Elevation of cerebral levels of nonessential amino acids in vivo by administration of large doses.

Taurine, aspartic acid, glutamic acid, glycine, and GABA were administered either intragastrically or in liquid diets to mice and rats. This resulted in a great increase in the plasma concentration of the administered amino acid, with plasma levels remaining elevated for several days. The prolonged increase in plasma levels resulted in significant increases in brain levels. Under these experimental conditions, taurine, aspartic acid, and glutamic acid were increased 30-60%; glycine and GABA 100%. During these experiments, plasma levels of taurine, aspartate, and glutamate were below brain levels; those of glycine and GABA were above. The findings show that even slowly penetrating amino acid levels can be increased in brain after parenteral administration of large doses.