A 32-year-old woman presents with galactorrhea, secondary amenorrhea, and a serum prolactin of 180 ng/mL. MRI reveals a 6 mm pituitary adenoma. Which physiological mechanism is responsible for the amenorrhea in hyperprolactinemia?

• A Direct inhibition of FSH synthesis in gonadotroph cells by prolactin
• B Suppression of GnRH pulsatility leading to decreased LH and FSH secretion ✓
• C Elevated prolactin competing with LH for ovarian granulosa cell receptors
• D Prolactin-induced increase in dopamine secretion inhibiting estrogen synthesis

Explanation

Hyperprolactinemia suppresses the hypothalamic GnRH pulse generator, reducing pulsatile LH and FSH release. Without proper LH/FSH pulsatility, follicular development is impaired, estrogen levels fall, and ovulation and menstruation cease. Prolactin does not directly inhibit FSH synthesis (option A) nor compete for LH receptors (option C). Option D is mechanistically backwards — it is increased dopamine from the hypothalamus that normally inhibits prolactin, not the reverse.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.