Regional tyrosine levels in rat brain after tyrosine administration.

Endogenous tyrosine concentrations varied two-fold among various rat brain regions, tending to be highest in brain stem structures. Administration of L-tyrosine (100 mg/kg) increased tyrosine concentrations in all brain areas; high relative increases were observed in areas with low initial tyrosine concentrations and vice versa, resulting in a more uniform distribution of tyrosine in the brain. Largest relative increases were observed in cortex and hippocampus. Tyrosine concentrations in all areas reached maximal levels 1 hour after tyrosine was given and declined gradually over the next 3 hours. The results suggest that tyrosine's effects on catecholamine synthesis and release might be amplified in cortex and hippocampus, where highest relative increases in tyrosine concentrations were observed.