A 30-year-old woman has amenorrhea and a serum prolactin of 180 ng/mL. A pituitary MRI shows a 12 mm adenoma. Which physiologic mechanism normally keeps prolactin low in non-pregnant women?

• A Tonic dopaminergic inhibition from hypothalamic tuberoinfundibular neurons via the portal circulation ✓
• B Continuous negative feedback of estrogen on pituitary lactotrophs
• C Somatostatin suppression of prolactin secretion via GHRH competition
• D GnRH pulsatility suppresses prolactin between LH pulses

Explanation

Prolactin is uniquely under tonic inhibition by dopamine (DA) released from tuberoinfundibular neurons into the hypothalamo-hypophyseal portal vessels. DA binds D2 receptors on lactotrophs, suppressing both prolactin synthesis and secretion. A prolactinoma autonomously secretes prolactin independent of this inhibition; alternatively, any stalk lesion disrupting DA delivery (stalk compression effect) raises prolactin by removing inhibition.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.