Abstract
Repeated administration of phenobarbital (80 mg/kg twice daily) to immature rats over a 3-day period is attended by increases in the ratio of RNA to DNA of hepatocyte nuclei and whole liver. This effect of phenobarbital does not appear to be mediated by cellular proliferation or an increase in ploidy of hepatocytes, since the DNA content per liver remained almost constant, or by reduced levels of intranuclear ribonuclease activity, since the latter was elevated in phenobarbital-treated rats. The increase in the ratio of nuclear RNA to DNA attains a maximum at 2 days, a time when the incorporation of L-[methyl-14C]-methionine into methylated nuclear RNAs (rRNA and tRNA) and the relative amounts of preribosomal RNAs also become maximal. The base composition of newly synthesized nuclear RNA shifts to a more guanylic acid-cytidylic acid-rich, ribosomal type of RNA composition after a single day of treatment and remains fairly constant thereafter, whereas the incorporation of 32Pi into nuclear RNA is progressively increased over the 3-day period of treatment. The increases in RNA content of nuclei, ratio of nuclear protein to DNA, liver weight, and ratio of liver RNA to DNA become maximal at 3 days after the repeated administration of phenobarbital. These results suggest that one of the effects of phenobarbital may be exerted upon the synthesis of nuclear preribosomal and polydisperse RNAs, which presumably perform an important function in increasing the level of protein components of the hepatic endoplasmic reticulum after phenobarbital administration.
ACKNOWLEDGMENTS The authors wish to thank Dr. C. A. Swenson for the use of the du Pont curve analyzer, and Mr. A. Campbell, Mrs. S. Rickert, and Mrs. G. Reynolds for technical assistance in part of this work.
- Copyright ©, 1972, by Academic Press, Inc.
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