Studies in vitro of effects of steroid hormones and the blastocyst on endometrial function in the sheep

Normal endometrial function is a result of regulation by the combination of ovarian steroids and local agents arising from within the embryo-maternal unit. We have used in vitro techniques to examine the role of steroid hormones and ovine trophoblast interferon on endometrial function in the ewe. Immunolocalization of oestrogen receptors in endometrial tissue demonstrated marked changes throughout the cycle and in early pregnancy with maximal concentrations during the follicular and very early luteal phases. Protein secretion from highly purified cultured ovine stromal and epithelial endometrial cells, and the direction of secretion from polarized epithelial cells, has been examined by incorporation of [35S]methionine and by one- and two-dimensional gel electrophoresis. Protein synthesis is greater in stromal than in epithelial cells and more protein is secreted apically than basally from epithelial cells. A number of common and some different proteins are secreted by the two cell types. One secreted protein is matrix metalloproteinase-3 (stromelysin) which degrades components of basement membranes. Ovine trophoblast interferon attenuates the production of prostaglandins from ovine endometrial cells but its action is not by an effect on localization or concentration of the enzyme prostaglandin synthase or on expression of the gene for prostaglandin synthase. Such studies in vitro contribute to our understanding of how the endometrium is prepared for implantation.