Ulipristal blocks ovulation by inhibiting progesterone receptor-dependent pathways intrinsic to the ovary

Abstract

Ulipristal acetate (UPA), a progesterone receptor (PR) modulator, is used as an emergency contraceptive in women. Here, using a mouse model, we investigated the mechanism of action of UPA as an ovulation blocker. In mice, ovulation is induced ~12 hours following the treatment with exogenous gonadotropins, including human chorionic gonadotropin (hCG), which mimics the action of luteinizing hormone (LH). When administered within 6 hours of hCG treatment, UPA is a potent blocker of ovulation. However, UPA's effectiveness declined significantly when it was given at 8 hours post hCG. Our study revealed that, when administered within 6 hours of hCG, UPA blocks ovulation by inhibiting PR-dependent pathways intrinsic to the ovary. At 8 hours post hCG, when the PR signaling has already occurred, UPA is unable to block ovulation efficiently. Collectively, these results indicated that UPA, when administered within a critical time window following the LH surge, blocks PR-dependent pathways in the ovary to function as an effective antiovulatory contraceptive.

Figure 1.

Ulipristal acetate (UPA) inhibits ovulation after the initiation of luteinizing hormone (LH) signaling. A, Schematic diagram depicts the superovulatory protocol used in our experiments. In this paradigm, mice are treated with pregnant mare serum gonadotropin (PMSG) for 48 hours, mimicking follicle-stimulating hormone (FSH), to foster follicular development; subsequent administration of human chorionic gonadotropin (hCG), mimicking the effects of the LH, induces ovulation. Typically, ovulation occurs 11 to 12 hours following hCG treatment. The total number of oocytes is counted 18 hours later to evaluate the ovulatory response. B, Vehicle or UPA was administered intraperitoneally at 2, 6, or 8 hours after hCG injection, and the number of oocytes was counted 18 hours later to evaluate the ovulatory response. The data are represented as mean ± standard error of the mean (SEM).

Figure 2.

Ulipristal acetate (UPA) does not affect cumulus expansion and follicular development but inhibits follicular rupture. A, Hematoxylin and eosin (H&E) staining of ovarian sections from vehicle-treated mice at 5 hours after hCG injection shows cumulus expansion (panels a and b), at 11 hours the ovarian sections show expanded follicles (panel c), and at 18 hours the ovarian sections show many corpora lutea (panel d). B, H&E staining of ovarian sections from UPA treated mice at 5 hours after hCG injection shows cumulus expansion (panels a and b), at 11 hours the ovarian sections show expanded follicles (panel c), and at 18 hours the ovarian sections show unruptured follicles (panel d). The UPA was administered 2 hours after hCG. CC indicates cumulus cells; CL, corpus luteum; F, follicle; O, oocyte; UF, unruptured follicles.

Figure 3.

Ulipristal acetate (UPA) inhibits the expression of progesterone receptor (PR)-regulated genes during ovulation. Mice (n = 12) were subjected to superovulation as described in Materials and Methods section. Vehicle or UPA was administered intraperitoneally 2 hours after human chorionic gonadotropin (hCG) injection. Ovaries were collected at 11 hours after hCG injection and the total RNA was isolated. A, Real-time polymerase chain reaction (PCR) was performed to analyze the expression of PR-regulated genes, ET-2, ADAMTS-1, PPARγ, and Hif1α, in response to vehicle and UPA treatments. The level of Rplp0 was used as an internal control to normalize the gene expression. The values are presented as the mean fold induction ± standard error of the mean (SEM), *P < .01, **P < .001, and ***P < .0001. B, Real-time PCR was performed to analyze the expression of Ankrd1, Bdnf, Cnn3, Cyr61, Errfi1, Runx1, and Socs3, in response to vehicle and UPA treatments. The level of Rplp0 was used as an internal control to normalize gene expression. The values are presented as the mean fold induction ± standard error of the mean (SEM), *P < .01, **P < .001, and ***P < .0001.

Figure 4.

Expression profile of progesterone receptor (PR) and its target genes before and after human chorionic gonadotropin/luteinizing hormone (hCG/LH) treatment. A, Mice (n = 20) were subjected to superovulation as described in Materials and Methods sections. Ovaries were collected at 0 hours (without hCG), 4, 8, and 11 hours after hCG injection and the total RNA was isolated. Real-time PCR was performed to analyze the expression of PR, Bdnf, Socs3, and Cyr61. The level of Rplp0 was used as internal control to normalize the gene expression. The messenger RNA (mRNA) levels are expressed as mean fold induction ± standard error of the mean (SEM). B, Mice (n = 21) were subjected to superovulation as described in Materials and Methods section. Vehicle or ulipristal acetate (UPA) was administered intraperitoneally at 8 hours after hCG injection. Ovaries were collected at 11 hours after hCG injection and the total RNA was isolated. Real-time PCR was performed to analyze the expression of PR-regulated genes Bdnf, Cyr61, Errfi1, Runx1, Socs3, and PPARγ in response to vehicle and UPA treatments. The level of Rplp0 was used as an internal control to normalize the gene expression.