1 Contraceptive Development Network, Centre for Reproductive Biology, University of Edinburgh, Academic Centre, 49 Little France Crescent, Old Dalkeith Road, Edinburgh EH16 4SB, 2 Medical School, Teviot Place, Edinburgh EH8 9AG, UK and 3 Shanghai Institute of Family Planning Technical Instruction, Shanghai, Peoples Republic of China 4 To whom correspondence should be addressed. e-mail: dtbaird{at}ed.ac.uk
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Abstract |
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Key words: antigestogen/antiproliferation/contraception/mifepristone
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Introduction |
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Mifepristone is a synthetic C19 norsteroid which is a potent antagonist of progesterone (Ulmann, 2000) and is licensed in most European countries for induction of abortion in early pregnancy (Sitruk-Ware, 2000
). Published data suggest that it is a highly effective emergency contraceptive and has potential as a once-a-month pill (Baird, 2001
). In daily doses between 2 and 10 mg, ovulation is suppressed although variable degree of follicular development continues (Ledger et al., 1992
; Croxatto et al., 1993
, Cameron et al., 1995
). We have previously reported that 90% of women who received 2 or 5 mg mifepristone per day were anovulatory and amenorrhoeic in spite of the fact that the levels of estradiol (E2) remained within the mid follicular range (Brown et al., 2002
). Concern has been expressed that the endometrium would undergo hyperplastic or even malignant changes due to the continued exposure to unopposed estrogen (Murphy et al., 1995
). However, studies in monkeys with mifepristone and other antigestogens have shown no evidence of endometrial hyperplasia (Van Vem et al., 1989
; Ishwad et al., 1993
). Rather there is a dose-related decrease in endometrial thickness associated with a reduction in mitotic index (Slayden et al., 1998
). In a previous study, in which women were treated with 2 mg mifepristone per day for 30 days, we demonstrated a persistent proliferative endometrium which displayed a reduction in mitotic activity in spite of prominent markers of cell divisions such as Ki67 (Cameron et al., 1996
). The molecular basis for this antiproliferative action of antigestogens is not clear but it has been suggested that there is an arrest of the cell cycle (Neulen et al., 1995
; Chwalisz et al., 2000
).
Before daily mifepristone is developed as a novel estrogen-free contraceptive pill is it important to demonstrate that it has no potentially harmful effects on the endometrium. In a previous paper, describing the endocrine profiles, we reported no obvious hyperplastic or malignant changes in the histological examination of endometrial biopsies from 90 women who had taken either 2 or 5 mg mifepristone per day for 120 days (Brown et al., 2002). The present paper reports detailed histological appearances of the endometrium in these women and relates the findings to the endocrine environment.
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Materials and methods |
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Subjects were studied for one pre-treatment cycle, for four cycles (120 days) of treatment, and for one post-treatment cycle. Subjects were randomly allocated to receive 2 or 5 mg of mifepristone daily for the 120 treatment days. The randomization was achieved from a table of random numbers and stratified by dose in groups of 10. The daily doses were issued in pre-packed identical bottles containing, either 2x1 mg mifepristone plus placebo, or 1x5 mg mifepristone plus two placebos. The investigator and subjects were both blinded to the dose that each subject was taking.
All 40 subjects in Shanghai and 10 women in Edinburgh used this method as the sole contraceptive. The remaining 40 women in Edinburgh were either not sexually active, using barrier contraceptives or were surgically sterilized.
Assessment of endometrial development
Endometrial biopsies were collected using a Pipelle endometrial sampling device (Prodimed, Neuilly-en-Thelle, France). Samples were collected in the late follicular phase of the pre-treatment cycle (day 12), after 60 days of mifepristone treatment, and after 120 days of treatment. Specimens were fixed in 100% neutral formalin, processed and embedded in paraffin wax. Sections (5 µm) were cut and then stained with haematoxylin and eosin. Histological assessment and semi-quantative mitotic scores of both glands and stroma were performed by two observers, who were blinded to sample timing and dose group. Mitotic score was assessed semiquantitatively as follows.
Glands: 0 = no mitoses seen per 20 intact gland profiles; 1 = 12 mitoses per 20 glands; 2 = 35 mitoses per 20 glands; 3 = >5 mitoses per 20 glands. Mitoses were only counted in intact glands, not in surface epithelium or disrupted strips. In specimens with <20 gland profiles, serial sections were assessed, or 10 glands assessed and the result doubled. Specimens with <10 glands were considered inadequate for assessment.
Stroma: 0 = no mitoses seen in five high power microscope fields (HPF) (x400); 1 = 1 or 2 mitoses per 5 HPF; 2 = 35 mitoses per 5HPF; 3 = >5 mitoses per five HPF.
Ki67 immunostaining
Ki67 immunostaining was detected using a mouse monoclonal primary antibody (NCL-Ki67-MM1, Novo Castra, Newcastle, UK) with an avidinbiotinhorse-radish peroxidase (ABC) detection system. Antigenic sites were unmasked using the microwave method of retrieval. Endogenous peroxidase was blocked by placing the slides in 3% hydrogen peroxide for 10 min at room temperature. A non-immune block was then performed by incubating the slides with normal horse serum for 20 min. The sections were then incubated with primary antibody (dilution 1:100) for 60 min at 37°C. The biotinylated secondary antibody and the ABC complex were then each applied for 30 min at room temperature. Diaminobenzidine tetrachloride was used to visualize the reaction, prior to counterstaining with haematoxylin. The number of positively stained cells (staining intensity) in glands and stroma viewed at x40 magnification were scored semi-quantitatively by two observers who were blinded to sample timing and dose group (score: 0 = no staining; 1 = mild staining; 2 = moderate staining; 3 = intense staining).
Transvaginal sonography
Endometrial thickness was measured by transvaginal sonography at the time of endometrial biopsy on day 12 of the pre-treatment cycle and after 60 and 120 days of treatment as previously reported (Brown et al., 2002). Measurement was performed in the sagittal plane, from one basal layer to the other, the diameter of any luminal fluid being subtracted from the measurement as previously reported.
Assessment of menstrual bleeding pattern
Each subject kept a menstrual diary for the duration of the study. Each day was classified as no bleeding, spotting, normal bleeding, or heavy bleeding.
Assessment of ovarian function
Estrone glucuronide (E1G) and pregnanediol glucuronide were measured in samples of early morning urine and the results expressed per mol of creatinine (Cr) as previously reported (Brown et al., 2002). E2 and progesterone were measured by radioimmunoassay in samples of plasma collected at the time of endometrial biopsies.
Ovarian follicular activity during treatment was compared to the baseline ovarian activity shown in the pre-treatment cycle, and each subject was categorized according to the following criteria: (i) total suppression, E1G throughout treatment is <50% above the mean baseline; (ii) partial suppression, E1G raised 50% above the mean baseline on 1 or 2 consecutive weeks; (iii) continued follicular activity, E1G raised
50% above the mean baseline on at least two separate occasions. Ovulation was deemed to occur if the excretion of pregnanediol glucuronide was >0.5 mmol/mol Cr and was
3-fold higher than that in the preceding week.
Statistical methods
Statistical analysis was carried out using SPSS (SPSS, Inc., Chicago, IL, USA) and Excel 97 (Microsoft Corporation). Wilcoxon signed rank, KruskalWallis and paired t-test were used to compare hormonal assays, endometrial thickness and endometrial scores at various time-points.
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Results |
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Ovarian function
Subjects in Edinburgh and Shanghai differed in the endocrine response to treatment and the results are therefore considered separately. We have previously reported the details of hormone profiles in blood and urine (Brown et al., 2002). In the present paper the mean excretion of E1G was calculated for two treatment phases, that is days 060 and days 60120 of treatment, to give an indication of estrogen exposure in the 2 months preceding the endometrial biopsies. The mean excretion of E1G was compared to that excreted in the follicular (i.e. weeks 1 and 2) phase of the pre-treatment cycle. In Edinburgh women the mean excretion of E1G during both treatment phases was not different from that excreted in the follicular phase of the pre-treatment cycle (Figure 1). Women in Edinburgh showed varying levels of follicular activity, with most women showing only partial suppression of ovarian activity or continued follicular activity. Most episodes of follicular activity, however, did not appear to continue through to ovulation, with only 10 ovulatory episodes identified by biochemical assay in the 104 months of treatment with 2 mg daily, and five ovulatory episodes in the 96 months of treatment with 5 mg daily.
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Menstrual bleeding patterns
In Edinburgh, 17/26 women (65%) receiving 2 mg daily were amenorrhoeic, as were 21/24 (88%) receiving 5 mg. The mean number of days bleeding during treatment was 4.4 days and 0.6 days for the 2 and 5 mg groups respectively. In Shanghai, 18/20 women (90%) in both dose groups were amenorrhoeic during treatment, with mean number of days bleeding of 0.4 and 0.7 respectively.
All subjects reported a menstrual bleed within 3 weeks of stopping mifepristone. There was a trend for this bleed to be longer than the normal pre-treatment bleed, but this increase was only significant in the group in Edinburgh treated with 2 mg daily (5.2 versus 10 days, P < 0.05).
Endometrial development
Transvaginal sonography
In Edinburgh women, there was a trend for the endometrial thickness to increase during treatment with mifepristone (Figure 2). This increase was significant by the end of 120 days of treatment in the 2 mg group (P < 0.01) and by 60 days of treatment in the 5 mg group (P = 0.015). Plasma E2 was measured at the time of endometrial assessment, and showed that normal pre-menopausal levels of E2 were maintained during treatment (2 mg, 436 ± 56 and 403 ± 61 pmol/l days 60 and 120; 5 mg, 438 ± 82 and 327 ± 56 pmol/l).
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In neither centre was there any correlation between endometrial thickness and plasma E2 level.
Histological appearances
Pre-treatment endometrial biopsies were collected on day 12 of the pre-treatment cycle. Samples were collected from all subjects, but three samples in the Edinburgh women (two in the 2 mg group, and one in the 5 mg group) were too small for assessment. The remaining 47 pre-treatment samples in Edinburgh all showed normal proliferative phase endometrium, as expected (Figure 3a).
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All subjects had further endometrial samples collected on days 60 and 120 of treatment. A few samples were unassessable due to inadequate sample size. In Edinburgh women, the most common appearance at both treatment time-points, in both dose groups, was of proliferative phase type endometrium, with straight or coiled glands in a compact stroma (Table I, Figure 3b).
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One subject showed a secretory type endometrium on the day 120 sample (Figure 3e) correlating with biochemical evidence of preceding ovulation, with a rise in urinary pregnanediol glucuronide to 0.57 mmol/mol Cr, and an elevated plasma progesterone of 88.8 nmol/l. Two subjects in the 2 mg group were also in the luteal phase following biochemical evidence of ovulation, but did not show any secretory change, suggesting asynchrony between the endocrine cycle and endometrial development (Figure 3f).
In the Shanghai women, the endometrial appearances were similar to the Edinburgh women, with the majority of women showing a proliferative type endometrium (Table I). The inactive cystic dilatation appearance was less commonly seen in the Shanghai women. Four subjects in Shanghai (one at each time-point in each dose group) showed some features of secretory change, but none of these subjects had biochemical evidence of preceding ovulation.
There was no relationship between histological appearance and endometrial thickness or degree of ovarian activity. Both proliferative and cystic changes were represented at all categories of ovarian activity. Three of the four subjects who showed secretory features were classified as showing total suppression of ovarian follicular activity.
Markers of proliferation
Mitotic figures were counted in sections of both control and treatment biopsies (Figure 4a and b). By day 60 there was a significant reduction in mitotic index in both dose groups and this was maintained after 120 days of treatment (Table II). This reduction in mitosis was confirmed by analysis of the Ki67 immunostaining which was performed on a sub-group of 40 subjects (20 in each dose group) in Edinburgh (Table II, Figure 4c and d). The samples from Shanghai subjects were too scanty to allow assessment of proliferation markers.
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Discussion |
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A striking feature of the endometrium obtained from women after treatment was the reduced indices of proliferation. There was a significant reduction in both mitotic index and Ki67 immunostaining on treatment as compared to endometrium on day 12 of control cycles. In a previous study we reported a reduction in mitotic index after 21 days of treatment with mifepristone although the Ki67 immunostaining was increased (Cameron et al., 1996). We suggested that initially mifepristone may block completion of the cell cycle so that Ki67 protein persists for some time after cell division has been arrested. Our present observations are similar to those reported in the experimental primate in which it was shown that mifepristone and other antigestogens inhibit the ability of estrogen to induce proliferation of the endometrium (Ishwad et al., 1993
; Heikinheimo et al., 1996
; Slayden et al., 1998
). The molecular basis for this antiproliferative action of antigestogens is not clear, but evidence from transfected cells suggests that it is mediated through the progesterone receptor (Chwalisz et al., 2000
).
It is of interest that in a recent study (Slayden et al., 2001) the androgen receptor was elevated by antiprogestin treatment, particularly in the glandular epithelium. Such an elevation of androgen receptor could result in enhanced androgen action in the endometrium (Brenner et al., 2002
). Androgens suppress estrogen-dependent endometrial proliferation. Thus elevated expression of the androgen receptor following antiprogestin administration is a further candidate for mediation of the proliferative effects of antiprogestin treatment.
Concern has been expressed previously that long-term use of antigestogens may lead to the risk of endometrial hyperplasia and possible malignancy due to the exposure of the endometrium to the effects of unopposed estrogen (Murphy et al., 1995). In a study in which women with pelvic endometriosis were treated with 50 mg mifepristone per day for 6 months, there was evidence of endometrial hyperplasia and numerous mitotic features. In a case report of a young woman treated with 400 mg mifepristone per day for 6 months because of inoperable Cushings syndrome, massive simple hyperplasia of the endometrium developed, which reversed after stopping therapy (Newfield et al., 2001
).
In both these reports, the daily dose of mifepristone was considerably higher than in our study and was sufficient to suppress ovarian function and ovarian E2 secretion. The antiglucocorticoid action of mifepristone at this dose was sufficient to stimulate an increased secretion of adrenal androgens such as androstenedione, which could be a precursor for extraglandular synthesis of estrogen in peripheral tissues including the endometrium (Kettel et al., 1991; Kettel et al.,1996
). Thus the absence of endometrial hyperplasia in our study and others could be due to the absence of significant effect on the pituitaryadrenal axis of daily doses of <10 mg.
Although ovulation occurred in a minority of cycles, there appeared to be asynchrony between the ovarian cycle and endometrial development. Of the 15 women in Edinburgh who showed biochemical evidence of ovulation at least once, only four reported a menstrual bleed subsequent to the rise in pregnanediol. In two subjects who had an endometrial sample collected (fortuitously) in the apparent luteal phase following an episode of presumed ovulation, there was no evidence of secretory change (Figure 3e). Conversely, four subjects from Shanghai who showed some evidence of secretory endometrium did not have biochemical evidence of ovulation. It has been previously reported in a study using 1 mg mifepristone per day that secretory changes can occur without preceding ovulation. It has been suggested that when endogenous progesterone levels are low, as in post-menopausal women, mifepristone can exert an agonist action (Gravanis et al., 1985). These results demonstrate that mifepristone, in addition to disturbing ovarian function, has a direct effect on the endometrium which makes it unlikely that a pregnancy could become established even if ovulation occurred.
The significant increase in the thickness of the endometrium as measured by pelvic ultrasound of women in Edinburgh is similar to that reported after treatment of women in Chile with mifepristone at a dose of 1 mg/day (Croxatto et al., 1998). It is likely that much of this apparent thickness is due to the collection of fluid within the lumen of dilated glands. However some women who showed thickening of the endometrium on ultrasound had no evidence of cystic glandular formation in the biopsy. It seems unlikely therefore that the apparent thickening of the endometrium is due to cystic glands in all women. In Shanghai, where there was an overall reduction in endometrial thickness during treatment, ovarian function and estrogen excretion were profoundly suppressed. The fact that there was no correlation between individual plasma E2 levels and endometrial thickness makes it unlikely that hormonal factors alone are responsible for the variation in endometrial structure. Rather the interaction between dose, effect on ovarian cyclicity, variation in individual and possible genetic sensitivity determine the response of the endometrium to mifepristone.
The basal excretion of E1G and concentration of E2 were lower in women in Shanghai than in Edinburgh. As previously discussed in detail, this difference is unlikely to be due to methodological factors and reflects a genuine difference in secretion and/or metabolism of estrogens between Chinese and Caucasian women (Key et al., 1990; Aldercreutz et al., 1994
; Brown et al., 2002
). Ovarian function and endometrial development were more easily suppressed by low doses of mifepristone in Shanghai women, suggesting that there may be ethnic differences in the metabolism of steroid hormones such as that suggested in men (Anderson and Wu, 1996
). Whether these differences are genetic or related to diet or other aspects of life style is not known.
In conclusion, the present study demonstrates that mifepristone in a dose of 2 or 5 mg per day for 120 days has effects that are likely to be contraceptive. There is suppression of ovulation and menstruation in the majority of cycles and asynchrony between endometrial and ovarian activity. After 120 days of treatment there are no features of endometrial hyperplasia and markers of endometrial proliferation are suppressed. Preliminary data confirm that in 50 women the dose is contraceptive. By inducing amenorrhoea, the method could have considerable health benefits by reducing the considerable morbidity associated with menstruation. Recent surveys suggest that a pill that abolished periods would be popular with a significant number of women in Western Europe (Den Tonkelaar and Oddens, 1999) and some developing countries (A.F.Glasier et al., unpublished data). It is now time to mount a long-term efficacy and safety study with the prospect of realizing the potential of mifepristone as a novel estrogen-free daily contraceptive pill.
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Acknowledgements |
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References |
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![]() ![]() ![]() ![]() ![]() ![]() ![]() |
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Anderson, R.A. and Wu, F.C.W. (1996) Comparison between testosterone enanthate-induced azoospermia and oligospermia in a male contraceptive study III: higher 5-reductase activity in oligospermic responders during testosterone enanthate administration. Clin. Endocrinol., 81, 902908.
Baird, D.T. (2001) Antigestogens: the holy grail of contraception. Reprod. Fertil. Dev., 13, 16.[ISI][Medline]
Baird, D.T. and Glasier, A.F. (1999) Science, medicine and the future: contraception. Br. Med. J., 319, 969972.
Brenner, R.M., Slayden, O.D. and Critchley, H.O.D. (2002) Antiproliferative effects of progesterone antagonists in the primate endometrium; a potential role for the androgen receptor. Reproduction, 124, 167172.
Brown, A., Cheng, L., Lin, S. and Baird, D.T. (2002) Daily low dose mifepristone has contraceptive potential by suppressing ovulation and menstruation: a double blind randomised control trial of 2 and 5mg per day for 120 days. J. Clin. Endocrinol. Metab., 87, 6370.
Cameron, S.T., Thong, K.J. and Baird, D.T. (1995) Effect of daily low dose mifepristone on the ovarian cycle and on the dynamics of follicle growth. Clin. Endocrinol., 43, 407414.[ISI][Medline]
Cameron, S.T., Critchley, H.O.D., Thong, K.J., Buckley, C.H., Williams, A.R. and Baird, D.T. (1996) Effects of daily low dose mifepristone on endometrial maturation and proliferation. Hum. Reprod., 11, 25182526.[Abstract]
Chwalisz, K., Brenner, R.M., Fuhrmann, U.U., Hess-Stump, H. and Elger, W. (2000) Antiproliferative effects of progesterone antagonists and progesterone receptor modulators on the endometrium. Steroids, 65, 741751.[CrossRef][ISI][Medline]
Croxatto, H.B., Salvatierra, A.M., Croxatto, H.D. and Fuentealba, B. (1993) Effects of continuous treatment with low dose mifepristone throughout one menstrual cycle. Hum. Reprod., 8, 201207.[Abstract]
Croxatto, H.B., Kovacs, L., Massai, R., Resch, B.A., Fuentealba, B., Salvatierra, A.M., Croxatto, H.D., Zalanyi, S., Viski, S. and Krenacs, L. (1998) Effects of long term low-dose mifepristone on reproductive function in women. Hum. Reprod., 13, 793798.[Abstract]
Den Tonkelaar, I. and Oddens, B.J. (1999) Preferred frequency and characteristics of menstrual bleeding in relation to reproductive status, oral contraceptive use and hormone replacement therapy use. Contraception, 59, 357362.[CrossRef][ISI][Medline]
Fraser, I.S. (2000) Progestogen-only contraception. In Glasier, A.F. and Gebbie, A. (eds), Handbook of Family Planning and Reproductive Healthcare. Churchill Livingstone, Edinburgh, pp. 77103.
Gravanis, A., Schaison, G., George, M., DeBrux, J., Satyaswaroop, G., Baulieu, E-E. and Rubel, P. (1985) Endometrial and pituitary responses to the steroid antiprogestogen RU486 in post menopausal women. J. Clin. Endocrinol. Metab., 60, 156163.[Abstract]
Heikinheimo, O.J.G., Hsiu, J.G., Gordon, K., Kim, S., Williams, R.F., Gibbons, W.E. and Hodgen, G.D. (1996) Endometrial effects of RU486 in primatesantiproliferative action despite signs of oestrogen action and increased cyclin-B expression. J. Steroid Biochem. Mol. Biol., 59, 179190.[CrossRef][ISI][Medline]
Ishwad, P.C., KatKam, R.R., Hinduta, I.N., Chwalisz, K., Elger, W. and Puri, C.D. (1993) Treatment with a progesterone antagonist ZK 98,299 delays endometrial development without blanking ovulation in Bonnet Monkeys. Contraception, 48, 5770.[CrossRef][ISI][Medline]
Kettel, L.M., Murphy, A.A., Mortola, J.F., Liu, J.H., Ulmann, A. and Yen, S.S.C. (1991) Endocrine responses to long-term administration of the antiprogesterone RU486 in patients with pelvic endometriosis. Fertil. Steril., 56, 402407.[ISI][Medline]
Kettel, L.M., Murphy, A.A., Morales, A.J., Baulieu, E-E. and Yen, S.S.C. (1996) Treatment of endometriosis with antiprogesterone mifepristone (RU486). Fertil. Steril., 65, 2328.[ISI][Medline]
Key, T.J.A., Chen, J., Wang, D.Y., Pike, M.C. and Boreham, J. (1990) Sex hormones in women in rural China and in Britain. Br. J. Cancer, 62, 631636.[ISI][Medline]
Kurman, R. and Norris, H.J. (1994) Endometrial hyperplasia and related cellular changes. Blausteins Pathology of the Female Genital Tract, 4th edn. Springer-Verlag, New York, p. 412.
Ledger, W.L., Sweeting, V.M., Hillier, H. and Baird, D.T. (1992) Inhibition of ovulation by low dose mifepristone (RU486). Hum. Reprod., 7, 945950.[Abstract]
Murphy, A.A., Kettel, L.M., Morales, A.J., Roberts, V., Parmley, T. and Yen, S.S.C. (1995) Endometrial effects of long-term low-dose administration of RU486. Fertil. Steril., 63, 761766.[ISI][Medline]
Neulen, J., Williams, R.F., Breckwoldt, M., Chwalisz, K., Baulieu, E-E. and Hodgen, G.D. (1995) Non-competitive anti-oestrogen actions of progesterone antagonists in primate endometrium: enhancement of oestrogen and progesterone receptors with blockade of post-receptor proliferative mechanisms. Hum. Reprod., 11, 15331537.
Newfield, R.S., Spitz, I.M., Isacson, C. and New, M.I. (2001) Long-term mifepristone (RU486) therapy resulting in massive benign endometrial hyperplasia. Clin. Endocrinol. (Oxf.), 54, 399404.[CrossRef][ISI][Medline]
Sitruk-Ware, R. (2000) Approval of mifepristone (RU486) in Europe. Zentrabl. Gynakol., 122, 241247.[Medline]
Skegg, D.C.G. (2000) Third generation oral contraceptives. Br. Med. J., 7255, 190191.[CrossRef]
Slayden, O.D., Zelinski-Wooten, M.B., Chwalisz, K., Stouffer, R.L. and Brenner, R.M. (1998) Chronic treatment of cycling rhesus monkeys with low doses of the antiprogestin ZK137316: morphometric analysis of the uterus and oviduct. Hum. Reprod., 13, 269277.[CrossRef][Medline]
Slayden, O.D., Nayak, N.R., Burton, N.R., Chwalisz, K., Cameron, S.T., Critchley, H.O.D., Baird, D.T. and Brenner, R.M. (2001) Progesterone antagonists increase androgen receptor expression in the rhesus macaque and human endometrium. J. Clin. Endocrinol. Metab., 86, 26682679.
Ulmann, A. (2000) The development of mifepristone: a pharmaceutical drama in three acts. J. Am. Med. Womens Assoc., 55 (Suppl. 3), 117120.
Van Vem, J.F.H.M., Hsiu, J.G., Chillik, C.F., Danforth, D.R., Ulmann, A., Baulieu, E-E. and Hodgen, G.D. (1989) Contraceptive potential of RU486 by ovulation inhibition: Pituitary versus ovarian action with blockade of estrogen induced endometrial proliferation. Contraception, 40, 171183.[ISI][Medline]
Submitted on July 1, 2002; resubmitted on August 27, 2002. accepted on October 1, 2002