Early endometrial microvascular response during implantation in the rat

The endometrial microvasculature becomes intimately involved in the events of early implantation. This paper reviews aspects of this microvascular involvement during implantation in the rat. There is a major increase in vascular permeability surrounding the implanting embryo, leading to significant local changes in microvascular architecture. This is followed by a shutdown of the capillaries closest to the embryo as the primary decidual zone develops. At this time, endometrial capillaries adjacent to the primary decidual zone become dilated, with over twice the average diameter of intersite capillaries. Endometrial neutrophils are reduced around the implanting blastocyst, mitigating against a role for these inflammatory mediators in vascular aspects of the implantation process. Angiogenesis does not appear to increase at the implantation site, although there is an increase in production of endometrial endothelial cell migratory signal a few hours prior to the commencement of implantation.