Inhibition of luteolysis and embryo-uterine interactions during the peri-implantation period in pigs.

Inhibition of luteolysis and establishment of pregnancy in pigs results from oestrogen secretion by the conceptuses and requires progesterone produced by the corpus luteum (CL). An integral part of maternal recognition of pregnancy in the pig is the redirection of prostaglandin (PG) F2alpha secretion from endocrine (blood) to exocrine (uterus) direction and an increase of PGE2 synthesis in both the endometrium and conceptus. Uterine and conceptus PGE2 synthases play an integrated role in establishing the PGE2:PGF2alpha ratio necessary for luteal maintenance. The luteolytic or luteotrophic changes in the CL are synchronised with the release of maternal pituitary and ovarian hormones. The presence of uterine oxytocin (OT) and luteinising hormone (LH) receptors are important for the luteolytic effect of PGF2alpha. Conceptus oestrogen secretion coincides with autocrine and paracrine dialogue between the multiple conceptuses and uterine biological compounds and their receptors in trophoblast and endometrium.