Estrogen has significant actions for the preservation of bone, blood vessel integrity, and contributes to brain function and the modulation of immunity. Estrogen also affects central nervous system functions and the neuroendocrine-gonadal axis in both sexes.
Two isoforms of nuclear estrogen receptors have been identified, cloned and characterized: ER-a and ER-b. They are distinct proteins encoded by separate genes located on different chromosomes.
The cDNA for the human ER-a was cloned in 1985. The discovery of estrogen receptor ER-b was reported in 1996.
ER-a exists as the predominant receptor in most classic estrogen target organs. A clear role for ER-b has been established in the ovary, cardiovascular system, and brain as well as in several animal models of inflammation including arthritis, endometriosis, inflammatory bowel disease, and sepsis (infection).
ER-a and ER-b proteins bind 17B-estradiol (E2) with nearly equal affinity and exhibit a very similar binding profile for a number of natural and synthetic ligands.
Ligands are molecules, either synthetic or of natural origin, that bind to certain proteins. In the case of natural ligands, such as hormones, or neurotransmitters the proteins they bind are called receptors.
Isoflavone phytoestrogens daidzein and genistein are well known ER-b selective compounds. They bind and activate human ER-a and ER-b with an up to 100 fold stronger activation of ER-b.
Source:
Experimental Dermatology 2006 pgs 85-87
Verdier-Sevrain et al
Mechanism of Estrogenic Vascular Protection
Am J Physiology Heart Circ Physiol 209: H507-H508, 2006
Cell localization, Physiology, and Nongenomic Actions of Estrogen Receptors
Ellis R. Levin
J Appl Physiol 91: 1860-1867, 2001
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