A 26-year-old male bodybuilder self-administering high-dose testosterone injections develops bilateral gynecomastia. The most likely mechanism is:

• A Suppression of prolactin secretion
• B Direct androgen receptor agonism in breast tissue
• C Peripheral aromatization of testosterone to estradiol ✓
• D Increased sex hormone-binding globulin raising free estrogen

Explanation

Testosterone is aromatized peripherally in adipose tissue and breast stromal cells to estradiol by the aromatase enzyme. Supraphysiologic doses generate enough estrogen to stimulate ductal proliferation, producing gynecomastia despite concurrent androgen excess. Exogenous testosterone also suppresses gonadotropins and endogenous spermatogenesis. Non-aromatizable androgens such as dihydrotestosterone cause far less gynecomastia, confirming that the estrogenic metabolite, not androgen receptor stimulation, drives the breast changes.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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