A Peptide from the Caudal Neurosecretory System of the Dogfish Scyliorhinus canicula That Is Structurally Related to Urotensin I

Using reversed-phase HPLC in combination with a radioimmunoassay for ovine corticotropin-releasing hormone (CRH), a peptide with CRH-like immunoreactivity was isolated in pure form from an extract of the caudal spinal cord region of the spotted dogfish, Scyliorhinus canicula. The primary structure of the peptide was established as Pro-Ala-Glu-Thr-Pro-Asn-Ser-Leu-Asp-Leu¹⁰-Thr-Phe-His-Leu-Leu -Arg-Glu-Met-Ile-Glu²⁰-Ile-Ala-Lys-His-Glu-Asn-Gln-Gln-Met-Gl n³⁰-Ala-Asp-Ser-Asn-Arg-Arg-Ile-Met-Asp-Thr⁴⁰-Ile · NH₂. This amino acid sequence shows moderate structural similarity to Catostomus urotensin I (51%) and to human CRH (56%). The data provide, therefore, chemical evidence to support the conclusions of earlier immunohistochemical studies that the diffuse caudal neurosecretory system of elasmobranchs produces a peptide that is immunochemically related to teleost urotensin I peptides. However, the primary structure of urotensin I has been poorly conserved during evolution.