gastrin

Gastrin release from antral G cells is regulated by the following mechanisms:

 luminal regulation:

• amino acids (particularly phenylalanine and tryptophan) are responsible for food-induced gastrin release.
• acidity of the gastric content is another major factor (alkaline pH is stimulatory and acidic pH is inhibitory).

 H. pylori:

• by producing an alkaline pH by acid-neutralizing ammonia catalyzed by the bacterial urease.
• by production of stimulatory cytokines (interleukin-1 beta and TNF-alpha) released from the T lymphocytes and monocytes present in the gastric inflammatory infiltrate.
  another possible mechanism is through inhibition of somatostatin that normally provides an inhibitory feedback to gastrin release.

 Neural and peptidergic regulation:

• gastrin release is stimulated by activation of preganglionic vagal fibers, and is resistant to atropine. Paradoxically, the intraluminal stimulation (by a protein meal) of gastrin release is inhibited by low doses of atropine.
• Bombesin and bombesin-like peptide (GRP) potently stimulate gastrin release which thereafter results in acid secretion.