A 35-year-old woman with carcinoid syndrome presents with episodic flushing, diarrhea, and wheezing. Treatment with octreotide is initiated. Its mechanism is:
- A Blockade of serotonin 5-HT3 receptors in the gut reducing diarrhea and of 5-HT2B receptors in the heart
- B Inhibition of tryptophan hydroxylase, reducing tumor serotonin synthesis
- C Somatostatin analog acting on SSTR2/5 receptors on tumor cells to reduce secretion of serotonin, bradykinin, substance P, and other vasoactive substances ✓
- D Alpha-1 adrenergic blockade preventing serotonin-induced vasoconstriction
Correct answer: C. Somatostatin analog acting on SSTR2/5 receptors on tumor cells to reduce secretion of serotonin, bradykinin, substance P, and other vasoactive substances
Explanation
Octreotide is a synthetic octapeptide analog of somatostatin with a much longer half-life (~2 hours vs 2 minutes for native somatostatin). It acts on somatostatin receptors (primarily SSTR2 and SSTR5) expressed on carcinoid tumor cells, inhibiting adenylyl cyclase and reducing exocytosis of secretory granules. This decreases release of serotonin, bradykinin, substance P, histamine, and other vasoactive amines responsible for the carcinoid syndrome symptoms. It is the mainstay medical therapy for symptom control in functional carcinoid tumors.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.