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A Comparative Study of in Vivo RNA and Protein Synthesis in Rat Liver and Lung¹

Department of Pharmacology, Faculty of Medicine, University of Montreal, Montreal, Québec, Canada

The incorporation of radioactive orotic acid and uridine into total RNA was measured in vivo in rat liver and lung. Orotic acid labeled hepatic RNA 10 times higher than pulmonary RNA. Uridine labeled pulmonary RNA about twice, as did orotic acid, and was incorporated very little into hepatic RNA. Specific activities of total acid-soluble UMP were measured in both organs. Comparison of pool sizes and labeling of RNA suggested that lung was about as effective in synthesizing RNA as was liver in its use of orotic acid as precursor, and it was slightly superior in its use of orotic acid as precursor, and it was slightly superior in its use of uridine. The activity of enzymes on the main pathway for pyrimidine synthesis (aspartate transcarbamylase and orotidine 5'-phosphate pyrophosphorylase and decarboxylase) was higher in liver high-speed supernatants, whereas uridine kinase and uridine phosphorylase were more active in lung. Actinomycin D and DL-ethionine blocked RNA synthesis in both liver and lung; nickel carbonyl affected hepatic RNA synthesis only; and N-nitrosodiethylamine, thioacetamide, and N-methyl-N-nitrosourethan produced no effect in the two organs. The incorporation of leucine into liver and pulmonary protein was linear up to 30 min after injection of the label. Cycloheximide and CCl₄ blocked incorporation in both organs, whereas ethionine inhibited protein synthesis in liver but not in lung.

¹ This work was supported by a grant from the National Cancer Institute of Canada and from the Canadian Medical Research Council.

² Member, Medical Research Council Group in Drug Toxicology.

Received 8/ 6/71. Accepted 4/24/72.

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