The protective effects of estrogen in the cardiovascular system results from both systemic effects and direct actions of the hormone on the blood vessels.
The artery is composed of three intricate layers of tissue. The inner most layer, closest to the blood is called the intima. The middle layer of the artery, the media is composed of smooth muscle cells. Middle layers fibers are primarily made of two proteins, collagen and elastin. The middle layer changes vessel diameter to regulate blood flow and blood pressure.
The outermost layer, the aventitia is composed of connective tissue and small blood vessels that feed the walls of large arteries. These three layers of the artery wall surround the lumen, the opening that blood flows through. Snuggled up to the intima is a thin layer of endothelial cells. These endothelial cells are the gatekeeper of the artery.
Receptors for estrogen have been identified in all components of the vascular wall: endothelium, smooth muscle, adventitial cells. As such, for post menopausal women diminished estrogen can effect the function of any layer of the artery. Estrogen administration promotes vasodilation in part by stimulating prostacyclin and nitric oxide synthesis.
17-beta estradiol is a natural agonist/binder for estrogen receptors alpha and beta. Genistein a soy derived phytoestrogen also binds to estrogen receptors alpha and beta.
Sources:
Mechanism of Estrogenic Vascular Protection
Jayachandran & Miller MD’s
Am J Physiol Heart Circ 2006
The Vascular Protective Effects of Estrogen
Farhat, Lavigne, Ramwell MD’s
The FASEB Journal Vol 10, 615-624
Aging Hearts & Arteries
National Institutes of Health April 2005
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