NUCLEIC ACID METABOLISM IN REGENERATING RAT LIVER 



USING CYTIDINE-Ht= 



RUTH G. KLEINFELD and E. von HAAM 



Department of Pathology, Ohio State University, 

 Columbus, Ohio 



A study was made of RNA and DNA synthesis in rat liver parenchymal 

 cells following 65—70% partial hepatectomy. Maie Wistar rats weighing 

 80—100 gm were given cytidine-H' (200 (mc per rat intraperitoneally) 18 

 hours following surgery. Animais were sacrificed in pairs (one laparoto- 

 mized and one partially hepatectomized) at %, 1, 2, 3, 4, 5, 8, 12, and 

 24 hours following isotope injection. Sections 2 (i thick were subjected 

 to differential extraction techniques making it possible to distinguish 

 between cytidine incorporation into RNA and DNA. 



In the 18-hour regenerating rat liver, approximately 50% of parenchymal 

 cells in the periportal régions of the lobule were synthesizing DNA in 

 contrast to 5% in the centrolobular régions. The period from the end of 

 DNA synthesis to the onset of mitosis (Gj time) was approximately 4 

 hours. 



A différence in the time course of incorporation of cytidine-H into 

 nucleolar RNA was found in the periportal versus the centrolobular cells. 

 Two RNA fractions having différent metabolic properties were indicated 

 in both nucleoli and chroma^tin. Nucleolar RNA synthesis was found to 

 occur in nuclei during the process of DNA synthesis. 



*Supported by U.S. P. H. S. Grant No. C-4077 and a grant from The American 

 Cancer Society. 



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