Angiogenesis in the human corpus luteum.

Angiogenesis is important for the formation and development of the corpus luteum and for maintenance of luteal function. Blood vessel regression is an important physiological phenomenon in the corpus luteum, which is associated with tissue involution during structural luteolysis. Angiogenesis actively occurs during the early luteal phase and is completed by the mid-luteal phase. Perivascular cells (pericytes) increase in number from the early luteal phase to the mid-luteal phase, suggesting that blood vessels are gradually stabilized until the mid-luteal phase. In the corpus luteum undergoing luteolysis, blood vessels and pericytes decrease in number, which is related to structural involution. In the corpus luteum of early pregnancy, the number of blood vessels with pericytes increases, suggesting that angiogenesis occurs again, accompanied by blood vessel stabilization. These changes in vasculature of the corpus luteum are regulated by the collaboration with vascular endothelial growth factor, which is involved in proliferation of vascular endothelial cells, and angiopoietins, which are involved in stabilization of blood vessels. This review focuses on angiogenesis, blood vessel stabilization and blood vessel regression during the divergent phases of luteal formation, luteal regression and luteal rescue by pregnancy. (Reprod Med Biol 2008; 7: 91-103).