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A Comparison of the Intracellular Composition of Regenerating Liver and Induced Liver Tumors^{* ,}

J. M. Price, Ph.D. and A. K. Laird, M.D.

(From McArdle Memorial Laboratory, the Medical School, University of Wisconsin, Madison 6, Wisconsin)

1. Homogenates of regenerating rat livers were separated by differential centrifugation into nuclear, large granule, small granule, and supernatant fluid fractions at various times in the first 8 days and at 23 days after partial hepatectomy. The original homogenate and the fractions were analyzed for protein nitrogen and nucleic acids. The nuclei in the homogenates were enumerated and the data expressed in terms of units per nucleus. Previous results on liver tumors (induced by 4-dimethylaminoazobenzene) were recalculated in terms of units per nucleus for comparison with normal and regenerating livers.

2. There were 131 million nuclei in a gram of normal liver. On the first day of regeneration there was a minimum of 98 million and at 4 days a maximum of 183 million nuclei per gram, and there after the number gradually returned to normal.

3. The desoxypentosenucleic acid in the average nucleus increased from 10.0 to 18.3 x 10^-12 gm. per nucleus between 12 and 24 hours after partial hepatectomy, and thereafter returned rapidly toward normal as cell division started.

4. In the first day the protein nitrogen of the average cell increased by 17 per cent and then fell to 68 per cent of normal by 4 days. The initial increases occurred in the nuclear and small granule fractions, and later decreases were noted in all the cytoplasmic fractions. By the eighth day all three cytoplasmic fractions contained subnormal amounts of protein nitrogen, but by the 23d day these had all returned to normal levels. The smaller tumor cells contained only 23 per cent as much protein nitrogen as the average normal liver cells, and the distribution in the cell was different from that in either normal or regenerating liver cells.

5. The average liver cell increased its pentose nucleic acid by 62 per cent between 12 and 24 hours after partial hepatectomy, as a result of an approximate doubling of this nucleic acid in the small granule and supernatant fluid fractions. In the period between 2 and 6 days the pentosenucleic acid content of the average cell fell to normal, with the greatest decrease in the same two fractions. The nuclear fraction reached a maximum 3 days after the operation, and the large granules changed relatively little during regeneration. The average tumor cell contained only 36 per cent as much pentosenucleic acid as the average normal liver cell, but the supernatant fluid of these tumor cells had a normal level of this nucleic acid.

6. As a result of increases in pentosenucleic acid during the first 2 days and decreases in protein nitrogen during the next 4 days, the ratio of pentosenucleic acid to protein nitrogen was increased in all fractions during rapid growth. In tumor cells these ratios were normal in the nuclear and small granule fractions, were elevated about half as much as regenerating liver in the large granules, and exceeded regenerating liver in the supernatant fluid.

7. The advantages of reporting the data in terms of units per nucleus are emphasized.

8. Acidophilic cytoplasmic inclusion bodies were found in all regenerating livers about 1 day after partial hepatectomy; they were no longer observed 2 days after the operation.

^* This work was supported in part by a grant from the National Cancer Institute, Public Health Service.

We are indebted to Drs. E. C. and J. A. Miller for their advice and continued interest in this project. We also wish to thank Dr. Hans Ris for his assistance in the Feulgen staining and his advice during the course of this work.

Postdoctoral Research Fellow, Public Health Service, 1949–50.

Received 7/22/50.

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