Immunochemical characterization of gastrinlike and cholecystokininlike peptides released in dogs in response to a peptone meal.

This study was designed to examine and compare the nature of gastrinlike and cholecystokininlike peptides released into the portal and peripheral venous circulation in response to a peptone meal. Six dogs were prepared with portal venous catheters and gastric fistulas. Portal and peripheral venous sera were obtained before and after gastric infusion of a 10% peptone meal. Serum levels of gastrin and cholecystokinin immunoreactive peptides were determined by radioimmunoassay using two distinct peptide region-specific antibody preparations. These separate antibody preparations demonstrated specificity for (a) C-terminal tetradecapeptide gastrin (4-17hG17), heptadecapeptide gastrin (G17), and big gastrin (G34) (gastrin antibody); and (b) all biologically active forms of gastrin and cholecystokinin (gastrin-cholecystokinin antibody). Using the antibody preparation with specificity for gastrin and not cholecystokinin, the mean basal immunoreactive gastrin from portal (8.33 +/- 2.4 fmol/ml, mean +/- SEM) and from peripheral (6.19 +/- 0.9 fmol/ml) venous sera both increased after peptone infusion, with an early peak (2 min in portal and 4 min in peripheral serum) and a second peak at 30 min in both circulations. Measurements using antibodies with specificity for both cholecystokinin and gastrin yielded strikingly different results. The portal venous serum peptide concentration (49 +/- 10 fmol/ml) increased sharply within 30 s after peptone infusion to a single peak at 2 min (139 +/- 37 fmol/ml). The basal peripheral venous serum peptide concentration (43 +/- 8.8 fmol/ml) increased more gradually to a single peak at 8 min (78 +/- 14 fmol/ml). Studies with Sephadex (G-50 superfine) gel chromatography indicated that gastrin released in response to the peptone meal was primarily G17. However, of the peptides released in response to the peptone meal that were recognized by the gastrin-cholecystokinin antibody, greater than 80% were shown to be distinct from gastrin. Gel chromatographic studies demonstrated that peptone meal-stimulated immunoreactive cholecystokinin release consisted of two major peaks, eluting in positions identical to those of intact cholecystokinin (CCK33) and the octapeptide of cholecystokinin (CCK8).