NUCLEIC ACID IN THE ORGANS OF THE RAT 



671 



If the bulk of the proteins present were not previously precipitated, 

 the colorimetric determination gave a higher value (6.9 mgm). The same 

 observation was made by Vowles (1940). 



The upper limit of the amount of desoxyribose nucleic acid built up 

 daily in the different organs of the rat is given in Table 4. 



Table 4. — Upper Limit of the Amount of Desoxybibose Nucleic Acid Built 

 UP Daily in the Different Organs of Rats Weighing on the Avkrage 275 gm 



Organ 



Weight in gm 



Nucleic acid 

 present in the 

 organ in mgm 



Upper limit of desoxy- 

 ribose nucleic acid built 

 up in the course of a day 

 in mgm 



Brain 



Kidney 



Testes 



Spleen 



Liver 



Mucosa of the small intestine 

 Muscle 



1.43— L53 

 1.72— L76 

 1.93—2.57 

 0.86—0.81 

 9.24—9.06 



4 

 111 — 109 



3.7 



5.8 

 12.8 



8.3 

 57.5 

 21 

 154 



0.02 



0.03 



0.34 



0.48 



0.61 



3.0 



3.4 



As already mentioned previously, when calculating the above figures 

 we assume that the nucleic acid found in an organ is built up in the organ. 

 This assumption may not hold strictly, as the blood contains some nucleic 

 acid which may have been carried from the organs into the circulation. 

 However, this amount is small. Assuming the rat blood to contain 

 the same nucleic acid concentration as human blood which, according 

 to Javillier and Allaire (1931) amounts to 0.3 mgm per gm blood,, 

 the total amount of desoxyribose + ribose nucleic acid present in the 

 circulation of a rat weighing 275 gm amounts to about 6 mgm, thus about 

 ^/jQ of the total nucleic acid content of the rat. 



Summary 



Labelled pliospliate is administered to adult rats by subcutaneous injection.. 

 After the lapse of 4 days, the rats are killed and the desoxyribose nucleic acid 

 present in different organs is extracted. By comparing the activity of X mgm desoxy- 

 ribose nucleic acid P with the activity of 1 mgm cellular inorganic P of the same 

 organ, data on the percentage renewal of the desoxyribose nucleic acid present in 

 the organs are obtained. 



In the course of 4 days, only a minor part of the desoxyribose nucleic acid pre- 

 sent in all the organs investigated is found to be labelled, i. e. formed in the course 

 of the experiment. The greatest daily formation of nucleic acid (15 per cent) 

 takes place in the mucosa of the small intestine. This is followed by the spleen 

 (5.8 per cent), the testes (2.6 per cent), the muscles (1.9 per cent), and the liver 

 (1.0 per cent). The lowest figures aie shown by the kidneys and the brain (0.6 per- 

 cent) . 



