The transport of tyrosine into the human brain as determined with L-[1-11C]tyrosine and PET.
An alteration of dopaminergic transmission in the brain has been proposed for schizophrenia. To explore this, the rate constant for the intransport of L-tyrosine across the blood-brain barrier in healthy controls and in patients with schizophrenia (DSM-III-R) was determined with PET and L-[1-11C] tyrosine as the tracer. Kinetics for tyrosine transport were determined according to a two-compartment model using radioactivity data of arterial blood and brain tissue sampled between 1 and 3.5 min after a bolus injection of L-[1-11C] tyrosine. Radioactivity was measured every second in the blood and in 10-sec intervals in the brain tissue. In the normal controls the brain intransport rate constant for tyrosine was 0.052 ml/g/min with an influx rate of 2.97 nmol/g/min. The patients had a similar intransport rate constant (0.045 ml/g/min) but a lower influx rate of tyrosine 1.95 nmol/g/min (p less than 0.05). The patients' tyrosine concentrations in the blood were lower. For data sampled between 5 and 25 min, the net accumulation rate of tyrosine into the brain was 0.015 ml/g/min in the controls which did not differ to the patients' rate. However, the net utilization of tyrosine was lower in the patients (0.672 nmol/g/min) than in the controls (0.883 nmol/g/min) despite similar tissue concentrations of tyrosine.
Department of Psychiatry, University of Uppsala, Sweden.
F A
FA
Wiesel
G
G
Blomqvist
C
C
Halldin
I
I
Sjögren
L
L
Bjerkenstedt
N
N
Venizelos
L
L
Hagenfeldt
D000328:Adult; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects; D001921:Brain / Q000000981:diagnostic imaging*; D002250:Carbon Radioisotopes; D006801:Humans; D008297:Male; D012559:Schizophrenia / Q000000981:diagnostic imaging* / Q000378:metabolism; D014055:Tomography, Emission-Computed; D014443:Tyrosine / Q000378:metabolism
D002250:Carbon Radioisotopes; D014443:Tyrosine