Influence of age on enzyme activities of pyrimidine metabolism in the chicken heart.

The effect of the aging on the activities of enzymes involved in UMP-CMP metabolism were evaluated in the heart of newborn (1-day-old), young (20-day-old), adult (12-month-old), and aged (30-month-old) chickens. In newborn animals, UMP metabolism proceeds preferentially towards cytidine compounds rather than to breakdown. In addition, two pathways different from those involved in de novo synthesis may contribute to the synthesis of UMP: one, through cytosine deaminase that shows its maximal activity; the other, by uridine kinase, the main "salvage" enzyme of pyrimidine nucleotides. In young chickens, pyrimidine metabolism regards especially UMP. In fact, the lower activities of cytidylate phosphatase and cytosine deaminase, together with the remarkable increase of uridine kinase indicate that the metabolic flux converges on the main salvage pathway. In adult chickens, pyrimidine catabolism is enhanced, as supported by the maximal activity of the enzymes involved in UMP-CMP breakdown. On the contrary, the remarkable reduction of the anabolic enzymes suggests a limited resort to the salvage pathways. Finally, in aged chickens a reduced pyrimidine catabolism and a greater utilization of the salvage pathways appear to take place, thus contributing to the maintenance of pyrimidine nucleotide pool.