Mechanism of the Stimulatory Effect of Fructose on Ethanol Oxidation in Perfused Rat Liver

Abstract

The stimulatory effect of fructose on ethanol oxidation was studied in livers from fasted rats perfused with Krebs-Henseleit-bicarbonate buffer in a non-recirculating system. Two series of experiments were performed: ethanol was infused with stepwise increasing concentrations (0.1-20 mM) in the presence of 4 mM fructose; fructose was infused with stepwise increasing concentrations (0.5-10 mM) in the presence of 2 mM ethanol. From measured metabolic rates the following parameters were calculated: energy-rich phosphates consumed for fructose metabolism which were provided from oxidative phosphorylation (.DELTA. .apprx. P); reducing equivalents derived from stimulated ethanol utilization which were disposed by mitochondrial oxidation (.DELTA.2H). Under the various conditions studied a linear relationship between these parameters was observed. The ratio .DELTA. .apprx. P/.DELTA.2H was about 2.0. Fructose may stimulate ethanol oxidation indirectly by increasing the energy consumption of the liver due to the production of glucose from fructose. Consequently, the rate of oxidative phosphorylation is increased and, therefore, the capacity of the respiratory chain for oxidizing reducing equivalents derived from ethanol is enhanced. The data support the more general hypothesis that the rate of ethanol oxidation depends upon the rate of hepatic energy consumption in a given metabolic state.