Endometrial vasculature in Norplant users.

Disrupted, prolonged and irregular endometrial bleeding are major unwanted side-effects of progestin-only contraceptives. The aim of this paper is to review current information on steroid control of the microvasculature, microvascular heterogeneity and microvascular fragility, with emphasis on the relevance of these issues to the endometrial microvasculature in women receiving Norplant implant contraception. Subjects were either Indonesian women with between 3 and 12 months exposure to Norplant (n = 191) or Caucasian controls recruited in Melbourne, Australia. Norplant endometrium was always thinner than control endometrium, with a varied histology that usually included a basalis-type appearance, signs of haemorrhage and some dilated and congested subepithelial vessels. Thin-walled vessels were seen which could have been either blood vascular or lymphatics. Steroid control of the vasculature can operate through numerous direct and indirect mechanisms, with up to 30 genes relevant to vascular function having consensus oestrogen response elements in their promoter regions. The vasoactive effects of progesterone are less well documented. However, experimental data for direct effects on the endometrial vasculature are mounting. Progestin-induced endometrial breakthrough bleeding is often focal, suggesting that microvascular heterogeneity may be an important factor in understanding this phenomenon. Increased susceptibility to bleeding may result from increased microvascular fragility, possibly as a consequence of progestins altering the balance of angiogenic promoters and inhibitors in the endometrium, thus leaving the vessels in a permanently weakened state.