Metabolism of galactose in the brain and liver of rats and its conversion into glutamate and other amino acids

Time- and dose-dependent measurements of metabolites of galactose (with glucose as control) in various organs of rats are discussed. Not only the liver but especially the brain and to a lesser extent the muscles also have the capacity to take up and metabolize galactose. Primarily, the concentrations of UDP-galactose, a pivotal compound in the metabolism of galactose, and UDP-glucose are measured. An important feature lies in the demonstration that galactose and glucose are metabolized to amino acids and that the only increases observed in the brain appear in the concentrations of glutamate, glutamine, GABA measured after acute galactose loads. In addition the increase in the amino acid concentrations after galactose has been administered persists for longer periods of time than after glucose administration. This conversion of hexoses, especially galactose, to amino acids requires the consumption of ammonia equivalents in the brain; this finding might stimulate the use of galactose as a new means of removal of this neurotoxic compound from the brain in patients suffering from hepatic encephalopathy or Alzheimer's disease.