Gastric inhibitory polypeptide (GIP) response to an oral glucose load in the patients with diabetes mellitus.

Plasma gastric inhibitory polypeptide (GIP) concentrations following an oral glucose load were measured in 27 diabetics and 10 normal subjects. Plasma GIP concentrations increased significantly from the mean basal value following an oral glucose load in both groups. Diabetics showed significantly higher levels of plasma GIP in association with delayed and diminished peak increases in plasma insulin levels. When diabetics were divided into two groups according to their basal levels of blood glucose, moderate and severe diabetics exhibited more exaggerated increments of plasma GIP than mild diabetics. This exaggerated GIP response to an oral glucose load in proportion to the glucose intolerance indicates a relative failure of the beta cell response to GIP in diabetics and that the mechanism involved in hypersecretion of GIP would be diminution of the inhibition of GIP release caused by insulin in diabetics.