In the ovarian follicle, which hormone primarily stimulates aromatase expression in granulosa cells to convert androgens to estrogens?

• A. FSH
• B. LH
• C. GnRH
• D. Prolactin

Answer: (A)

FSH drives aromatase expression in granulosa cells, enabling the conversion of androgens to estrogens within the developing follicle. In the two-cell model, theca interna cells respond to LH by making androgens, which then diffuse to granulosa cells. There, aromatase (CYP19A1) — upregulated by FSH through cAMP/PKA signaling — converts these androgens into estrogens, mainly estradiol, supporting follicle growth and ovulation readiness. LH’s main role here is to stimulate androgen production in the theca cells, not to directly boost aromatase in granulosa cells. GnRH regulates the release of FSH and LH, and prolactin does not drive this estrogen synthesis pathway in the follicle.