Effects of acute respiratory acidosis on water and electrolyte transport in the human ileum.

Abstract

Animal experiments have shown that acute respiratory acidosis stimulates water, Na and Cl absorption and HCO3 secretion in the ileum. The aim of this study was to investigate whether the human ileum also responds to changes in systemic acid-base balance. Seven healthy volunteers (mean age 24, range 21-29 years) underwent segmental ileal perfusion using a multi-lumen tube assembly with a proximal occluding balloon. A 30 cm test segment was perfused under steady state conditions with a plasma-like electrolyte solution containing PEG as a non-absorbable volume marker. After a control period, respiratory acidosis (blood pCO2 56.2 mmHg, pH 7.29 and [HCO3] 26.4 mmol l-1) was induced by CO2-breathing over a period of 50 min. Acute respiratory acidosis stimulated net HCO3 secretion in patients secreting HCO3 and reduced absorption in patients exhibiting net HCO3 absorption. These changes were immediate and appeared to be at least partly reversible. Net water, Na, K and Cl movement were not affected. The data suggest that HCO3 transport in the human ileum responds to acute respiratory acidosis.