title: [D-Phe4]peptide histidine-isoleucinamide ([D-Phe4]PHI), a highly selective vasoactive-intestinal-peptide (VIP) agonist, discriminates VIP-preferring from secretin-preferring receptors in rat pancreatic membranes.
abstract: The capacity of vasoactive intestinal peptide (VIP), peptide histidine-isoleucinamide (PHI), secretin, and a series of analogs to discriminate between VIP-preferring and secretin-preferring receptors that coexist in rat pancreatic plasma membranes was evaluated by their ability to inhibit [125I]iodo-VIP and [125I]iodo-secretin binding and to activate adenylate cyclase. VIP, the VIP analogs [D-His1]VIP, [D-Ser2]VIP, [D-Asp3]VIP and [D-Ala4]VIP, PHI, [D-Phe4]PHI, and secretin inhibited the binding of both ligands in a concentration range of 10(-11) M to 10(-5) M and with a selectivity factor varying from 18,000 to 0.1. The only exception was [D-Phe4]PHI that inhibited 125I-VIP binding only, with an IC50 of 7 nM, and with no inhibition of 125I-secretin binding at 10 microM. The peptides tested stimulated adenylate cyclase in the same membranes and the slope of the dose-effect curves indicated that all peptides, except [D-Phe4]PHI, interacted with at least two classes of receptors: VIP-preferring and secretin-preferring receptors. By contrast, the dose-effect curve of [D-Phe4]PHI activation of adenylate cyclase was monophasic and competitively modified by [D-Phe2]VIP (a VIP antagonist) but not by secretin(7-27) (a secretin antagonist), indicating an interaction with VIP-preferring receptors only. Thus, [D-Phe4]PHI appears to be a highly selective tool to characterize these receptors.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D010179:Pancreas / Q000378:metabolism*; D010451:Peptide PHI / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone / Q000378:metabolism; D018005:Receptors, Vasoactive Intestinal Peptide; D012633:Secretin / Q000378:metabolism*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
chemical_list: D010451:Peptide PHI; D043562:Receptors, G-Protein-Coupled; D011964:Receptors, Gastrointestinal Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; C029937:secretin receptor; C052927:peptide PHI, Phe(4)-; D012633:Secretin; D014660:Vasoactive Intestinal Peptide; D000262:Adenylyl Cyclases