Effect of acid perfusion of the terminal ileum on plasma immunoreactive secretin and pancreatic secretion in the rat.

The distribution of immunoreactive secretin in acid extracts of the alimentary tract of the rat was determined. It was found to be contained in higher concentrations in the duodenum and in the terminal ileum than in other parts of the intestine. To elucidate the possible role of secretin contained in the terminal ileum, this part of the intestine was perfused with hydrochloric acid, a potent secretin secretagogue, and changes in plasma immunoreactive secretin levels and in pancreatic secretion were investigated in anaesthetized rats. Plasma immunoreactive secretin was increased from 65 +/- 5 pg/ml to 108 +/- 13 pg/ml during a 10 minutes perfusion with hydrochloric acid. This was significantly higher than that of saline perfusion but significantly lower than that of duodenal perfusion with hydrochloric acid. Acid perfusion of the terminal ileum also caused a three-fold increase in pancreatic flow rate and a twofold increase in bicarbonate concentration. These results suggest that the terminal ileum, through release of secretin, might play a role in regulating the pancreatic secretion of water and bicarbonate in response to changes in intraluminal fluids in the distal intestine in the rat.