Which of the following compounds is not a precursor of the estrogens?

• A. Progesterone
• B. Testosterone
• C. Cholesterol
• D. Aldosterone

Answer: (D)

Steroid hormones are built from cholesterol through a sequence that supplies precursors to estrogens. Cholesterol is the starting material for all these pathways. From there, pregnenolone and then progesterone can be converted into androgens, and aromatase finally converts these androgens into estrogens such as estradiol. Testosterone is directly convertible to estradiol by aromatase, making it a clear precursor to estrogens. Progesterone also sits in the chain toward estrogen synthesis as an intermediate.

Aldosterone follows a side branch in the adrenal cortex aimed at producing mineralocorticoids for electrolyte balance. Its pathway does not feed into estrogen production, so it is not a precursor of estrogens.