Epithelial peroxidase and endometrial granulocytes in the normal cyclic human endometrium

Studies in animal models have clearly shown a relationship between the administration of estrogens and the appearance of peroxidase activity in growth-responsive estrogen target tissues (endometrium, cervix, vagina, breast, and DMBA rat mammary tumor). We have studied the ultrastructural localization of endogenous peroxidase activity in the normal cyclic human endometrium. Endogenous peroxidase activity was not identified in proliferative phase endometria, with the exception of one very late proliferative phase endometrium. Most secretory phase endometria showed at least some ultrastructurally identified peroxidase activity in glandular epithelial cells. The number of epithelial cells showing peroxidase activity varied from less than 10% to 85%. The peroxidase activity was present throughout the endoplasmic reticulum of these epithelial cells, extending from the perinuclear cistern to the most peripheral portions of the endoplasmic reticulum adjacent to the apical lumen. Biochemical assays of peroxidase activity in these endometria were compared with the ultrastructurally identified epithelial peroxidase and the endometrial granulocyte count. Uterine granulocyte peroxidase appeared to make a substantial contribution to the total peroxidase activity assayed by biochemical methods. Standard biochemical techniques alone, therefore were not considered to be adequate to evaluate epithelial peroxidase activity.