Different mechanisms of hydrogen ion removal in stomach and duodenum.

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Abstract
The acid-removing capability of the duodenal mucosa itself, without the secretions of Brunner''s glands, the pancreas or liver, has recently become recognized. This acid loss may occur by backdiffusion of H+, bicarbonate neutralization, a combination of the above 2 processes, or some other mechanism. In dogs with chronic distal duodenal pouches or with gastric fundal pouches, acid loss and CO2 levels were measured simultaneously in situ. If bicarbonate neutralization of acid was going on, CO2 would appear in the pouches as a result of the reaction H+ + HCO3 .fwdarw. H2O + CO2. In the duodenal pouches, P[partial pressure]CO2 did rise as acid was lost. For 22 experimental observations, the net acid loss from the pouches (JH+) correlated directly with pouch PCO2 generation. PCO2 levels were not increased in dogs with gastric pouches when the barrier was broken and acid loss occurred. When the system was run with a plastic cannula replacing the duodenal mucosal pouches and bicarbonate was infused to simulate the rates of acid loss seen in the duodenum, PCO2 levels in the plastic cannulas were similar to those seen in vivo. Bicarbonate neutralization is responsible, at least in part, for acid loss in isolated canine duodenal loops.

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