Antisecretory factor enhances in vivo internalization of cholera toxin and of horseradish peroxidase into rat enterocytes.

The in vivo effect of antisecretory factor (ASF, derived from pig plasma) on the ability of cholera toxin (CT) and of horseradish peroxidase (HRP) to bind to and penetrate into epithelial cells of the rat small intestine was evaluated in the absence of anesthetics. The potency of intravenously administrated ASF was demonstrated by some 70% inhibition of CT-induced secretion in ligated small intestinal loops. Using immunohistochemical methods for visualization, we found ASF to enhance internalization of both CT and HRP after 30 to 60 min of challenge, without interfering with the initial binding to the enterocyte brush border region. The internalization process started in the upper 2/3 of the villus region. After 5 h, no CT or HRP could be seen bound to the enterocytes. The results suggest that ASF might enhance small intestinal absorption.