The effect of allyl alcohol (AA) administration on the induction of glutathione S-transferase placental form (GST-P) positive foci in medium term liver bioassay was investigated for the detection of initiation activities. In experiment I, the cell kinetics of rat liver after AA administration (0.1 ml/kg, i.g.) was analyzed by the 5-bromo-2'deoxyuridine (BrdU) labeling method. Cytochrome P450 (CYP) 2E1 protein, which is involved in the bioactivation of 1,2-dimethylhydrazine (DMH), was quantificated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDSPAGE) and the immunohistochemical localization of CYP2E1 was also examined. In experiment II, the induction of GST-P positive foci by DMH was evaluated in a modified in vivo five-weeks initiation assay model using AA treatment to induce cell proliferation. AA induced periportal necrosis and led to regenerative proliferation. High BrdU labeling indices were observed from 24 h to 48 h (5-6%). CYP2E1 protein contents decreased transiently to approximately 40% of control after AA administration, but subsequently recovered to the control level. Immunohistochemically, CYP2E1 was localized in the centrilobular area each time, and the staining pattern was constant. The numbers and areas of GSTP positive foci were highly induced in the animals given DMH at 12 h after AA administration, compared to before the high BrdU labeling term. There was a correlation between the kinetics of cell proliferation and the induction of GSTP positive foci. Although CYP2E1 decreased after AA treatment, it is likely that the enzyme remained enough to metabolize DMH. These results suggest that AA-induced cell proliferation is an effective proliferative stimulus in medium-term initiation assay.
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