Estrogen/Estrogen Receptor action and the Pregnant Myometrium

Estrogen and estrogen action in the myometrium are necessary for a successful pregnancy. Estrogen is required for both the myometrial hyperplastic phase of gestation as well as the contractile response that leads to parturition at term. The excessive levels of circulating estrogens during pregnancy, pose a signalling conundrum. How do different tissues that have varying spatial and temporal needs for estrogen deal with this high estrogen ligand level? Insulin like growth factor (IGF1) and its receptor are important to the process of hyperplasia and are estrogen responsive. Although IGF1 is necessary for a successful pregnancy, myometrial production of IGF1 seems to be redundant for myometrial expansion. This review discusses the newly investigated functionality of estrogen receptor alpha splice isoforms in uterine myometrial contractility and quiescence while also covering the role of estrogen and IGF1 in uterine myometrial hyperplasia during pregnancy.