Incorporation of exogenous precursors into uridine and ribonucleic acid. Nucleotide compartmentation in the renal cortex in vivo

Abstract

The possibility of compartmentation of UTP in vivo was investigated in the renal cortex of unanaesthetized rats. In addition, liver and spleen were studied in order to compare tissues with different utilization of precursors for pyrimidine nucleotide synthesis. After continuous 2h infusions of [(3)H]uridine or [(3)H]orotate, their incorporation into UTP, UDP-sugars and RNA was quantified. Rates of RNA synthesis were calculated by dividing the incorporation of precursor into RNA by the average specific radioactivity of the UTP pool. Although similar RNA-synthesis rates might have been expected with the two precursors, higher rates were found with uridine than with orotate. The relative incorporation into UDP-sugars of these precursors was also different. Similar results were obtained in the liver. In the spleen, equal amounts of both precursors were incorporated into UTP, but [(3)H]orotate incorporation did not lead to labelling of RNA. To evaluate the heterogeneity of cells with respect to the metabolism of pyrimidines, precursor incorporation was studied in isolated glomeruli and by radioautography. Incorporation into glomeruli was qualitatively similar to but quantitatively different from results in the renal cortex. Although there is obvious tissue heterogeneity, compartmentation of UTP pools is the most credible explanation for the results obtained with the renal cortex and liver. Consequently RNA and UDP-sugars may originate from two different UTP pools. Tissue heterogeneity is the likely explanation for the results obtained in the spleen. Studies of synthesis of pyrimidine and RNA, particularly in relation to growth and regeneration, must take into consideration the precursor used, the apparent existence of UTP compartmentation and the degree of cellular heterogeneity.

Pyrimidine nucleotide metabolism in rat hepatocytes: evidence for compartmentation of nucleotide pools

“…The opposite is true for the nucleus-localized synthesis of RNA. This is in agreement with results found by others in various cell types [26,[31][32][33][34]. Compartmentation of the de novo and salvage pathways has also been described in the nucleus [16,30,35].…”

Pyrimidine metabolism and sugar nucleotide synthesis in rat liver

“…Although the average 14C specific radioactivity of UTP remained much higher than of CTP, the value of the latter hardly increased, in spite of the fact that this small pool turns over rapidly because of the synthesis of RNA [19]. So, the 14C label in ['4C]CTP from the de novo pathway is continually strongly diluted by CTP from the salvage pathway or CTP is synthesized from an UTP pool with a lower specific radioactivity than the average UTP value.…”

“…The combined fractions from the Partisil-SAX column could be freeze-dried and rechromatographed without desalting, because they contained low concentrations of phosphate. We also collected fractions con [17][18][19][20] and attributable to high uridine catabolism in the liver [17,21,22]. As reported by Moyer et al [20] and Dahnke [23], [3H]cytidine was much better incorporated into soluble nucleotides and RNA.…”

Relationship Between Renal Function and Metabolic Alterations in Early Streptozocin-Induced Diabetes in Rats

“…As suggested in earlier studies, nucleotide triphosphate compartmentation is the likely cause of different rates of RNA synthesis in the normal renal cortex when different radiolabeled precursors, incorporated into the same nucleotide pool, are used for RNA labeling (41). However, when compared with controls, the RNA synthesis rate was increased similarly in the diabetic renal cortex, whether it was calculated as the incorporation of UTP or ATP (Tables 2 and 3), suggesting a true difference between both groups.…”

“…Although the effect of most of these variables is obviated by relating the amount incorporated to the specific radioactivity of the immediate precursor pool (40), this evaluation does not consider intracellular compartmentation of nucleotide pools (41,42).…”