Orotate decreases the inhibitory effect of ethanol on galactose elimination in the perfused rat liver

Abstract

1. The galactose-elimination rate in perfused livers from starved rats was decreased in the presence of ethanol (2-28mM) to one-third of the control values. Orotate injections partly reversed the effect of ethanol, so that the galactose-elimination rate was about two-thirds of the control values. Orotate alone had no effect on the galactose-elimination rate. 2. Ethanol increased [galactose 1-phosphate] and [UDP-galactose], and decreased (UDP-glucose] and [UTP], both with and without orotate. Orotate increased [UTP], [UDP-galactose], both with and without ethanol. The increase of [galactose 1-phosphate] in the presence of ethanol was inhibited by orotate. Orotate alone had no appreciable effect on [galactose 1-phosphate]. 3. Both the effect of ethanol and that of orotate on the galactose-elimination rate can be accounted for by assuming inhibition of galactokinase by galactose 1-phosphate with K_i about 0.2mM, the inhibition being either non-competitive or uncompetitive. 4. The primary effect of ethanol seems to be inhibition of UDP-glucose epimerase (EC 5.1.3.2), followed by accumulation of UDP-galactose, trapping of UDP-glucose and increase of [galactose 1-phosphate]. Orotate decreased the effect of ethanol, probably by increasing [UDP-glucose].