Human endometrial angiogenesis

Angiogenesis is the development of new microvessels from existing vessels, a process that involves microvascular endothelial cells. Physiological angi ogenesis rarely occurs in adults except in the ovary and endometrium during the reproductive life of females. Angiogenesis occurs by sprouting and non -sprouting mechanisms. Since endothelial sprouts are not observed in human endometrium, we hypothesized that non-sprouting mechanisms such as intussus ception and elongation are involved in endometrial angiogenesis. The demand for angiogenesis differs spatially and temporally in the endometrium: angi ogenesis occurs in the basalis layer during menstruation and in the functio nalis and subepithelial capillary plexus during the proliferative and early secretory stages. Most studies have failed to demonstrate a link between e xpression of endometrial angiogenic factors and new vessel growth. However, we demonstrated recently a strong relationship between vascular endothelia l growth factor (VEGF) immunolocalized in intravascular neutrophils and end othelial cell proliferation in each of the subepithelial capillary plexus, functionalis and basalis regions of the human endometrium. Our data also in dicate that focal neutrophil VEGF has a role in the development of the sube pithelial capillary plexus and functionalis microvessels during the prolife rative phase of the menstrual cycle. We propose that neutrophils are an int ravascular source of VEGF for vessels that undergo angiogenesis by intussus ception and elongation.