Mechanism of cytotoxicity of paraquat. II. Organ specificity of paraquat-stimulated lipid peroxidation in the inner membrane of mitochondria.

The production of superoxide anion (O2-) statistically increased, stimulated by paraquat (1,1'dimethyl-4,4'-bipyridylium dichloride) in lung, liver, kidney and heart submitochondrial particles (SMP) isolated from rats given paraquat intravenously. Paraquat also stimulated O2- production in bovine liver NADH-ubiquinone oxidoreductase (complex I). The reaction mixture used in these assays turned its color into blue proving the occurrence of paraquat free radicals. The pH optimum for NADH dependent O2- production with paraquat was 9.5. O2- production was stimulated by paraquat even in the presence of rotenone, one of the mitochondrial respiratory chain inhibitors. The lipid peroxidation increased in lung SMP but not in heart SMP of paraquat-treated rats. These results may suggest that paraquat was reduced by complex I, but there was difference in the lipid peroxidation by the paraquat radical between rat lung and heart.