Synthetic estrogen 17α-ethinyl estradiol induces pattern of uterine gene expression similar to endogenous estrogen 17β-estradiol

17α-Ethinyl estradiol is one of most widely prescribed estrogens. We compared the effects of this synthetic estrogen to those of the endogenous ovarian hormone 17β-estradiol on the expression of four estrogen-inducible genes in the rat uterus. The genes examined include c-fos, c-jun, vascular endothelial growth factor, and creatine kinase B, which are all known to be primary responses to estrogen administration. Both estrogens induced the four target genes with similar time courses and produced the same pattern of cell- specific expression of c-fos and vascular endothelial growth factor in the uterine epithelium and stroma, respectively. Dose-response studies established that the potency and efficacy of both estrogens in the uterus were the same for all four hormone-regulated genes. These studies suggest that 17α-ethinyl and 17β-estradiol produce similar if not identical patterns of gene expression in the uterus.