Tyrosine increases tissue dopamine concentration in the rat.

Dopamine and norepinephrine concentrations in the stomach, duodenum, and brain were measured after subcutaneous injection of tyrosine methyl ester in the rat. Tyrosine significantly increased dopamine concentrations in each tissue without altering norepinephrine levels. The increase in dopamine concentration in the stomach or duodenum was observed 1 h after tyrosine methyl ester injection, but it returned to normal 4 h after the administration of the chemical.