In vivo effects of enterotoxin from Clostridium perfringens type A in the rabbit colon: binding vs. biologic activity

Rabbit colonic loops were exposed to purified enterotoxin from Clostridium perfringens type A and perfused for analysis of the effects of the enterotoxin on transport and surface structure of the colon. The colon showed no apparent response to the enterotoxin in the transport of fluid and electrolytes as compared with untreated animals. There was a significant increase in levels of luminal fluid protein, corresponding to an observed increase in secretion of mucus. Histologic sections showed no epithelial damage, but scanning electron microscopy showed an increase in the number of mucous fields over the value in control animals. The colon showed little or no overt response to enterotoxin treatment, but isolated colonic epithelial cells bound 125I-labeled enterotoxin at levels even greater than those observed in cells from the ileum, where the enterotoxin has considerable biologic activity. Thus, although binding of enterotoxin is necessary for its biologic activity, biologic activity does not necessarily follow binding to specific receptors.