Endometrial endothelial cell proliferation in long-term users of subdermal levonorgestrel

The aim of the present study was to quantify endothelial cell proliferation (a component of angiogenesis) using immunohistochemistry, in the endometrium of users of subdermal levonorgestrel (Norplant). It was postulated that the increased endometrial microvascular density seen in Norplant users, compared to normally cycling women, was associated with an increased rate of endothelial cell proliferation. The results, however, showed that the endometrial endothelial cell proliferative index of Norplant users (0.39 +/- 0.16%; mean +/- SEM) was significantly reduced compared to that seen in normally cycling women (8.99 +/- 1.64). At the same time, total numbers of endometrial endothelial cells per mm2 in Norplant users (317.40 +/- 13.88) were significantly higher than in normally cycling women (223.35 +/- 10.31). It is possible that in the endometrium with levonorgestrel use, there is either a reduced rate of regression of the blood vessels relative to the rest of the tissue, or there is a reduced rate of endothelial cell death or turnover. Peripheral oestrogen and progesterone concentrations, bleeding pattern over the previous 90 days, and the histological appearance of the endometrium did not appear to be associated with the endothelial cell proliferative index. The results suggest that subdermal levonorgestrel use affects the mechanisms that dictate the normal relationship between endometrial blood vessel growth and regression, and the surrounding non-vascular tissue.