Structural requirements for galanin action in the guinea-pig ileum.

Galanin fragments and galanin analogues were tested on neurally evoked muscle contractions in guinea-pig ileum in vitro. Galanin fragments inhibited the neurally evoked circular muscle contractions with the following order of potency: Galanin(1-29), galanin(2-29), galanin(1-15). In contrast, galanin(3-29), galanin(10-29), galanin(21-29), [D-Trp2]galanin, [Phe2]galanin and [Tyr2]galanin were ineffective. Galanin(1-29), galanin(2-29) and galanin(1-15) did not affect the neurally evoked longitudinal muscle contractions. These results indicate that (1) the two N-terminal amino acid residues of the galanin molecule are essential for the inhibitory action of galanin on neurally-evoked circular muscle contraction and (2) for the full potency also the C-terminal end is required.