at 37 C. During long periods (18 h) of tissue culture incubation, the determination of adenylate cyclase activity was 200to 300-fold more sensitive than quantitating fluid accumulation in the adult rabbit ileal loop model. Decreasing the incubation time appreciably reduced the sensitivity of the epithelial cells to enterotoxin. E. coli enterotoxin is an effective activator of nonintestinal adenylate cyclase systems. Treatment of KB and HEp-2 cell lines with enterotoxin also resulted in significant enzyme stimulation. The intestinal epithelial cell tissue culture model provides a sensitive homogenous biological system for studying the response of intestinal adenylate cyclase to enterotoxin while eliminating the numerous cellular and tissue components present in the ligated ileal loop model.It is generally postulated that the action of Escherichia coli enterotoxin in causing acute dehydrating diarrhea is mediated by the stimulation of adenylate cyclase activity in intestinal cell membranes (17,24,28), resulting in a net secretion of water and electrolytes into the gut lumen (1,24,39). Studies on adenylate cyclase stimulation by enterotoxins, however, have been carried out primarily in the rabbit ileal loop model (17,20,28). In such an in vivo animal model, quantitative interpretations are difficult because of the complex nature of the numerous cellular and tissue components present.
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