title: Induction of the hepatic microsomal cytochrome P-450 system by trialkyl phosphorothioates in rats.
abstract: Single i.p. doses of O,O,O-triethyl phosphorothioate [OOO-Et(S)], one of the suicide substrates for cytochrome P-450, caused a rapid increase of NADPH-cytochrome c reductase activity in rat liver microsomes. The increase was dose dependent but did not coincide with the recovery from the inhibition of drug-metabolizing activities. There was no change of Km value of the reductase in the induced state. The co-administration of cycloheximide repressed the stimulatory effect of OOO-Et(S), suggesting that a de novo synthesis of enzyme protein may be responsible for the increase in activity. Of four homologous tri-n-alkyl esters tested, the triethyl compound was the most effective at 24 and 48 hr after administration. Triethyl phosphate, the oxygen analog of OOO-Et(S), also caused an increase of the reductase activity, but carbon disulfide had no influence on this activity. Although O,O,S-triethyl phosphorodithioate [OOS-Et(S)] and its n-alkyl homologs also caused the inhibition of drug-metabolizing activities and the increase of the reductase activity, the recovery and the stimulation of enzyme activity were different from that of O,O,O-tri-n-aklyl phosphorothioates.
mesh_terms: D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction; D007700:Kinetics; D008099:Liver / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000032:analysis; D063086:Organothiophosphates / Q000494:pharmacology* / Q000633:toxicity; D009946:Organothiophosphorus Compounds / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013329:Structure-Activity Relationship; D013997:Time Factors
chemical_list: D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; C052516:O,O,O-triethyl phosphorothioate; D003577:Cytochrome P-450 Enzyme System; D003513:Cycloheximide; D009251:NADPH-Ferrihemoprotein Reductase