FREE AMINO ACIDS OF BLOOD AND URINE 239 
amino acid clearance is very low, although there is a considerable individual variation 
as shown by Table V (refs. 26, 27, 29, 30, 32, 33, 38). According to their average 
clearance values, the amino acids may be distributed into three more or less well 
defined groups: 
1) Clearance lower than 1 ml/min: lysine, ornithine, valine, alanine and leucine. 
2) Clearance comprised between 1 and 2 ml/min: arginine, phenylalanine, tyrosine, 
isoleucine, serine and methionine. 
3) Clearance higher than 2 ml/min but not higher than 20 ml/min: glycine, aspartic 
acid, taurine and histidine. 
It appears therefore that the reabsorption is accomplished at various degrees of 
efficiency for the different amino acids. 
TABLE VI 
ESTIMATED EFFICIENCY OF FREE AMINO ACID REABSORPTION BY THE KIDNEY 

: Percent Gi filtered load reabsorbed* Filtered 
Amino acid Range ~ arses load** 
Histidine 87.3 —98.4 92.5 20 
Taurine 90.2 —97.4 94.2 22 
Aspartic acid 87.2 —98.6 95-4 I 
Glycine 94-7 —98.1 96.0 38 
Methionine 94.12—99.34 90.8 6 
Serine 97.10—99.20 98.2 2 
Isoleucine 97.40-99.47 98.55 14 
Tyrosine 98.21—99.56 98.64 14 
Threonine 98.34-99.72 99.07 38 
Phenylalanine 98.44—-99.07 99.26 17 
Arginine 99.15-99.72 99.43 22 
Leucine 99.31-99.83 99.53 25 
Alanine 99.29-99.84 99.54 58 
Valine 99.05—-99.87 99.70 44 
Ornithine 99.77-99.87 99.83 12 
Lysine 99.77-99.97 99.89 38 
Proline 100 100 34 

* For method of calculation see text. 
** Relative to that of aspartic acid taken as unity. 
A quantitative evaluation of the efficiency of individual amino acid reabsorption 
may be obtained in the following way: assuming that the glomerular filtrate amounts 
in the average to a volume of 183 1 in 24 h®®, that the concentration of the free amino 
acids is the same in the glomerular filtrate and in plasma and that the free amino 
acid plasma levels remain reasonably constant during a 24-h urine collection period, 
the percentage of the reabsorption may be approximately calculated for each of 
the amino acids. Such calculation has been done from data collected by SouPART 
in a group of five normal subjects?*. Results are shown in Table VI and Fig. 7, in which 
the calculated percentage range of reabsorption for each amino acid is compared 
to the individual filtered load, clearly shows that there is no relationship in normal 
conditions between the amounts of amino acid filtered and their reabsorption. In 
References p. 261/262 
