Granuliberin-R and various fragment peptides were synthesized and their histaminereleasing activities were examined. The relative potencies of granuliberin-R, H-Phe-Gly-Phe-Leu-Pro-Ile-Tyr-Arg-Arg-Pro-Ala-Ser-NH2, as liberators of histamine from mast cells are very similar to those of substance P and bradykinin. Studies on the histamine-releasing activity of various fragment peptides of granuliberin-R showed that a 4-amino acid central sequence, -Ile-Tyr-Arg-Arg-, is the minimum requirement for the releasing action of this frog skin peptide.
