Germ free rats provide a unique model in which to assess biological response to environment. In 48 germ-free male, Sprague-Dawley rats we examined the consequences of oral exposure to nordihydroguaiaretic acid (NDGA), a nephrotoxin; to Staphylococcus epidermidis and bacillus species, non-endotoxin-containing bacteria; to Escherichia coli and Proteus mirabilis, endotoxin-containing bacteria; and injected E. coli endotoxin on peripheral leukocyte counts and renal morphology. Morphological changes were evaluated by light microscopy and scored blindly on a 0 to 4+ scale for 15 parameters of renal structure. Means of these renal 'pathology scores' correlated with counts of polymorphonuclear leukocytes and lymphocytes in the peripheral blood. The highest counts and scores were found in rats given NDGA and exposed to endotoxin, either by injection or by oral feeding of endotoxin-containing bacteria. Counts and scores were lower in the absence of endotoxin and with non-endotoxin-containing bacteria, given alone or in combination with either NDGA or endotoxin. Results exclude bacterial colonization and intrarenal accumulation of NDGA as causes of nephropathy. They indicate that endotoxin and NDGA act synergistically to provoke renal damage in the germ free NDGA-fed rat and suggest that leukocytes are involved in the process.
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