secretion of the major progesterone-induced proteins of the sheep uterus by caruncular and intercaruncular endometrium of the pregnant ewe from days 20–140 of gestation

An experiment was performed to evaluate the types and quantity of proteins secreted by intercaruncular endometrium at days 20, 60, 100 and 140 of gestation and caruncular endometrium from days 100 and 140 of gestation. Tissues were obtained from ewes made unilaterally pregnant. Based on SDS polyacrylamide gel electrophoresis (SDS-PAGE), the major proteins present in uterine fluid at days 60–140 of gestation were the uterine milk proteins (UTM-proteins), a pair of structurally-related, progesterone-induced polypeptides with molecular weights of 55,000 and 57,000. These proteins were also present in uterine fluid at day 20, but the major protein at this time migrated coincident with albumin. Cultured explants of endometrium at all days of pregnancy produced UTM-proteins as their major radiolabelled product for both caruncular and intercaruncular endometrium. The amount of protein secretion in vitro was greater (P<.04) for intercaruncular endometrium than for caruncular endometrium but was not significantly affected by stage of gestation or local presence of the conceptus. Immunohistochemical analysis revealed that UTM-proteins were present in glandular and luminal epithelium of intercaruncular endometrium and in both epithelial and stromal elements of caruncular endometrium. It was concluded that the UTM-proteins are produced earlier than previously described (i.e., day 20). In addition, caruncles contribute to the uterine secretory protein milieu through the secretion of proteins that are similar to that produced by the glandular intercaruncular epithelium.