Diet and uptake of aldomet by the brain: competition with natural large neutral amino acids.

The rise in levels of aldomet in the brains of rats after an injection of the alpha-methylated amino acid was depressed when large neutral amino acids, but not acidic amino acids, were coadministered with the drug. This result suggests that aldomet is transported into brain by the carrier for natural large neutral amino acids. The prior ingestion of a carbohydrate meal, which lowers levels of neural amino acids in the serum, enhanced the uptake of aldomet into brain; the consumption of a protein-containing meal inhibited the subsequent uptake of aldomet into the brain. Antecedent diet can thus affect the availability of aldomet to the central nervous system; the mechanism of this effect probably involves the blood-brain barrier uptake system for large neutral amino acids.