The Deuterium Isotope Effect on Ethanol Metabolism in Perfused Rat Liver: Effect of Reversed Perfusion on Ethanol and Oxygen Uptake

Livers from rats fasted for 24 hr were subjected to nonrecirculating perfusion with Krebs-Ringer bicarbonate solution containing 10 mm ethanol. The deuterium isotope effect was measured using (1- R )-[1-¹⁴C, 1-²H]ethanol. A value of 2.57 ± 0.09 (SO) was obtained independent of the direction of perfusion. Oxygen uptake and ethanol metab-olism in contrast were significantly increased when reverse perfusion (i.e., from vena cava to vena portae) was used. The magnitude of the isotope effect indicates that contribution from microsomal ethanol-oxidizing system if this is the only supplementary system is 9.8% under the experimental conditions. At high ethanol concentrations, the contribution would approach 18%. Equal activities of microsomal ethanol-oxidizing system and catalase under the experimental conditions would mean that both contribute 7.3% of the total ethanol metabolism. At high ethanol concentrations (80 mm), how-ever, catalase will be 6.8% and microsomal ethanol-oxidizing system is calculated to 13.3%. Preliminary experiments with rats pretreated with phenobarbital showed no change in the isotope effect or in the rate of ethanol metabolism, but a 40–50% increase in oxygen consumption. The acetaldehyde concentration in the effluent medium was below 1 μM.