Action of cholecystokinin analogues on exocrine and endocrine rat pancreas

In the present study we have examined the abilities of cholecystokinin-(26-33)-amide [CCK-(26-33)-NH2, CCK-8], nonsulfated CCK-(26-33)-NH2 (desulfated CCK-8), CCK-(30-33)-NH2 (CCK-4), CCK-(26-33)-OH (deamidated CCK-8), and succinyl CCK-(27-31)-NH2 (Suc-Des-Asp6,Phe7-CCK-7) to stimulate exocrine pancreatic secretion from both isolated pancreatic acini and isolated perfused pancreas. We have also compared this action with their ability to cause insulin release. The modification of either the N- or C-terminal amino acid residues of CCK-8 decreased in potency, but the magnitude of the stimulation of enzyme secretion caused by a maximally effective peptide concentration was the same. The minimal effective concentration of CCK-8, desulfated CCK-8, and CCK-4 for insulin release from the isolated rat pancreas in the presence of 8.3 mM glucose was the same as that for pancreatic exocrine secretion. In contrast, the concentrations of deamidated CCK-8 and Suc-Des-Asp6,Phe7-CCK-7 required to produce insulin release were 5-10 times higher than those required to cause stimulation of pancreatic enzyme and juice secretion. It is concluded therefore that the N-terminal 4-amino acid residues or the C-terminal 2-amino acid residues of CCK-8 are not essential for biological activity but do contribute to its potency. In addition, the C-terminal 2-amino acid residues and an amide group in the C-terminal phenylalanine residue of CCK-8 appear to be important determinants of the insulin-releasing activity of the CCK peptides.