Biochemical aspects of conceptus–endometrial interactions

Abstract

Mammalian conceptuses must provide a chemical signal to the maternal system to insure maintenance of corpus luteum (CL) function and of progesterone production and continuation of uterine endometrial secretory activity. These events insure that the developing conceptus is provided with appropriate nutrients, regulatory enzymes and endocrine state to allow successful establishment and maintenance of pregnancy. Pig blastocysts begin to produce estrogens by Day 11 of pregnancy, which prevents secretion of the uterine luteolytic factor (PGF2 alpha) in an endocrine direction, but allows secretion in an exocrine direction, i.e., into the uterine lumen. Therefore, CL are "protected." Blastocyst estrogens also trigger secretion of a group of proteins, including uteroferrin, an iron transport protein, and a family of protease inhibitors whose biosynthesis within the uterine glandular epithelium is under the control of progesterone. Estrogen also appears to promote accumulation of glucose and fructose within the uterine lumen. A complex in vivo "culture medium" is thereby established to promote conceptus development. Pig blastocysts do not undergo invasive implantation within the uterine lumen although they produce the protease, plasminogen activator. Invasion may be prevented by endometrial secretion of progesterone-induced protease inhibitors which are produced in large amounts. In addition to estrogens of conceptus origin, calcium and prostaglandins PGF2 alpha and E2 may affect the uterine vasculature, water and electrolyte transport, capillary permeability, conceptus steroid production, and related events during pregnancy. The blastocysts of the large domestic animals also secrete proteins which include a large glycoprotein (Mr approximately 600,000) and a small acidic protein (Mr approximately 17,000). The latter has been purified from sheep and named ovine trophoblast protein I. These proteins may play unique roles in early pregnancy with respect to establishment and maintenance of pregnancy in the ewe, sow, mare, and cow.

Interferon‐gamma gene and protein are spontaneously expressed by the porcine trophectoderm early in gestation

“…During this period, trophoblastic tissues represent the major part of the conceptus and establish intimate structural and functional relationships with the endometrium [19,37]. The fact that the porcine embryonic trophectoderm expresses an important immunoregulatory molecule suggests that the conceptus allograft plays an active role in early interactions with the maternal immune system before placental formation.…”

Pregnancy and interferon τ regulate DDX58 and PLSCR1 in the ovine uterus during the peri-implantation period

“…Implantation and establishment of pregnancy require that the peri-implantation ruminant conceptuses enter a receptive uterus and secrete IFNT (Bazer & Roberts 1983, Spencer et al 1996, 2010. Ovine IFNT prevents development of the luteolytic mechanism in the endometrium and acts as a pregnancy recognition signal, which communicates between the conceptus and maternal endometrium to allow for the establishment and maintenance of pregnancy, including implantation and synepitheliochorial placentation (Bazer et al , 2010.…”

Does inadequate luteal function limit the establishment of pregnancy in the early post-partum ewe?

“…Communication between the maternal uterine environment and the embryo is known to be vitally important to the establishment of pregnancy in normally cycling ewes and is mediated via secretions from both the endometrium and the embryo (Bazer & Roberts, 1983;Bazer et al, 1986). As yet we have no information on the biochemical nature of the endometrial/ conceptus secretions in the early post-partum ewe but it is possible that abnormal or asynch¬ ronous bi-directional signalling between them may be contributing to pregnancy failure in…”