A male patient with a craniopharyngioma compressing the pituitary stalk shows paradoxically elevated serum prolactin. Which mechanism best explains this finding?

• A Craniopharyngioma cells autonomously secrete prolactin
• B Compression increases TRH delivery to lactotrophs, stimulating prolactin
• C Loss of somatostatin suppression upregulates prolactin gene expression
• D Stalk compression interrupts dopamine delivery to lactotrophs, removing tonic inhibition ✓

Explanation

Prolactin is unique among anterior pituitary hormones in that it is under tonic inhibitory control by dopamine (also called prolactin-inhibiting factor) released from tuberoinfundibular neurons. Stalk section or compression interrupts dopamine delivery through the portal system, releasing lactotrophs from inhibition and raising prolactin. This is called the 'stalk effect' and can raise prolactin to 100–150 ng/mL (lower than a true prolactinoma which usually exceeds 200 ng/mL).

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

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Written and medically reviewed by the StethoPrep medical team.