[Significance of alkali secretion in acid tolerance of the rabbit duodenum]

Different rates of alkaline secretion and their effect on acid tolerance were investigated in segments of proximal duodenum of anaesthetized New Zealand white rabbits in situ. Metabolic alkalosis and glucagon led to a significant increase in alkaline secretion, while metabolic acidosis, vasopressin and furosemide significantly reduced alkaline secretion. Mucosal blood flow was significantly increased by glucagon and decreased by vasopressin. Alkaline secretion after an acid challenge was significantly higher than preacid secretion in animals with metabolic alkalosis, glucagon and NaCl, whereas vasopressin reduced alkaline secretion significantly. No significant change was observed during treatment with furosemide or metabolic acidosis. After perfusion with acid, 51.8% of the villi showed superficial damage (stage 1) under control conditions. Damage was significantly reduced after administration of bicarbonate or glucagon, while NH4Cl, vasopressin or furosemide increased damage both quantitatively and qualitatively. There was a direct linear correlation between the degree of damage and alkaline secretion. The proximal duodenum showed considerably less damage than the distal segment. We conclude that a decrease in alkaline secretion is associated with a reduced tolerance of duodenal mucosa to luminal acid, whereas stimulation of alkaline secretion improves mucosal protection. These results support the hypothesis that alkaline secretion is an important factor in the protection of the duodenum against luminal acid.