THE ROLE OF PROSTAGLANDINS IN BLASTOCYST IMPLANTATION

This review summarizes the information available on the involvement of prostaglandins in blastocyst implantation, and examines their interac tions with three other inflammatory mediators, platelet-activating fac tor (PAF), interleukin 1 (IL-1) and corticotrophin-releasing factor (C RF), Essential elements of this information, consistent with the assum ption that prostaglandins play an important role in implantation, appe ar to be: (i) the burst of endometrial prostaglandin production, follo wing the blastocyst signal(s) or an artificial stimulus; (ii) the main localization of this production at the luminal epithelium and release towards the stroma; and (iii) the presence at the stromal level of sp ecific progesterone-dependent binding sites for prostaglandin E(2) In addition, accumulated data indicate a paracrine interaction at the end ometrial level between PAF and prostaglandin E(2), which could serve, among others, to amplify the embryonic signal(s), Pro-inflammatory cyt okines IL-1 alpha and IL-1 beta may also play a significant role in en dometrial response via the modulation of prostaglandin E(2) production , Prostaglandins and IL-1 induce the expression of CRF, which acts as an autocrine/paracrine inflammatory regulator, CRF exhibits a strong v asoactivity in skin tests, inducing a local increase of capillary perm eability at a concentrations of 10(-10) M, Levels of CRF and its mRNA were found to be higher in rat implantation sites compared with those in the interimplantation regions, Stromal cells were found to be posit ive for immunoreactive CRF at the implantation sites only, It is sugge sted that CRF may be involved in the local increase of capillary perme ability seen in implantation sites, and that its production by stromal cells may be the consequence of a paracrine action of epithelial pros taglandin, released under the effect of PAF and IL-1, derived from or produced by blastocysts in endometrial cells.