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.