Effects of portacaval shunt on the rat stomach

In portacaval-shunted rats, basal but not pentagastrin-stimulated acid secretion was higher than in sham-operated controls. The basal serum gastrin concentration was unchanged and the postprandial serum gastrin concentration lowered following portacaval shunt. Thus, gastrin is not responsible for the elevated basal acid secretion. The present study provides evidence that there is no trophic effect on the oxyntic mucosa as a whole and that there is no change in parietal cell-associated gastrin receptors after portacaval shunting. Interestingly, however, endocrine cells in the oxyntic mucosa (the histamine-containing ECL cells) proliferated greatly and the pentagastrin- and cholecystokinin octapeptide-induced activation of the histamine-forming enzyme, histidine decarboxylase, in these cells was much greater than in control rats. Analysis of the dose-response curves for the enzyme-activating effect of pentagastrin and cholecystokinin-octapeptide indicated that the D50 values for these two stimulants were not altered by shunting but that the maximal enzyme activation was greatly elevated. The enhanced enzyme activation can be partly, but not fully, explained by the fact that the ECL cells were increased in number. The enhanced response following portacaval shunt probably reflects also an increased number of gastrin receptors per ECL cell. The effect of portacaval shunting on gastric ECL cells can perhaps be explained by impaired degradation in the liver of intestinal substance(s) exerting a highly specific trophic effect on the ECL cells or, alternatively, causing an enrichment of gastrin receptors on these cells, thereby making them more sensitive to the trophic effect of gastrin. The ECL cell hyperplasia is manifest about 4 weeks after the shunting. A modified procedure for portacaval shunting which left the gastroduodenal vein (otherwise ligated) drained to the liver produced the same trophic effect as conventional portacaval shunt, suggesting an intestinal rather than gastroduodenal origin of the agent(s) responsible for the trophic action.