Nucleic Acid Labeling with [3H]Orotic Acid and Nucleotide Profile in Rats in Protein Deprivation, Enteral and Parenteral Essential Amino Acid Administration, and 5‐Fluorouracil Treatment

Abstract

Rats were fed a 0% casein diet for 1 week, with or without enteral or parenteral administration of essential amino acids, or a 25% casein diet, in one group supplemented with 5-fluorouracil treatment. Ninety minutes before sacrifice the rats were given a tracer of [3H]orotic acid. Incorporation into the acid soluble fraction, RNA, and DNA was determined in liver, small intestine, bone marrow, and kidney. Nucleotide profile was examined in liver and intestine. Protein deficiency caused inter alia a decrease in body weight; a decrease in RNA/DNA ratio and an increase in the specific RNA labeling in liver and kidney; an altered nucleotide profile in the liver; an increase in the nucleotide/DNA and RNA/DNA ratios and a decrease in the specific labeling of the acid soluble fraction, RNA, and DNA in the bone marrow. These changes were prevented to the same extent by giving essential amino acids, either orally or intravenously. The minor changes in intestinal nucleotide profile in protein deprivation were prevented to a slightly larger extent by amino acids orally than parenterally. 5-Fluorouracil treatment gave a decrease in the RNA/DNA ratio in the liver and kidney but an increase in the nucleotide/DNA and RNA/DNA ratios in the bone marrow. Nucleotide profiles were unaltered. The amount of DNA per gram of tissue decreased in bone marrow and increased in kidney. Parenteral administration per se resulted in almost no changes.

Incorporation of 5-fluorouracil into hepatoma and normal tissue RNA at protein depletion in the rat

“…Protein malnutrition decreases the cellularity of the bone marrow [3,19], which to some degree parallels the decrease in body weight [19] but without increased 5-FU toxicity. On refeeding protein, when cellular proliferation resumes in blood-forming tissues, the 5-FU toxicity is temporarily increased [19].…”

“…Furthermore, the ribosomal RNA synthesis appears to be increased in protein deprivation as suggested by increase in polymerase I activity [11,12] and increase in nucleolar size [5]. Normal labelled precursors such as orotic acid and cytidine [2,3] also show enhanced incorporation into liver RNA at protein deprivation. In addition, the activity of the 5-FU-degrading enzyme, dihydropyrimidine dehydrogenase, is decreased in protein deprivation [13].…”

“…Incorporation into the acid soluble fraction (ASF) and DNA is measured in the same analysis. Protein malnutrition is of special interest in this context, as it is well known to alter nucleic acid synthesis in several tissues and to increase the incorporation of precursors into liver RNA [2,3]. In addition, tumorbearing mice fed on a high protein diet and treated with 5-FU survived longer than mice fed on a low protein diet [4].…”