Abstract
Platelet‐activating factor (PAF) is an important phospholipid messenger involved in diverse physiological and pathological conditions. Actions of PAF are mediated by a specific PAF receptor (PAF‐R) and the inhibition of biological activity by PAF acetylhydrolase (PAF‐AH). To elucidate the potential role of PAF in stimulating angiogenesis and trophoblast giant cell migration during gestation, we examined the expression and localization of PAF‐R mRNA and protein as well as PAF‐AH mRNA in the bovine placenta. RT‐PCR, in situ hybridization and immunohistochemistry were applied to placentomes from days 20, 80, 150, 200, 240, 270 of gestation, and immediately pre‐partum (around day 280). PAF‐R mRNA and protein were colocalized in immature trophoblast giant cells (TGC), uterine epithelial cells, and endothelial cells of fetal and maternal vessels. There was no apparent difference in placental PAF‐R mRNA or protein levels until day 270. In contrast, in placentomes taken immediately pre‐partum the localization of the immunohistochemical and hybridization signals switched from immature TGC and maternal epithelium to cells of the maternal stroma, particularly endothelial cells of maternal vessels. mRNAs for PAF‐AH isoforms Ib (β‐ and γ‐subunit), II, and plasma‐isoform were detected by RT‐PCR in placentomes throughout gestation. In tissue sections mRNA of the PAF specific PAF‐AH‐Ib β‐subunit was predominantly found in TGC, while the intensity of the signal was weaker in maternal epithelium and endothelium of fetal and maternal vessels. Corresponding to the PAF‐R expression, mRNA of PAF‐AH Ib was detected mainly in maternal endothelial cells prior to parturition. The constitutive expression and localization of PAF‐R and PAF‐AH in epithelial and endothelial cells during gestation, together with the parturition‐related switch to the maternal stroma suggests a functional role of PAF for the interaction of TGC with the maternal epithelium, and thus may be associated with TGC migration, placental angiogenesis and pre‐partum tissue programming.Acknowledgement: This study was supported by the German Research Foundation.
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