A 31-year-old woman with secondary amenorrhoea has galactorrhoea and a serum prolactin of 180 ng/mL. MRI shows a 7 mm pituitary microadenoma. Which mechanism explains her amenorrhoea?
- A Inhibition of GnRH pulse frequency through dopamine-mediated hypothalamic action ✓
- B Suppression of GnRH pulsatility via dopamine-independent pathways
- C Direct destruction of GnRH neurons by tumour expansion
- D Ovarian resistance to FSH induced by hyperprolactinaemia
Correct answer: A. Inhibition of GnRH pulse frequency through dopamine-mediated hypothalamic action
Explanation
Hyperprolactinaemia suppresses hypothalamic dopamine-mediated regulation such that increased dopaminergic tone inhibits GnRH pulsatile secretion, lowering LH pulses and producing hypoestrogenic anovulation. The pituitary lesion itself is tiny and does not destroy GnRH neurons, which lie in the hypothalamus. Ovaries remain structurally responsive; the defect is central, which is why dopamine agonist therapy restores ovulation.
Reference: Ganong's Review of Medical Physiology, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.