Differential patterns of secretory protein localization within the pig uterine endometrium

We have compared the distribution of two of the major secreted proteins of the porcine uterus within the endometrium of ovariectomized pigs which had received hormone replacement therapy for 30 days. The proteins studied, plasmin/trypsin inhibitor (PI) and uteroferrin (Uf), an iron-containing acid phosphatase, were both secreted into the uterine lumen by ovariectomized gilts given progesterone (P4) or P4 and 17 beta-estradiol but not by animals given 17 beta-estradiol alone or corn oil. The two proteins were localized immunocytochemically within the endometrium using an immunoperoxidase procedure. The results confirmed that production of PI and Uf was P4-dependent and demonstrated that the primary site of synthesis of PI was the surface and upper glandular epithelium, while Uf synthesis was confined to the glandular epithelium. A similar localization of PI and of Uf was found in endometrial tissue from pigs at day 13 (late luteal phase) of the estrous cycle. These results suggest that the uterine epithelium of the pig is regionally differentiated with regard to the production of P4-induced proteins.