Deuterium isotope effects on ethanol oxidation in perfused rat liver and in rats and rabbits in vivo: application to determine the contribution of various pathways.

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The kinetic deuterium isotope effect, D(V/K), on ethanol oxidation was measured by the radiometric, competitive method using 14C-labelled ethanol containing deuterium in the (1-R) position. Acetate was isolated and used for the determination. Experiments were performed on rats either anaesthetized and laparotomized, or provided with indwelling catheters in a. carotis, v. cava and v. portae. Experiments were also made on perfused liver from rats pretreated with acetone, or a mixture of acetone and phenobarbital. Finally, intact non-anaesthetized rabbits were used. The apparent isotope effect in all in vivo experiments decreased rapidly in the presence of acetaldehyde as a consequence of the reversibility of the ADH reaction. In the case of rabbits and catheterized rats this problem was tackled by taking blood samples in quick succession, thus permitting extrapolation of the apparent isotope effect to the time of injection of the labelled ethanol. In anaesthetized rats injection of the ADH inhibitor isobutyramide was used to reduce the concentration of acetaldehyde and thereby the rate of decline of the apparent isotope effect. At high doses of isobutyramide the isotope effect was constant with time at about 1.9 suggesting the presence of non-ADH activity. In all three kinds of in vivo experiments the isotope effect ranged from 2.66 to 2.93. In the case of anaesthetized rats the mean value was 2.89 +/- 0.05 (S.D.). This figure is significantly different from that of rat liver ADH, P less than 0.001. As the figures for the initial isotope effects are minimum values the contribution of non-ADH ethanol oxidizing systems is likely to be small, probably less than 10 percent.