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Controlled intragastric pH and cimetidine inhibition of histamine-stimulated gastric acid secretion in the dog.

This study tested a circulating intragastric titration system with an examination of the kinetics of cimetidine inhibition of histamine-stimulated gastric acid secretion of pH 7.0. Dogs were anesthetized, intubated with a biluminal nasogastric device, and connected to the titrating system. The dogs were stimulated with histamine at 0.0, 0.25, 0.50, 1.0, 2.0, and 4.0 microgram/kg/min IV. The dose variations were repeated on separate days with cimetidine infusion at 0.0, 20, and 40 microgram/kg/min IV. Calculated maximal response was 4.52 mEq/kg/hr. Histamine D50 was 0.60 microgram/kg/min. Cimetidine ID50 was 22.6 microgram/kg/min when histamine was given at 1.0 microgram/kg/min. Although acid secretion was higher than other published values, cimetidine inhibition kinetics were not significantly different from published values. A positive correlation was found between cimetidine ID50 and the logarithm of the histamine infusion rate. Our data suggest that (1) a simple circulating intragastric titration system can give accurate results in acid secretion studies, (2) increased gastric pH may enhance histamine-stimulated acid secretion, (3) neutralization of gastric contents does not interfere with cimetidine inhibition kinetics which is competitive, and (4) at artifically high rates of histamine infusion, cimetidine can actually increase acid secretion. We suggest that a circulating intragastric system may be tested in a surgical intensive care unit to evaluate potential clinical value in antiulcer therapy.