Neuroendocrine peptides (NPY, GRP, VIP, somatostatin) from the brain and stomach of the alligator.

Despite the important position of the reptiles in phylogeny, relatively few regulatory peptides from reptilian species have been characterized structurally. Neuropeptide Y was isolated from the brain of the alligator, Alligator mississippiensis, and vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), its COOH-terminal decapeptide (GRP-10), and somatostatin-14 were isolated from the alligator stomach. The primary structures of NPY and somatostatin-14 are the same as the corresponding peptides from the human, whereas alligator VIP is identical to chicken VIP. The amino acid sequence of GRP (Ala-Pro-Ala-Pro-Ser-Gly-Gly-Gly-Ser-Ala10-Pro-Leu-Ala-Lys-Ile-Tyr -Pro-Arg-Gly-Ser20-His-Trp-Ala-Val-Gly-His-Leu-Met-NH2) contains an additional residue and six substitutions compared with chicken GRP, but alligator GRP-10 is the same as chicken GRP-10. Bombesin was not detected in the stomach extract. The data confirm that evolutionary pressure to conserve the amino acid sequence of NPY and somatostatin-14 has been very strong but demonstrate that pressure to conserve the complete primary structure of GRP has been less than that for other neuroendocrine peptides. The identity of chicken and alligator VIP is consistent with the known close phylogenetic relationship between crocodilians and birds.