Changes in endovascular trophoblast invasion and spiral artery remodelling at term in a transgenic preeclamptic rat model

Histological section of a day 21 implantation site including the placenta and its associated mesometrial triangle. A maternal arterial channel is visible in the central part of the placenta. The mesometrial triangle is divided into three depth levels (1, 2 and 3).

Diagram illustrating the measurements and calculations performed on individual spiral artery cross-sections. Stretches of endovascular trophoblast (ET, light blue) are traced on the lumen contour (yellow), delineating sub-ET (sum of light blue traced lengths) and extra-ET (non-traced) parts of the lumen contour. Similarly stretches of fibrinoid (magenta), vascular smooth muscle (green) and endothelium (dark blue) are projected on the lumen contour, and can thus be related either to the total lumen contour or to the presence or absence of endovascular trophoblast.

Parallel cross-sections of an invaded spiral artery immunostained for cytokeratin (A) and the endothelial marker CD31 (B). The intraluminal endovascular trophoblast (arrow) is associated with fibrinoid (A), the intramural endovascular trophoblast is flattened (A) (arrowheads). Reendothelialization has occurred in the contour part not covered by intraluminal trophoblast (between bars) (B).

Parallel cross-sections of a partially invaded spiral artery immunostained for cytokeratin (A) and the endothelial marker CD31 (B). Endovascular trophoblasts (arrow) show CD31 positivity at a lower staining intensity than the endothelial cells (arrowhead). Notice the different cell size of trophoblasts and endothelial cells.