Sites of endometrial vascular leakage during implantation in the rabbit

Vascular labelling with carbon suspension was used to identify endometrial vessels demonstrating macromolecular leakage at implantation sites in the rabbit. Extravasation was seen first in venous components of the deep endometrial stroma on the mesometrial aspect of implantation sites. Carbon labelling was apparent in such vessels at 7 d, 0 hr post coitum, (p.c.), and was attributed to gap formation between endothelial cells. Later in the implantation process, leakage was seen as microextravasations of carbon in the lateral and antimesometrial walls of implantation chambers. Here, penetration of vessels by trophoblast was apparent and membranous processes from the trophoblast projected into vessel lumina. Extravasated material (carbon, platelets) was localized to a labyrinthine system of membranes within the trophoblast, and a potential role for the labyrinth in handling of ingested plasma constituents is discussed. A similar process of trophoblastic penetration of vessels occurred on the mesometrial aspect of implantation sites several hours later. Systemic administration of the anti-inflammatory agent indomethacin blocked vascular leakage due to endothelial gap formation but had little or no effect on trophoblast knob penetration of vessels. This observation may explain the results of previous studies in which treatment with anti-inflammatory agents reduced, but could not inhibit completely, the vascular permeability changes at implantation sites.