Endogenous Estrogens

In addition to direct interaction with ERs, phytoestrogens may also act indirectly to modulate the concentration of endogenous estrogens. 

Endogenous estrogens are known to be active in a number of areas of the brain. There are indications that estrogens may play a role in mood, locomotor activity, pain sensitivity, vulnerability to neurodegenerative diseases and cognition (McEwan, 1999). In humans, the blood brain barrier is not fiilly developed at birth and, for this reason, the central nervous system (CNS) may be more sensitive to phytoestrogens in utero or at birth. As ERs are expressed in the CNS, phytoestrogens may also be active in this area. 

Estradiol is the predominant and most active form of endogenous estrogens. Given orally, it is metabolized by intestinal mucosa and liver (10% reaches the circulation as free estradiol), and resultant estrone concentrations are three to six times those of estradiol. 

Davison S, Davis SR (2003) New markers for cardiovascular disease risk in women impact of endogenous estrogen status and exogenous postmenopausal hormone therapy. J Clin Endocrinol Metab 88 2470-2478... 

Toniolo PG, LevitzM, Zeleniuch-Jacquotte N (1995) A prospective study of endogenous estrogens and breast cancer in postmenopausal women. J Natl Cancer Inst 87 190-197... 

Endogenous estrogen production IM 125 to 250 mg beginning on the tenth day of cycle and repeated every 7 days until suppression is no longer desired. 

It is a triphenyl ethylene compound and a competitive partial agonist inhibitor of endogenous estrogen. It can produce regression of estrogen induced proliferative endometrium. It can also prolong the luteal phase in normal menstruating women. 

Clomiphene is an older partial agonist, a weak estrogen that also acts as a competitive inhibitor of endogenous estrogens (Figure 40-5). It has found use as an ovulation-inducing agent (see below). 

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