Endometrial angiogenesis throughout the human menstrual cycle

BACKGROUND: The timing and mechanisms of new blood vessel formation in the endometrium during the menstrual cycle are still largely unknown. In the pr esent study we used the chick embryo chorioallantoic membrane (CAM) as an i n-vivo assay for angiogenesis to assess the angiogenic potential of endomet rium obtained at different stages of the menstrual cycle. METHODS: Endometr ial fragments were explanted onto the CAM and, after 4 days of incubation, slides of the treated area were taken in ovo through a microscope for compu terized image analysis. The vascular density index (VDI), a stereological e stimate of vessel number and length, was obtained by counting the intersect ions of vessels with five concentric circles of a circular grid superimpose d on the computerized image. RESULTS: We demonstrated that human endometriu m has angiogenic potential throughout the menstrual cycle. Furthermore, the re was a significant difference in angiogenic response between the stages o f the menstrual cycle (P = 0.01). The VDIs of the early proliferative, earl y and late secretory stage were significantly higher than the VDI of the la te proliferative phase. CONCLUSIONS: Elongation of existing vessels during the early proliferative phase as well as growth and coiling of the spiral v essels during the secretory phase may demand far higher angiogenic activity than outgrowth and maintenance of vessels during the late proliferative ph ase.