204 K. SCHREIER 
CRUMPLER e¢ al.18, DUSTIN et al.19: 2°, SERENI e¢ al.?1, and others?2-25). In Table II the 
average value of 13, mainly microbiologically determined amino acids in the cord 
plasma®® is compared with the values obtained from children and adults by the same 
technique. It is evident that the single amino acids are not increased proportionately. 
It should be noted that the results obtained so far in studies of mammals demon- 
strate the same trend. CHRISTENSEN ef al.?” have found an increase of amino acids 
AVMSILIT, 1H 
AMINO ACID VALUES IN ADULTS, INFANTS, AND CORD BLOOD 
Average values in mg % 


Amino acid Adults Infants Cord blood 
Alanine 3.8 3-9 4.8 
Arginine Beit 2.2 313 
Glycine 2.8 2.6 3.4 
Histidine 77 1.8 3-4 
Isoleucine 1.6 7) 258 
Leucine 2.0 2.3 2.5 
Lysine 2.8 2.4 8.1 
Methionine 0.35 0.3 0.5 
Phenylalanine 1.6 1.6 253 
Threonine 2.0 253 2.8 
Tryptophane Iteit 0.8 1.7 
Tyrosine I.4 1.6 23 
Valine 3.0 Be 4.9 

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in the fetal circulation of various species of mammals which is two to five times 
that of the maternal value. The same is true for glutathione”®. 
As one would expect from the data of LICHTENSTEIN?*, during the intra-uterine 
period, the free amino acid pool is not constant. In Fig. 1 the content of free amino 
acids in brain of rabbit fetus, during the last days of gestation, is shown. This 
curve was obtained by plotting the values of free amino acids in brain of fetus 
which received 14C-labeled lysine intraperitoneally while 7m utero. 
It is evident that a decrease in the specific activity of the deproteinized body 
fluids occurs, reaching its lowest value at the time of birth. There is no doubt, there- 
fore, that the placenta is able to concentrate single amino acids in the direction of 
the fetus. This ability necessitates an active transport mechanism, although it could 
be also an accumulation mechanism akin to that for vitamin C. Almost nothing is 
known of the essentials of this process. PAGE ef al.?® have been able to demonstrate 
that this mechanism is stereo-specific by showing that the physiological L-amino 
acids are transported much faster through the placenta than the D-isomers. Further- 
more, a certain concurrence of the single amino acid is very probable. One can also 
accept as possible the fact that a saturation effect exists*®?. 
It is evident that the concentration capacity of single cells for amino acids limits 
the growth intensity of the organ*!. This has not only been shown for normal 
embryonic cells, but ZAMECNIK et al.32 have found a higher concentration of free 
amino acids in certain malignant tissues as compared to healthy structures. The 
References p. 279/283 
