Maternal uteroplacental blood flow increases during pregnancy. Altered uteroplacental blood flow is a core predictor of abnormal pregnancy. Normally, the uteroplacental arteries are invaded by endovascular trophoblast and remodeled into dilated, inelastic tubes without maternal vasomotor control. Disturbed remodeling is associated with maintenance of high uteroplacental vascular resistance and intrauterine growth restriction (IUGR) and preeclampsia. Herein, we review routes, mechanisms, and control of endovascular trophoblast invasion. The reviewed data suggest that endovascular trophoblast invasion involves a side route of interstitial invasion. Failure of vascular invasion is preceded by impaired interstitial trophoblast invasion. Extravillous trophoblast synthesis of nitric oxide is discussed in relation to arterial dilation that paves the way for endovascular trophoblast. Moreover, molecular mimicry of invading trophoblast-expressing endothelial adhesion molecules is discussed in relation to replacement of endothelium by trophoblast. Also, maternal uterine endothelial cells actively prepare endovascular invasion by expression of selectins that enable trophoblast to adhere to maternal endothelium. Finally, the mother can prevent endovascular invasion by activated macrophage-induced apoptosis of trophoblast. These data are partially controversial because of methodological restrictions associated with limitations of human tissue investigations and animal studies. Animal models require special care when extrapolating data to the human due to extreme species variations regarding trophoblast invasion. Basal plates of delivered placentas or curettage specimens have been used to describe failure of trophoblast invasion associated with IUGR and preeclampsia; however, they are unsuitable for these kinds of studies, since they do not include the area of pathogenic events, i.e., the placental bed.

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Following attenuation of progesterone production corpora lutea are selectively cleared, a process associated with recruitment of macrophages. In the rabbit little is known about luteal immune cell phenotypes and expression of cytokines, which influence immune cells and resident luteal cells, during luteolysis. Consequently, we studied luteal immune cells by immunohistochemistry as well as luteal IL-10, TNFα, MCP-1, IFN-γ, and IL-1β mRNA expression by semiquantitative RT-PCR from day 8 to day 20 in pseudopregnant rabbits (d8-d20 p.hCG). Luteal function was assayed by serum progesterone levels. Functional luteolysis commenced by d14 p.hCG as indicated by attenuation of serum progesterone levels. X4 + tissue macrophage levels increased transiently on d12 and d14 p.hCG, whereas CD5 + T-cell levels transiently declined on these two days. CD68 + macrophages increased progressively after d16 p.hCG. The luteal mRNA level of the anti-inflammatory cytokine IL-10 as well as the mRNA levels of the proinflammatory cytokines TNFα and MCP-1 increased after d16 p.hCG and remained elevated up to d20 p.hCG. IFN-γ and IL-1β mRNA expression did not vary systematically. In summary, luteolysis was associated with an initial transient increase of X4 + macrophages and decrease of CD5 + T-cells, and later recruitment of CD68 + macrophages. During structural regression pro-and antiinflammatory cytokines are upregulated possibly to control immune cell function.Functional and structural regression of the rabbit corpus luteum is associated with altered luteal immune cell phenotypes and cytokine expression patterns