Ethanol oxidation by isolated rat-liver cells. Stimulatory effects of fructose

Isolated liver cells from starved or fed rats were used to examine the mechanisms by which fructose stimulates hepatic ethanol oxidation, particularly in relation to the role of intercompartmental hydrogen transfer. The presence of added fructose stimulated ethanol oxidation, the degree of stimulation being directly related to the initial fructose concentration up to a level of 10--20 mM. In the presence of fructose and ethanol, sorbitol, glycerol and glycerol 3-phosphate accumulated. The stimulation of ethanol oxidation by fructose could be attributed to its ability to promote the oxidation of cytoplasmic NADH by the provision both of cytoplasmic hydrogen sinks and components of the glycerol 3-phosphate shuttle. Shuttles mediated by malate dehydrogenase were unimportant for fructose-stimulated ethanol oxidation. Rates of respiration and gluconeogenesis were similar over a fructose range of 5--20 mM although ethanol oxidation was faster at higher fructose concentrations. Hence the stimulation of ethanol oxidation by fructose is not merely a direct function of the energy demands of gluconeogenesis.