The effect of RU 486 administered during the early luteal phase on bleeding pattern hormonal parameters and endometrium.

This study investigated the effect of a single dose of RU 486 administered very early in the secretory phase on endometrial development and levels of progesterone receptors on plasma levels of gonadotropins and ovarian hormones and on the pattern of menstrual bleeding. 24 regularly menstruating subjects participated and were studied during a control a treatment and a follow-up cycle. In the treatment cycle a single dose of 200 mg of RU 486 was given in the evening of the 2nd day after urinary LH peak. Plasma was collected from cycle day 10 until menstruation in both control and treatment cycles. The lengths of the control treatment and follow-up cycles were equal. 3 of the subjects had slight vaginal bleeding in association with RU 486 intake which however did not disturb their normal menstrual rhythm. Plasma levels of estradiol progesterone and FSH were not affected in the treatment cycle whereas LH levels increased slightly. The elimination 1/2-life of RU 486 was 28.6 hours. An endometrial biopsy was taken 12 36 or 84 hours (LH + 3 LH + 4 and LH + 6) after drug intake (8 subjects in each group) and another biopsy was taken on the corresponding day in the control cycle. The specimens were assessed by morphometric analysis and for cytosolic progesterone receptor concentrations. Endometrial biopsies taken 12 hours (on LH + 3) after RU 486 intake contained significantly (p<0.001) lower levels of cytosolic progesterone receptors than in the control cycle but levels at 36 and 84 hours were similar. Morphometric analysis revealed a retardation of endometrial development as early as 12 hours after RU 486 intake. The degree of retardation was more marked after 36 and 84 hours. These results suggest that the effect on the endometrium of a single dose of RU 486 immediately after the LH peak may be sufficient to prevent implantation. Thus treatment with RU 486 in the early secretory phase of the menstrual cycle might be considered for use as a once-a-month pill for fertility control. (authors)