Doctor sThesis from Karolinska Institutet . Ovulation and endometrial development as well as contraceptive efficacy was studied after treatment with the antiprogestin mifepristone. Mechanism of action after treatment with the gestagen levonorgestrel or mifepristone in doses effective for emergency contraception was also evaluated.
Mifepristone binds to the progesterone receptor and blocks the action.
The effect in reproductive pathways depends on when the drug is administered and the dose given. Subjects were treated with different doses of mifepristone, 0.5 mg daily, 5mg once weekly or 200 mg as a single dose in early luteal phase. Immunohistochemistry and electron microscopy were used for analysis of implantation on markers and ovarian steroid production was followed by daily urine samples. The expression of integrin subunits alpha4 and beta3, suggested as important for blastocyst implantation, was also reduced. This effect was also shown after administration with 5mg weekly and 0.5 mg daily.