The Implantation Reaction

Abstract

Implantation involves the attachment of the blastocyst to the wall of the uterus with, in some cases, the embedding of the entire ovum in the uterine wall. Associated with it are very profound and characteristic changes in the endometrium both during preparation for implantation and following attachment of the blastocyst. In this chapter, the uterine changes that take place during preparation will be considered first and then the changes during the process of implantation. The former occur regularly and frequently throughout the life of most female mammals, whereas the latter are rarer events, especially in women. This division of the subject is also convenient for the consideration of the control mechanism involved. Whereas the preparative changes are largely directed by the varying levels of the hormones secreted by the ovary, once the implantation process has been initiated hormones playa largely permissive role.There is considerable species variation in the reaction of the uterus in preparation for and during implantation. De Feo (1967) reviewed this subject very thoroughly in the first edition of this book. The great majority of research investigations have been carried out on laboratory rodents, with very little on primates or the larger domestic animals. It follows therefore that any general account of implantation will lean heavily on information acquired from laboratory animals. Although one would like to have a much more general coverage, one cannot escape the reality that information acquired from many experiments on large numbers of laboratory animals provides a sound foundation on which to build. Information from primates or wild mammals will always tend to be fragmentary because of the difficulty of obtaining large numbers of specimens. Anyone who has worked with rats or mice knows how easy it is to be misled by the results from two or three animals. The only sensible course therefore is to get as

Failure of platelet-activating factor (PAF-acether) to induce decidualization in mice and failure of antagonists of PAF to inhibit implantation

“…In other situations, PAF has been implicated in many aspects of inflammation including the activation of platelets and leucocytes and the liberation of vasoactive substances such as prostaglandins. Since the response of the uterus to an implanting blastocyst appears to resemble an inflammatory-like reaction (Finn, 1977) and is characterized by an increase in vascular permeability (Psychoyos, 1961), some involvement of PAF would not be unexpected.…”

1,25-Dihydroxyvitamin D3 induces in vivo the decidualization of rat endometrial cells

“…Uterine weight increases dramatically during decidualization, due to hyperplasia and hyperproliferation of endometrial cells (Finn, 1977), and endometrial cells differentiate into enlarged decidual cells with large nuclei and increased chromatin surface, some of these cells being binucleate (Kennedy, 1986). Similar events can be induced in the rat uterus by local artificial stimuli, provided the stimulus is given when the uterus is most sensitive to deciduoma induction, at Day 5 of pseudopregnancy (De Feo, 1963).…”

“…Vitamin D3 metabolites or solvents were injected into the uterine lumen with a I-ml plastic syringe and a 16/5 mm needle (Terumo, Haaszode, Belgium) via the upper part of the left uterine horn. Care was taken not to alter the uterine wall, as it is well known that local injury of the uterine epithelium can by itself induce decidualization (De Feo, 1967;Finn, 1977). The caudal end of the uterus was not ligatured to avoid a stress-induced decidualization.…”

Estradiol supplementation during the luteal phase in poor responder patients undergoing in vitro fertilization: a randomized clinical trial

“…The role of progesterone (P) supplementation in the luteal phase of in vitro fertilization (IVF) cycles is well established worldwide [12], but the influence of the luteal phase E2 level on implantation is not clearly defined [13][14][15]. First Stewart et al revealed a significant difference in E2 levels between fertile and infertile cycles of fertile women who underwent donor insemination [16].…”