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Old 05-03-2011
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Question If we block Testosterone then how come Gynecomastia!

What is the mechanism of ketoconazole causing gynecomastia? If it blocks testosterone synthesis, how can it then increases estrogen?

Thanks friends
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Old 05-03-2011
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Good question,

The idea is that when we say we block the synthesis of Testosterone, we don't mean completely blocking it. There's no drug that can do that.

The thing is that Ketoconazole and other antiandrogens simply alter the testosterone / estradiol balance. In other words they increase the availability of estrogen as opposed to the availability of testosterone.
Ref: http://www.ncbi.nlm.nih.gov/pubmed/4040740

That's in elderly men, they start to develop breasts because their estrogen/testosterone ratio starts to increase.

Also, another thing. Specifically regarding Ketoconazole, it has been recently discovered that it might also have antiandrogen receptor blocking activity.
Ref: http://en.wikipedia.org/wiki/Ketocon...nism_of_action

Other references I looked up:
http://www.endotext.org/male/male14/male14.html
http://www.johnleemd.com/store/male_hormone.html
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Old 05-03-2011
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Also in context to this.. The Fish says the following to help you remember:

"there are two things that cause men to have breasts, ketoconazole and fatness"

Ketoconazole for the reasons stated above

and fatness meaning increased obesity.. and Adipose having ability to produce Estrogen
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