Effect of shigella enterotoxin 1 (ShET1) on rabbit intestine in vitro and in vivo

Background-Shigella enterotoxin 1 is a novel enterotoxin elaborated by Shigella flexneri 2a that causes fluid accumulation in rabbit ileal loops and a rise in short circuit current in Ussing chambers. Aims-To gain insights into the mechanism of action of shigella enterotoxin 1. Methods-Supernatants from genetically engineered clones either overexpressing shigella enterotoxin 1 or producing deletion mutants of the toxin were tested in rabbit ileum both in vitro and in vivo. Results-In rabbit ileum shigella enterotoxin 1 induced an irreversible rise in short circuit current that was not mediated by any of the recognised intracellular mediators of secretion. Deletion of 90% of the A subunit of the holotoxin ablated its enterotoxicity. In the in vivo perfusion model, the toxin induced a time dependent decrease in water absorption, whereas no changes were detected in the segment perfused with supernatants obtained from the deletion mutant. Finally, partially purified toxin induced a dose dependent increment in short circuit current that reached its plateau at a toxin concentration of 4 x 10(-6) M. Conclusions-Shigella enterotoxin 1 induces a time and dose dependent intestinal secretion in the rabbit animal model, suggesting that it may be responsible for the watery phase of Shigella flexneri 2a infection.