COMPARATIVE 90-DAY FEEDING STUDY WITH LOW-VISCOSITY WHITE MINERAL-OILIN FISCHER-344 AND SPRAGUE-DAWLEY-DERIVED CRL-CD RATS

A 90-day study was conducted to compare the effects of dietary adminis tration of a food-grade white oil in female Fischer-344 (F-344) and Sp rague-Dawley-derived (CRL:CD) rats. Animals were fed a low viscosity ( 15 mm(2)/sec at 40 degrees C) paraffinic white oil (designated as P 15 [H]) at 0, 0.2, or 2.0% of the diet for 30, 61, or 92 days. There were no significant adverse clinical observations or unscheduled deaths, I n the F-344 rats, occasional treatment-related changes were seen in he matology and clinical chemistry parameters. At necropsy, mesenteric ly mph nodes were enlarged, and there was an increase in absolute and rel ative liver, mesenteric lymph node, and spleen weights as compared to controls. Histopathologic effects included hepatic and mesenteric lymp h node microgranulomas and mesenteric lymph node histiocytosis. In CRL :CD rats, the only effects noted were accumulations of chronic inflamm atory cells in the liver at the high dose only, without the formation of discrete microgranulomas. A dose-related increase in mineral hydroc arbon (MHC) material in the liver and mesenteric lymph nodes was obser ved in both F-344 and CRL:CD rats. Although increased, liver MHC conte nt was significantly less (approximately 50%) in CRL:CD rats than the levels detected in the F-344 rats. Mesenteric lymph node MHC levels di d not differ significantly between the strains. This study demonstrate d strain differences among rats in histopathologic effects of white oi l, with the CRL:CD rat essentially showing no response compared to the F-344 rat. The differences in the pathologic responses between the 2 strains appears to result from the higher MHC tissue content and a gre ater sensitivity of the F-344 rat to the presence of the MHC material.