Release of Gastric Inhibitory Peptide Following a Peptone Meal in the Dog

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Release of gastric inhibitory peptide into the circulation after peptone ingestion has not been demonstrated previously. In the present studies, 5 alert dogs with indwelling polyethylene portal venous catheters and gastric fistulas were studied. A meal of 10% peptone in 150 ml 0.9% NaCl, pH 7 was infused through the gastric fistula into the stomach. Gastric inhibitory peptide was measured by a specific and sensitive radioimmunoassay in sera obtained simultaneously from portal and cephalic veins before and at 1, 4, 8, 15, 30, 60, and 90 min after peptone infusion. Cephalic venous serum insulin and glucose concentrations were measured at the same time points. Mean basal portal and cephalic vein serum gastric inhibitory peptide concentrations were 136 +/- 22 and 34 +/- 10 (SEM) pg/ml, respectively. After infusion of the peptone meal, immediate increases in serum gastric inhibitory peptide levels were noted in both portal and peripheral circulation, with a peak of 597 +/- 151 pg/ml (p less than 0.02) at 8 min in portal venous serum and 323 +/- 95 pg/ml (p less than 0.05) at 15 min in cephalic venous serum. No significant increases in peripheral venous serum insulin concentration were detected throughout the entire collection period, whereas peripheral venous serum glucose levels increased slightly from a fasting level of 56 +/- 5 mg/dl to 72 +/- 5 mg/dl (p less than 0.05) at 90 min. The mean half-time of disappearance of intravenously administered gastric inhibitory peptide was found to be 7.6 +/- 1.5 (SEM) min. Results of these studies demonstrate prompt stimulation of gastric inhibitory peptide response to peptone, with peak serum gastric inhibitory peptide concentrations which are higher and occur earlier in portal than in peripheral blood. Gastric inhibitory peptide was found to have a brief half-time of disappearance, similar to that of other structurally related gastrointestinal peptides.