Low acid output in Pima Indians. A possible cause for the rarity of duodenal ulcer in this population.

Duodenal ulcer has not been observed in full-heritage Pima Indians, while gastric cancer is relatively frequent. To investigate possible underlying factors for this phenomenon, we determined gastric acid output, gastric emptying rate, and plasma levels of gastrin, pepsinogen I, and pepsinogen II in apparently healthy Pima Indians and in Caucasian controls. The Pimas had significantly lower basal and stimulated outputs of gastric acid and higher fasting and postprandial plasma gastrin concentrations than the Caucasians. Plasma pepsinogen I levels were similar in the two groups, but plasma pepsinogen II was significantly higher and the ratio of pepsinogen I to pepsinogen II was significantly lower in the Pima Indians. In addition, gastric emptying of acaloric liquid meal was significantly delayed in the Pimas. The results suggest that the absence of duodenal ulcer in Pima Indians may be related to low gastric acid production and a slow rate of gastric emptying in this population. The associated findings of hypergastrinemia, hyperpepsinogenemia II, and a low ratio of pepsinogen I to pepsinogen II suggest that the hypochlorhydria may reflect an increased prevalence of chronic gastritis in full-heritage Pima Indians. This, in turn, could represent a risk factor for the development of gastric cancer in this population.