EFFECTS OF SALT AND WATER LOADING ON CARBOHYDRATE AND ENERGY METABOLISM AND LEVELS OF SELECTED AMINO ACIDS IN THE BRAINS OF YOUNG MICE

—This is a report of the effect of extreme changes in plasma sodium concentration induced by chronic (5 d) water deprivation and hypertonic saline injections and acute (4 h) overhydration with hypotonic glucose or fructose on the water and electrolyte content and levels of selected metabolites in the brains of young mice. In the dehydrated hypernatremic mice (plasma Na⁺, 186 × 3 mequiv./1) significant increases were found in brain glucose (82%), alanine (16%), aspartate (45%), glutamate (19%), gamma‐amino butyrate (34%) and glutamine (42%) concentrations. In striking contrast, water‐intoxicated mice (plasma Na⁺, 110 × 4 mequiv./1) had significantly decreased levels of alanine (17%), aspartate (38%) and glutamate (33%). Significant reductions in brain lactate (30–40%) and malate concentrations (23%) in both groups of experimental mice are suggestive of reduced cerebral metabolic rate. During adaptation to increased or decreased environmental salinity, levels of amino acids in amphibian brain increase or decrease, respectively, to maintain osmotic equilibrium and to limit the loss or gain of water in brain. The data show that a similar protective response can be evoked in mammalian brain.