Importance of the ileum in neurotensin released by fat

Neurotensin is a potent stimulant of pancreatic exocrine secretion. Ileal mucosa is the storage site for about 90% of total neurotensin. Release occurs rapidly after a fatty meal and during perfusion of the duodenum and jejunum with fat but not during perfusion of the ileum with fat. To determine the origin of neurotensin released after fat stimulation, we studied the pattern of release of neurotensin before and after resection of the distal two thirds of the small bowel. Six dogs with gastric and duodenal fistulas were studied on different days. All dogs received infusions (in random order) of intraduodenal corn oil (Lipomul) (3 ml/kg/hr) and intravenous calcium chloride (0.36 mmol/kg intravenous bolus, followed by 0.36 mmol/kg/hr infusion) before and 6 weeks after resection of the distal two thirds of the small bowel with preservation of the ileocecal valve. Plasma levels of neurotensin were measured by specific radioimmunoassay. We found that release of neurotensin, in response to both intraduodenal Lipomul and intravenous calcium chloride stimulation, was abolished by resection of the distal small bowel. Before surgery, Lipomul-stimulated release of neurotensin rose to a peak concentration of 51 ± 17 pg/ml at 30 minutes. After surgery there was no release (the levels were unchanged from basal). Before surgery, intravenous calcium chloride produced a peak release of neurotensin (52 ± 15 pg/ml) 2 minutes after bolus injection. After surgery, neurotensin was not released by intravenous calcium. We conclude that the source of neurotensin released by perfusion of the proximal gut and by intravenous calcium infusion is the ileum. The release of neurotensin from the distal gut appears to be dependent on a signal from proximal to distal gut. The identity of the signal is unknown but is either a nerve reflex or a peptide agent.