Effect of the antiprogestin RU486 on human ovarian steroidogenesis

Effect of progesterone on in vitro meiotic maturation of canine oocytes associated with Cx37 and Cx43 gene expression

Progesterone (P4) concentrations in canines are exceptionally high in the periovulatory period. However, the mechanisms by which P4 modulates final oocyte development in dogs remain to be characterized. The aim of this study was to evaluate the effect of P4 on meiotic development related to the gene expression of connexin 37 (Cx37) and connexin 43 (Cx43) in the canine cumlus oocyte complexes (COCs). COCs were isolated from 120 canine ovaries after a routine ovariohysterectomy. In each experiment, groups of COCs retrieved from the antral follicles were subjected to in vitro maturation (IVM) for 72 h without (control) or with P4 (50 μg/mL and 100 μg/mL) or the P4 receptor antagonist, aglepristone (RU534 at 1 μM and 10 μM). Some of the COCs recovered (from each group) after 72 h of IVM were subjected to meiotic evaluation; the remaining COCs, and those not subjected to IVM, were used to analyze the gene expression of Cx37 and Cx43 by qPCR. The results were evaluated using ANOVA. The addition of P4 increased (P < 0.05) the meiotic development compared to that in the control or aglepristone groups. The highest (P < 0.05) percentage of oocytes in the MII stage was observed upon P4 supplementation. In contrast, the highest percentage (P < 0.05) of oocytes arrested in the GV stage and the lowest (P < 0.05) percentages in the MII stage were observed for COCs cultured with aglepristone. Although a significant decrease in the mRNA levels of both connexins was observed after culturing, no effect on Cx37 and Cx43 gene expression was observed when exogenous P4 was added compared to those of the control group. However, COCs cultured with aglepristone exhibited higher (P < 0.05) expression of Cx37 and Cx43 than COCs in the control IVM-group, regardless of the concentration. In conclusion, our results suggest that a high dosage of P4 during IVM enhances the nuclear maturation of canine oocytes without altering the gene expression levels of Cx37 and Cx43. However, the increase in their expression upon treatment with a P4 antagonist indicates an in vivo role for this hormone in the endogenous modulation of both Cx37 and Cx43.

Progesterone receptor antagonists Org 31710 and RU 486 increase apoptosis in human periovulatory granulosa cells

OBJECTIVE

To investigate if progesterone receptor (PR)-mediated effects are involved in regulating the susceptibility to apoptosis in LH receptor-stimulated human luteinizing granulosa cells.

DESIGN

Laboratory study.

SETTING

Göteborg University and an in vitro fertilization laboratory of a university hospital.

PATIENT(S)

Women undergoing oocyte retrieval for in vitro fertilization after ovulation induction with gonadotropins.

INTERVENTION(S)

Luteinizing granulosa cells were isolated from follicular aspirates after oocyte removal. The cells were treated with or without RU 486 (1 microM-100 microM), Org 31710 (1 microM-100 microM), progesterone (1 nM-10 microM), dexamethasone (0.5 microM-100 microM), dihydrotestosterone (1 nM-25 microM), RU 486 (10 microM-100 microM) + dexamethasone (50 microM), and picrotoxin (1 microM-100 microM) and were cultured under serum-free conditions.

MAIN OUTCOME MEASURE(S)

Measurement of caspase-3 activity; detection of internucleosomal DNA fragmentation using gel electrophoresis and fluorospectrophotometry; progesterone analysis of spent medium.

RESULT(S)

Addition of the PR antagonists RU 486 or Org 31710 in vitro to human luteinizing granulosa cells caused an increase in caspase-3 activity and a dose-dependent increase in internucleosomal DNA fragmentation. No effect on DNA fragmentation was seen after addition of dexamethasone, dihydrotestosterone, or picrotoxin.

CONCLUSION(S)

Nuclear PR-mediated effects are involved in regulating the susceptibility to apoptosis in LH receptor-stimulated human luteinizing granulosa cells.

Flow cytometry of porcine ovarian cells: antiprogestins play an important role in progesterone receptor upregulation

To investigate the mechanism of antiprogestins in the regulation of ovarian function, a dual-chamber culture system was prepared with the amnion membrane of human placenta. Isolated porcine granulosa and thecal cells were grown on both sides of the amnion and co-cultured with or without RU486 and ZK98, 734. After 48 h incubation, the progesterone receptor (PR) and estrogen receptor (ER) of both cells were detected by flow cytometry. Progesterone and estradiol concentrations in the media were measured by radioimmunoassay. The results showed that antiprogestins increased PR contents in both cells; no significant change was found for ER. At the same time the progesterone and estradiol production by granulosa cells was inhibited; the progesterone production by thecal cells was reduced also. These data suggest that progesterone regulates progesterone synthesis. This autocrine/paracrine action may be the approach through which progesterone controls PR upregulation. It could be one mechanism for the inhibition of follicle development and steroidogenic function by antiprogestins.

Expression of steroid receptors and steroidogenic enzymes in the baboon (Papio anubis) corpus luteum during the menstrual cycle and early pregnancy

As estrogen and progesterone are proposed regulators of luteal function, this study was undertaken to correlate the presence of receptors for these steroids with luteal function during early pregnancy. Corpora lutea (CL) were obtained from nonpregnant baboons during the midluteal [ML; days 7-8 postovulation (PO)] and late luteal (LL: days 11-12 PO) phases of the menstrual cycle or from pregnant baboons on days 18, 25, 29, or 31-33 PO. Estrogen and progestin receptors (ER and PR, respectively) and 3 beta-hydroxysteroid dehydrogenase (3 beta HSD) were detected by immunocytochemistry using specific monoclonal (H222 for ER; JZB39 for PR) or polyclonal (S683 for 3 beta HSD) antibodies. In addition, ribonucleic acid (RNA) was extracted from CL, processed for Northern blot analysis, and probed with complementary DNAs to human PR, human 3 beta HSD, and rat aromatase. Levels of messenger RNA (mRNA) for 3 beta HSD were quantified by laser densitometric scanning, and the data were normalized to the expression of a housekeeping gene (glyceraldehyde-3-phosphate dehydrogenase) to correct for loading differences. CL did not demonstrate specific nuclear, stain for ER at any stage of the menstrual cycle or pregnancy. In contrast, PR-positive cells were present during the ML phase, but decreased during the LL phase (P < 0.05). PR-positive cells were maintained during early pregnancy at levels comparable to the ML phase (P < 0.05). Staining for 3 beta HSD was present at all stages of the cycle and pregnancy. Although the percent of 3 beta HSD-positive cells appeared to decrease as pregnancy proceeded, this was not statistically different (P > 0.05). The complementary DNA to PR hybridized to multiple transcripts (approximately 4.4, 3.1, 1.6, and 0.95 kilobases) in CL of the cycle. A single transcript (approximately 1.8 kilobases) for 3 beta HSD was present in CL at all stages of the cycle and pregnancy. The level of 3 beta HSD mRNA was highest during the ML phase and declined significantly (P < 0.05) during the LL phase and early pregnancy. Three transcripts (approximately 3.6, 3.0, and 1.7 kilobases) for aromatase were detected in CL of the cycle and pregnancy. Aromatase mRNA increased during early pregnancy. These results support the concept of PR-mediated events, but not ER-regulated processes in the primate CL. Further-more, the data suggest that the steroidogenic enzymes 3 beta HSD and aromatase are differentially regulated during early pregnancy.

Mifepristone and ovarian function

In summary, RU 486 has been a powerful instrument in delineating progesterone action on the ovary. However, early experiments using RU 486 must be interpreted with the understanding that systemic administration of the antiprogestin may have had extraovarian sites of action, such as at the hypothalamic-pituitary axis or at the adrenal, that in turn led to indirect ovarian responses. Treatment with progesterone, agonist, or antagonist at periods during which the ovary lacks progesterone receptors would further suggest extraovarian sites of action or nongenomic mechanisms of action. Furthermore, the dose of ligand or antagonist administered and the hormonal milieu at the time of administration may dictate the ovarian response (Espey L, personal communication). For example, low doses of exogenous progesterone may elicit a biologic response, whereas high doses are without effect or may inhibit the biologic effect observed at lower doses. Although RU 486 is classically described as an antiprogestin, agonist actions have been observed in addition to its the well documented antiglucocorticoid effects. All of these variables may contribute to the confounding observations of progesterone and RU 486 action on the ovary. Regardless of these caveats, experimental paradigms have demonstrated that RU 486, either indirectly or directly, regulates ovarian folliculogenesis, stimulates and/or inhibits steroidogenesis depending on the species and time of RU 486 administration, inhibits ovulation, and modulates luteal function. These findings supports a progesterone-dependent mechanism in these varied aspects of ovarian function.

Antiprogesterone (RU486) effects on metalloproteinase inhibitor activity in human and rat granulosa cells

OBJECTIVE

To determine if granulosa cells are a source of metalloproteinase inhibitor activity and whether P regulates this activity.

DESIGN

Inhibitor activity was measured in media from human and rat granulosa cells cultured with the antiprogesterone mifepristone (RU486). Human granulosa cells were obtained at the time of oocyte retrieval from gonadotropin-stimulated patients after hCG administration. Rat cells were collected from gonadotropin-primed animals before the LH surge. Human and rat cells were cultured for 24 hours in the absence or presence of LH (100 ng/mL or 3.3 nmol/L) and/or RU486 (5 microM or 50 microM). Inhibitor activity and P were measured in the media.

SETTING

Reproductive Endocrinology Laboratories, University of Kentucky.

RESULTS

Media from human granulosa cells contained metalloproteinase inhibitor activity and the addition of LH did not change this activity. RU486 at 50 microM decreased inhibitor activity in cells cultured in the absence or presence of LH (0.59 +/- 0.12- and 0.24 +/- 0.18-fold change, respectively, versus control cultures; mean +/- SEM). In rat granulosa cells, inhibitor activity increased with LH treatment (1.97 +/- 0.12-fold change). RU486 decreased the activity present in cells cultured in the presence of LH. Progesterone production was stimulated by LH in both human and rat granulosa cells (3.71 +/- 0.90- and 7.18 +/- 0.24-fold change, respectively). In the human cells, RU486 inhibited P production whereas RU486 stimulated P production in the rat cells.

CONCLUSIONS

These findings demonstrate for the first time that human granulosa cells are a source of metalloproteinase inhibitor activity. The decrease in granulosa cell-derived inhibitor activity by RU486 suggests that P stimulates inhibitor activity. Thus, P may regulate proteolysis associated with follicular rupture via its ability to stimulate granulosa cell production of metalloproteinase inhibitors. Differences in P production between the human and rat cells may be due to differences in hormonal stimulation regimens (i.e., hCG exposure).

Dose-response relationships of RU 486

Clinical experience has indicated that the effects of RU 486 can be divided into dose-dependent and dose-independent effects. Examples of the dose-dependent effects include the antiglucocorticoid effects of RU 486, whereas pregnancy termination or dilatation of the cervix can be considered dose-independent with the various regimens tested so far. Following oral intake in man, the serum levels of RU 486 are in the micromolar range, and the half-life is approximately 30 hours. The concentrations of RU 486 in myometrial tissue are approximately one-third of those measured in serum. However, due to saturation of alpha 1-acid glycoprotein (AAG), the serum binding protein for RU 486, the serum levels remain similar within the dose range of 100-800 mg of RU 486. The unbound RU 486 is metabolized by two-step demethylation or by hydroxylation. The demethylated and hydroxylated metabolites of RU 486 retain considerable affinities of 9-21% towards the human progesterone receptor, and 45-61% towards the human glucocorticoid receptor (RU 486 = 100%), suggesting a biological role for the metabolites. Rat serum lacks a specific binding protein for RU 486. Even though the levels of RU 486 in rat adipose tissue are 40 times as high as those seen in serum, the concentrations of RU 486 in rat brain are only 28% of the serum levels. This indicates that diffusion of RU 486 into the central nervous system is restricted by the blood-brain barrier. Hence, the dose-dependency of certain centrally mediated effects of RU 486 might be explained by the limited diffusion of RU 486 into hypothalamic/hypophyseal sites, which seem to be reached only after ingestion of high doses of RU 486. However, the peripheral effects of RU 486, such as termination of pregnancy, are mediated via steroid receptors in target tissues. This suggests that similar biological effects can be attained at considerably lower doses than the ones currently in use.

Inhibition of induction of 20 alpha-hydroxysteroid dehydrogenase activity in rat corpora lutea in vitro by the progesterone antagonist RU486

To determine if the antiprogestagen RU486 has a direct effect on luteal progesterone secretion, whole corpora lutea or dispersed luteal cells were incubated in the presence of RU486. Whole corpora lutea, isolated from rats at day 5 of pseudopregnancy, were incubated individually in hormone-free medium. The concentrations of progesterone and 20 alpha-dihydroprogesterone in the medium plus corpus luteum was measured before and after 24 h of incubation. In the absence of RU486 the concentration of 20 alpha-dihydro-progesterone increased, while that of progesterone remained unchanged. In the presence of RU486 (230 microM) the concentration of both progesterone and 20 alpha-dihydro-progesterone was increased. Dispersed luteal cells were incubated for 24 h in the presence of various amounts of RU486. In the absence and in the presence of 0.2 and 2.3 microM RU486 a high ratio between 20 alpha-dihydro-progesterone and progesterone was found, while in the presence of 23 microM RU486 the concentrations of progesterone and 20 alpha-dihydro-progesterone were equal. 20 alpha-Hydroxysteroid dehydrogenase (20 alpha-HSD) activity measured in luteal homogenates started to increase between 6 and 12 h of incubation. This increase could be prevented after incubation of the corpora lutea in the presence of 23 or 230 microM RU486 for 24 hrs. It is concluded that the progesterone antagonist RU486 can have a direct effect on luteal progesterone production. RU486 prevents the increase in 20 alpha-HSD activity that normally occurs during in vitro incubation. However, since these effects in vitro can only be obtained with high concentrations of RU486, it is unlikely that this antiluteolytic effect plays a role after injection of RU486 in vivo.

Contragestion and other clinical applications of RU 486, an antiprogesterone at the receptor

RU 486, a steroid with high affinity for the progesterone receptor, is the first available active antiprogesterone. It has been used successfully as a medical alternative for early pregnancy interruption, and it also has other potential applications in medicine and for biochemical and pathophysiological endocrine research.

Anti-progesterones: background and clinical physiology

The development of anti-progesterones has provided a probe to examine the role of progesterone both in the normal cycle and in pregnancy. The most widely used of these agents, mifepristone, appears to act both directly at the endometrial progesterone receptor, and centrally by reducing circulating gonadotrophin concentrations. In addition, ovarian steroidogenesis may be modified. The clinical application of these agents for the interruption of pregnancy will be considered in the following chapters.