The effects of continuous low dose mifepristone (RU 486) 10, 5 or 1 mg/day on the menstrual cycle were assessed in groups of five volunteers, who were treated for 30 days from the beginning of the cycle. Hormonal determinations in blood and urine samples, ovarian ultrasonography and an endometrial biopsy taken on day 22-29 of treatment were used to monitor the cycle. Pre- and post-treatment cycles presented a normal profile. During treatment, concentrations of RU 486 in plasma ranged from 65 nmol/l with 1 mg/day to 1000 nmol/l with 10 mg/day. With 10 or 5 mg/day, all treated cycles were prolonged as a result of arrested or slower follicular growth during treatment. Gonadotrophins, sex steroids and their urinary metabolites remained at early follicular phase levels throughout treatment, whereas androstenedione, prolactin and cortisol were unaffected. Follicular maturation resumed after discontinuation of treatment and several days later a luteinizing hormone surge followed by a luteal phase was observed in all cases. Ovulation was suppressed during treatment only in one of the five cycles treated with 1 mg/day. Endometrial maturation was disturbed by all doses. These data demonstrate a differential threshold of the follicle and the endometrium to mifepristone. This finding has potential application in the contraceptive field.
Low-dose antiprogestin administration has been proposed as a new contraceptive modality to interference with endometrial receptivity without disturbing ovarian function. The effects of 1 mg/day mifepristone for 150 days on the menstrual cycle were assessed in 21 surgically sterilized women. The aim was to study each woman for one control cycle and during months 1, 3 and 5 of treatment. Ovulation, endometrial thickness, serum oestradiol and progesterone, urinary luteinizing hormone, endometrial morphology and cervical mucus were assessed. Luteal phase progesterone concentrations were observed in 36 of the 60 treated months assessed and less frequently as treatment progressed. The bleeding pattern was regular in most biphasic cycles, while prolonged interbleeding intervals or no bleeding were associated with monophasic cycles. Altered endometrial morphology was found in all cases irrespective of the occurrence of luteal activity. Increased endometrial thickness and dilated glands were observed in 25 and 34% respectively of the monophasic cycles. Mifepristone, 1 mg/day, interferes with endometrial development while allowing the occurrence of biphasic ovarian cycles and regular bleeding. However, it also prevents ovarian cyclicity in a high proportion of treated months, and this is associated with increased endometrial growth in some women, which may be of concern.
In cycling and pregnant rats, the eggs stay in the oviduct for approximately 66 and 90 h, respectively. The influence of progesterone in these timings was investigated. An excess or a simulated deficit of progesterone was induced with exogenous progesterone or the antiprogesterone RU486, respectively, beginning on the day of ovulation. The effect of these treatments on egg transport in cycling and pregnant rats was assessed in detail and complemented with determinations of estradiol and progesterone circulating levels and progesterone receptor levels in the oviduct. Accelerated transport of ova followed treatment with RU486 in cycling and pregnant rats but with different features. In cycling rats, acceleration began 24 h after the onset of treatment and was not associated with changes in estradiol levels; in pregnant rats, it started 72 h after treatment and was associated with a 5-fold increase in estradiol circulating levels. Thus, RU486 failed to accelerate ovum transport during the first three days of treatment in pregnant rats, in spite of the fact that no progesterone receptors were available in the oviduct as early as 24 h of treatment. Progesterone administration caused egg retention in the oviducts and a 50% reduction in circulating estradiol levels in cycling rats, whereas in pregnant rats progesterone excess did not change estradiol circulating levels and had no effect on the location of embryos on Days 4 and 5. These results demonstrate a different physiological importance of endogenous progesterone in slowing down oviductal ovum transport in cycling and pregnant rats.(ABSTRACT TRUNCATED AT 250 WORDS)
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