ABSTRACT
Histamine injured. Histamine is found in enterochromaffin-like (ECL) cells, and both gastrin and acetylcholine (ACh) stimulate its release, while somatostatin and omeprazole act as inhibitors (Part H). Histamine plays a central role (along with gastrin and ACh) in the direct stimulation of gastric parietal cell HCl secretion. Synergism exists between gastrin and histamine, and between ACh and histamine in stimulating parietal cell acid secretion, but not necessarily between gastrin and ACh (since intracellular cAMP levels may not be elevated). Cimetidine, a drug that blocks histamine (H2) receptors on parietal cells, blocks much of the effect of either elevated serum gastrin or abnormally high parasympathetic (vagal) discharge since cAMP levels are reduced. Less well understood roles for histamine include its ability to enhance gut motility (similar to prostaglandins), vasodilate arterioles of the digestive tract (an H1 receptor action), enhance gastric pepsinogen release, and decrease pressure of the lower esophageal sphincter (LES).
