Endometrial vascular features prior to and following exposure to levonorgestrel.

A study of endometrial vasculature, mast cell numbers and tissue levels of tissue plasminogen activator (tPA) prior to and following exposure to levonorgestrel (20 micrograms/day) administered via a vaginal ring was undertaken. Following exposure to levonorgestrel, significantly fewer arterioles were present in the endometrium. During the early secretory phase of the control cycle, a positive correlation was found between mast cell numbers and progesterone levels. Levonorgestrel-exposed biopsies had significantly higher numbers of vessels with endothelial gaps and haemostatic plugs when compared with early secretory endometrium and significantly higher numbers of haemostatic plugs when compared with mid-late secretory endometrium. During the early secretory phase, the numbers of vessels possessing haemostatic plugs positively correlated with the peripheral blood levels of oestradiol and the number of contracted endothelial cells showed a positive correlation with progesterone levels. In mid-late secretory biopsies, the numbers of vessels with contracted endothelial cells were found to correlate negatively with oestradiol levels and the difference in the levels of contracted endothelial cells between the mid-late secretory endometrium and levonorgestrel-exposed endometrium correlated positively with progesterone levels of post-treatment cycles.