New observations on the physiology of menstruation.

Endometrium was studies histologically, histochemically, and ultrastructurally in a series of biopsies taken from 3 normal, ovulating patients on Days 1-9 of the cycle. The occurrence of ovulation and the adequacy of progesterone were determined by radioimmunoassay. The most striking feature of menstruating endometrium was its vigorous attempt to survive. This was manifested by lysosomal activity, lipid accumulation, expulsion of glycoproteins, and the uptake of stromal debris by epithelial cells for passage to the uterine cavity. Regression, rather than cell death, was the chief event of menstruation. While some cells of the spongiosa underwent necrosis, the vast majority remained viable and underwent remodeling to participate in the new cycle. These studies may lead to further understanding of the process of menstruation and the pathophysiology of anovulatory bleeding and irregular shedding of the endometrium.