Reduced plasma levels of tyrosine, precursor of brain catecholamines, and of essential amino acids in patients with severe traumatic brain injury after rehabilitation

OBJECTIVE: To investigate whether levels of plasma tyrosine and tryptophan, precursors of brain catecholamine and serotonin neurotransmitters, respectively, and other essential amino acids (EAA) may return to normal in patients with severe traumatic brain injury (TBI) after 2 months in a hospital rehabilitation center. DESIGN: Peripheral plasma concentrations of tyrosine, tryptophan, and other EAAs in subjects with severe TBI, both at admission (44+/-11d postinjury) and at discharge from the center (110+/-15d after acute event) were compared with concentrations in control subjects. SETTING: Tertiary care rehabilitation setting in Italy. PARTICIPANTS: Ten men (26.6+/-12.6y) with TBI and 6 healthy subjects (controls) matched for age, sex, voluntary loss of body weight, and sedentary lifestyle. INTERVENTIONS: Not applicable. Main Outcome Measures: Concentrations of brain neurotransmitter precursor amino acids and of EAA. RESULTS: On admission, patients had lower plasma tyrosine, leucine, valine, methionine, and phenylalanine concentrations than did control subjects. The plasma concentrations of tryptophan were similar in the 2 groups. These amino acid abnormalities were still present at discharge. CONCLUSION: The levels of plasma tyrosine and many EAA in patients with TBI did not recover by discharge (110+/-15d) from rehabilitation. Plasma tryptophan concentrations were similar in patients and controls.