Peptide characterization of secretin preparations.

The present study was designed to examine and compare the peptide composition and relative immunochemical purity of GIH and Boots secretin preparations. Gastrointestinal peptides were measured by radioimmunoassay using antibodies to secretin, gastrin, immunoreactive cholecystokinin, vasoactive intestinal peptide, gastric inhibitory peptide, and somatostatin. Boots secretin was found to contain substantial quantities of gastrin, immunoreactive cholecystokinin, vasoactive intestinal peptide, gastric inhibitory peptide, and somatostatin. In contrast, GIH secretin contained only a very small amount of vasoactive intestinal peptide. GIH also contained approximately three to four times more secretin per unit as did Boots secretin. Intravenous infusion of Boots, but not GIH, secretin in seven healthy volunteers produced significant increases in venous plasma of all peptides. Results of these studies indicate that Boots secretin contains large and variable quantities of gastrointestinal peptides other than secretin and that the contents of both secretin and the other peptides vary among different lots. Because the quantity of these peptides is sufficient to increase significantly their blood levels and consequent biological effects, it is concluded that GIH is preferable to Boots secretin in the clinical evaluation of patients with suspected chronic pancreatitis or gastrinoma.