Gastric Inhibitory Polypeptide, Cholecystokinin, and Secretin Effects on Insulin and Glucagon Secretion by Islet Cultures

Abstract

Using an in vitro [rat] islet cell culture assay system, GIP [gastric inhibitory polypeptide] and CCK-OP [carboxy-terminal octapeptide of choleocystokinin] appear to be about equally potent insulinotropic agents. Secretin has only a very slight stimulatory effect on insulin release, and only at a very high peptide concentration. GIP plus CCK-OP and GIP plus secretin appear to have synergistic insulinogenic actions. If supraphysiologic GIP concentrations are tested, glucose is not necessary at an insulin stimulatory concentration for GIP to stimulate insulin secretion. Glucagon release is enhanced only by GIP at physiologic peptide concentrations. Both secretin and CCK-OP have only very slight glucagonotropic actions even at high concentrations.