Localization of gastric inhibitory polypeptide release by intestinal glucose perfusion in man

To determine the site of endogenous release of gastric inhibitory polypeptide (GIP), glucose perfusions (556 mmoles per liter) of duodenum, proximal jejunum, midjejunum, and ileum were performed in human volunteers using an occluding balloon perfusion technique. Preperfusion GIP concentrations were below assay sensitivity (125 pg per ml) in all subjects. After glucose perfusion, maximal serum GIP concentrations for the four groups were: duodenum, 1383 +/- 152 pg per ml; proximal jejunum, 904 +/- 87 pg per ml; midjejunum, 545 +/- 91 pg per ml, and ileum 305 +/- 38 pg per ml. Integrated GIP secretion was significantly greater with duodenal perfusion (111 +/- 21 ng-min ml-1) d proximal jejunal perfusion (69 +/- 5 ng-min ml-1), as compared to either midjejunal (47 +/- 7 ng-min ml-1) or ileal (25 +/- 6 ng-min ml-1) perfusions. Peak serum insulin concentrations and integrated insulin secretion were also significantly greater with perfusion of the duodenum or proximal jejunum. Serum glucose concentrations, integrated serum glucose, and glucose absorption were similar for the four areas perfused. The results of this study indicate that the proximal small intestine is the primary site of endogenous GIP release in man, but that smaller quantities are also released by the distal small bowel.