Galactose as a regulatory factor of its own metabolism by rat liver

As part of a series of studies to assess the regulation of hepatic galactose-metabolizing enzymes, galactokinase, galactose-1-phosphate uridyltransferase, and UDPgalactose-4-epimerase, the effect of feeding a high galactose-containing diet to normal adult and pregnant female rats was examined. Sixteen days of galactose exposure of adult virgin females produced a different response in the specific activity of each of the enzymes, that of galactokinase being lower, transferase higher, and epimerase transiently elevated. Galactose feeding increased the specific activity of transferase in pregnant rat liver above the elevated level that already exists in the pregnant state but failed to influence the enzyme of the developing fetal liver. Galactose added to liver homogenates did not activate transferase. The increased activity in liver of adult, fed animals was not associated with a change in isoenzyme patterns examined by isoelectric gel electrophoresis but was characterized on kinetic analysis by an increase in Vmax for UDPglucose. The changes in enzyme specific activity in liver of animals fed galactose appear to have physiologic significance because hepatocytes isolated from galactose exposed livers take up more galactose and convert more to glucose and lactate than cells from control animals.