Endometrial angiogenesis.

The endometrium is one of the few tissues in the adult where physiological angiogenesis occurs. Studies of endometrial angiogenesis are complicated by the continual changes in tissue growth and regression during the menstrual cycle, and differences between the two different zones of the endometrium--the functionalis and basalis. The mechanisms of angiogenesis in the endometrium may be different to those in solid tumours, requiring a re-evaluation of the relative importance of various angiogenesis promoters and inhibitors. None of the angiogenesis promoters or inhibitors have yet been demonstrated beyond doubt to have a biological role in endometrial angiogenesis in vivo. Thus, the mechanisms, timing and control of angiogenesis in the endometrium are far from being fully understood.