In vivo and in vitro effects of a novel enterotoxin, STb, produced by Escherichia coli.

Escherichia coli may produce a heat-labile enterotoxin (LT) or two heat-stable enterotoxins (STa, STb). STb consistently causes secretion in vivo in 5-hr weaned-pig intestinal loops (P less than .0001). In Ussing chambers in vitro, crude culture filtrates of STb initiate a prompt increase in short circuit current (SCC; P less than or equal to .0001) and potential difference (P less than or equal to .0001) when compared with nontoxigenic culture filtrates. In bidirectional in vitro studies of ion flux (22Na and 36Cl), STb did not alter 22Na or 36Cl unidirectional or net fluxes. The calculated residual ion flux increased significantly (P less than .03), however, in tissues treated with STb and fully accounted for the STb-induced increase in SCC. Measurement of the electrolyte content of ligated intestinal segments in vivo further suggested that STb stimulated bicarbonate secretion. Relative to controls, significant accumulation of Na and Cl also occurred intraluminally in vivo. These data indicate that STb is a unique enterotoxin that causes net secretion in pig jejunum in vivo. In vitro and in vivo studies show that STb stimulates active secretion of nonchloride anion. We postulate that STb causes active bicarbonate secretion in weaned-piglet jejunum.