Somatostatin-gastrin interactions in the rat stomach

Sustained cholecystokinin-B/gastrin receptor blockade does not impair basal or histamine-stimulated acid secretion in chronic gastric fistula rats

Gastrin is a physiologically important secretagogue. It is thought to stimulate parietal cells indirectly by mobilizing histamine from enterochromaffin-like (ECL) cells in the oxyntic mucosa. Gastrin stimulates the secretory activity and growth of the ECL cells via an action on cholecystokinin-B/gastrin receptors. Acute cholecystokinin-B/gastrin receptor blockade is known to inhibit gastrin-stimulated acid secretion but whether sustained cholecystokinin-B/gastrin receptor blockade will impair basal, gastrin- and histamine-stimulated acid secretion remains uncertain. The present study was designed to study the effect of long-term (4 weeks) cholecystokinin-B/gastrin receptor blockade on basal and stimulated acid secretion in conscious rats. The selective cholecystokinin-B/gastrin receptor antagonist YM022 (3 mumol.kg-1.hr-1) was given to gastric fistula rats by continuous subcutaneous infusion via osmotic minipumps for various times from 2 hr to 4 weeks. Basal, gastrin- and histamine-stimulated acid secretion were examined during and after cessation of treatment. Basal and histamine-stimulated acid secretion was not affected by YM022 during the 4 week period of administration, whereas gastrin-induced acid secretion was inhibited. YM022 induced hypergastrinaemia in freely fed rats but did not affect the serum gastrin level in fasted rats. The serum gastrin concentration and gastrin-induced acid secretion returned to control levels 3-7 days after termination of YM022 administration.

Rat gastric somatostatin and gastrin release: interactions of exendin-4 and truncated glucagon-like peptide-1 (GLP-1) amide

The effect of exendin-4, a peptide of the secretin-glucagon family with high homology of amino acid sequence with glucagon-like peptide-1 (GLP-1), on gastric hormone release was investigated in the isolated perfused rat stomach. Exendin-4 dose dependently stimulated somatostatin release up to 9-fold at a concentration of 10(-7) M whereas gastrin release was inversely inhibited by up to 63%. These effects could partially be reduced by concomitant perfusion of truncated exendin-4, exendin(9-39)amide. Similarly, stimulation of somatostatin secretion and inhibition of gastrin release induced by GLP-1(7-36)amide was partially reversed by exendin-4 (9-39)amide. These data are consistent with the assumption that exendin-4 and truncated GLP-1amide exert their effects on gastric D and G cell by interaction with the same receptor.

Role of cholecystokinin in the control of gastric somatostatin in the rat: in vivo and in vitro studies

Cholecystokinin (CCK) has been shown to be a powerful stimulus for somatostatin release from isolated canine fundic D-cells in short-term culture. The influence of the CCK analogue caerulein on the secretory activity of the D-cell in the intact stomach in vitro and the effect of elevated plasma levels of endogenous CCK on gastric somatostatin stores in vivo were investigated in the rat. Basal somatostatin secretion from the isolated, vascularly perfused rat stomach preparation was not affected by various doses of caerulein. Slight stimulation of somatostatin-like immunoreactivity (SLI) release by epinephrine was significantly inhibited by caerulein, whereas caerulein did not alter half-maximal stimulation of SLI secretion by isoproterenol. Rats with chronically elevated plasma CCK levels induced by experimental exocrine pancreatic insufficiency did not show any change in tissue concentrations of SLI or in D-cell number, both in the antrum and corpus. These data suggest that CCK--in contrast to dogs--is not an important modulator of gastric somatostatin in the rat.

Effect of glucagon-like peptide-1 on gastric somatostatin and gastrin secretion in the rat

The effect of glucagon-like peptide-1 (GLP-1) amide on gastric somatostatin and gastrin secretion was investigated in the isolated, vascularly perfused rat stomach preparation. GLP-1 (7-36) amide, 10(-12) to 10(-7)M, dose-dependently increased gastric somatostatin release, achieving maximal stimulation (314 +/- 15% above basal) at the highest dose. The somatostatin response to 10(-8)M GLP-1 (7-36) amide was not affected by concomitant perfusion with tetrodotoxin. GLP-1 (1-36) amide did not affect somatostatin release. Both basal and acetylcholine-stimulated gastrin were inhibited by GLP-1 (7-36) amide but were not influenced by GLP-1 (1-36) amide. In is concluded that GLP-1 (7-36) amide is the biologically effective peptide that stimulates gastric somatostatin and inhibits gastrin secretion, probably via non-neural pathways. GLP-1 (7-36) amide-induced inhibition of gastric acid secretion may, at least in part, be due to enhanced somatostatin and/or decreased gastrin release.