THE NUCLEIC ACID CONTENT OF TISSUES AND CELLS 33 



change in their cultures of chick embryo lung and intestine after the addi- 

 tion of cortisone acetate to the medium. 



Mandel et al.^^ report that, after the injection of thyroxine (1 mg. per 

 days) into rats, kidney weight increased 21 to 32%, protein content 15 

 to 26 %, PXA 26 to 33 %, and DNA 22 to 32 %. Similar increases in spleen 

 ranged from 35 to 60 %}'^^ The absence of any change in cell composition 

 indicates that increase in kidney size was solely the result of cell prolifera- 

 tion (hyperplasia). A single injection of thyroxine into male mice has the 

 effect of raising the proportion of PNA and protein relative to DNA in the 

 liver after 48 hr.®^ ^s the PNA-P per unit PN continues to increase until 

 120 hr., total PNA formation appears to exceed the formation of new pro- 

 tein at this stage. 



The treatment of immature pullets'" with estrogen increases liver weight 

 and total liver protein. The treatment was shown to raise significantly the 

 number of hepatic cells and the total DNA per liver,'^ although not to the 

 extent that it increased PNA content. Campbell et al}'''^ reported similar 

 results for rat liver after injection of estradiol into the intact, but not into 

 the hypophysectomized, animal (Table X, ref. 171). Forty-eight hours 

 after a single injection of estradiol into rats, there is a 192% increase in 

 PNA per uterus, but only a 12% increase in DNA content; at 72 hr. the 

 PNA-P increase over the initial amount per uterus is reduced to 137 %, 

 while the corresponding DNA-P increase has risen to 54 %.'" Testosterone 

 had no effect on the pullet liver; neither did testosterone nor progesterone 

 influence the action of estradiol."" Both Mandel et aiy^^ and Coromon et alP 

 find higher nucleic acid concentrations in the blood serum during estrogen 

 treatment. 



The stimulation of pigeon crop gland by lactogenic hormone has been 

 studied by McShan et al?^ From their data it can be shown that after 5 

 days of treatment the total weight of the gland increased by 280%, the 

 PNA-P content by 850 %, and DNA-P by 400 %. These authors noted that 

 DNA-P content per organ increased on the second and third days, when 

 the histological picture showed maximal mitotic activity. 



Insulin, acting at concentrations of 2 to 3 units/ml. in the growth-pro- 

 moting medium, increased the total DNA-P and PN contents of chick 

 heart explants well above the control values after 6 days' growth; the stim- 

 ulus to PNA synthesis was even greater, the PNA-P/DNA-P ratio and the 

 PNA-P per unit PN both increasing appreciably (Table X'^^). Thus, 

 cortisone, ^^' *^ insulin,'^' estradiol,''^" and thyroxine^- all produce a rise in 



"6 L. Mandel, M. Jacob, and P. Mandel, Experientia 8, 426 (1952). 



1" D. G. Chapman, A. A. Hanson, R. H. Common, and W. A. Maw, Can. J. Research. 



27, 200 (1949). 

 "8 P. Mandel, J. Clavert, and R. Bieth, Compt. rend. soc. biol. 141, 1262 (1947). 



