Inductive effect of polychlorinated biphenyls mixture and individual isomers on the hepatic microsomal enzymes.

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The inductive effect of Kanechlor 400 (KC-400), the Japanese polychlorinated biphenyl (PCB) preparation containing 48% chlorine, and several individual PCB isomers on the hepatic microsomal enzymes of rats was investigated. Pretreatment with KC-400 increased significantly the activity of microsomal aminopyrine (AM) demethylase, aniline (AN) hydroxylase and NADPH-cytochrome c reductase, and the content of cytochromes P-450 and b5 just like phenobarbital (PB)-pretreatment. However, it afforded the CO-difference spectrum revealing the peak at 448 nm same as pretreatment with 3-methylcholanthrene (MC). The inhibitory effect of SKF 525-A and 7, 8-benzoflavone on AM demethylation and AN hydroxylation, respectively, in KC-400-induced microsomes also resembled that in microsomes induced by PB plus MC. Further studies using individual PCBs indicated that these compounds were divided into two groups ; namely, 4, 4'-dichlorobiphenyl (DCB), 2, 5, 2', 5'-and 2, 4, 3', 4'-tetrachlorobiphenyl (TCB) were categorized as PB-type, whereas the other group including 3, 4, 3', 4'-TCB, 3, 4, 5, 3', 4'-pentachlorobiphenyl (PenCB) and 3, 4, 5, 3', 4', 5'-hexachlorobiphenyl (HCB) was categorized as MC-type inducers. Decachlorobiphenyl, the completely chlorinated biphenyl derivative, was found to belong to PB-type. These conclusions were further supported by a spectral study with hexobarbital, which induced type I spectral changes with microsomes from control and 2, 4, 3', 4'-TCB-treated rats, and caused modified type II spectral change with microsomes from 3, 4, 5, 3', 4'-PenCB-treated rats. Considering these results with individual PCBs, it can be assumed that chlorination of both of the para-(4, 4') and two of the meta-positions (3, 3' or 5, 5') of biphenyl is a minimum requirement for the structure to induce cytochrome P-448.

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