Gastric inhibitory polypeptide (GIP). Intestinal distribution and stimulation by amino acids and medium-chain triglycerides.

Radioimmunoassayable gastric inhibitory polypeptide was measured in extracts of canine antrum, duodenum, jejunum, and ileum. The highest GIP concentrations were found in the duodenum (347 +/- 53 ng/g) and jejunum (300 +/- 68 ng/g). An immunochemical similarity was demonstrable between porcine GIP and canine GIP. Dogs prepared with Mann Bollman fistulae were given an amino acid (AA) mixture or medium-chain triglycerides (MTC) by intraduodenal perfusion. With AA, a peak mean serum concentration of 672 +/- 106 pg/ml was reached 15 min after starting the perfusion. MCT resulted in a peak mean serum GIP concentration of 504 +/- 55 pg/ml 30 min after beginning the perfusion. When compared to results previously reported from this laboratory, AA and MCT are not as potent as corn oil (long-chain triglyceride) or glucose in stimulating GIP release. We conclude: (1) Immunoassayable GIP concentrations are highest in the canine proximal small intestine. (2) AA and MCT are weak stimulants of GIP release in the dog.