Gastrin Secretion and Circadian Rhythm
Yes, gastrin secretion does increase at night, particularly during nocturnal hours when basal acid secretion is elevated. This physiological pattern is clinically significant because histamine H2-receptor antagonists strongly inhibit both basal and nocturnal gastric secretion 1.
Physiological Pattern of Gastrin Secretion
Gastrin follows a circadian rhythm with two principal biological effects: stimulation of acid secretion from gastric parietal cells and stimulation of mucosal growth in the acid-secreting part of the stomach 2. The nocturnal increase in gastrin secretion is part of the normal regulatory mechanism for gastric acid production.
Key Characteristics of Nocturnal Gastrin Secretion:
Basal gastrin secretion is elevated during nighttime hours, contributing to the nocturnal acid secretion pattern that occurs independent of meal stimulation 1
Histamine acts as the final common chemical mediator at the parietal cell, with interactions between histamine, gastrin, and acetylcholine occurring through potentiation mechanisms 1
Circulating gastrin regulates the increase in acid secretion that occurs after meals, but also maintains basal secretion during fasting states including overnight periods 2
Clinical Implications
Acid Suppression Therapy:
Histamine H2-receptor antagonists are particularly effective at inhibiting nocturnal gastric secretion because they block the histamine-mediated pathway that potentiates gastrin's effects 1
Proton pump inhibitors (PPIs) cause hypergastrinemia by blocking acid feedback inhibition, which can result in elevated gastrin levels both day and night 3, 4
Diagnostic Considerations:
Fasting gastrin levels should be measured after an overnight fast to establish baseline values, as recommended for evaluation of conditions like Zollinger-Ellison syndrome 5, 6
PPIs should be withdrawn with great caution and ideally stopped 10 days to 2 weeks before any planned estimation of circulating fasting gastrin 5
Mechanism of Gastrin Action
Gastrin does not directly stimulate parietal cells in humans but rather requires histamine and muscarinic mechanisms as essential mediators 4. When gastrin binds to its receptor, it triggers phosphatidylinositol biphosphate conversion to inositol 1,4,5-triphosphate, which increases intracellular calcium and initiates acid secretion 7.
Important Caveats:
Potentiating interactions occur between histamine and gastrin, histamine and acetylcholine, and between all three mediators, but not between gastrin and acetylcholine alone because all potentiating interactions require histamine 1
Complete blockade of acid secretion with supramaximal doses of famotidine abolishes both basal and gastrin-stimulated acid secretion, demonstrating that histamine is an essential mediator of gastrin's effects 4