Migration of intravascular trophoblast cells in uterine arteries of the golden hamster: a scanning electron microscopic study.

Intravascular trophoblast (IVT) cells, derived from the trophoblast of the developing hamster embryo, are known to migrate in retrograde fashion into the uterine arteries. There they migrate to a certain point, destroy and replace the endothelial lining, and modify the smooth muscle of the arteries. The dilated vessels that result presumably enhance the flow of blood to the placental exchange area. The morphology of IVT cells in the hamster placenta was investigated by scanning and transmission electron microscopy. Although occasional single migrating cells were observed, the IVT generally appear as sheets of large, contiguous, sometimes overlapping cells that spread over the endothelial surfaces of the uterine central terminal arteries and vascular knot arteries. This process seems to be aided by the appearance of filopodia, which make contact either with other intravascular trophoblast cells or the endothelium. After consolidation, the IVT cells act as a functional part of the vessel lining and are readily distinguished from the surrounding endothelium by their numerous microvilli. The final distribution of the IVT cells is patchy rather than uniform.