Response of the canine duodenum to intraluminal challenge with cholera exotoxin.

In response to intraluminal challenge with crude cholera exotoxin, canine Thiry-Vella duodenal loops consistently produced isotonic fluid for a 24-36 hr period. Isotonic fluid production generally began within 15 min after challenge. Mean bicarbonate concentration of fluid produced by duodenal loops was 24+/-6 (SD) mEq/liter. Perfusion of exotoxin-treated duodenal loops with an isotonic electrolyte solution containing glucose 60 mOsm/liter caused a significant decrease in exotoxin-induced isotonic fluid output. The net effects of glucose on isotonic fluid absorption by perfused duodenal loops were not significantly different before and after administration of crude cholera exotoxin. The response of canine duodenal loops to challenge by cholera exotoxin differs from responses of jejunal and ileal loops in a) absence of a detectable "lag period" between administration of exotoxin and initiation of net fluid output; b) a longer period of fluid production following exotoxin administration; and c) a significantly greater net fluid output per unit length of gut. The mean bicarbonate concentration of the fluid produced by duodenum is less than that produced by ileum, but is not significantly different from that produced by jejunum. The duodenal response is similar to that of the more distal small bowel segments in that an effect on isotonic fluid movement is observed shortly after exotoxin administration and the maximum rate of exotoxin-induced isotonic fluid production is not reached until 4-5 hr after exotoxin administration. The basis for the consistent delay of 4-5 hr between intraluminal exotoxin administration and maximum gut fluid production has not yet been determined. Current data are consistent with the hypothesis that the rate of secretion of isotonic fluid induced by cholera exotoxin is not significantly different per unit length, in duodenum and ileum and that the lesser net fluid output in the ileum is due to the greater capacity for isotonic fluid absorption by the more distal small bowel segment.