Modulation of estrogen action during preimplantation period and in immature estradiol-primed rat uterus by anti-implantation agent, ormeloxifene

Ormeloxifene also induced 3H-progesterone (P) uptake by immature rat uterus. However, in the presence of E2, it significantly reduced 3H-P uptake. The in vitro competitive binding experiments did not reveal any displacement of 3H-R5020 either by ormeloxifene or by its hydroxy derivative from PR. The results suggest that in addition to its competitive antagonism at estrogen receptor level, ormeloxifene enhances the inactivation of intracellular E2 to estrone, a biologically less active form, thus declining estrogen receptor pool. Moreover, it causes indirect anti-progestational effects in the uterus by virtue of its anti-estrogenic profile rather than by blocking the PRs.