Reconsidering the roles of endogenous estrogens and xenoestrogens: the membrane estradiol receptor G protein-coupled receptor 30 (GPR30) mediates the effects of various estrogens.

Estrone (El) and estriol (E3) are considered "weak" estrogens, which exert suppressive effects through estrogen receptors alpha and beta. However, recent studies have demonstrated that El and E3, as well as estradiol (E2), suppress gonadotropin-releasing hormone-induced luteinizing hormone secretion from bovine gonadotrophs via G-protein-coupled receptor 30, which is expressed in various reproductive organs. Currently, there is a lack of fundamental knowledge regarding E1 and E3, including their blood levels. In addition, xenoestrogens may remain in the body over long time periods because of enterohepatic circulation. Therefore, it is time to reconsider the roles of endogenous estrogens and xenoestrogens for reproduction.