RESPONSE OF THE GERM-FREE RAT COLONIC MUCOSA TO DIETARY ENDOTOXINS

Suggestive to induce an immunoreactive response in the colon mucosa of germfree rats 3 diets, autoclaved or gamma-irradiated, respectively, were administered to groups of 30 days old GF Ztm:SPRD rats. Diets and rats were studied in parallel after a feeding period of 20 days. The microbiological controls confirmed the sterility of diets and animals. The aqueous suspensions of one diet displayed obviously dead yeast an d Gram positive and negative bacteria, which consistently were evident in colonic cast preparations of animals fed with this diet. These fin dings apparently were not related to the pathohistological alterations , observed in hematoxilin-eosin stained colon sections. However, dieta ry endotoxin concentrations between 0.6 and 10 mu g LPS/g corresponded with the endotoxin concentrations in feces (0.3 to 3.1 mu g LPS/g wet weight) and in colonic tissue (0.01 to 0.6 mu g LPS/g wet weight). Th ese endotoxins obviously mediated a dose-dependent immunoreactive resp onse of the colonic mucosa: in parallel to the dietary endotoxin conte nt, the cellular infiltrations ranged from single mononuclear cells to severe, cell mediated, mucosal alteration. GF rats, used as an experi mental animal model for inflammatory disorders of the intestine obviou sly necessitate diets with low endotoxin concentrations.