Synthesis and some pharmacological properties of the 23-peptide 15-lysine-secretin-(5--27). Special role of the residue in position 15 in biological activity of the vasoactive intestinal polypeptide.

The 23-peptide 15-lysine-secretin-(5-27) [S(5-27)] was synthesized on an insoluble support. The residue in position 15 of secretin, aspartic acid, was replaced by lysine, which occupies that position in the vasoactive intestinal polypeptide (VIP), a member of the secretin family. The resulting analogue showed increased VIP-like activity on smooth muscle preparations and unaltered secretin-like activity on pancreatic juice secretion in the rat. The affinity of the new analogue was high-affinity secretin receptors in acinar cells from guinea pig pancreas was less than that of S(5-27) but was higher than that of S(5-27) for high-affinity VIP receptors in the same cells.