AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 3 300-G307, Copyright © 1986 by American Physiological Society
Chromatographic and immunochemical studies on postsecretory processing of gastrin in the pig
D. M. Power, N. Bunnett and R. Dimaline
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.
