HUMAN GALANIN MODULATES HUMAN COLONIC MOTILITY IN-VITRO - CHARACTERIZATION OF STRUCTURAL REQUIREMENTS

Background: Human galanin (hGal) is a 30-residue non-amidated gut-brai n peptide that shows considerable sequence divergence compared with ga lanin (Gal) forms of other species. Conflicting results have been repo rted with regard to the structural requirements for its modulatory act ion on gut motility. Methods: We investigated the effect of human and rat Gal and substituted analogues of Gal on the contractility of longi tudinal muscle strips of the human colon in vitro. Results: Both hGal and rGal contracted the preparations in a concentration-dependent and tetrodotoxin-resistant manner without difference in sensitivity. The N H2-terminally truncated peptides hGal (3-30) and rGal (3-29) were inac tive, whereas the NH2-terminal fragments, hGal (1-21) and rGal (1-18), remained fully responsive. Single amino acid substitutions at NH2-ter minal positions showed divergent results: substitution of Trp(2) reduc ed significantly potency and efficacy, whereas substitutions at positi ons 1, 3, 4, or 5 did not markedly modify the bioactivity of Gal. Gala ntide, a high-affinity Gal antagonist in the central nervous system, i s a full agonist in human colonic smooth muscle. Conclusion: The COOH- terminal part of Gal contributes mainly the receptor-binding affinity of the peptide, whereas the NH2-terminal region is essential for biolo gic activity.