Effect of Ethanol and Fructose on Galactose Elimination in Rat

Abstract

The elimination rate of galactose was determined in intact 200 g rats by intravenous infusion of galactose during simultaneous infusion of ethanol (arterial ethanol concentrations about 7 mmol/l) or fructose (arterial fructose concentrations about 6 mmol/l). The galactose elimination capacity, defined as the elimination rate at blood galactose concentrations between 2 and 7 mmol/l, during ethanol infusion was, on the average, 80 μmol/h per whole animal, or two-thirds the value observed in comparable experiments without ethanol. Fructose did not change the galactose elimination capacity. The galactose elimination during ethanol infusion could be described by Michaëlis-Menten kinetics. The calculated V_max was significantly lower than that obtained in experiments without ethanol. The pattern of the metabolites observed in liver tissue is compatible with an inhibitory effect of ethanol on UDP-glucose-4-epimerase, but with the phosphorylation of galactose by galactokinase as the rate-limiting step, inhibited by accumulation of galactose-1-phosphate. The galactose-1-phosphate concentration observed indicates a considerably smaller K_i for the inhibition of galactokinase by galactose-1-phosphate towards galactose than that observed by in vitro studies.

Key Words:

• Ethanol
• fructose
• galactose
• liver metabolism
• metabolic regulation