Increased potency of some substituted short peptide analogues in comparison to galanin(1-15)-NH2in rat fundus strips

Abstract The activity of short porcine galanin (Gal) analogues was tested in vitro using rat gastric fundus strips. The peptides contracted longitudinal smooth muscle in a concentration-dependent manner with the following order of potency: Gal(1–29) >[Cit 14 ]Gal(1– 15) >[Asp 14 ]Gal(1– 15) >[Dab 14 ]Gal(1– 15) >[Nle 14 ] Gal(1–15) >[Dpr 14 ]Gal(1– 15) >[Arg 14 ]Gal(1– 15) >[Orn 14 ]Gal(1– 15) >Gal(1–15). Only in the case of two peptides, namely [Cit 14 ]Gal(1–15) and [Dab 14 ]Gal(1–15) did the values of Hill coefficients, estimated from the appropriate concentration–contraction curves, differ significantly from unity. Our results indicate that both N- and C-terminals of Gal molecule contribute towards the affinity and activity of Gal in rat gastric smooth muscle cell receptors, indicating that their integrity is essential for its full excitatory myogenic action. The substitution of histidine with citruline, aspartic acid, norleucine or diaminobutyric acid in position 14 of the amino acid chain led to a considerable increase in potency, suggesting that amino acids located at this position might play a crucial role where the strength of short analogues is concerned.