title: Pancreatic somatostatinoma: abundance of somatostatin-28(1-12)-like immunoreactivity in tumor and plasma.
abstract: In the present study we characterized and compared the relative amounts of the different molecular forms of somatostatin-14 like immunoreactivity (S-14 LI) and of somatostatin-28(1-12) like immunoreactivity (S-28(1-12) LI) in extracts of tumor and peripheral plasma of a patient with a pancreatic somatostatinoma. Tissue and plasma were chromatographed on Sephadex G-50 columns equilibrated with 6 M urea. Immunoreactivity in the eluting fractions was assayed with two separate, region specific RIAs using antibodies R149 (S-14 LI) and S309 (S-28(1-12)LI). RIA R149 recognizes the 6-8 and 14 regions of the S-14 sequence and detects S-14, S-28, and prosomatostatin, an approximately 14,000 mol wt precursor for the two peptides. RIA S309 recognizes the 2-11 segment of S-28 and reacts with S-28, S-28(1-12), and higher mol wt S-28(1-12) LI but not S-14. Total tumor S-14 LI was 190 pmol/mg protein and consisted of three peaks of immunoreactivity of apparent 14,000 mol wt (14K S-14 LI), 3,200 mol wt (3.2K corresponding to S-28) and 1,600 mol wt (1.6K corresponding to S-14). The three peaks comprised, respectively, 7%, 57%, and 36% of total S-14 LI. Total tumor S-28(1-12) LI was 594 pmol/mg protein and eluted as four major peaks of immunoreactivity as follows: peak I (mol wt 15,000, 10% of total S-28(1-12) LI); peak II (mol wt 8,000, 20% of S-28(1-12) LI), peak III (corresponding to S-28, 19% of S-28(1-12) LI); peak IV (corresponding to S-28(1-12), approximately 50% of total S-28(1-12) LI). Total plasma concentration of S-14 LI was 714 pM, being made up of the three peaks found in tumor but in the following relative amounts (14K S-14 LI, 22%; 3.2K, 29%; 1.6 K, 49%). Plasma S-28(1-12) LI was 4 times higher (2879 pM) than S-14 LI and contained immunoreactivity corresponding to each of the four peaks found in the tumor.
  
  
  CONCLUSIONS
  1) The tumor and plasma concentrations of S-28(1-12) LI were greater than that of S-14 LI. 2) Both tumor and plasma S-14 LI and S-28 LI were heterogeneous and comprised species corresponding not only to S-14 but also S-28, S-28(1-12), prosomatostatin, and other higher mol wt forms of S-28.(ABSTRACT TRUNCATED AT 400 WORDS)
mesh_terms: D007516:Adenoma, Islet Cell / Q000032:analysis*; D002850:Chromatography, Gel; D005260:Female; D006801:Humans; D008875:Middle Aged; D010190:Pancreatic Neoplasms / Q000032:analysis*; D010455:Peptides / Q000032:analysis; D011498:Protein Precursors / Q000032:analysis; D011863:Radioimmunoassay; D013004:Somatostatin / Q000031:analogs & derivatives / Q000032:analysis* / Q000097:blood; D053561:Somatostatin-28; D013005:Somatostatinoma / Q000032:analysis*
chemical_list: D010455:Peptides; D011498:Protein Precursors; C029993:somatostatin-like peptides; D013004:Somatostatin; C028456:prosomatostatin; D053561:Somatostatin-28