THE DEOXYKIBONUCLEIC ACID CONTENT OF THE NUCLEUS 169 



could result in an apparent increase in the average DNA content per nu- 

 cleus. 



The action of hormones does not seem to affect seriously the DNA con- 

 tent of nuclei. Alfert and Bern^^ showed that the injection of estrogen into 

 ovariectomized rats does not change the DXA of the nuclei in the uterine 

 gland cells although the protein content is doubled. Di Stephano et al.^^ 

 noted that hypophysectomy does not change the DNA content of the nuclei 

 of rat liver. But Bergerard and Tuchmann-Duplessis^ found a slight de- 

 crease in the DNA content of nuclei B (tetraploid) in rat liver after hypo- 

 physectomy, the injection of somatotrope hormone bringing these nuclei 

 back to a normal value. The fact that these authors worked on young rats 

 might perhaps explain their discrepancy with Di Stephano et al.^^ 



Fukada and Sibatani^* noted that the DNA content of nuclei in the 

 guinea pig liver is not affected by experimental ascorbic acid deficiency. A 

 thiamine-deficient diet, a high-fat diet, administratioa of a diabetogenic 

 dose of alloxan, or administration of thioacetamide does not change the 

 DNA content per nucleus in rat liver (Thomson et al."). 



Factors such as age, sex, strain, and body weight^^ have no noticeable 

 influence upon the amount of DNA per nucleus, but we must note here that 

 the degree of polyploidy is higher in adult rats than in young animals. ^^' ^^ 



Finally, it should be noted that the onset of pathological changes does 

 not seem to affect directly the DNA of the nucleus, which remains un- 

 changed until an advanced stage of cell degeneration. Leuchtenberger,^* 

 studying pycnotic degeneration of neoplastic and normal nuclei in mice, 

 showed that the DNA content is unchanged in an advanced state of pycno- 

 sis whereas the nucleus has already lost an important part of its protein 

 content, nor is the amount of DNA per nucleus affected even in cases 

 where the amounts of PNA, protein, and other substances are considerably 

 altered. 



Mark and Ris®^ showed that the nuclei of cholangioma and hepatoma 

 have the same content of DNA as have normal rat liver nuclei. Cunningham 

 et at., ®^' ^^ studying normal, precancerous, and neoplastic rat tissues found 

 in all these cases the same average value of DNA per nucleus; the precan- 

 cerous changes were obtained by feeding ^\dth acetylaminofluorene or 



s'' M. Alfert and H. A. Bern, Proc. Natl. Acad. Sci. U. S. 37, 202 (1951). 



" H. S. Di Stephano, A. D. Bass, H. F. Diermeier, and J. Tepperman, Endocrinology 



51, 386 (1952). 

 " J. Bergerard and H. Tuchmann-Duplessis, Compt. rend. 236, 1080 (1953). 

 " M. Fukuda and A. Sibatani, Experientia 9, 27 (1953). 

 *^ C. Leuchtenberger, Chromosoma 3, 449 (1950). 

 6? D. D. Mark and H. Ris, Proc. Soc. Exptl. Biol. Med. 71, 727 (1949). 

 «8 L. Cunningham, A. C. Griffin, and J. M. Luck, Cancer Research 10, 211 (1950). 

 69 L. Cunningham, A. C. Griffin, and J. M. Luck, /. Gen. Physiol. 34, 59 (1950). 



