The entire vasoactive intestinal polypeptide molecule is required for the activation of the vasoactive intestinal polypeptide receptor: functional and binding studies on opossum internal anal sphincter smooth muscle.
Because no significant information exists regarding the structure-activity of vasoactive intestinal polypeptide (VIP) to gut smooth muscle, we performed functional studies in vitro on opossum internal anal sphincter (IAS) smooth muscle strips and supplemented them with binding studies to assess the ability of VIP, its fragments and analogs to inhibit [125I]VIP binding to IAS smooth muscle membranes. Binding of radiolabeled VIP to its receptor was specific, saturable and time- and temperature-dependent. Of all the substances tested, VIP was the most potent in causing a fall in the resting tension of the IAS and inhibiting [125I]VIP binding. VIP 2-28, VIP 10-28 and the putative VIP antagonists (1 x 10(-6) M) [4Cl-D-Phe6,Leu17]VIP (VIP analog) and (N-Ac-Tyr1, D-Phe2)-growth hormone-releasing factor [GRF] (1-29)-NH2 (GRF analog) caused significant inhibition of [125I]VIP binding, but had only minimal effect on the resting tension of the IAS. VIP 9-18 and VIP 1-12 had neither any significant effect nor inhibition of receptor binding. The rank order of potencies for inhibition of binding was VIP > VIP analog > VIP 10-28 = VIP 2-28 > GRF analog > peptide histidine isoleucine > VIP 9-18. The IC50 values for VIP, VIP analog, VIP 10-28, VIP 2-28, GRF analog and peptide histidine isoleucine were 9.6 x 10(-9), 1.6 x 10(-7), 5.5 x 10(-7), 6.2 x 10(-7), 1.2 x 10(-6) and 1.2 x 10(-5) M, respectively.


CONCLUSIONS
the full action of VIP is critically dependent upon the integrity of the entire VIP molecule.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania.
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Chakder
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Rattan
D000595:Amino Acid Sequence; D001003:Anal Canal / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009893:Opossums; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology*; D011964:Receptors, Gastrointestinal Hormone / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018005:Receptors, Vasoactive Intestinal Peptide; D017337:Sermorelin / Q000031:analogs & derivatives / Q000494:pharmacology; D013329:Structure-Activity Relationship; D014660:Vasoactive Intestinal Peptide / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology
D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D011964:Receptors, Gastrointestinal Hormone; D018005:Receptors, Vasoactive Intestinal Peptide; C048507:vasoactive intestinal peptide, 4-chloro-Phe(6)-Leu(17)-; D014660:Vasoactive Intestinal Peptide; D017337:Sermorelin; C045616:somatotropin releasing hormone (1-29)-amide, N-Ac-Tyr(1)-Phe(2)-