Effect of stimulation of mucosal HCO3- secretion on acid-induced injury to porcine duodenal mucosa.

The effect of stimulation of duodenal mucosal bicarbonate secretion with vasoactive intestinal peptide (VIP) on acid-induced damage to the duodenal mucosa was studied in anaesthetized pigs in which bile and pancreatic juice were diverted from the duodenum. Mucosal damage was quantitatively assessed histologically, and mucosal blood flow was determined by means of radioactively labelled microspheres. Compared with placebo, intravenous infusion of VIP (500 pmol/kg/h) significantly stimulated duodenal mucosal bicarbonate secretion (47 +/- 13 versus 249 +/- 53 mumol/h) without concomitant changes in mucosal blood flow (51.5 +/- 7.8 versus 48.5 +/- 9.1 ml/min/100 g) or arterial bicarbonate concentration (24.2 +/- 1.1 versus 23.4 +/- 0.9 mM). The same dose of VIP increased the acid disappearance rate in the duodenum (2.2 +/- 0.14 versus 3.3 +/- 0.09 mmol/h) and reduced the extent of damage to the duodenal surface (16 +/- 2% versus 7 +/- 2%) during duodenal infusion of 0.03 M HCl but not 0.1 M HCl. We conclude that the protection offered by VIP against the small dose of acid is most likely secondary to the effect of VIP on mucosal bicarbonate secretion. Thus, this study suggests that duodenal mucosal bicarbonate secretion, independent of mucosal blood flow, is an integral factor in duodenal mucosal defence.