Nucleic acid metabolism in regenerating rat liver. V. Comparison of results in vivo and in tissue slices.

Abstract

Summary The labeling of RNA and DNA pyrimidine nucleotides in rat liver tissue slices incubated in the presence of orotic acid-6-C 14 has been described. It was shown that DNA labeling was minimal in tissue slices of normal liver and that the increase in the rate of DNA labeling observed during liver regeneration in vivo , which was previously equated with DNA synthesis, could be demonstrated in slices of regenerating liver. A comparison of the relative rate of DNA labeling in regenerating liver was made on individual animals under in vivo and in vitro conditions, and it was found in each case but one that the relative rate of DNA labeling observed in vitro was directly proportional to the rate of DNA labeling observed in vivo . In fact it was not possible to alter the rate of DNA labeling under the in vitro incubation conditions employed, over time periods during which the rate observed in individual animals increased markedly. These findings suggest that a physiological state reached in regenerating livers in vivo is reflected in the metabolic activity of slices of the tissue in in vitro experiments. Ten hours before the beginning of the period of active DNA synthesis and throughout the period of rapid liver regeneration there was a marked increase in the rate of RNA labeling. The intracellular changes in the RNA metabolism were examined, and a decided increase in the accumulation of label was observed predominantly in the cytoplasmic RNA fractions.