Acidosis and lipopolysaccharide from Escherichia coli B:055 cause hyperpermeability of rumen and colon tissues.

The objective of the present investigation was to evaluate the effects of acidic pH of the perfusate and presence of lipopolysaccharide (LPS) on permeability of rumen and colon mucosal tissues to mannitol and LPS using the Ussing chamber system. Rumen and colon tissues (n = 8), obtained from slaughtered feedlot steers, were tested for changes in permeability to (3)H-mannitol under pH of 4.5, 5.5, and 6.5 for rumen and at 5.5, 6.5, and 7.4 for colon, with or without LPS from Escherichia coli B:055 at 500 microg/mL. The (3)H-Mannitol was added at 10 microL (525.4 GBq/mmol) on the mucosal side of the Ussing chamber to detect changes in permeability, and 4 samples were taken at 20, 25, 30, and 35 min from the serosal side. Permeability of rumen and colon mucosa to (3)H-mannitol increased 6- and 5-fold, respectively, at acidic pH values of 4.5 and 5.5 and in the presence of 500 micro/mL of LPS. In contrast, LPS did not affect rumen and colon permeability at pH that ranged from 5.5 and 7.4. Translocation of LPS across the rumen and colon mucosa of cattle was not pH dependent. The LPS translocated through these tissues if present at the mucosal side. In conclusion, the permeability of rumen and colon tissues to (3)H-mannitol increased in presence of LPS and under acidic pH, whereas LPS permeated through mucosal tissues independently of the pH of the perfusate. Further research is warranted to understand the mechanism(s) by which acidic pH of the rumen digesta and presence of LPS make rumen and colon tissues "leaky".