88 Factors that influence instances of increased gut permeability.

Abstract Epithelial cells lining the gastrointestinal tract (GIT) maintain a selectively permeable barrier, facilitating ion and nutrient movement while regulating transcellular movement of molecules. Disruption of this selectively permeable barrier may permit the movement of compounds across the GIT that are harmful or toxic, thereby compromising animal health. Considering this, researchers have aimed to identify instances where there is increased risk for loss of GIT barrier function. In ruminants, total tract gastrointestinal permeability appears to be affected by luminal osmolality, age, dietary nutrient supply, and may be affected by systemic inflammation originating from other organs. For instance, hyperosmotic conditions within the lumen of the GIT increase risk for greater permeability, at least when measured ex vivo. Abrupt weaning of milk fed calves has been reported to increase total tract permeability shortly after the weaning phase. In mature ruminants, exposure to short-term feed restriction also transiently increases GIT permeability, with greater responses occurring 2 d after exposure to feed restriction relative to 5 d after exposure. Based on movement of mannitol across the isolated ruminal epithelium ex vivo, it appears that pre-gastric and hindgut regions of the GIT have lower permeability than regions of the small intestine. However, ex vivo movement of a much larger molecule, inulin, does not follow the same response, with greater flux rates observed across the ruminal and omasal epithelia than other regions. That said, exposure of beef or dairy cattle to low feed intake appears to disproportionately increase post-ruminal permeability when measured in vivo, supporting the suggestion that intestinal regions may be at greater risk for barrier dysfunction. Overall, the current data are interpreted to suggest that 55 to 82% of the total tract permeability occurs in the post-ruminal regions. While few studies have assessed GIT permeability in response to non-gastric infectious disease, infusing lipopolysaccharide into the mammary gland resulted in lesser GIT permeability. In conclusion, exposure to low feed intake appears to transiently increase permeability of the gastrointestinal tract with post-ruminal regions being affected to a greater extent. Effects arising from systemic inflammation or infectious disease targeting non-gastrointestinal tract organs requires further investigation.