A 25-year-old woman on risperidone develops bilateral galactorrhea and secondary amenorrhea. Serum prolactin is markedly elevated. The mechanism of this adverse effect is:
- A Blockade of D2 receptors in the tuberoinfundibular pathway, removing tonic inhibition of prolactin release ✓
- B Direct stimulation of lactotroph D2 receptors
- C Blockade of 5-HT2A receptors in the hypothalamus
- D Estrogenic agonism at the pituitary
Correct answer: A. Blockade of D2 receptors in the tuberoinfundibular pathway, removing tonic inhibition of prolactin release
Explanation
Tuberoinfundibular dopamine neurons tonically inhibit prolactin secretion from the anterior pituitary. Risperidone potently blocks these D2 receptors, disinhibiting prolactin release and causing galactorrhea, amenorrhea, and sexual dysfunction. Among atypical agents, risperidone carries the highest hyperprolactinemia risk, whereas aripiprazole lowers prolactin because it is a D2 partial agonist. Serotonin blockade is not the mechanism.
Reference: Katzung's Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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