Effect of fundic distension on gastric bicarbonate secretion in man

Human gastric mucosa secretes small amounts of bicarbonate into the mucus layer to maintain the pH at the cell surface as close to neutrality as possible. We have measured gastric bicarbonate secretion continuously with a computer-based system, using recordings of pH and PCO2. The formula of Henderson and Hasselbalch was used in the calculations. Graded fundic distension of the stomach with a balloon in six healthy subjects increased the gastric bicarbonate output by 46% (p less than 0.05), 28% (NS), and 84% (p less than 0.05) during 1 h of distension to 150 ml, 300 ml, and 600 ml, respectively. Continuous fundic distension during 2 1/2 h with a volume of 300 ml elicited a response that peaked after 45 min and vanished after 90 min. The rather short duration of gastric bicarbonate secretion response to fundic distension may be due to a fading caused by a volume adaptation or, alternatively, to an activation of inhibitory mechanisms. Seven duodenal ulcer patients who had undergone proximal gastric vagotomy showed virtually the same gastric bicarbonate secretion response to graded fundic distension. The anticholinergic drug benzilonium bromide totally inhibited the gastric bicarbonate response to 30 min of fundic distension to 150 ml, whereas indomethacin did not significantly affect the response to distension. These studies indicate that the gastric bicarbonate response to fundic distension is mainly mediated by short intramural neural cholinergic pathways and is independent of mucosal production of prostaglandins.