Gastroduodenal alkaline response to acid and taurocholate in conscious dogs

Alkaline secretion was measured in the fundic and antral portions of the stomach and in the upper and distal portions of the duodenum in conscious dogs under basal conditions, in response to luminal exposure of HCl and taurocholate, and after feeding. Topical application of HCl (6.7-100 mM) resulted in an increase in HCO-3 output, particularly from the upper duodenum, and this was associated with the rise in prostaglandin (PG) E2 release. Since both these effects were abolished by pretreatment with indomethacin, it was concluded that the stimulation of alkaline secretion by topical HCl is mediated by mucosal PGs. HCl instilled into the main stomach or feeding a meat meal also caused an increase in alkaline secretion from the isolated (non-acid-perfused) gastric and duodenal portions, but this effect was not affected by indomethacin, suggesting that it was not mediated by endogenous PGs. Direct exposure of the mucosa to luminal taurocholate (0.62-20 mM) adjusted to pH 6.0 also increased gastroduodenal HCO-3 output, but this effect was not affected by indomethacin and accompanied by a fall in transmucosal PD value, suggesting that it could be due to the damage of the mucosa and increased mucosal permeability to HCO-3. We conclude that gastroduodenal HCO-3 output increases in response to natural substances such as HCl, taurocholate, or feeding, and the mechanism of this increase differs depending on the stimulant used.