A 35-year-old woman presents with galactorrhoea, amenorrhoea, and a serum prolactin of 180 ng/mL. MRI shows a 6 mm pituitary microadenoma. Prolactin secretion from lactotrophs is tonically inhibited by which hypothalamic mediator?
- A Thyrotropin-releasing hormone (TRH)
- B Gonadotropin-releasing hormone (GnRH)
- C Dopamine (acting on D2 receptors on lactotrophs) ✓
- D Somatostatin
Correct answer: C. Dopamine (acting on D2 receptors on lactotrophs)
Explanation
Dopamine, released from the tuberoinfundibular pathway of the hypothalamus, tonically inhibits prolactin secretion via D2 receptors on pituitary lactotrophs. A prolactinoma secretes prolactin autonomously, bypassing this inhibition. TRH is a stimulator of prolactin (explaining hyperprolactinaemia in hypothyroidism); somatostatin inhibits GH and TSH; GnRH regulates gonadotropins.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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