Pentagastrin gastroprotection against acid is related to H2 receptor activation but not acid secretion

Background - Pentagastrin enhances gastric mucosal defence mechanisms against acid and protects the gastric mucosa from experimental injury. Aims - To investigate whether this gastroprotection is mediated by histamine receptors or occurs as a secondary effect of acid secretion stimulation. Methods - The effects of omeprazole (100 mu mol/kg), ranitidine (20 mg/kg), and pyrilamine (10 mg/kg) on pentagastrin (80 mu g/kg/h) induced gastroprotection against acidified aspirin injury were examined in a luminal pH controlled model. The effects of these compounds on pentagastrin enhanced gastroprotective mechanisms were investigated using intravital microscopy, in which intracellular pH of gastric surface cells (pH(i)), mucus gel thickness, gastric mucosal blood flow, and acid output were measured simultaneously. Results - Pentagastrin protected rat gastric mucosa from acidified aspirin injury. This gastroprotection was abolished by ranitidine, but not omeprazole or pyrilamine. Pentagastrin induced a hyperaemic response to luminal acid challenge, increased mucus gel thickness, and elevated pH(i) during acid challenge. Ranitidine reversed these enhanced defence mechanisms, whereas omeprazole and pyrilamine preserved these effects. Conclusions - These data indicate that pentagastrin associated gastroprotection and enhanced defence mechanisms against acid result mainly from activation of histamine H-2 receptors, and not as an effect of the stimulation of acid secretion.