Intestinal transmucosal fluxes of bicarbonate

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Abstract
Isoosmotic solutions composed of NaCl and NaHCO3 and containing from 0 to 154 mEq bicarbonate/liter were placed in chronic Thiry-Vella loops of jejunum, ileum, or colon of healthy unanesthetized dogs and the changes in composition in the solutions estimated after a fixed period. This method allowed determination of the concentration which each segment establishes in its contents. This equilibrium concentration of CO2 was 5 mEq/liter in the proximal jejunum and 75 mEq/liter in the distal ileum and proximal colon. Regardless of the initial concentration of CO2, it always changed toward the equilibrium value. Net sorption of CO2 from upper jejunum and distal ileum was dependent upon its concentration in the luminal fluid. In the colon net flux of CO2 was not closely related to luminal concentration. Addition of bicarbonate labeled with 14C established that CO2 moved in both directions across the mucosa of each of the segments. Insorption of CO2 at all locations increased with increasing luminal concentration; exsorption of CO2, especially in the distal ileum and in the colon was independent of luminal concentrations.[long dash]Authors.

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