A model for studying the pathophysiology of diarrhea has been developed by inducing salmonella enterocolitis in rats. In vivo intestinal net water and electrolyte transport rates were determined in infected rats with and without diarrhea and were compared with control animals. The only significant alteration in net water and electrolyte transport between control animals and infected animals without diarrhea was a diminution of ileal absorption and a reversal of ileal HCO, transport from secretion to absorption. In the infected animals with diarrhea, jejunal and large intestinal transport was not significantly different from that in infected animals without diarrhea. However, in all animals with diarrhea there was ileal secretion of H2O, Na, K, and Cl. Thus ileal secretion appeared to be a major physiological determinant of diarrhea in this disease model. Among the possible mechanisms to explain the net blood to lumen transport, the most likely are either (1) a passive transudation of fluid and electrolyte secondary to increased hydrostatic pressure in the lamina propria or (2) active electrolyte secretion by the mucosa.
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