Mechanisms of acid disposal in canine duodenum

Distal duodenal pouches chronically excluded from the intestinal stream were perfused in seven awake dogs by a constant-circulation technique using isomolar solutions containing 60-120 mM HCl. The rate of disappearance of hydrogen ions (H+) and net ion movements was measured. In all experiments there was a loss of H+ from the perfusate accompanied by a gain of sodium (Na+), potassium (K+) and chloride (Cl-), together with an increase in volume and a decrease in osmolality. The magnitude of this H+ loss was a function of instillate [H+]. The H+ lost by neutralization was separated from that lost by diffusion by calculations based on the assumption that the observed changes in somolality were the result of neutralization by bicarbonate (HCO3-). The bulk of the acid (67%) was lost by neutralization, the remainder back-diffusing in a one-to-one exchange for diffusable Na+. This ability to dispose of acid decreased with increasing age of the pouches due to a diminished volume of HCO3- secretion, the magnitude lost by backdiffusion remaining unchanged.