AMINO ACIDS IN PRE- AND POST-NATAL PERIODS 267 
lower in fetal as compared to maternal tissue*®. COHEN AND HEKHUuIS*’ and BEATON 
et al.48 stress the fact, that glutamic-oxalacetic and glutamic-pyruvate transaminase 
activity vary inversely with proteosynthetic activity. Indeed, in prematures the 
transaminase activity is lower than in full-term newborns". 
Possibly the higher permeability of all cell membranes contributes to the hyper- 
aminoacidemia, especially since the lowering of pH due to the metabolic and respi- 
ratory acidosis increases it further. It has been shown that such pH-dependent 
changes of the cell membrane observed post-natally also have an influence in later 
life on the amino acid content of the tissue. For instance, in potassium deficiency the 
level of basic amino acids is increased, whereas that of monoaminodicarboxylic acids 
is decreased’; °°, 
I assume that the higher turnover rate of almost all body proteins during early 
youth, as we have shown to be the case in humans, rats and rabbits, necessitates an 
increase in their breakdown to amino acids, and, therefore, an increase of the free 
amino acid pool. In support of this concept, one may cite the fact that in later life 
diseases which increase the protein turnover rate (e.g., leukemias, surgical trauma, 
etc.) usually show a hyperaminoacidemia®*: 1-3, It should be mentioned that this 
higher rate of turnover in youth has a parallel in the increased “minimal nitrogen 
turnover” and in the basal metabolic rate*?. 
It is not likely that STH (somatropic hormone) is the reason for post-natal hyper- 
aminoacidemia, since STH increases the permeability of the cell membrane to all 
amino acids including the non-physiological amino acids so far studied, and leads in 
this way to a decline of amino acids in the blood*®*—*’. Furthermore, the incorporation 
of amino acids into proteins is increased*®. 
It is well known that the so-called “birth stress” leads to excretion of steroid hor- 
mones, which function in various ways. Among other effects they show a marked 
influence on the cell membrane®® and on amino acid turnover, thereby increasing 
the amino acid values in blood®-®. The instability of blood amino acid values, 
with their tendency to increase, usually continues much longer than one would ex- 
pect, when the after-effects of birth trauma are considered. Similarities to the 
changes observed after surgical trauma or severe burns nevertheless are evident. It 
may be noteworthy in !this connection that the turnover rate of [3°S]methionine- 
labeled body proteins is increased significantly after an abdominal operation in 
rats’. 
In addition to these two hormone groups (STH and steroids), insulin apparently 
also plays an essential role in protein metabolism in the early period of life. It appears 
rather certain (KORNER AND MANCHESTER) that this hormone has a direct influence 
on amino acids, independent of any effect on carbohydrate metabolism®. The most 
plausible interpretation of all available findings at this time is that insulin has a 
positive effect on the permeation of amino acids into cells. 
In well-controlled cases of diabetes mellitus in adults and children the amino acid 
levels in the plasma are within the normal range. In coma diabeticum, however, 
several essential and non-essential amino acids, such as leucine, isoleucine, valine, 
lysine, phenylalanine, etc., are elevated. The degree of hyperaminoaciduria depends 
not only on the plasma value of the amino acid, but also on the condition of the kid- 
neys and several extrarenal factors®. Our results have been fully verified by Czyzyx®. 
Diabetic subjects are said to have a disturbance in tryptophane metabolism®’ (see 
References p. 279/283 
