Inhibition of gastrin release by gastric inhibitory peptide mediated by somatostatin.

The present studies were directed to examine the effect of gastric inhibitory peptide (GIP) on gastrin release and to determine the potential role of somatostatin in mediating this effect, utilizing rat antral mucosa in short-term tissue culture. Antral mucosa was incubated at 37 degrees C in Krebs-Henseleit buffer (pH 7.4) continuously gassed with 95% O2-5% CO2. Inclusion of carbachol (2.5 X 10(-6) M) in the culture medium increased media gastrin concentrations from 3.29 +/- 0.76 (SE) (control) to 6.77 +/- 0.76 ng/mg tissue prot (P less than 0.02). Rat antral mucosa was then incubated in the presence of GIP (10(-10) to 10(-7) M) to determine its effect on carbachol-stimulated gastrin release. GIP significantly inhibited carbachol-stimulated gastrin release into the culture media at all concentrations examined. To determine whether inhibition of carbachol-stimulated gastrin release by GIP was mediated by somatostatin, antral mucosa was incubated in the presence of carbachol, GIP (10(-10) to 10(-7) M), and specific antibodies to somatostatin in excess. Inclusion of antibodies to somatostatin in the culture medium abolished the capacity of GIP (10(9) to 10(-7) M) to inhibit carbachol-stimulated gastrin release. Results of these studies indicate 1) that GIP inhibits carbachol-stimulated gastrin release and 2) that, under the conditions of these experiments, GIP inhibition of gastrin release may be mediated locally through release of antral somatostatin.

Effect of GRP on beta-adrenergic-stimulated gastrin and somatostatin release in the isolated rat stomach.

The present studies were directed toward examining the effects of gastrin-releasing peptide (GRP) on acid secretion and on beta-adrenergic-stimulated gastrin and somatostatin release using the isolated vascularly perfused rat stomach. Including pentagastrin in perfusion buffer increased acid output from 2.2 +/- 0.4 mueq H+/h during control perfusion to 18.8 +/- 1.8 mueq H+/h (P less than 0.01). No significant changes in acid secretion were detected when either GRP or specific antibodies to GRP were included in perfusate in the absence or presence of pentagastrin. Inclusion of 10(-9) M isoproterenol in the perfusate did not change acid output with respect to control; however, gastrin and somatostatin release into the portal venous effluent was significantly enhanced. Peak gastrin and somatostatin concentrations observed at 15 min were 753 +/- 43% (P less than 0.001) and 345 +/- 43% (P less than 0.01), respectively, of basal levels. When antibodies to GRP were included in perfusate containing isoproterenol, gastrin and somatostatin release into the portal venous effluent was significantly inhibited. The results of these studies indicate that GRP does not affect basal or pentagastrin-stimulated gastric acid secretion in the isolated perfused rat stomach. However, under the conditions of these experiments, beta-adrenergic stimulation of gastrin and somatostatin release appears to be mediated, at least in part, through GRP.

Specificity of commercially available antibodies used for gastrin measurement.

We examined the specificity of commercially available antibodies used in measurement of serum gastrin. Antibodies were obtained from five commercial laboratories, and antibody immunoreactivity with gastrin and cross-reactivity with cholecystokinin (CCK) were determined. All antibodies were equally immunoreactive with gastrin, and cross-reactivity of three antibodies with CCK was minimal (less than 5%). In contrast, substantial cross-reactivity with CCK was found with two antibodies. To determine the clinical significance of cross-reactivity with CCK, secretin injection tests were performed in 24 individuals: seven in normal health, four with Zollinger-Ellison syndrome, three with antral gastrin cell hyperfunction, six with ordinary duodenal ulcer disease, and four with atrophic gastritis. Serum gastrin levels were measured with all five gastrin antibodies. The response to secretin was negative in all normal subjects and in those with duodenal ulcer and antral gastrin cell hyperfunction. The response to secretin was positive in all four patients with gastrinoma with use of the five antisera. All four patients with atrophic gastritis had normal responses to secretin when antibodies with minimal CCK cross-reactivity were used; however, two of four had false positive secretin test results when serum gastrin levels were measured with the two antibodies with a high degree of cross-reactivity with CCK. These studies indicate that significant cross-reactivity of gastrin antibodies with CCK can result in false positive secretin injection test results and can lead potentially to the erroneous diagnosis of Zollinger-Ellison syndrome.

Effects of carbachol on gastrin and somatostatin release in rat antral tissue culture.

Recent studies have demonstrated that somatostatin-containing cells are in close anatomic proximity to gastrin-producing cells in antral mucosa, suggesting a potential local regulatory role for somatostatin. The purpose of this study was to examine further the relationships between gastrin and somatostatin and the effects of the cholinergic agonist carbachol on content and release of gastrin and somatostatin using rat antral mucosa in tissue culture. Antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h, the culture medium was decanted and the tissue was boiled to extract mucosal gastrin and somatostatin. Inclusion of carbachol 2.5 X 10(-6) M in the culture medium decreased medium somatostatin from 1.91 +/- 0.28 (SEM) ng/mg tissue protein to 0.62 +/- 0.12 ng/mg (p less than 0.01), extracted mucosal somatostatin from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (p less than 0.001), and percentage of somatostatin released from 42% +/- 2.6% to 27% +/- 2.2% (p less than 0.01). Carbachol also increased culture media gastrin from 14 +/- 2.5 to 27 +/- 3.0 ng/mg protein (p less than 0.01). Tissue content and release of gastrin and somatostatin were also examined during culture of rat antral mucosa in culture media containing antibodies to somatostatin in the presence and in the absence of carbachol. Incubation with somatostatin antisera, both with and without carbachol, markedly increased culture media concentrations of somatostatin, all of which was effectively bound by antibodies present in the media. Antibody binding of somatostatin was accompanied by significant increases in culture media gastrin concentrations, both in the presence and in the absence of carbachol. Results of these studies support the hypothesis that antral somatostatin exerts a local regulatory effect on gastrin release and that cholinergic stimulation of gastrin release is mediated, at least in part, through inhibition of somatostatin synthesis and release.

Inhibition of gastrin release by secretin is mediated by somatostatin in cultured rat antral mucosa.

Somatostatin-containing cells have been shown to be in close anatomic proximity to gastrin-producing cells in rat antral mucosa. The present studies were directed to examine the effect of secretin on carbachol-stimulated gastrin release and to assess the potential role of somatostatin in mediating this effect. Rat antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h the culture medium was decanted and mucosal gastrin and somatostatin were extracted. Carbachol (2.5 X 10(-6) M) in the culture medium increased gastrin level in the medium from 14.1 +/- 2.5 to 26.9 +/- 3.0 ng/mg tissue protein (P less than 0.02), and decreased somatostatin-like immunoreactivity in the medium from 1.91 +/- 0.28 to 0.62 +/- 0.12 ng/mg (P less than 0.01) and extracted mucosal somatostatin-like immunoreactivity from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (P less than 0.001). Rat antral mucosa was then cultured in the presence of secretin to determine its effect on carbachol-stimulated gastrin release. Inclusion of secretin (10(-9)-10(-7) M) inhibited significantly carbachol-stimulated gastrin release into the medium, decreasing gastrin from 26.9 +/- 3.0 to 13.6 +/- 3.2 ng/mg (10(-9) M secretin) (P less than 0.05), to 11.9 +/- 1.7 ng/mg (10(-8) secretin) (P less than 0.02), and to 10.8 +/- 4.0 ng/mg (10(-7) M secretin) (P less than 0.02). Secretin (10(-7) and 10(-8) M) also increased concomitantly culture medium somatostatin concentration. To determine whether secretion inhibition of carbachol-stimulated gastrin release was mediated by somatostatin, antral mucosa was cultured with carbachol, secretin (10(-9)-10(-7) M), and antibodies to somatostatin. Inclusion of somatostatin antibodies in the culture medium abolished the capacity of secretin (10(-7) and 10(-8) M) to inhibit carbachol-stimulated gastrin release. Results of these studies indicate (a) that secretin inhibits carbachol-stimulated gastrin release and (b) that under the conditions of these experiments secretin inhibition of gastrin release is mediated, at least in part, locally through release of antral somatostatin.