The effect of RU486 and progesterone on luteal function during pregnancy

In order to investigate the role of progesterone in the maintenance of pregnancy, an anti-progesterone agent, RU486 (RU) was injected subcutaneously into pregnant rats on day 12 (D12), and morphological changes of the uterus as well as endocrinological changes were observed. In all rats injected with RU, abortion occurred with macroscopic and microscopic intrauterine hemorrhage and degeneration or delivery of conceptuses. Endocrinologically, the levels of progesterone decreased rapidly 48 hours after the injection, while the levels of estradiol showed a tendency to increase. As progesterone is mainly produced by the corpus luteum but not by the placenta in rats, the decrease in progesterone is suspected to be due to luteolysis. Then in order to clarify the mechanism of luteolysis induced by RU and the effects of progesterone on this phenomenon, the dynamics of the luteotrophic factors (estradiol, LH, PRL) and specific binding capacity of the ovaries to LH/hCG were investigated in D7 pregnant rats treated with RU 1 mg/kg alone (RU group) or with both RU 1 mg/kg and progesterone 50mg/kg (RU + P group). The serum levels of progesterone in the RU group decreased significantly after 72 hours of administration, while those in the RU + P group remained within the levels of the control group. However, serum levels of luteotrophic factors in the RU group did not decrease, and some of them were even higher than those in the control group. In the RU + P group, luteotrophic factors remained within control levels. On the other hand, the specific bindings of LH/hCG to ovarian homogenates decreased significantly after 72 hours in the RU group. But in the RU + P group, the specific bindings were kept at the same levels as the controls. Scatchard analysis of these results disclosed that in the RU group, both affinity and numbers of receptors decreased compared to the controls, and that in the RU + P group only affinity decreased transiently and afterwards recovered quickly. From these results, it is concluded that deterioration of affinity and numbers of ovarian LH/hCG receptors seems to be one of the factors which induce luteolysis in pregnant rats treated with RU, and that progesterone can spare the effect of RU on the corpus luteum during pregnancy.     

Differential interaction of RU486 with the progesterone and glucocorticoid receptors

Steroid hormone receptor antagonists are widely used in clinical medicine, but their use is often complicated by the lack of receptor specificity to presently available drugs. We previously demonstrated an important role of a widely conserved helix 3 (H3)-helix 5 (H5) interaction in determining the sensitivity and specificity of steroid hormone receptors to receptor agonists. Intriguingly, the same H3 residues also play a crucial role in receptor antagonism; mutation of these residues alters the response of these receptors to antagonists. Given the close interaction of H3 and H5 residues at this site, we asked whether H5 residues might also play a role in the sensitivity of these receptors to antagonists. We demonstrate here that modification of H5 residues produces marked changes in the sensitivities of the glucocorticoid and progesterone receptor (PR) to RU486 antagonism. Moreover, while we confirm previous reports that alteration of the H3 residue, Gly 722 prevents RU486-mediated inhibition of the PR, we show that the corresponding substitution in the glucocorticoid receptor does not inhibit RU486-mediated receptor antagonism. Taken together, our data support the notion that RU486 binds differently to these two receptors, providing a potential target for the design of more specific antiglucocorticoid and antiprogestin drugs.     

Effects of the progesterone antagonist RU486 on ovarian activity in the rat

Adult female rats were treated for 2 or 4 weeks with the progesterone antagonist RU486 to study its effect on the regulation of ovarian function. In rats with 5-day ovarian cycles, the vaginal cyclicity disappeared. Uninterrupted vaginal cornification emerged within 4 days after the start of treatment and cornification persisted for the whole period of treatment. It took more than 2 weeks after cessation of 2-4 weeks of treatment before 5-day vaginal cycles reappeared. Ovarian weights increased rapidly resulting from the accumulation of large numbers of corpora lutea. In addition, the ovaries developed occasional follicular cysts which could reach an extremely large size (2 mm or more). Analysis of serial histological sections of ovaries, combined with plasma concentrations of estradiol-17 beta and progesterone, indicated cyclic ovulation and corpus luteum formation together with persistence of functional activity of already existing and newly formed corpora lutea. RU486 seems to have the unique property of dissociating cessation of luteal activity and ovulation in rats. After treatment with RU486, pituitary enlargement and mammary gland alveolar development were observed. It is hypothesized that these effects result from unopposed estrogen action on PRL secretion. The effects of RU486 are reversible: 4 to 5 weeks after the end of treatment ovarian activity seems normal (as evidenced by reduction of ovarian weights and 5-day vaginal cycles) except for the presence of occasional large follicular cysts which may require longer periods for their regression.     

Expression and localization of the progesterone receptor in mouse and human reproductive organs

The effects of gonadotropins on progesterone receptor (PR) expression and localization in the mouse oviduct, uterus, and ovary was examined. In the oviduct ciliated epithelial cells of adult mice and human revealed a unique PR localization to the lower half of the motile cilia whereas the nuclei were unstained or faintly stained. Pubertal female mice were further studied by confocal laser scanning microscopy and western blotting before and after injection with FSH and LH followed by human chorionic gonadotropin (hCG) injection after a 48-h period. PR immunolocalization to the oviduct cilia was greatly increased in pubertal mice upon hCG stimulation. In neighboring goblet cells, the PR staining was confined to the nuclei. Nuclear PR localization was evident in epithelial cells of the uterus as well as in a fraction of stromal and muscle cells. Staining intensity and number of stained cells was not affected by hormone stimulation. In the ovary, weak PR immunolocalization was observed in unprimed animals but increased significantly after hCG stimulation. In granulosa cells of preovulatory follicles PR was exclusively observed in mural cells, whereas cumulus cells remained negative. At all stages examined, primary granulosa cell cilia lacked PR staining. SDS-PAGE and western blotting analysis of tissues from oviduct, uterus, and ovary confirmed antibody specificity, and identified two bands corresponding to the PR isoforms PR-A and PR-B. Upon hCG stimulation, a new band cross-reacting with anti-PR emerged above the PR-A form in oviduct fractions, suggesting LH-induced phosphorylation of PR-A. We suggest that ciliary PR in the oviduct plays a role in progesterone signaling after ovulation, possibly via non-genomic events. These novel findings warrant further studies of oviduct and postovulatory signaling events and suggest a sensory role for oviduct cilia in the process of oocyte transport/fertilization.     

Effects of RU486 on progesterone secretion by human preovulatory granulosa cells in culture

The effects of RU486 on progesterone synthesis were studied in human preovulatory granulosa cells in culture. No effect was observed at 1 and 10 micrograms/mL, but at 100 micrograms/mL, RU486 inhibited the simulation of progesterone secretion induced by LH and cAMP. It is suggested that the main target of RU486 is the cytochrome P450scc function [catalyzing the formation of pregnenolone (D5P) from cholesterol], since no accumulation of D5P or hydroxy derivatives of progesterone was observed. As RU486 is an antiglucocorticosteroid and antiprogesterone agent, the effects of dexamethasone and progesterone were also investigated. Dexamethasone did not modify progesterone secretion, but progesterone inhibited its own synthesis in both the presence and absence of LH. Thus, under these experimental conditions RU486 displayed a progesterone-like effect. However, since the effect of RU486 was observed only at a concentration around 10(-4) M, the mechanism of action may not involve a receptor pathway and may not apply to most clinical circumstances.     

Effects of the antiglucocorticoid RU 486 on adrenal function in dogs

We studied the antiglucocorticoid effects of RU 486 given orally in doses of 5 (low), 20 (intermediate), and 50 mg/kg (high) daily for 10 days to seven female mongrel dogs. No changes in plasma ACTH or cortisol levels were produced by the 5 mg/kg dose. Plasma ACTH levels increased 3-fold with both intermediate and high dosages. Plasma cortisol levels rose 4-fold (P less than 0.05) within 2 days of commencing the high dose schedule and within 3 days with the intermediate dosage. Plasma aldosterone concentrations increased significantly only with the highest dose schedule. Plasma RU 486 levels rose progressively during the 10 days of RU 486 administration and with the highest dose remained elevated for 7 days after it was stopped. Plasma RU 486 levels measured by RIA and high pressure liquid chromatography were comparable. The monodemethylated metabolite of RU 486 changed in parallel to the parent compound. During the high dose of RU 486, there was a 4% increase in body weight, with a reduction in hematocrit and plasma protein concentration. Plasma electrolyte levels and osmolality did not change. We conclude that in dogs a daily RU 486 dose of 5 mg/kg does not alter adrenal function, whereas higher doses (20 and 50 mg/kg) induce increases in plasma ACTH and cortisol concentrations. Despite the blockade of glucocorticoid receptors by RU 486, the presence of isotonic hypervolemia suggests that there was no functional deficiency of cortisol at the renal tubule or it was overshadowed by augmented mineralocorticoid production and action.     

RU 486 (mifepristone): induction of dose dependent elevations of estradiol receptor in endometrium from ovariectomized monkeys

This study was designed to investigate the effect of the anti-progestin RU 486 on estradiol receptor concentrations in the endometrium of monkeys given physiologic estrogen replacement therapy. Estradiol-17 beta (E2) silastic implants were inserted infrascapularly into 12 long-term ovariectomized cynomolgus monkeys (Macaca fascicularis) resulting in an average peripheral serum level of approximately 100 pg/ml estradiol. On day 6 of E2 treatment four treatment groups were initiated: Group I--estradiol implants only; Group II--estradiol implants plus 11 mumol progesterone/kg bodyweight in sesame oil via im injections on days 6,7,8; Group III--estradiol implants plus 2.2 mumol RU 486/kg in sesame oil via im injections on day 6,7,8; Group IV--estradiol implants plus 11 mumol RU 486/kg via im injections on day 6,7,8. On treatment day 9 endometrial biopsies were removed by hysterotomies. Cytosolic and nuclear estradiol receptor contents of tissues were estimated by charcoal method. In Group I, the tissue contained 376 +/- 123 pmol bound H-E2/g protein; the nuclear portion was about 16%. In Group II, the tissue contained 216 +/- 64 pmol bound 3H-E2/g protein; the nuclear portion was only 8%. In Group III, tissue contained 654 +/- 47 pmol bound H-E2/g protein; the nuclear portion was about 22%. In Group IV, the tissue contained 1198 +/- 172 pmol bound 3H-E2/g protein; the nuclear portion was about 17%. Scatchard plot analysis indicated a Kd app of 1.04 x 10(-9) M. This study demonstrates that after physiologic E2 replacement therapy estradiol receptor concentrations rise dramatically following anti-progestin treatment; this effect was dose dependent.     

The effects of RU 486 on immune function and steroid-induced immunosuppression in vitro

The effect of RU 486 [17 beta-hydroxy-11 beta-(4-dimethylamino-phenol)17 alpha-(prop-1-ynyl)estra- 4,9diene-3-one] on [3H]thymidine incorporation into Concanavalin-A-stimulated human peripheral blood mononuclear cells and its influence on the suppressive effects of cortisol and progesterone were investigated. Cortisol suppressed lymphocyte thymidine incorporation at 10(-5), 10(-6), and 10(-7) M (17.6%, 20%, and 38% of control, respectively; P less than 0.01). Cortisol-induced suppression was reversed when low concentrations of RU 486 (10(-7) and 10(-6) M) were added. RU 486 at 10(-5) M further suppressed lymphocyte thymidine incorporation when added to cultures with cortisol. Progesterone significantly inhibited lymphocyte thymidine incorporation at 10(-5) M (8.2% of control; P less than 0.01). No reversal of progesterone-induced suppression of thymidine incorporation was seen when RU 486 was added to cultures; rather, further suppression of thymidine incorporation was seen. RU 486 alone in culture at concentrations achieved therapeutically (10(-5) M) significantly inhibited thymidine incorporation (7.2% of control; P less than 0.01). These findings suggest that RU 486 may have dose-dependent mixed agonist/antagonist effects on cortisol-induced immunosuppression. The lack of an antagonist effect of RU 486 on progesterone suggests that progesterone's immunosuppressive effects may not be receptor mediated. Finally, our findings would suggest that some immunosuppression may be seen at currently used doses of RU 486.     

RU486, a progestin and glucocorticoid antagonist, inhibits the growth of breast cancer cells via the progesterone receptor

The progestin and glucocorticoid antagonist RU486 was tested on the growth of several cell lines in culture. RU486 inhibited the growth of two progesterone receptor (RP) positive human breast cancer cell lines (MCF7 and T47D). The antiproliferative effect was dose dependent and its magnitude correlated with the RP content of the tested cells (T47D greater than estradiol-primed MCF7 greater than withdrawn MCF7). Cell growth inhibition was not prevented by the addition of dexamethasone, dihydrotestosterone, or estradiol, but the cells were rescued by low concentrations of the progestin R5020. RU486 had no effect on the growth of two RP negative human breast cancer cell lines and a rat fibroblast cell line. Moreover, RU486 had no progestin agonist activity in T47D cells when evaluated by measuring the 35S-labeling of two progestin-regulated proteins with mol wts of 48,000 and 250,000, but it totally prevented the induction of these two proteins by R5020. In conclusion, RU486 selectively inhibited the growth of human breast cancer cell lines with unoccupied RP sites and its effect was correlated with the RP concentration of these cells. We propose that RU486 is a RP-targeted drug of potential utility in breast cancer treatment.     

Effects of RU 486 on hippocampal slice electrophysiology in normal and adrenalectomized BALB/c mice

Modulation of the electrophysiological properties (amplitude, latency, paired-pulse facilitation) of the CA1 hippocampal field by different concentrations of RU 486 was studied in hippocampal slice preparations from normal (sham) and adrenalectomized BALB/c mice. In the sham group as well as in the adrenalectomized group, RU 486 had no effect with the lower concentrations used (0.05 and 0.5 nM), but produced a decrease in the population spike amplitude for the higher concentrations used (5 and 50 nM). This decrease was delayed and sustained. Combined application of RU 486 at 5 nM and corticosterone at 0.5 or 5 nM displayed an excitatory effect, but no inhibitory effect. Combined application of RU 486 and dexamethasone showed no significant effect. These results are related to the antagonist and agonist properties of RU 486 and to the different steroid receptor systems in the hippocampus.     

Altered structure and function of reproductive organs in transgenic male mice overexpressing human aromatase

Aromatization of androgens is a key step in estrogen production, and it regulates the delicate balance between estrogens and androgens in the gonads and sex steroid target tissues. In the present study, we generated transgenic mice (AROM(+)) bearing the human ubiquitin C promoter/human P450 aromatase fusion gene. AROM(+) male mice are characterized by an imbalance in sex hormone metabolism, resulting in elevated serum E(2) concentrations, combined with significantly reduced testosterone and FSH levels, and elevated levels of PRL and corticosterone. AROM(+) males present a multitude of severe structural and functional alterations in the reproductive organs, such as cryptorchidism associated with Leydig cell hyperplasia, dysmorphic seminiferous tubules, and disrupted spermatogenesis. The males also have small or rudimentary accessory sex glands with abnormal morphology; a prominent prostatic utricle with squamous epithelial metaplasia, and edema in the ejaculatory ducts and vas deferens. In addition, the abdominal muscle wall is thin, and the adrenal glands are enlarged, with cortical hyperplasia. Some of the abnormalities, such as undescended testes and undeveloped prostate, resemble those observed in animals exposed perinatally to high levels of exogenous estrogen, indicating that the elevated aromatase activity results in excessive estrogen exposure during early phases of development. Some of the disorders in the reproductive organs, furthermore, can be explained by the fact that AROM(+) males are hypoandrogenic, and have elevated levels of serum PRL and corticosterone. Thus, the AROM(+) mouse model provides a novel tool to investigate the consequences of a prolonged increase in conversion of androgens to estrogens which results in complex hormonal disturbances altering the structure and function of various male reproductive organs.     

RU486 antagonizes the inhibitory action of progesterone on prostacyclin and thromboxane A2 synthesis in cultured rat myometrial explants

A myometrial explant culture system was developed to investigate the effect of progesterone and the antiprogestagen RU486 on prostacyclin (PGI2) and thromboxane A2 (TXA2) synthesis by the rat myometrium. After culture, eicosanoid synthesis was stimulated with arachidonic acid (AA) and the calcium ionophore A23187 (A23187). Spontaneous release of eicosanoids was also studied. Progesterone inhibited the spontaneous release of PGI2 and TXA2 release by myometrial explants in a concentration- and time-dependent manner. Adequate inhibition of myometrial eicosanoid synthesis by physiological concentrations was achieved at 18 h of culture: all subsequent studies were carried out after an 18-h culture of explants. A23187- and AA-stimulated PGI2 and TXA2 synthesis were inhibited equipotently by progesterone. 17 beta-Estradiol alone was without effect on spontaneous AA- or A23187-stimulated PGI2 or TXA2 synthesis and was without effect on progesterone-elicited inhibition of eicosanoid synthesis in the myometrial explants. The protein synthesis inhibitors, actinomycin D and cycloheximide, did not block the inhibitory action of progesterone on A23187- or AA-stimulated eicosanoid synthesis by the myometrial explants and alone mimicked the inhibitory action of progesterone. The inhibitory action of progesterone on AA- and A23187-stimulated PGI2 and TXA2 synthesis was antagonized in a concentration-dependent manner by RU486. These data indicate that within this ex vivo system, progesterone probably inhibits myometrial cycloxygenase, that progesterone may exert this action through inhibition of a modulating or permissive protein, and that the antiprogestagen RU486 is an effective in vitro antagonist or progesterone.     

Acute effects of progesterone and the antiprogestin RU 486 on gonadotropin secretion in the follicular phase of the menstrual cycle

Considerable controversy still exists concerning the role of progesterone in the initiation of the midcycle gonadotropin surge in humans. We, therefore, carried out a prospective randomized study to determine the potential of progesterone to initiate a gonadotropin surge and the acute effects of a potent progesterone antagonist (RU 486) on follicular phase gonadotropin secretion in normal women. The women underwent frequent blood sampling for 4 in the midfollicular (day 6) or late follicular phase (day 10). They then received either progesterone (10 mg, im) or RU 486 (10 or 100 mg, orally), and blood sampling was continued for an additional 8 h. Four women received each of the drug regimens in the early follicular phase, and four received each regimen in the late follicular phase. Two additional women were studied as control subjects at each stage of the cycle. Progesterone administration in the mid- and late follicular phases resulted in an acute increase in plasma LH and FSH concentrations, and the increases correlated with the base line plasma estradiol concentrations (P less than 0.05). In contrast to progesterone, the women who received RU 486 in the mid- and late follicular phases had a reduction in plasma LH and FSH concentrations after drug administration. The response in the mid-follicular phase was considerably less than that in the late follicular phase, and the extent of the response correlated with the baseline plasma estradiol concentrations (P less than 0.005). The changes were similar in response to both RU 486 doses. We conclude that progesterone can initiate a gonadotropin surge in the late follicular phase of the menstrual cycle. The inhibitory effect of the progesterone antagonist RU 486 suggests that a positive feedback mechanism involving progesterone may be influential some time before the surge onset.     

Distribution of RU 486 and its demethylated metabolites in humans

The concentrations of RU 486 and its demethylated metabolites were determined by RIA in samples of myometrium, abdominal adipose tissue, and serum, which were collected at hysterectomies performed 12-15 h after oral administration of 200 mg RU 486. The RU 486 concentrations in myometrium were similar in the five women studied, with a mean of 148 +/- 58 (+/- SD) ng/g (344 +/- 135 pmol/g). The adipose tissue RU 486 levels varied more, the mean concentration being 447 +/- 191 ng/g (1041 +/- 445 pmol/g). The serum RU 486 concentrations ranged from 175-899 ng/ml [mean, 396 +/- 259 ng/mL (922 +/- 603 nmol/L)]. In these women the nonprotein-bound fraction of [6,7-3H]RU 486 varied from 1.4-3.1% (mean, 2.3%). The approximate concentrations of the combined mono- and didemethylated metabolites of RU 486 were 1.4, 3.1, and 5.2 times higher in adipose tissue, myometrial tissue, and serum, respectively, than those of the parent RU 486. In vitro, rapid and nonsaturable accumulation of [6,7-3H]RU 486 from phosphate buffer into adipose tissue was inhibited by the addition of alpha 1-acid glycoprotein, the specific serum transport protein for RU 486, to the buffer medium. Accumulation of [6,7-3H]RU 486 in myometrial specimens was poor. The enterohepatic cycling of RU 486 was assessed in four normal subjects by repetitive intake of charcoal subsequent to ingestion of 200 mg RU 486. Compared to other normal subjects, the serum levels and areas under the concentration curves were lower and t1/2 values shorter in the group given charcoal, suggesting that in vivo RU 486 may be partly pooled in the enterohepatic cycle. Our studies suggest that despite the low volume of distribution and the effective serum binding of RU 486, the myometrial and adipose tissue concentrations of RU 486 and its metabolites were similar (approximately 10(-9)-10(-10) mol/g) after oral intake of RU 486.     

Blockade of the spontaneous midcycle gonadotropin surge in monkeys by RU 486: a progesterone antagonist or agonist?

Preovulatory ovarian secretion of progesterone (P4), several hours before the onset of the typical midcycle gonadotropin surge, occurs in humans and monkeys. We investigated the potentially obligatory role of preovulatory P4 secretion in stimulating the midcycle LH surge by administering a potent P4 antagonist, RU 486(17 beta-hydroxy-11 beta-[4-dimethylaminophenyl-1]17 alpha-[prop-1-ynyl]estra-4,9-dien-3-one), to sexually mature, normally ovulatory cynomolgus monkeys on days 10-12 of the menstrual cycle (n = 18). Monkeys were randomized to receive RU 486 alone (5 mg/day, im; group I); RU 486 plus dexamethasone (1 mg/day, im; group II); dexamethasone alone (group III); or vehicle (ethanol; 0.5 ml; group IV). Before drug treatment, the follicular phases were quite similar among groups. The administration of RU 486 blocked (delayed) the expected gonadotropin surge, despite rising estrogen concentrations (greater than 250 pg/ml). The expected LH surge was delayed by RU 486 (n = 5) or RU 486 with dexamethasone (n = 3) until 36 +/- 7 (+/- SEM) and 27 +/- 8 days in groups I and II, respectively. In contrast, groups III (n = 3) and IV (n = 5) had timely midcycle surges after the administration of dexamethasone or vehicle alone (4 +/- 2 and 6 +/- 2 days, respectively). The intermenstrual interval was lengthened by RU 486 administration in both group I and II animals (61 +/- 6 and 54 +/- 6 days) compared to controls (30 +/- 2; P less than 0.0001). In summary, RU 486 effectively blocked imminent midcycle gonadotropin surges, delayed subsequent folliculogenesis, and significantly extended the menstrual cycle length. If RU 486 acted as a pure P4 antagonist, then P4 is necessary for timely midcycle gonadotropin surges to occur. However, recent evidence showing agonistic properties of RU 486 (in the virtual absence of P4) at both endometrial and pituitary levels may favor a P4-like (agonistic) blockade of the estrogen-induced FSH/LH surges by RU 486.     

Effects of RU 486 on adrenal steroidogenesis in the guinea-pig.

Recent reports have shown that RU 486, a synthetic glucocorticoid and progestin antagonist, has direct effects on tissues secreting steroids. In order to characterize the effects of RU 486 on steroidogenesis further, guinea-pig fasciculata-glomerulosa (FG) cells in primary culture were treated for 48 h with RU 486. RU 486 caused an alteration of basal as well as ACTH-stimulated steroid secretion. Corticosterone and cortisol secretion decreased by 50% while the secretion of 17-hydroxyprogesterone and C19 steroids were increased. The activity of steroidogenic enzymes was measured using tritiated steroids. In RU 486-treated cells, the activity of 21-hydroxylase was dramatically inhibited while there was an increase in 17-hydroxylase and 17,20-desmolase activities. The effects of RU 486 on enzyme activities were dependent upon dose and time. The effects of the compound were not reversed by concomitant treatment of FG cells with R-5020 or dexamethasone, thus suggesting that RU 486 acted directly on steroidogenic enzymes to alter their activity.     

Differences in the interaction of RU 486 and ketoconazole with the second binding site of the glucocorticoid receptor

Ketoconazole and RU 486 are both antagonists of glucocorticoid hormone action at the target cell level. Both inhibit the binding of agonists to the receptor, although RU 486 is many-fold more potent. As reported here, ketoconazole, like all naturally occurring steroidal antiglucocorticoids, enhances the rate at which agonists dissociate from the glucocorticoid receptor. This indicates that this antiglucocorticoid interacts with the receptor at a site other than the agonist-binding site. RU 486, on the other hand, does not accelerate dissociation, suggesting that it does not interact with the putative allosteric regulatory site on the glucocorticoid receptor. Combining these findings with previous reports leads to the hypothesis that glucocorticoid antagonists can be divided into two classes: those that act through a second regulatory site on the glucocorticoid receptor and those that act by direct competition with agonists at the agonist-binding site.