Jejunal toxin inactivation regulates susceptibility of the immature rat to STa

The immature rat jejunum demonstrates an increased response, sensitivity, and susceptibility to heat-stable enterotoxin. In the present study, the hypothesis that this increased secretory response results from diminished jejunal toxin inactivation and persistence of biologically active toxin was tested. A modification of toxin injected into ligated jejunal loops was observed in both adult and immature rats. However, in the immature jejunum there was also persistence of biologically active toxin and continued toxin-induced secretion. In contrast, in the adult jejunum there was inactivation of toxin and cessation of secretion. Incubation of toxin with luminal fluid, pancreatic fluid, or jejunal brush border membranes resulted in toxin alteration. However, a completely inactive toxin species was generated only after incubation with jejunal organ culture slices. It is concluded that (a) incomplete toxin inactivation in the immature rat jejunum contributes to prolonged intestinal secretion and that (b) the inactivation process is multifactorial, but it is likely that final toxin inactivation requires the participation of the enterocyte. These findings may help explain the increased responsiveness of the immature intestine to heat-stable enterotoxin.