Interaction of peptides related to secretin with hormone receptors on pancreatic acinar cells.

Three analogues of the carboxyl-terminal tricosapeptide of secretin (S5-27), one with glutamine replacing glutamic acid in position 9 (9-Gln-S5-27), a second with asparagine substituted for aspartic acid in position 15 (15-Asn-S5-27), and a third with both replacements (9-Gln-15-Asn-S5-27) were tested for their ability to interact with hormone receptors on dispersed pancreatic acinar cells. Each of these analogues inhibited binding of 125I-labeled vasoactive intestinal peptide (VIP). None of the analogues increased cellular cyclic AMP but each inhibited the increase in cellular cyclic AMP produced by secretin or VIP. At the high affinity VIP receptor (the low affinity secretin receptor) each analogue had an apparent affinity which was greater than that for S5-27, whereas at he low affinity VIP receptor (the high affinity secretin receptor), each of the analogues had an apparent affinity which was the same as that for S5-27. Thus, in S5-27, substituting glutamine in position 9 or asparagine in position 15 makes the fragment more VIP-like but not less secretin-like. These results also provide additional evidence that the receptor having a low affinity for secretin and a high affinity for VIP is functionally distinct from the receptor having a high affinity for secretin and a low affinity for VIP.