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 °C in KrebsHenseleit 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 × 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 < 0.01), extracted mucosal somatostatin from 2.60 ± 0.30 to 1.52 ± 0.16 ng/mg (p < 0.001), and percentage of somatostatin released from 42% ± 2.6% to 27% ± 2.2% (p < 0.01). Carbachol also increased culture media gastrin from 14 ± 2.5 to 27 ± 3.0 ng/mg protein (p < 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.