FREE AMINO ACIDS OF BLOOD AND URINE 237 
glutamic acid level is much more elevated in children than in adults, in contrast 
with all other concentrations which, as a rule, tend to be lower in children. 
Apart from these data, collected by Dr. H. Vis, there are rather few others to 
be found in the literature at the present time. WESTALL e¢ al.34 have given normal 
ranges, but they include values given by STEIN AND Moore for adults!?. Such is 
also the case for values given by IBER ef al.*°. HUISMAN®® on the other hand, refers 
only to the child. 
Factors affecting free amino acid levels in plasma of normal adults. As in the case 
of free amino acid urinary excretion, there is rather little reliable information to 
be found on this point up to date. Among the factors which may affect the plasma 
levels, the following may be listed: menstrual cycle and normal pregnancy, which 
are in fact ultimately controlled by endocrine factors, effects of hormonal factors 
and effects of high protein diet. 
1) Menstrual cycle. SouUPART®® has studied fasting free amino acid plasma levels 
in a group of five healthy females, at the beginning of both follicular and luteal 
phases of their cycle. Analysis of the results showed that the shift from follicular to 
luteal phase induces a general lowering of the average plasma levels for all amino 
acids. The difference between average levels was statistically significant for the 
following amino acids: proline and threonine (P < 0.05), serine and lysine (P < 0.01), 
and alanine (P < 0.001). This variation of plasma levels seems at first to characterize 
a systematic phenomenon, involving all amino acids, but the fact that the lowering 
of average concentrations is statistically significant only for five of them strongly 
suggests that it reflects a more specific phenomenon, not yet understood, but related 
in some way to the physiological rebuilding involved in the menstrual cycle. 
2) Normal pregnancy. As previously stated (see p.229) normal pregnancy is 
accompanied by the hyperexcretion of the following amino acids: histidine, glycine, 
threonine, serine, alanine, tyrosine, phenylalanine, isoleucine and arginine. Glutamine 
should also be added to this group, notwithstanding the approximation which affects 
its determination (see p. 222). SOUPART® has compared free amino acid levels in a 
group of normal pregnant females to those found in a group of five non-pregnant 
individuals. Although statistical analysis was not practicable in this study, owing 
to the lack of homogeneity of the group of pregnant females investigated with 
regard to the age of pregnancy, it appears that at any age of pregnancy studied plasma 
free amino acid levels were of the same order of magnitude, or even Jower, than 
those observed in the luteal phase of menstrual cycle; the only two exceptions to 
this rule are glutamic and aspartic acids. Their concentration is definitely higher in 
pregnant than in non-pregnant women. Interpretation of the effect of pregnancy on 
free amino acid plasma levels will be found in the section Renal handling of free amino 
acids. 
3) Effects of some hormonal factors. Administration of large doses of estrogens 
(estradiol benzoate) does not influence free amino acid plasma levels, except that 
of glycine, which is lowered at the same time that glycine is hyperexcreted in urine®. 
Concentrations of almost all amino acids present in plasma are decreased when 
large doses of hydrocortisone are given, when compared with plasma levels of a 
control period®. This lowering of free amino acid plasma levels is quite similar to 
that observed during pregnancy. 
References p. 261/262 
