Actions of GIP

Two structurally similar peptides were isolated from a preparation of GIP using an HPLC system. The major peptide corresponds to GIP1-42 and the minor has the sequence GIP3-42. GIP1-42 has both insulinotropic and somatostatinotropic activities, whereas GIP3-42 has only insignificant activity. GIP was also shown to potentiate insulin release initiated by D-glyceraldehyde, L-leucine/L-glutamine and 2-keto-isocaproic acid. No potentiation was observed with 2-ketocaproate. The 4 substrates studied are all metabolized but via different mechanisms.