A 42-year-old man has recurrent jejunal ulcers and diarrhoea. Fasting serum gastrin is 320 pg/mL (normal up to 100), which is equivocal. Intravenous secretin is administered. Serum gastrin rises to 950 pg/mL within 15 minutes. What is the explanation for this paradoxical rise?
- A Secretin stimulates gastrin release directly from G cells in the antrum
- B Secretin inhibits acid output, causing reflex hypergastrinaemia
- C Gastrinoma cells aberrantly express secretin receptors, triggering gastrin secretion ✓
- D Secretin cross-reacts with the gastrin assay, giving a false elevation
Correct answer: C. Gastrinoma cells aberrantly express secretin receptors, triggering gastrin secretion
Explanation
In normal physiology secretin inhibits acid secretion and lowers gastrin. Gastrinoma cells aberrantly express secretin receptors, so secretin paradoxically increases gastrin release. A rise of more than 120 pg/mL over basal confirms Zollinger-Ellison syndrome and is useful when fasting gastrin is equivocal. The rise reflects genuine hormone secretion from tumour cells, not assay cross-reactivity or G-cell stimulation.
Reference: Williams Textbook of Endocrinology, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.