Effect of intraluminal pH on the release of somatostatin and gastrin into antral, bulbar and ileal pouches of conscious dogs

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Abstract
Experiments were performed on conscious dogs with chronic pouches of the antrum, the duodenal bulb or the ileum, which were perfused with solutions of varying pH. Gastrin and somatostatin levels were measured in the perfusates. When the pouches were perfused with 0.15 M NaCl only small amounts of gastrin and somatostatin (1 pmol/min) were released into the lumen of the antrum and of the duodenal bulb. By lowering pH of the perfusion fluid a pH dependent release of somatostatin was induced into the lumen of the antrum and the duodenal bulb. Perfusion with 0.1 M HCl caused a large output of somatostatin (6-60 pmol/min) into the pouches. The upper pH limit for stimulation of the intraantral or intrabulbar somatostatin release appeared to be .apprx. pH 3-4. Somatostatin was also released into ileal perfusates at intraluminal pH below 3-4. Lowering of pH in the antral pouches caused an increased intraluminal gastrin release, which was quantitatively less impressive than that of somatostatin. Occasionally the gastrin release into the duodenal bulb increased during perfusion with 0.1 M HCl, whereas no such release was induced by acidification of the lumen of the ileum. The inhibition of gastrin release observed at low intraantral pH is probably mediated by a local effect of somatostatin, since this peptide is released in a pH dependent manner in the antropyloric region. Acidification of any region of the gastrointestinal tract may stimulate release of peptides from all endocrine cells of the open type, probably by an unspecific effect on the membrane. Gastrin and somatostatin are released by acidification of the antrum, but in the presence of high local levels of somatostatin the release of gastrin is substantially inhibited.