title: On the inhibition of microsomal drug metabolism by polychlorinated biphenyls (PCB) and related phenolic compounds.
abstract: The in vitro metabolism of p-nitroanisole, aminopyrine, and aniline by rat liver microsomal monoxygenases were studied in the presence of different polychlorinated biphenyl (PCB) mixtures and some related hydroxybiphenyls. The tested PCB mixtures contained preferably dichloro- (di-CB), tetrachloro- (tetra-CB), or hexachlorobiphenyls (hexa-CB). All PCB were competitive inhibitors of only aminopyrine demethylation by normal microsomes (Ki 22-39 micron). In microsomes of PCB-pretreated rats the aminopyrine demethylation was inhibited noncompetitively by di-CB and hexa-CB whereas tetra-CB remained a competitive inhibitor (Ki 12 micron). Moreover, after PCB pretreatment all PCB were competitive inhibitors of p-nitroanisole demethylation. 2-OH-biphenyl and 4-OH-biphenyl caused competitive inhibition of aminopyrine demethylation and aniline hydroxylation but failed to inhibit p-nitroanisole metabolism by normal microsomes. Chlorinated 4-hydroxybiphenyls inhibited competitively the metabolism of both type I and type II substrates. However, after PCB pretreatment all phenolic compounds caused uncompetitive inhibition of aniline hydroxylation.
mesh_terms: D000633:Aminopyrine N-Demethylase / Q000378:metabolism*; D000815:Aniline Hydroxylase / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D003580:Cytochromes / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009575:Nitroanisole O-Demethylase / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*; D010105:Oxygenases / Q000378:metabolism*; D010636:Phenols / Q000494:pharmacology*; D011078:Polychlorinated Biphenyls / Q000494:pharmacology*; D051381:Rats
chemical_list: D003580:Cytochromes; D010636:Phenols; D003577:Cytochrome P-450 Enzyme System; D011078:Polychlorinated Biphenyls; D009575:Nitroanisole O-Demethylase; D010088:Oxidoreductases; D010105:Oxygenases; D000815:Aniline Hydroxylase; D001189:Aryl Hydrocarbon Hydroxylases; D000633:Aminopyrine N-Demethylase; D009251:NADPH-Ferrihemoprotein Reductase