[Incorporation in vivo of 14C-precursors into pyrimidine nucleotides of chicken liver and spleen tissues].

Maximum incorporation of the label after administration of 14C-bicarbonate to free pyrimidine nucleotides begins by the 60th minute. Radioactivity of cytidine nucleotides at all time points is four-eight times as low as that of uridine nucleotides. 2-14C-orotic acid is incorporated into acid-soluble nucleotides and RNA of the liver and spleen tissues. 60 min after administration of the isotope 20% of radioactivity was found in the liver and 0.3% in the spleen, in both tissues radioactivity of RNA is 20% of 14C-radioactivity in the acid-soluble fraction. The formation rate for cytidine nucleotides from uridine ones in the liver and spleen tissues is low, about 2-6% of uridine nucleotides radioactivity is found in them only, that may be due to a low activity of CTP-synthetase. The content of cytidine nucleotides in these organs is three-life times as low as compared to uridine nucleotides.