Cardiac hypertrophy was induced in rats either by
isoprenaline treatment or by experimental abdominal
aortic stenosis. In both models, the
UTP content increased in the hypertrophying heart, while the
ATP level remained depressed. The rate of net synthesis of
uracil nucleotides, estimated by
phosphate incorporation into alpha-
phosphate groups, was largely increased during the first stage of
hypertrophy (X 3.6 and 2.6, respectively). At identical stages of
hypertrophy, the rate of synthesis of
ribosomal RNA, measured after continuous intracardiac infusion of 3H-uridine, was increased by 1.6 and 2.5 times. A comparison of the changes in time course of the levels of
UTP and
RNA and their turnover suggests that the metabolism of
uracil nucleotides and that of
ribosomal RNA are closely interrelated. The increase in the rate of synthesis of
pyrimidine is interpreted as an adaptational change in
nucleotide metabolism in response to the increased requirement of precursors for
RNA synthesis. The possible limiting role of
pyrimidine nucleotides in the hypertrophic process is discussed.