Abstract
The ability to assess the importance of VIP in different physiological processes is limited by the lack of specific potent antagonists. In the present study, we have adopted two different approaches used successfully with other peptides in an attempt to identify new VIP receptor antagonists. One involves the formation of pseudopeptides by insertion of reduced peptide bonds in the NH 2-terminus from position 2 to 8 of VIP. The other methodology involves the formation of a COOH-terminal chimeric analogue by combining VIP(6–28) and PACAP(28–38). The ability of each of these peptides to function as an antagonist was compared with reported VIP antagonists. All of the peptides inhibited [ 125I]VIP binding to VIP receptors on guinea pig pancreatic acini. For the pseudopeptides the affinities were: [ ψ3–4]VIP (0.2 μM) = 4 × [ ψ4–5]VIP = 8 × [ ψ8–9]VIP = 14 × [ ψ6–7]VIP, [ ψ2–3]VIP = 25 × [ ψ5–6]VIP. Each nonpseudopeptide analogue also inhibited VIP binding with relative potencies of VIP(6–28)- PACAP(28–38) (1 μM) = 2.5 × [4- Cl- d- Phe 6, Leu 17] VIP , VIP(10–28), neurotensin(6–11)- VIP(7–28) = 6 × [ Ac-Tyr 1 , d- Phe 2] GRF . All pseudopeptides were agonists with relative potencies: [ ψ3–4]VIP > [ ψ6–7], [ ψ4–5]VIP > [ ψ5–6] > [ ψ8–9]VIP > [ ψ2–3]VIP. The reported VIP receptor antagonist, neurotensin(6–11)-VIP(7–28), was also an agonist. Each of the remaining peptides had no agonist activity; however, each inhibited VIP-stimulated amylase release with potencies of: VIP(6–28)- PACAP(28–38) = VIP(6–28) (K i = 0.3 μM) = 2 × [4- Cl- d- Phe 6, Leu 17] VIP = 3 × VIP(10–28) = 9 × [ Ac- Tyr 1, d- Phe 2] GRF . We conclude that the strategy of making reduced peptide bond analogues at the NH 2-terminus of VIP does not result in receptor antagonists as it did with secretin or GRF. A chimeric analogue, VIP(6–28)-PACAP(28–38), is two times more potent than any existing VIP antagonist; however, its increase in affinity is due to the presence of the VIP(6–28) moiety entirely. This raises the possibility that additional, more potent, antagonists may be developed by modifying VIP(6–28).
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
