UPTAKE OF TYROSINE BY BRAIN 547 
TABEEATE 
EFFECT OF OTHER AMINO ACIDS ON TYROSINE DISTRIBUTION 
Brain to plasma ratio 
(30 min) 
Control 0.72 
L-Tryptophane 0.18 
p-Fluoro-pL-phenylalanine 0.24 
L-Leucine 0.24 
L-Isoleucine 0.28 
L-Valine 0.31 
L-Cysteine 0.37 
L-Histidine 0.38 
L-Alanine 0.88 
L-Serine 0.94 
L-Threonine 747 
L-Arginine 0.84 
L-Lysine 0.83 
L-Glutamate 0.81 

* Amino acids injected 5 min before L-tyrosine (400 mg/ 
kg). Between 0.8 and 1.7 mmoles of other amino acids 
used!. 
In a separate study!® of the comparative uptakes of tyrosine by other tissues it 
has been concluded that stereoselectivity can also be observed in uptake by muscle 
(Fig. 3). It can be seen that the uptake of D-tyrosine by muscle was less than that 
of the L-isomer but that comparatively large amounts of the D-isomer entered muscle 
compared to the small amounts which entered brain under similar circumstances. 
On the other hand, the inhibition of tyrosine uptake by other amino acids observed 
in brain did not occur in muscle (Table III). Some non-specific reduction in tyrosine 
uptake did seem to occur regardless of the identity of the second compound. Muscle, 











10———= acne 
y £-TYROSINE 
60- 
50|- 
X<-METHYL - DL -TYROSINE 
(0.66) 
40- 
a 
30}- * D-TYROSINE 
TYRAMINE 
\ A023) 
20 - 7 
se P-HYOROXYPHENYL ACETIC ACID _| 
@) — — _ — — + — — 
0 30 60 90 120 
MINUTES 
Fig. 2. Uptake of tyrosine and related compounds by rat brain in vivo. 
References p. 553 
