A peptide of the pancreatic polypeptide (PP) family was isolated in pure form from the pancreas of an elasmobranch fish, Scyliorhinus canicula (European common dogfish). The primary structure of the peptide was established as: Tyr-Pro-Pro-Lys-Pro-Glu-Asn-Pro-Gly-Glu10-Asp-Ala-Pro- Pro-Glu-Glu-Leu-Ala-Lys-Tyr20-Tyr-Ser-Ala-Leu-Arg-His- Tyr-Ile-Asn-Leu30-Ile-Thr-Arg-Gln-Arg-Tyr.NH2. This sequence contains 86% amino acid sequence homology with human neuropeptide Y, and the COOH-terminal region (residues 20-36) has been fully conserved. Bolus injection of a synthetic replicate of the peptide (0.5-4 nmol) into the celiac artery of conscious dogfish resulted in a significant (P less than 0.01) and dose-dependent increase in arterial blood pressure. A maximum rise in mean pressure (67 +/- 11% over mean basal values; n = 6) was elicited by an injection of 2 nmol peptide. Bolus injections of human neuropeptide Y (0.5-4 nmol) also elicited dose-dependent rises in blood pressure, and the effects produced by the dogfish and human peptides were not significantly different at any dose. The data are consistent with a physiological role for neuropeptide Y-related peptide in cardiovascular regulation in elasmobranch fish.