Histological and clinical features of menstruation induced by the antiprogestin mifepristone (RU486) compared to menstruation occurring spontaneously.

Abstract

The clinical and histological features of menstruation induced by a single oral dose of mifepristone were compared to those in normal spontaneous menstruation to aid understanding of the mechanism of endometrial shedding. 30 healthy volunteers, sterilized or seeking sterilization, were given a single oral dose, ranging from 5-200 mg mifepristone (RU-486) in the 1st half of the luteal phase, timed by the LH surge. Endometrial biopsies were taken on that day or the day after the 1st episode of bleeding for histological examination. Quantitative histological features on a 15 item scale were compared to those seen in women having spontaneous menses. 7 of 15 features differed between the 2 groups. Bleeding induced by mifepristone was associated with the following endometrial characteristics: increased gland cell height, reduced secretion in gland lumen, increased volume fraction of gland occupied by cells and nuclei, increased pseudostratification of gland cells, reduced stromal predecidual reaction, as judged by glycogen and fat content, and reduced leukocyte infiltration in the stroma. Thus there was less gland activity and an appearance of more cell packing, taller and more pseudostratified cells. The features in common with normal menses were mitotic activity in both glands and stroma, secretory vacuoles, edema and extravasation. Clinically the amount and duration of menstrual flow induced by mifepristone was similar to normal menses, suggestive of a similar hemostatic process.