Stimulation of insulin secretion by peptides analogous to the C-terminal tetrapeptide amide of cholecystokinin.

Two tetrapeptides, Glp-Met-Asp-Phe-NH2 (I) and Pro-Met-Asp-Phe-NH2 (II), analogous to the C-terminal tetrapeptide amide of cholecystokinin (CCK-4) have been synthesized and their effect on the release of insulin from the isolated Langerhans islets of rat pancreas compared with that of synthetic CCK-4. Both the new congeners exhibited significant insulin-releasing activity at 10(-8) M and 10(-6) M concentrations, suggesting that the biological activity is retained when the N-terminal Trp residue of CCK-4 is replaced by Glp or Pro.