Estrogens
Abstract
Estrogens (17β-estraiol, estrone, and estriol) are steroid hormones produced by the developing follicles of the ovary. Although estrogens are primarily females sex hormones, males also produce estrogens. As lipophilic molecules they are believed to penetrate cell membranes and retained only in cells expressing estrogen receptors. Estrogens are transported via serum hormone binding globulin (SHBG) and only the free fractions are biologically active. Estrogen may bind to the classical nuclear receptors (ERα and ERβ) which are ligand-activated transcription factors, or membrane ERs (GPR30, ER-X) which are coupled with signal transduction pathways and are responsible for the rapid non-genomic signaling events. Estrogen are lipophilic and therefore cannot be taken orally but modifications in their structure has resulted in several compounds with increased hydrophilic properties which can be taken orally.