Effects of isolated heat-stable enterotoxin produced by Escherichia coli on fluid secretion and cyclic nucleotide levels in the jejunum of the weanling pig

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Abstract
Fluid secretory responses and associated changes in cyclic nucleotide concentration caused by the heat-stable enterotoxin of Escherichia coli (ST) have been investigated in the jejunum of weanling pigs. Effects associated with ST treatment have been compared with the actions of cholera toxin (CT) in the same experimental model. Positive correlations were obtained for the log of the ST dose correlating with net fluid secretion and with mucosal cyclic GMP (cGMP) concentration. Net fluid secretion rates could be predicted by mucosal cGMP concentration except for a brief interval when secretion was returning to control levels following ST removal from loops. Secretion rates in this post-ST period correlated more closely with the ratio of cGMP to cAMP concentration than with cGMP levels alone. Attempts to decrease the cGMP concentration and the secretory rate by combining CT and ST treatment were not successful. We conclude that the previously observed lack of cAMP response to CT in the pig may not be due to major differences in secretory control in that species. The pig is similar to other animal models where changes in mucosal cGMP concentration are associated with net jejunal fluid secretion induced by ST.