482 ANIMAL BIOCHEMISTRY 



TABLE 20-3. The Principal Nitrogen Compounds in Urine 

 of an Adult Human Being 



Quantity, 

 Component g. of N per day 



Ammonium ion 0.4 -1.0 



Amino acids 0.08-0.15 



Creadnine 0.3 -0.8 



Hippuric acid 0.04-0.08 



Peptides 0.3 - 0.7 



Urea 6 -18 



Uric acid 0.25- 0.7 



centrate it in the urine by a large factor, equal in human beings to 

 about 60 times the concentration in the plasma. Various abnormali- 

 ties render the kidneys incapable of this power of concentrating urea, 

 which then acctimulates in the blood. Although urea is not toxic, 

 abnormally high concentrations of it indicate kidney malfunction 

 and are usually accompanied by toxic symptoms due to other urine 

 components. Such diseases are known as uremias. 



As with other components, the quantity of ammonium ion excreted 

 daily varies by a factor of 2 to 3, depending on the diet and the 

 individual. Variations outside this range indicate a disturbance of 

 normal function. Originally it was supposed that the ammonium ion 

 appeared after decomposition of urea. However, tracer studies with 

 isotopes show that this is not the case biu that the ammonium ion 

 results from deaminations of amino acids. Since ammonium ion is 

 used in the formation of urea, it must be assumed that the urea 

 cycle does not utilize all the NH4 + , or that the ion appears in tissues 

 not synthesizing urea, or perhaps both. 



Uric acid in man and birds and allantoin in mammals other than 

 primates appear after the breakdown of purines. Hence the levels 

 depend upon the intakes of purines and nucleic acids. However, the 

 levels ordinarily do not drop below the normal range even on a 

 purine-free diet. Since animals also make their own purines from 

 amino acids, synthesis and degradation seem to occur at a constant 

 rate as long as ingested amino acids are available. Aside from dietary 

 effects, uric acid may increase in the urine of leukemia patients. 

 There may be enormous excretions when certain drugs are used to 

 treat arthritis. Since uric acid and its salts are not very soluble, these 

 compounds can crystallize in the urinary tract. On the other hand, a 

 reduced excretion of uric acid is believed to precede an attack of goixt, 



