Galactose metabolism in isolated perfused suckling-rat liver

The metabolic conversion of 1, 2, or 4 mM galactose to glucose was studied in isolated livers of suckling rats. Whereas galactose uptake during perfusion with 1 and 2 mM galactose was linear throughout the 90-min experiment, uptake was delayed for 35 min when 4 mM galactose was perfused. Studies with radioactive galactose revealed a parallel disappearance of galactose and the appearance of [14C]glucose; about 80% of the galactose taken up was converted to glucose. Galactose perfusion appeared to reduce the basal amount of glucose derived from substrates other than galactose. The specific activities in the galactose-perfused livers of the three major galactose metabolizing enzymes, galactokinase, galactose-1-phosphate uridylyltransferase, and uridine diphosphogalactose-4-epimerase, revealed that the transferase was significantly lower, whereas that of galactokinase and epimerase were significantly higher than in livers perfused without galactose. No meaningful changes were observed in the levels of either phosphorylated or uridylated hexoses in these studies.