The potential of carbon tetrachloride (CCl4) to induce pre-neoplastic lesions in rat liver using a medium-term liver assay (Ito method) for the prediction of carcinogenicity was examined by nose-only inhalation exposure of male rats (15/group) to CCl4vapor at concentrations of 0, 1, 5, 25, 125 ppm for 6 h/day, 6 day/week, for a period of 6 weeks. The numbers and area of glutathione S-transferase placental (GST-P) positive foci were then determined. Additionally, other histopathological observations on the livers were recorded and serum chemical parameters and CCl4concentrations in blood were measured. The areas and numbers of GST-P positive foci significantly increased in the CCl4-exposed rats at 25 and 125 ppm; but not at concentrations of 1 and 5 ppm. CCl4blood concentration 24 h after initiation of exposure in the 125 ppm group remained at about 5% of the 6 h maximum concentration. These data from CCl4-exposed rats clearly show that inhalation exposure can be used in the rat medium-term liver assay, the method is available for the screening of volatile chemicals and is therefore a useful tool in cancer risk assessment. This is the first report of the use of inhalation exposure in this medium-term predictive assay. © 2007 Elsevier Ireland Ltd. All rights reserved.
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