Journal of Applied Physiology Millar Instruments
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J Appl Physiol 54: 1089-1093, 1983;
8750-7587/83 $5.00
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Journal of Applied Physiology, Vol 54, Issue 4 1089-1093, Copyright © 1983 by American Physiological Society

ARTICLES

Paraquat inhibits mixed-function oxidation by rat lung

T. K. Aldrich, A. B. Fisher and H. J. Forman

The effect of paraquat on 7-ethoxycoumarin (7-EC)deethylation, an NADPH-dependent cytochrome P-450-linked reaction, was studied in isolated rat lungs. Control lungs oxidatively deethylated 7-EC at a constant rate, metabolizing 178 +/- 12 nmol/g dry wt in 50 min (n=3, mean +/- SE). When glucose was omitted from the perfusate, 7-EC deethylation was lower (85 +/- 17 nmol/g, P less than 0.05), and the rate progressively decreased, suggesting inadequate pentose shunt regeneration of NADPH. During perfusion with paraquat (10(-3) M), 7-EC metabolism was still lower (75 +/- 5 nmol/g in the presence of glucose and 18 +/- 4 nmol/g in the absence of glucose, P less than 0.05). Addition of lactate plus pyruvate partially restored 7-EC deethylase activity in control lungs but had no effect in lungs perfused with paraquat. Varying perfusate paraquat concentrations (10(-6) to 10(-3) M) inhibited 7-EC deethylation in a dose-dependent fashion (r = 0.79, P less than 0.02). Oxidative demethylation of p-nitroanisole, another cytochrome P-450-linked reaction, was similarly inhibited by paraquat. In contrast, microsomes isolated from paraquat-perfused lungs showed no inhibition of 7-EC metabolism (measured in the presence of an NADPH-regenerating system). We conclude that paraquat depletes NADPH in the isolated lung to a sufficient extent to impair mixed-function oxidation. Such NADPH depletion may play a role in the toxicity of paraquat.


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R. Brigelius, L. A. Dostal, J. K. Horton, and J. R. Bend
Alteration of the Redox State of Nadph and Glutathione in Perfused Rabbit Lung By Paraquat
Toxicology and Industrial Health, January 1, 1986; 2(4): 417 - 428.
[Abstract] [PDF]


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