ISOLATION AND CHARACTERIZATION OF A 30-KDA ENDOMETRIAL GLYCOPROTEIN SYNTHESIZED DURING THE ESTROUS-CYCLE AND EARLY-PREGNANCY OF THE PIG

Endometrial polypeptide synthesis, which is regulated through ovarian steroid secretion and steroid production by the developing conceptus, not only provides the necessary secretory components vital to conceptus development but also presents the adhesive changes in the epithelial surface essential for conceptus attachment. In the present study, a 30-kDa, basic endometrial glycoprotein (pGP30) was isolated and characterized during the estrous cycle and early pregnancy of the pig. Uterine flushings and endometrial culture media were obtained from gilts on Days 0, 5, 10, 12, 15, and 18 of the estrous cycle and Days 10, 12, 15, and 18 of pregnancy. A polyclonal antibody was generated to pGP30 after isolation of medium from Day 15 pregnant endometrial cultures separated by gel filtration and PAGE, Western blot analysis indicated that the antiserum reacted with isoforms of pGP30 and cross-reacted with a 90-kDa component in serum that was not removed after cleavage of the oligosaccharide chains from the 90-kDa glycoprotein. Antiserum did not detect a 30-kDa band in media from cultures of kidney, fat, heart, muscle, liver, or serum; however, heart and muscle did contain bands of different molecular masses that cross-reacted with the antiserum. Multiple bands of higher molecular mass (35-40 kDa) were detected in the endometrial cultures from gilts on Days 0 through 10 of the estrous cycle. Treatment of ovariectomized gilts with estradiol-17 beta stimulated a similar response. During the mid- to late luteal phase of the estrous cycle (Days 12-18), the 30-kDa band as well as an additional 32-kDa band was present on Western blots. Administration of progesterone for 14 days stimulated the synthesis of both the 30- and 32-kDa products in ovariectomized gilts. However, only the pGP30 was detected on Days 12-18 of pregnancy. Immunocytochemical localization with antiserum to pGP30 indicated that the glycoprotein is present in the endometrial epithelium, with the surface epithelium demonstrating the strongest reaction product. Discrete changes in staining and cellular localization were observed during the early stages of the estrous cycle (Days 0-5) and the midluteal (Day 10) phase. A similar response was achieved with administration of steroids to ovariectomized gilts. Data indicate that discrete changes in epithelial synthesis of the endometrial glycoprotein occur at the time of conceptus trophoblastic elongation and placental attachment in the pig.