This study examines the effects of endotoxin on intestinal water and electrolyte transport in adult male rats. Endotoxin (1.55 mg/kg, intravenously) reduced in vivo colonic saline absorption 61% in 1 hour. In vitro unidirectional and net 22Na and 36Cl fluxes showed that endotoxin significantly decreased net colonic 22Na absorption compared with control colons (0.3 +/- 1.7 vs. 4.8 +/- 1.1 microEq/h x cm2). Although endotoxin had no significant effect on basal short circuit current (Isc) and conductance, 3H-inulin flux studies suggested an increase in colonic permeability. Isc responses to the 5'-cyclic adenosine monophosphate (cAMP)-dependent secretagogues prostaglandin E2 (1 mumol/L) and vasoactive intestinal peptide (0.1 mumol/L) were diminished by 80% and 50%, respectively. However, cytosolic cAMP-dependent protein kinase activity under basal and stimulated (6 mumol/L 8-bromo-cAMP) conditions was not altered by endotoxin treatment. The Isc responses to 10 mumol/L bethanechol, a Ca(2+)-dependent agonist, were not effected by endotoxin treatment. It was concluded that endotoxin significantly affects colonic transport function and may contribute to the development of diarrhea in inflammatory bowel diseases.