PubMed1986
Immunoreactive forms of gastrin in antral mucosal extracts and in gastric venous plasma of the pig were compared using ion-exchange and gel-filtration chromatography and radioimmunoassay using three region-specific antiserums. In antral mucosal extracts, gastrin heptadecapeptide (G-17) accounted for over 90% of the total C-terminal immunoreactivity, but in gastric venous plasma it accounted for only 47% of total C-terminal immunoreactivity. The remaining C-terminal immunoreactivity was accounted for by shorter C-terminal forms. Unsulfated and sulfated G-17 contributed 44.1 and 49.2%, respectively, of C-terminal immunoreactivity in antral mucosa. In contrast, they contributed 14 and 30%, respectively, to total C-terminal immunoreactivity in gastric venous plasma. Incubation of antral extracts with plasma in vitro resulted in a slow loss of intact G-17 (32.3% in 60 min) that could not account for the production of C-terminal fragments in vivo. Moreover, when antral extracts were infused into the gastroepiploic artery, over 90% of the gastrin present in the antral venous outflow corresponded to G-17. These observations suggest that it is unlikely that enzymes involved in the generation of the C-terminal forms are located either in blood or on the luminal side of the endothelial membrane. It is proposed, then, that antral gastrin is converted into shorter C-terminal fragments at or before the time it enters the circulation and that the major storage forms of gastrin in tissue account for less than 50% of the material in the gastric venous outflow.