AMINO ACIDS IN PRE -AND POST-NATAL PERIODS 2793 
biosynthesis of hydroxyproline is still unclear®. We know that proline can be syn- 
thesized from glutamic acid 7m vivo and in vitrol®, ® but until the present the direct 
oxidation to hydroxyproline could not be ascertained. Apparently the formation of 
hydroxyproline is intimately connected with collagen synthesis! 1%. GERBER e¢ al.1° 
speculate that two different metabolic pools of collagen and of prolin derivatives 
exist. Free hydroxyprolinis not incorporated into cartilage!™. One may postulate that 
the increased excretion of this amino acid is due to a higher turnover rate of the 
growing collagen in infancy, especially since syndromes with disturbances of cartilage 
synthesis, like Marfan’s disease, are said to show a hydroxyprolinuria. 
TABLE IV 
CLEARANCE VALUES OF HUMAN ADULTS, INFANTS AND PREMATURES 




Adults Infants Prematures 
Amino acid == === == = $$ —- - 
Doolan'*® Evered**! Sereni** Sereni*! Schreier'®® Sereni™ Schreier'®® 
Histidine 6.38 4.70 5.38 10.00 7.96 10.20 7-91 
Leucine 0.27 0.40 0.43** 0.50** 0.40 OW 4Awe 0.70 
Lysine 0.22 0.30 1.65* NOLS 7 = 1.23 7.09* 1.44 
Threonine 0.79 0.87 1.22 4.13 1.01 6.00 3.18 
Tryptophane 1.37 = — — 0.97 — 1.58 
Tyrosine 1.65 ie23 1.57 2.64 1.63 1.47 1a7/ 
Creatinine — — — 92.307**) 1 60:40 45.60*** 39.58 


* Lysine—arginine clearance values. 
** Teucine—isoleucine clearance values. 
*** Method Hare. 
In evaluating the extent of infantile hyperaminoaciduria it must be born in mind 
that the total N elimination in early infancy is only approx. 0.075 g/kg/day as com- 
pared with approx. 0.175 in the adult!®. Parallel to this the glomerular filtration rate, 
the urea clearance and the osmolar concentration are reduced in the full-term infant’®’. 
A leaking of plasma into the interstitium also occurs. This displacement is especially 
impressive in prematures!®, 
The inability to secrete a urine as concentrated as that produced by adults under 
comparable conditions is not to be attributed to a reduced response to the antidiuretic 
hormone!®*—!7, In addition to the tremendous difference in nutritional composition, 
the inability to produce an interstitial ionic hypertonia also must be taken into 
consideration!”, Protein-rich feedings produce an increase in the concentration capa- 
city of the infantile and adult kidney!”. 
The length of the loops of Henle, which is now considered as a counter-current 
distribution system, is at birth very short but extends itself rapidly. The tubuli like- 
wise have not reached the definite morphological structure. I should like to emphasize 
particularly the fact that the maturation of the kidney in respect to amino acid 
handling shows a great individual variation. In some children this organ reaches the 
functional capacity of the adult apparently within a few months, while in others it takes 
up to 2 years toreachthisstage of development. Besidesthe immaturity of the reabsorp- 
References p. 279/283 
