A 28-year-old woman has galactorrhea and amenorrhea. Her serum prolactin is markedly elevated. The neuroendocrine mechanism most directly responsible for hyperprolactinemia in a prolactin-secreting pituitary adenoma (prolactinoma) is:

• A Loss of tonic dopaminergic inhibition of prolactin secretion ✓
• B Increased TRH stimulation of pituitary lactotrophs
• C Increased estrogen feedback on hypothalamic prolactin-releasing peptide
• D Elevated VIP secretion from the hypothalamus stimulating lactotrophs

Explanation

Prolactin is unique among anterior pituitary hormones in being under predominant tonic inhibition by dopamine (prolactin-inhibiting factor, PIF) secreted from hypothalamic tuberoinfundibular neurons. Prolactinoma cells autonomously secrete prolactin regardless of dopamine levels; however, the tumor disrupts normal portal delivery of dopamine and may compress the pituitary stalk, further removing tonic inhibition. This is why dopamine agonists (cabergoline, bromocriptine) are the primary medical treatment. TRH can stimulate prolactin but is not the primary driver.

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

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Written and medically reviewed by the StethoPrep medical team.