Receptors, enzymes, and hormonal responses of endometrial cells.

Studies of hormone-related biochemical parameters of human endometrium are facilitated by the availability of a variety of types of endometrial tissue resulting from changes in hormonal environment during the menstrual cycle or from decidual, hyperplastic, and neoplastic transformations. Estrogen and progesterone receptors levels, rates of metabolism of ovarian hormones, enzymatic activities regulated by hormones or affecting intracellular concentrations of steroids, rates of production of prolactin and prostaglandins, and endogenous levels of hormones have been measured in samples of endometrial tissue and in separated glands and stroma. These studies have also included an evaluation of effects of estrogens and progestins administered to patients or added to the medium during in vito incubations of endometrium under organ culture conditions. Epithelial cells derived from isolated glands and stromal cells have been grown in primary cultures and also subcultured. These studies have revealed two mechanisms by which progestins exert an antiestrogenic effect on the endometrial tissue: viz, they were found to provoke a decline in estrogen receptor levels and to increase the metabolism of E2 through stimulation of estradiol 17 beta-dehydrogenase activity. In addition, studies of cells in culture have led to the unexpected finding of wide and rapid fluctuations in the levels of estrogen receptors, thus providing an opportunity to investigate factors involved in the regulation of concentrations of specific E2-binding sites.