Secretory effects of gastric inhibitory polypeptide on the isolated perfused porcine pancreas.

The effect of gastric inhibitory polypeptide (GIP) in physiological concentrations (250, 500, 1,000 and 2,000 pg/ml) upon endocrine and exocrine secretion from the isolated perfused porcine pancreas was studied at various glucose concentrations in the perfusate. GIP increased insulin release in a dose-dependent manner. The sensitivity of the beta-cells to GIP was glucose independent. No effect was observed on glucagon or exocrine secretion regardless of the glucose concentration in the perfusate. We conclude that GIP is powerful insulin-stimulator even in low physiological concentrations in the presence of glucose concentrations comparable to those seen during an oral glucose load, which makes GIP to one of the strongest incretin candidates known, i.e. the factor(s) contributing to the augmented insulin response after ingestion of glucose.