Intestinal permeability changes in rodents: a possible mechanism for degraded carrageenan-induced colitis

Rats and guinea-pigs were treated with degraded carrageenan (50 g/litre in the drinking-water) and their intestinal permeability was studied at weekly intervals over the last 4 wk of the test period by determining the recovery of orally administered tracer doses of [3H]polyethylene glycol (PEG-900) or D-[3H]mannitol in 16-hr urine collections. A freely diffusible dye, Azure A, was administered simultaneously to compensate for non-intestinal factors that could modify renal excretion. Animals were killed after a total treatment period of 5 months for rats and 6 wk for guinea-pigs. After 3 wk of carrageenan treatment, excretion of PEG-900 (expressed as a ratio of the Azure A excretion) in guinea-pigs showed a statistically significant increase over that in the control group. At autopsy, the caeca showed numerous macroscopically visible erosions of the entire mucosal surface and histological examination showed ulcerations largely in the mucosa with abscesses in the crypts. Although no such histological changes were seen in the intestines of the treated rats, even after 5 months, a statistically significant increase in PEG-900 excretion was again found compared with the control group. This increase did not occur when deoxycholate was administered with the carrageenan solution. No effect of carrageenan treatment on mucosal permeability to D-[3H]mannitol was demonstrated in either species. The results suggest that degraded carrageenan-induced colitis could be a result of increased intestinal permeability, since ingestion of this polysaccharide by rats increased PEG-900 absorption without causing mucosal damage.