Maternal Recognition and Establishment of Pregnancy in Domestic Animals

Abstract

Introduction Implantation is a critical step in the progress of pregnancy, during which the coceptus acquires a fixed position within the uterine lumen and leads to the establishment of the placental structure. This process implies some cellular modifications of both the uterine epithelium and the trophoblast to ensure cell adhesion between the two tissues. In ruminants, the implantation process is characterized ‘by three main steps: a long pre-attachment period lasting 2-3 weeks during which the coceptus elongates considerably; an opposition stage when cellular contacts are established between the trophoblast and the uterine epithelium, and an adhesion stage which ends the process and gives rise to the cellular structure of an epithelio-chorial placenta. Acquisition of the coceptus to its designated position in the uterus underlines the need for the concepts to be recognized by its mother. - Maternal recognition of pregnancy can be considered as the interaction between the matemal unit and products of conception that signals to the mother the need to maintain pregnancy. To feature the concept of recognition of the dam to its pregnancy, forges the need to a thorough stepping over PGFQQ and factors controlling its secretion and action; oxytocin receptors and its deep implication on pregnancy; metalloproteinase's involvement in maintenance of pregnancy and all and above, the cellular interaction of the matemal and conceptual tissues. (1) Cellular Interactions During Implantation in Ruminants The blastocyst implantation involves major synchronized changes in both the uterine endometrium and the trophoblast that allow a close adhesion between the two tissues throughout pregnancy. Before any cell contact, the embryo and the uterine environment exert a mutual influence to favor the growth and the development of the coceptus as well as maintenance of pregnancy. As implantation progresses, interactions between the coceptus and the maternal compartment shift from a distant molecular dialogue by means of secreted factors , to more intimate and local exchanges mediated by cell to cell contacts.