Gel filtration studies on immunoreactive gastrin in serum from Zollinger-Ellison patients

Sera from 15 patients with the Zollinger-Ellison syndrome were subjected to gel filtration on Sephadex G-50 superfine columns (10 x 2000 mm). The concentration of gastrin in the effluent was determined by a sensitive radioimmunoassay. Immunoreactive gastrin was eluted in four components in 14 sera. (1) Component I, eluted in the same position as proinsulin, constituted 9.7 +/- 1.2 (mean +/- SEM)% of the total immunoreactivity. (2) Component II (;big gastrin') eluted between proinsulin and insulin constituted 57.8 +/- 4.1% (mean +/- SEM) of immunoreactive gastrin. In three sera with the highest concentration of gastrin, component II appeared biphasic. (3) Component III (;little gastrin') was distributed in two peaks; the first one eluted in the same position as the heptadecapeptide gastrin II made up 17.4 +/- 2.7 (mean +/- SEM)% of the total immunoreactivity; the second one eluted in the same position as gastrin I constituted 9.5 +/- 1.3 (mean +/- SEM)%. (4) Component IV (;minigastrin') was eluted immediately before the salt peak and constituted 5.6 +/- 1.4 (mean +/- SEM)%. In one serum only components I and II were present. After incubation with trypsin all immunoreactivity in components I and II was converted to heptadecapeptide-like gastrins.The findings suggest that immunoreactive gastrin in serum from Zollinger-Ellison patients is circulating in at least four components of different molecular size.