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

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Abstract
Sera from 15 patients with the Zollinger-Ellison syndrome were subjected to gel filtration on Sephadex G-50 superfine columns (10 × 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.