Luminal salmonella endotoxin affects epithelial and mast cell function in the proximal colon of pigs

Background: Salmonellosis and systemic endotoxaemia affect intestinal function. However, little is known about the functional importance of luminal Salmonella (S.) endotoxin during intestinal infection. Methods: Pigs were either given or not given lipopolysaccharide (LPS, 30 mg day(-1)) of S. Typhimurium DT-104 orally for 14 days. Blood samples were taken weekly. After slaughter (day 14), epithelia of the proximal colon were investigated in Ussing chambers. Bacterial translocations to lung, liver, spleen and several lymph nodes were determined by culture. Results: Endotoxin feeding increased plasma C-reactive protein (CRP) and histamine levels without evoking clinical signs. Postmortem, proximal colonic epithelia of LPS-treated animals showed both a decreased histamine release after mast cell stimulation with A23187 and a smaller increase in short-circuit current after A23187 application. Addition of the nitric oxide donor, sodium nitroprusside (SNP), also elicited lower increases in short-circuit current in the proximal colon of endotoxin-treated pigs. Endotoxin pre-feeding decreased colonic ion conductance, although mannitol and histamine fluxes were high in some epithelia of this group. Luminal Salmonella endotoxin increased bacterial translocation to proximal jejunal lymph nodes. LPS applied to colonic epithelia in vitro had no electrophysiological effects. Conclusions: Luminal endotoxin elicits an acute phase response and affects intestinal electrolyte transport and mast cell function. Furthermore, LPS induces epithelial spots of increased mannitol permeability that could be identical to spots of enhanced bacterial translocation.