Radioimmunoassay for catfish pancreatic somatostatin-22.

Abstract

Abstract An antiserum to purified catfish pancreatic somatostatin-22 (anti-CPS-22) was obtained and a radioimmunoassay developed which was highly specific for CPS-22. Displacement by tetradecapeptide somatostatin (SST-14) was at least 1000-fold less than with homologous peptide. A discrete population of catfish islet cells were stained in sections treated with anti-CPS-22, which appeared to be somatostatin containing D-cells identified by characteristic granule morphology on electron microscopy. Both SST-14 and CPS-22, presumably the products of two non-allelic somatostatin genes, have been identified in catfish pancreatic islets (Andrews, P.C. and Dixon, J.E. (1981) J. Biol. Chem., 256, 8267). Using the anti-CPS-22 and anti-SST-14 assays, it was estimated that CPS-22 comprised approximately 90%, and SST-14 5–10% of total immunoreactive catfish pancreatic somatostatin. The anti-CPS-22 assay was used on other pancreatic extracts to look for non-allelic forms of somatostatin. Anti-CPS-22 reacted poorly with pigeon pancreas extracts, but in rat pancreas extracts there was as much immunoreactive somatostatin measured with the CPS-22 as with the SST-14 assay. Similar immunochemical determinants in fish and rat somatostatins were suggested by parallel displacement of labeled CPS-22 from anti-CPS-22 with pancreatic extracts. Chromatography on Biogel P-60 in 2.5 M propionic acid, although not a vigorously denaturing condition, indicated that the majority of fish and rat immunoreactive pancreatic somatostatin detected with anti-CPS-22 migrated as a 4000 molecular weight peptide, larger than SST-14. These preliminary observations suggest that anti-CPS-22 may be useful in further characterization of somatostatin-like peptides from mammals as well as more primitive vertebrates.