The interaction of gastrin and secretin, in the regulation of human lower esophageal sphincter competence, was studied in 54 normal subjects. A dose-response curve, for the lower esophageal sphincter, was constructed from the rapid intravenous injections of synthetic gastrin I (amino acid sequence 2-17). This curve was sigmoid shaped and showed a peak response that was 460.0 ±24.0% (mean ±2 SE) of the initial sphincter pressure, at a dose of 0.7 μg/kg of gastrin I. Secretin, either endogenously released by duodenal acidification, or exogenously administered as a single intravenous injection, markedly reduced the peak response of the sphincter to gastrin I. To ascertain the character of this inhibition, a gastrin I dose-response curve was obtained during a continuous intravenous secretin infusion. This curve showed a parallel shift to the right, with the maximal sphincter response to gastrin I still attainable at higher doses. A sphincter, endogenously stimulated by gastrin, showed a dose-related reduction in pressure with rapid intravenous injections of secretin. At the level of resting sphincter pressure, response to secretin diminished, and larger doses were required for comparable reduction in pressure. These studies indicate; (a) Secretin interacts with gastrin in the physiological regulation of human lower esophageal sphincter competence; (b) Secretin is a sensitive inhibitor to gastrin stimulation of the lower esophageal sphincter; (c) This inhibitory effect of secretin is competitive in character.
Sidney Cohen, William Lipshutz