Effects of caffeine on amino acid transport in the brain.

Chronic administration of caffeine to mice did not alter cellular (low-affinity) transport as measured in brain slices of the amino acids ?-aminobutyric acid, glutamic acid, and glycine. Chronic caffeine administration did, however, increase the long-term (60-min) uptake of ?-aminoisobutyric acid and valine into brain slices. A similar tendency, although not statistically significant, towards increased amino acid uptake was also seen in the transport of phenylalanine and lysine across the blood-brain barrier in chronically treated rats. The increase in neutral amino acid uptake seems unrelated to changes in brain protein metabolism, since chronic caffeine administration did not significantly alter brain protein synthesis rates. In vitro, caffeine (0.01-1 mM) did not alter brain slice transport of the amino acids ?-aminobutyric acid, glutamic acid, glycine, valine, and the amino acid analog ?-aminoisobutyric acid. Caffeine (1-100 ?M) was also ineffective in altering the synaptosomal (high-affinity) transport of the neurotransmitter amino acids ?-aminobutyric acid, glutamic acid, and glycine. These data support the idea that caffeine is a mildly stimulating drug with no significant effect on neurotransmitter amino acid transport systems in rodent brain.