Effects of Escherichia coli heat-stable enterotoxin STb on intestines of mice, rats, rabbits, and piglets.

There are at least two classes of Escherichia coli heat-stable enterotoxins, STa and STb. Unlike STa, which is active in suckling mice and piglets, STb is inactive in suckling mice but active in piglets and older, weaned pigs. This study examined the activity of STb in several animals and its effect on intestinal histology and cyclic GMP levels in intestinal mucosal cells. STb did not cause fluid secretion in suckling mice up to 12 days old or in rat or rabbit intestinal-loop preparations. STb-induced fluid secretion in weaned-pig intestinal loops occurred by 30 min and became maximal by 3 to 6 h. STb did not disrupt intestinal histology and did not alter cyclic GMP levels in intestinal mucosal cells from piglet intestinal loops after 0.5- and 6-h incubations. Our studies support the concept that STb is a second heat-stable E. coli enterotoxin with properties and a mechanism of action unlike those of STa.