Embryo‐maternal dialogue during pregnancy establishment and implantation in the pig

Abstract

Porcine conceptuses secrete pregnancy-recognition signals (estrogens, including estradiol-17β) that inhibit luteolysis, thereby prolonging progesterone production by corpora lutea. The supportive mechanism by which the conceptus also inhibits luteolysis is by shifting endometrial prostaglandin (PG) synthesis to luteoprotective PGE2.Progesterone stimulates endometrial production of factors that are essential for conceptus development. Priming the uterus by progesterone and loss of progesterone receptors from the uterine epithelium by Day 10-12 after estrus are key for achieving endometrial receptivity for implantation. Conceptus implantation involves a series of events, many resembling the inflammatory reaction, that are greatly influenced by cytokines, growth factors, and prostaglandins. We herein present a novel, dual role for PGF2α in corpora lutea that depends on the acquisition of luteolytic sensitivity, based on the knowledge that PGF2α triggers pathways involved in luteolysis during the estrous cycle or/and may have an alternative function in maintaining progesterone synthesis during pregnancy. We also point out a new role for PGF2α that, together with PGE2, can act as embryonic signal mediators. PGF2α, which until recently was considered undesirable for promoting pregnancy, is now known to stimulate conceptus-maternal interactions and angiogenesis in the endometrium. This function is in line with other important prostaglandin functions, such as stimulating adhesion of trophoblasts (PGE2, PGI2) as well as endometrial vascular functions and trophoblast cell proliferation (PGI2).

Estradiol-17β-Induced Changes in the Porcine Endometrial Transcriptome In Vivo

“…Pregnancy losses significantly decrease the profitability in animal production. The reasons for unsuccessful implantation are associated with the embryo e.g., insufficient conceptus signaling [1], genetic disorders, and impaired endometrial receptivity (reviewed in [2]). In most mammals, estradiol-17β (E2) serves as a pivotal molecule regulating reproductive functions of the female reproductive tract.…”

“…The presented results provide a valuable resource for further targeted studies considering genes and pathways regulated by conceptus-derived estrogens and their role in pregnancy establishment.During early pregnancy in the pig, porcine conceptuses (embryos with associated membranes) secrete E2, which is regarded as the pregnancy recognition signal required for prolonged progesterone synthesis and secretion by corpora lutea (CLs). Porcine conceptuses secrete estrogens in a biphasic manner-the first increase of conceptus-derived estrogens occurs on days 11-13 after fertilization and the second is between days 15 and 25-30 after fertilization (reviewed in [2]). However, the levels of conceptus-derived estrogens in the uterine lumen may also vary depending on the number of conceptuses [1].…”

Changes in calcium levels in the endometrium throughout pregnancy and the role of calcium on endometrial gene expression at the time of conceptus implantation in pigs

“…Conceptus‐derived estrogen redirects PGF 2α secretion from the uterine vasculature to the uterine lumen to prevent CL regression and maintain the production of progesterone in the CL during early pregnancy in pigs (Bazer & Johnson, ). PGE 2 derived from the endometrium as well as the implanting conceptus has a luteoprotective and antiluteolytic function (Waclawik, Kaczmarek, Blitek, Kaczynski, & Ziecik, ). Estrogen injection into cyclic pigs on Day 11 of the estrous cycle induced increased secretion of calcium into the uterine lumen after 12–24 hr and a decline in calcium in the uterine lumen at 48 and 72 hr resulted in increased PGE 2 secretion at 72 hr (Geisert et al, ).…”

Embryo presence regulates NODAL/LEFTY2 system in the rat oviduct in vivo

“…The early maternal‐embryo dialog between the endometrium and the developing embryo has been well documented (Spencer, Forde, & Lonergan, ; Waclawik, Kaczmarek, Blitek, Kaczynski, & Ziecik, ). Besides the uterus, the oviduct also participates in this phenomenon; certainly, new evidence for reciprocal crosstalk during the transit of the embryo through the oviduct has been reported (Lee & Yeung, ; Maillo et al, ).…”