Alkaline phosphatase in the bovine endometrium and trophoblast during the early phase of implantation.

Alkaline phosphatase in the endometrial and chorionic epithelium from the 22nd to 24th day post insemination was investigated according to the method of Hugon and Borgers (1966a, b). In the precontact phase the reaction products of this enzyme were found light microscopically in the caruncular and intercaruncular area in the apical part of the uterine surface epithelium. Although a definite, continuing reaction line between the maternal and fetal epithelium was present in the apposition phase, there was no activity of this phospho-monoesterase ascertainable following consolidated adhesion. Independent of implantation, lead salt precipitate was observed in the apical cytoplasma in the upper third of the uterine epithelial glands. Electron microscopic investigations in the precontact phase demonstrated the localisation of the reaction products of this hydrolase as electron dense grains on the outer plasma lamella of the uterine microvilli. During apposition this reaction appeared on the microvilli of the dark uterine epithelium and the cell membrane of the trophoblast cells. In addition to the existence of alkaline phosphatase on the microvilli of the uterine glandular cells, reaction products were discernable in the kinocilia between the inner lamellar of their plasma membranes and the tubules ring, as well as between the latter and the central tubule pair. There is a possibility that this hydrolase plays a role in the transport of metabolites for the purpose of histiogenic uterine milk production.