Postprandial increase in the duodenal pH and the effect of intravenous secretin injection on ionic compositions of duodenal fluid and plasma in sheep

Testing five castrated male sheep with a pH-electrode inserted into the duodenal digesta through a T-shaped cannula, we found that the pH of the duodenal digesta was significantly increased from 3.11 ± 0.11 to 3.47 ± 0.09 after a meal. Secretin (2.5 CHR U/kg) was intravenously injected to mimic the duodenal pH increase. The administration significantly increased the duodenal digesta pH from 3.32 ± 0.18 to 4.85 ± 0.61, which was accompanied by an increase in sodium concentration, but by a decrease in potassium and chloride concentrations. It also significantly decreased the arterial blood pH from 7.543 ± 0.002 to 7.515 ± 0.008, which was accompanied by a reduced plasma HCO^-₃ concentration. From these results, we conclude that in sheep, feeding increases the duodenal digesta pH, and the postprandial pH increase in the duodenal fluid would be due to the raised HCO^-₃ secretion from the gastrointestinal tract.