THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 25 



PN content per organ was of the order of 30 to 75 % in liver, kidney, muscle, 

 and spleen. Brain tissue provided a striking contrast, since it lost none of 

 its PNA, DNA, or PN in the course of severe protein deficiency/^ 



Another aspect of liver metabolism in rats has been investigated by 

 Munro and his colleagues. ^^ When the diets contained adequate protein, 

 the PNA content per liver increased with the increasing energy intake; 

 for additional carbohydrate, the regression coefficient was +1.96 mg. 

 PNA-P per hver per 1000 kcal., and, for fat, +2.01 mg. PNA-P per 1000 

 Cal. In the case of rats on a protein-free diet, which, of course, initially re- 

 duces the PNA-P content of the liver, the total PNA-P only increased by 

 5 to 10% for each 1000 Cal. supplied as carbohydrate; no change was pro- 

 duced by additional fat. At the same time these authors studied the P^^ 

 uptake by PNA-P and concluded that "protein intake plays a dominant 

 role in determining the amount of PNA per liver, whereas energy intake 

 determines the amount of phosphorus incorporation." 



The amount of PNA-P relative to the total cell substances (that is, the 

 concentration per unit fresh weight) decreases on a protein-deficient diet 

 lasting one week, but increases again in liver, at least, during a more pro- 

 longed period of deficiency (Table VII, ^■*' '**■ ^^^). Drabkin^'^ reported a two- 

 fold increase in PNA concentration in regenerating rat liver when the an- 

 imals were fed on a protein-free diet, the control group receiving a full diet. 

 According to Vendrely and Vendrely"^ and Munt\\yler et al.^^^^'^ the loss 

 of PNA (and of protein also) occurs chiefly in the microsomal fraction, 

 which normally contains nearly 50 % of the total PNA of the liver cell. 

 Lagerstedt's work'^* supports the view that PNA loss involves the disap- 

 pearance of intracellular cytoplasmic particles, although he holds the opin- 

 ion that the microsomes may be artificial breakdown products of the mito- 

 chondria. 



Both PNA and DNA concentrations"' ^^ and the number of nuclei per 

 unit weight of liver^^ are significantly reduced when the animals are made 

 deficient in vitamin B12 . Since Rose and Schweigert" report that the aver- 

 age DNA and PNA contents per cell are unchanged during vitamin B12 

 deficiency, the lower concentrations of both nucleic acids per unit weight 

 and per unit PA''" must be the result of the build-up of protein and perhaps 

 other constituents in the cells, without a corresponding increase in the nu- 

 cleic acids. Vitamin B12 deficiency appears to have no effect on the nucleic 

 acids of kidney or spleen," but addition of vitamin B12 to deficient animals 

 increases the basophilia due to PNA in rat nerve cells. ^*^ In guinea pigs 



'" C. Vendrely and R. Vendrely, Compt. rend. 230, 333 (1950). 



'" S. Lagerstedt, Acta. Anat. Suppl. IX (1949). 



i« W. F. Alexander and B. S. Backler, Proc. Soc. Exptl. Biol. Med. 78, 181 (1951). 



