A 28-year-old woman presents with galactorrhea and secondary amenorrhea. Serum prolactin is 95 ng/mL. Which of the following best explains why dopamine normally suppresses prolactin secretion?
- A Dopamine stimulates somatostatin release from the median eminence, which then inhibits lactotrophs
- B Dopamine inhibits GnRH neurons, indirectly reducing prolactin via gonadal steroids
- C Dopamine activates D2 receptors on lactotrophs, inhibiting adenylyl cyclase and reducing cAMP-mediated prolactin gene transcription ✓
- D Dopamine acts on Pit-1 transcription factor to reduce lactotroph cell number
Correct answer: C. Dopamine activates D2 receptors on lactotrophs, inhibiting adenylyl cyclase and reducing cAMP-mediated prolactin gene transcription
Explanation
Dopamine is the principal prolactin-inhibitory factor (PIF). It binds D2 receptors on anterior pituitary lactotrophs, coupling to Gi protein to inhibit adenylyl cyclase; the resulting fall in cAMP reduces protein kinase A activity and decreases prolactin gene transcription. Loss of dopaminergic tone (as with dopamine antagonists or a pituitary stalk section) releases this tonic inhibition, causing hyperprolactinemia. Options B–D are incorrect mechanisms not directly responsible for the primary prolactin-inhibitory pathway.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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