Gastrin

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Subject: Gastrin

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Definition

  • Gastrin is a hormone secreted by the G-cells of the antrum of the stomach and the pancreatic islet of Langerhans. Its secretion is stimulated by alkalinity, by distention of the stomach by the antrum, by vagal stimulation, and by the presence of peptides, amino acids, alcohol, or calcium in the stomach. Its secretion is inhibited by gastric acidity via negative feedback system.

  • Principal forms of gastrin in the blood are G-34 (big gastrin), G-17 (little gastrin), and G-14 (mini gastrin). Each of these circulates in nonsulfated and sulfated forms.

  • The gastric stimulation test after calcium infusion (15 mg of Ca/kg in 500 mL normal saline over 4 hours) is useful in patients with marked elevation of gastrin levels. This test should be reserved for patients with a negative secretin test, gastric acid hypersecretion, and a strong suspicion of Z-E syndrome.

  • Normal range:

    • Gastrin: 0–100 pg/mL

    • Gastrin stimulation test (after secretin): no response or slight suppression

    • Gastrin stimulation test (after calcium infusion): little or no increase over baseline

Use

  • Diagnosis of Z-E syndrome: The gastrin test after secretin (2–3 U/kg injected over 30 seconds) is preferred provocative test for patients suspected of having Z-E syndrome.

  • Diagnosis of gastrinoma: Basal and secretin-stimulated serum gastrin measurements are the best laboratory tests for gastrinoma.

  • Investigation of patients with achlorhydria or pernicious anemia.

Interpretation

Increased In

  • Increased serum gastrin without gastric acid hypersecretion

    • Atrophic gastritis, especially when associated with circulating parietal cell antibodies

    • PA in approximately 75% of patients

    • Some cases of carcinoma of the body of the stomach, a reflection of the atrophic gastritis that is present

    • Gastric acid inhibitor therapy

    • After vagotomy

  • Increased serum gastrin with gastric acid hypersecretion

    • Z-E syndrome

    • Hyperplasia of antral gastrin cells

    • Isolated retained antrum (a condition of gastric acid hypersecretion and recurrent ulceration after antrectomy and gastrojejunostomy that occurs when the duodenal stump contains antral mucosa)

  • Increased serum gastrin with gastric acid normal or slight hypersecretion

    • RA

    • DM

    • Pheochromocytoma

    • Vitiligo

    • Chronic renal failure with serum creatinine >3 mg/dL; occurs in 50% of patients

  • Pyloric obstruction with gastric distention

  • Short-bowel syndrome due to massive resection or extensive regional enteritis

  • Incomplete vagotomy

Decreased In

  • Antrectomy with vagotomy

  • Hypothyroidism

  • Drugs, including anticholinergics and tricyclic antidepressants

Limitations

  • Gastrin levels follow circadian rhythms (lowest in early morning and highest during the day).

  • No consistent relationship has been established between H. pylori and gastric acid secretion or serum gastrin levels.

 
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