BACKGROUND Escherichia coli heat stable enterotoxin (STa) is a major cause of secretory diarrhoea in humans.

AIMS To assess the effects of instilling STa into the ileum on remote fluid secretion in the jejunum and colon in rats in vivo by a gravimetric technique.

METHODS AND RESULTS Ileal STa (55 ng/ml) stimulated fluid secretion in both ileal and jejunal loops but not in the colon. The fluid secretion induced by ileal STa was inhibited by l-NAME (N^ω -nitro-l-arginine methyl ester, 40 mg/kg intraperitoneally) but not by d-NAME (N^ω -nitro-d-arginine methyl ester). Ileal carbachol (183 mg/ml) instilled into the lumen stimulated ileal secretion but not jejunal secretion, and was unaffected by l-NAME. Capsaicin (10 μM), instilled luminally with STa in the ileum, blocked both the ileal and jejunal fluid secretion. Acute bilateral vagotomy prevented luminal ileal STa from inducing jejunal fluid secretion but not from activating ileal fluid secretion.

CONCLUSION IlealE coli STa stimulates remote secretion in the rat jejunum but not in the colon, probably by a nitrinergic, vagal reflex mediated by C fibres. This neural pathway will amplify the action of the toxin in its generation of secretory diarrhoea.