Mechanism of Action of Estrogens

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Chapter: Essential pharmacology : Estrogens, Progestins and Contraceptives

Estrogens bind to specific nuclear receptors in target cells and produce effects by regulating protein synthesis. Estrogen receptors (ERs) have been demonstrated in female sex organs, breast, pituitary, liver, bone, blood vessels, heart, CNS and in certain hormone responsive breast carcinoma cells.


MECHANISM OF ACTION

 

Estrogens bind to specific nuclear receptors in target cells and produce effects by regulating protein synthesis. Estrogen receptors (ERs) have been demonstrated in female sex organs, breast, pituitary, liver, bone, blood vessels, heart, CNS and in certain hormone responsive breast carcinoma cells. The ER is analogous to other steroid receptors: agonist binding to the ligand binding domain brings about receptor dimerization and interaction with ‘estrogen response elements’ (EREs) of target genes. Gene transcription is promoted through certain coactivator proteins. On binding an estrogen antagonist the receptor assumes a different conformation and interacts with other corepressor proteins inhibiting gene transcription.

 

Two ERs designated ERα and ERβ have been identified, cloned and structurally characterized. Most tissues express both subtypes but ERα predominates in uterus, vagina, breast, hypothalamus and blood vessels, while ERβ predominates in prostate gland of males and ovaries in females. Estradiol binds to both ERα and ERβ with equal affinity, but certain ligands may have differing affinities. More importantly ERα and ERβ may have a different pattern of interaction with coactivators and corepressors.

 

Few nongenomic rapid actions of estrogens in certain tissues mediated through the same ER have also been observed.

 

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