266 K. SCHREIER 
after a comparable surgical trauma depending on the nutritional state of the indi- 
vidual?. 
2. Hormones and central mechanisms. For a short time after the start of feeding, we 
have a moderate hyperaminoacidemia in fasting prematures and most full-term 
newborns. A definite stabilization of the behavior of amino acid metabolism, as 
demonstrated in children and adults, is reached around the 3rd post-natal month. 
It is noteworthy that at about the same time the activity of the blood trans- 
aminases declines to the adult level**. I should like to emphasize that individual 
variation in respect to the regulation of the blood levels of amino acids is great. 
Counts/min 
8000 
\ 
| 
\ We “ 5 
eh A} eee Ns 
5 - . NN . . 
Pe ne SU N 
2000 

1000 


5 10 15 20 25 30 
Days 
Fig. 2. Specific activity of soluble and insoluble liver proteins and of total nucleic acids of rabbits, 
1-30 days of age. Counts/min/1o mg, insoluble proteins: 1; soluble proteins: 2; total nucleic acids: 3. 
Until the 6th year of life a lowering of the different amino acid values in the fasting 
blood often occurs (e.g., KrrRBy*®; SCHREIER!), But the physiological and indivi- 
dual variations of the single amino acid values are so large that a decrease cannot be 
ascertained statistically. The trend toward a hypoaminoacidemia is unequivocal. 
Since the protein synthesis rate of the thriving premature infant proceeds with 
an increased activity, one would actually expect a decrease of the amino acids 
in the body fluids, particularly since the concentration capacity of juvenile cells for 
amino acids is exceptionally good. 
As a cause for the hyperaminoacidemia in prematures one would first of all 
presume that a diminished catabolic activity, especially in the oxidizing enzymes, 
occurs. It has been shown recently that particularly those enzymes which oxidize the 
cyclic amino acids have a very low activity during the post-natal period (see below). 
Of course, an increased proteolysis would lead to higher levels in blood too; but we 
have no evidence for such activity. In fact, catheptic activity has been found to be 
References p. 279/283 
