Protective action of cardiac DT-diaphorase against menadione toxicity in guinea pig isolated atria.
In myocardial preparations isolated from guinea pigs, 2-methyl-1, 4-naphthoquinone (menadione) causes an increase in contractility that is strictly related to the generation of reactive oxygen species (ROS) as a consequence of quinone metabolism. In heart, menadione undergoes one-electron reduction to semiquinone, a reaction mainly catalysed by mitochondrial NADH: ubiquinone oxidoreductase. It is also converted to hydroquinone by the soluble two-electron reductase, DT-diaphorase, and is conjugated with GSH by glutathione S-transferase. In order to assess the role of DT-diaphorase in cardiac responses to menadione, we examined the effects of both a specific inhibitor (dicoumarol) and an inducer (beta-naphthoflavone) of the enzyme on the inotropic action of the quinone. In electrically driven left atria of guinea pig, 4 microM dicoumarol significantly enhanced the positive inotropic effect of menadione, especially at the lower concentrations of the quinone. In myocardial preparations isolated from guinea pigs treated with beta-naphthoflavone (80 mg/kg i.p.for 2 days), DT-diaphorase activity was enhanced (+36% with respect to control animals, P < 0. 01), whereas the activities of the other enzymes involved in menadione metabolism were not modified. In these preparations, menadione caused a significantly lower increase in the force of contraction than in atria from untreated animals; moreover, pretreatment with beta-naphthoflavone caused a significant decrease in the menadione-induced oxidative stress, as evaluated from the GSH redox index. Taken together, these results demonstrate that cardiac DT-diaphorase does not contribute to ROS generation, but represents a detoxification system.
Floreani
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Department of Pharmacology, University of Padova, Padova, Italy. floreani@ux1.unipd.it
Napoli
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Palatini
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D000704:Analysis of Variance; D000818:Animals; D001728:Dicumarol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D006325:Heart Atria / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000494:pharmacology*; D020011:Protective Agents / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D014812:Vitamin K / Q000633:toxicity*; D019324:beta-Naphthoflavone / Q000494:pharmacology
D004791:Enzyme Inhibitors; D020011:Protective Agents; D017382:Reactive Oxygen Species; D014812:Vitamin K; D008748:Methylcholanthrene; D019324:beta-Naphthoflavone; D001728:Dicumarol; D016660:NAD(P)H Dehydrogenase (Quinone)