38 I. LESLIE 



the proportion of PNA-P to protein in the cells of rat and rabbit liver or 

 embryonic chick heart. When insulin, cortisone, and growth hormone are 

 all present in the medium, the action of insulin in increasing the PNA/DNA 

 ratio is added to the general growth stimulus of the last two hormones."* 



The control of the pituitary over the nucleic acid content of rat liver has 

 been shown by the fall in PNA-P concentration and in PNA-P/DNA-P 

 ratio follomng hypophysectomy (Table XP^^' "«■ '^o. isi). Di Stefano et al,'^^ 

 who found no change in the average DNA per nucleus in the livers of hypo- 

 physectomized rats, restored the protein and PNA contents per cell to nor- 

 mal or above normal by injection of growth hormone. 



Rats made diabetic with alloxan show a reduction in the liver PNA-P/ 

 DNA-P ratio,"' ^^- although in one case the decrease is not significant." 

 There is agreement, however, that the concentrations of liver PNA-P and 

 DNA-P increase in alloxan-treated rats. That protein is lost from the cells 

 follows from the 33 % increase in DNA-P per unit PN^*- and from the fact 

 that the average amount of DNA-P per nucleus remains unchanged." 



Since the earlier observations'^^ that there is a significant increase in DNA 

 content of rat liver during pregnancy and a remarkable rise in the PNA/ 

 DNA ratio, Campbell el al. (Table XP^O have studied extensively the hor- 

 monal effects on rat liver composition. The "excess PNA" (i.e., increase in 

 PNA/DNA above expected value, calculated on the basis of protein content 

 of the cells) is also a feature of liver composition in pregnant mice and 

 guinea pigs but not in cats.'^* "Excess PNA" could be eliminated by removal 

 of fetuses, placentae, and ovaries at the fourteenth day of gestation, or by 

 hypophysectomy, even when food intake was maintained at the normal 

 level. 1^' Adrenalectomy caused both the PNA and DNA per liver to increase 

 in pregnant rats. The authors conclude"' that there are two independent 

 PNA fractions in pregnant rat livers; one varies linearly with protein con- 

 tent, as in nonpregnant rats; the other, "excess PNA," is quite independ- 

 ent of the protein content, or the amount of protein eaten, but "it varies 

 linearly with the amount of energy consumed with the food and with the 

 weight of the placentae." 



The PNA/DNA ratio of mouse uterus, which reaches a peak value at 

 estrus, is greatly diminished by castration (Table XP"''). It can be restored 



>79 A. Canzanelli, R. Guild, and D. Rapport, Endocrinology 45, 91 (1947). 



180 I. Geschwind, C. H. Li, and H. N. Evans, Arch. Biochem. 28, 73 (1950). 



18' H. S. Di Stefano, A. D. Bass, H. F. Diermeier, and J. Tepperman, Endocrinology 



51, 386 (1952). 

 '82 H. F. Diermeier, H. S. Di Stefano, J. Tepperman, and A. D. Bass, Proc. Soc. Exptl. 



Biol. Med. 77, 769 (1951). 

 '83 H. W. Kosterlitz and R. M. Campbell, Nature 160, 675 (1947). 

 '84 R. M. Campbell and H. W. Kosterlitz, J. Endocrinol. 9, 45 (1953). 

 '85 M. L. Dasher (a) J. Exptl. Zool. 119, 3.33 (1952) (b) 122, .385 (1953). 



