Exendin-4 is a high potency agonist and truncated exendin-(9-39)-amide an antagonist at the glucagon-like peptide 1-(7-36)-amide receptor of insulin-secreting beta-cells. - Göke,R.; Fehmann,HC.; Linn,T.; Schmidt,H.; Krause,M.; Eng,J.; Göke,B. (J Biol Chem, 1993)