Angiogenic growth factor expression in placenta.

New blood vessel growth is generally a rare event in the healthy adult. However, a notable exception to this is the female reproductive tract where cyclic angiogenesis occurs. Striking new vessel growth and remodeling also occurs during placentation; thus angiogenesis is essential for reproductive success. Vascular endothelial growth factor is a potent stimulator of this process and its production and action is tightly regulated. Indeed the placenta is a rich source of a soluble variant of the flt-1 receptor which seems to protect the placenta from the effects of excess vascular endothelial growth factor. The balance between new vessel growth (in the placental villi for example) and endothelial cell loss in the spiral arteries within the decidua is a delicate one. This is influenced by the local production of promotors and inhibitors of endothelial cell activation. Perturbation of this may lead to maternal pathology during pregnancy.