Observation of the activity of factor VIII in the endometrium of women with regular menstrual cycles.

An immunoperoxidase reaction was used to detect Factor VIII activity in the endometrial endothelium during the normal menstrual cycle. Fifty-three women of fertile age, having regular menstrual cycles, participated in the study. Endometrial material was obtained from 33 women in the preovulatory phase and from 20 women in the post-ovulatory phase. The immunoperoxidase reaction was evaluated using a scoring system. Cyclic changes related to the pre- and post-ovulatory phase were observed in the Factor VIII activity of the endometrial endothelial cells; a gradual increase occurred from the early to the late proliferative phase and thus activity gradually decreased during the secretory phase. No activity was observed in the late secretory or in the menstrual phase.