Anti-proliferative effects of progesterone antagonists in the primate endometrium: a potential role for the androgen receptor

In women and non-human primates, treatment with anti-progestins suppresses oestrogen-dependent mitotic activity in the endometrial glands. This anti-proliferative effect is paradoxical, because anti-progestins do not bind to the oestrogen receptor. Although this phenomenon has been termed a 'non-competitive anti-oestrogenic effect', it does not occur in all species or in other regions of the primate reproductive tract, so is best referred to as an 'endometrial anti-proliferative effect'. The abundance of androgen receptors is greatly increased by anti-progestin treatment, especially in the glandular epithelium in non-human primates and women. Such an increase could lead to an enhancement of androgen action in the endometrium. As androgens suppress oestrogen-dependent endometrial proliferation, the increased abundance of androgen receptors could mediate the anti-proliferative effects of anti-progestin treatment. This brief review evaluates the implications of these findings.