A 28-year-old woman presents with galactorrhea and secondary amenorrhea. MRI shows a 6 mm pituitary microadenoma. Her serum prolactin is 180 ng/mL. Which hypothalamic factor is responsible for the tonic inhibition of prolactin secretion under normal circumstances?

• A Thyrotropin-releasing hormone (TRH)
• B Vasoactive intestinal peptide (VIP)
• C Gonadotropin-releasing hormone (GnRH)
• D Dopamine (Prolactin-inhibiting factor) ✓

Explanation

Dopamine secreted by tuberoinfundibular neurons is the principal prolactin-inhibiting factor; it acts on D2 receptors on lactotrophs to suppress both synthesis and release of prolactin. TRH and VIP are actually prolactin-stimulating factors. Loss of this tonic inhibition (e.g., stalk compression, dopamine antagonists, or autonomous adenoma) results in hyperprolactinemia causing galactorrhea and amenorrhea.

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

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Written and medically reviewed by the StethoPrep medical team.