Gastric acid regulates the release of plasma secretin in man.

Fasting plasma secretin determined in nine healthy subjects, twelve patients with active duodenal ulcer and four with Zollinger-Ellison syndrome were 3.2 +/- 0.4, 5.1 +/- 1.2 and 20.3 +/- 1.3 pmol/l respectively (mean +/- SEM). Cimetidine significantly (P less than 0.05) reduced levels in those with duodenal ulcer, as did gastric aspiration in the Zollinger-Ellison group. A significant correlation (P less than 0.001) was found between basal acid output and mean fasting plasma secretin. After a solid meal and subsequent liquid soft drink, no sustained mean rise in plasma secretin was observed; changes in secretin appeared to coincide in time with rapid falls in duodenal pH, though little relationship could be established between the absolute level of pH and changes in plasma secretin. The mean peak post-prandial rise in plasma secretin observed after solids was significantly (P less than 0.05) greater in duodenal ulcer patients than controls (9.1 +/- 1.1 versus 6.7 +/- 0.5 pmol/l) as was the mean integrated post-prandial release (1002 +/- 110 versus 710 +/- 67 pmol min-1 1(-1)). Cimetidine reduced both rises (P less than 0.05) and was associated with significantly less duodenal pH readings below 4 (P less than 0.001). These results suggest that gastric acid is a major release mechanism for plasma secretin both fasting and after meals but it is likely the acid load rather than absolute pH in the duodenum which determines circulating levels.