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Aromatase is the enzyme that catalyzes a key aromatization step in the synthesis of estrogen. It converts the enone ring of androgen precursors such as testosterone, to a phenol, completing the synthesis of estrogen. As such, AIs are estrogen synthesis inhibitors. Because hormone-positive breast and ovarian cancers are dependent on estrogen for ...
Antiestrogens, also known as estrogen antagonists or estrogen blockers, are a class of drugs which prevent estrogens like estradiol from mediating their biological effects in the body. They act by blocking the estrogen receptor (ER) and/or inhibiting or suppressing estrogen production .
Gynecomastia is thought to be caused by an altered ratio of estrogens to androgens mediated by an increase in estrogen action, a decrease in androgen action, or a combination of these two factors. [7] Estrogen and androgens have opposing actions on breast tissue: estrogens stimulate proliferation while androgens inhibit proliferation.
Anastrozole is surprisingly ineffective at treating gynecomastia, in contrast to selective estrogen receptor modulators like tamoxifen. [33] [34] Anastrozole was under development for the treatment of female infertility but did not complete development and hence was never approved for this indication. [35]
It is a mixed agonist and antagonist of the estrogen receptor (ER). Clomifene activates the ERα in the setting of low baseline estrogen levels and partially blocks the receptor in the context of high baseline estrogen levels. [18] Conversely, it is an antagonist of the ERβ. [18] Clomifene has antiestrogenic effects in the uterus. [32]
[264] [265] Gynecomastia was first reported with spironolactone in 1962, [107] [266] and the antiandrogenic activity of the medication was first described in 1969. [267] This shortly followed the discovery in 1967 that gynecomastia is an important and major side effect of AR antagonists.
High-dose estrogen therapy is associated with poor tolerability and safety, namely gynecomastia and cardiovascular complications such as thrombosis. [ additional citation(s) needed ] For this reason, has largely been replaced by newer antiandrogens such as gonadotropin-releasing hormone analogues and nonsteroidal antiandrogens .
The gynecomastia associated with cimetidine is thought to be due to blockade of ARs in the breasts, which results in estrogen action unopposed by androgens in this tissue, although increased levels of estrogens due to inhibition of estrogen metabolism is another possible mechanism. [52]
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