Electrolyte and amino acid changes in rat brain during maturation

¹ Departments of Anatomy and Pharmacology, University of Utah College of Medicine, Salt Lake City, Utah

Rats 1–45 days old were studied. Plasma Na and Cl concentrations changed little with age, whereas K concentration decreased. Total brain water content and total Na and Cl concentrations decreased progressively, whereas total K concentration increased during maturation. Brain Na and Cl spaces decreased with maturation. Adult brain levels were attained at approximately 21 days. Concentrations of total and protein nitrogen [trichloroacetic acid (TCA)-insoluble] fractions progressively increased with age. The lipid nitrogen fraction (TCA-insoluble and ether-ethanol-soluble) increased progressively, but not markedly, with age, whereas the concentration of TCA-soluble nitrogen did not appear to change during maturation Changes in brain free amino acid concentrations during maturation were as follows: glutamic, -aminobutyric, and aspartic acid and glutamine concentrations progressively increased during maturation. In contrast, threonine concentration did not change. Changes in brain Cl space with age were analyzed and found to support the concept that Cl is homogeneously distributed in young rats but becomes progressively more heterogeneously distributed as the animals mature.