How does GnRH therapy cause gynecomastia?

[SonarBob]

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Hey guys, if a patient has prostate cancer and is undergoing GnRH agonist therapy as androgen deprivation therapy (constant, non-pulsatile fashion), why would would he be more likely to experience gynecomastia? Where is the estrogen coming from?

 

[slz1900]

Estrogen is coming from peripheral conversion of androgens to estrogens, and in men most of the androgens that are aromatized do not come from the testes. GnRH agonists will lead to decreased testosterone production by Leydig cells, but androtensedione production by the adrenals will not be directly affected and since that is the main source of androgen for peripheral conversion, estrogens will still be produced. The result is a greater estrogen:testosterone ratio and development of gynecomastia.

 

[SonarBob]

Thanks for the clear explanation.