gene and protein expression was ubiquitously decreased throughout pregnancy as a direct consequence of RU486 administration. The overall effects of postcoital RU486 administration during early pregnancy indicate highly effective inhibition of progesterone and estrogen effects on the endometrium, mediated by their receptors. More specifically, the expression and localization of the progesterone receptor mirrors that described in ovariectomized animal models, suggesting a hormonally under-stimulated endometrium. Clearly from the present study, the precise priming of the endometrium by progesterone, in preparation for blastocyst implantation, is severely impaired by RU486, thus predisposing the uterus to pregnancy failure.
Asunto(s)
Anticonceptivos Sintéticos Poscoito , Implantación del Embrión/efectos de los fármacos , Endometrio/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Mifepristona , Progesterona/antagonistas & inhibidores , Receptores de Progesterona/antagonistas & inhibidores , Animales , Anticonceptivos Sintéticos Poscoito/administración & dosificación , Endometrio/citología , Endometrio/metabolismo , Antagonistas del Receptor de Estrógeno/administración & dosificación , Femenino , Técnica del Anticuerpo Fluorescente Indirecta , Inyecciones Subcutáneas , Mifepristona/administración & dosificación , Embarazo , Progesterona/metabolismo , Transporte de Proteínas/efectos de los fármacos , Ratas Wistar , Receptores de Progesterona/genética , Receptores de Progesterona/metabolismo , Transducción de Señal/efectos de los fármacosRESUMEN
An increase in apoptotic activity has been observed in both the rabbit and the rat endometria following treatment with RU486. The aim of this study was to assess whether Bax and Bcl-2 signaling, in response to RU486, could be crucial role players mediating apoptosis in the rat uterus during early pregnancy. RU486 is a partial progesterone (P4) and estrogen receptor antagonist, functioning to actively silence P4 receptor gene-associated transcription. Although an increase in apoptosis as a result of RU486 administration has been previously reported in rabbits, the specific apoptotic factors and pathways involved in driving this process have not yet been established. Immunofluorescent techniques were used to determine protein expression levels of both Bax and Bcl-2 in RU486-treated endometria at days 4.5, 5.5 and 6.5 of pregnancy. The Bax/Bcl-2 index was used to determine the overall pro- or anti-apoptotic setting at each day of pregnancy, following RU486 administration. Changes in the Bax and Bcl-2 gene expression levels as a consequence of RU486 administration were evaluated using RT-qPCR. Both the protein and gene expression analyses suggest that RU486 induces a change toward an overall anti-apoptotic signal within the Bax/Bcl-2 pathway. These results suggest that the observed increase in apoptosis following RU486 administration is not driven by a shift in the Bax/Bcl-2 ratio toward cell death, when the P4 and estrogen receptors are partially inactivated by RU486, but is possibly regulated by another apoptotic pathway.