Molecular Pharmacology, Vol 10, 248-256, Copyright © 1974 by the American Society for Pharmacology and Experimental Therapeutics

Further Studies on Post-transcriptional Stabilization of Ribosomal Precursor Ribonucleic Acid by Phenobarbital

¹ Department of Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033

To study the effect of phenobarbital on transcription of hepatic ribosomal precursor RNA (45 S RNA), three experiments were performed in adult male rats receiving single daily intraperitoneal injections of 0.9% NaCl or phenobarbital (100 mg/kg) for 1 or 4 days: measurement of the labeling of hepatic nuclear RNA with L-[methyl-³H]methionine, determination of nucleolar RNA polymerase activity, and measurement of alkaline nuclear ribonuclease activity. Labeling of nuclear RNA with [methyl-³H]methionine increased approximately 100% and 50% in rats treated for 1 and 4 days, respectively, with phenobarbital. Phenobarbital for 1 or 4 days did not affect nucleolar RNA polymerase activity measured in the presence of high ionic media and -amanitin. With nonlabeled ribosomal RNA or 45 S [³H]RNA as substrate, nuclear alkalne ribonuclease activity in phenobarbital-treated rats was unaltered. These data confirm our previous finding that phenobarbital-induced stabilizations of 45 S RNA molecules accounts for the approximately 2-fold increase in cellular concentration of 45 S RNA in rats treated for 4 days with phenobarbital. A single dose of phenobarbital may stimulate methylation of newly formed 45 S RNA molecules normally degraded in the nucleus, thereby increasing transport of ribsomal subunits to the cytoplams.