RNA synthesis and RNA content of nuclei prepared from hearts during hypertrophy

Abstract

Rat heart nuclei were isolated and contents of DNA, RNA and protein, and activity of DNA-dependent RNA polymerase were determined during development of cardiac hypertrophy. Both protein/DNA and RNA/DNA ratios of isolated nuclei were increased within 24 hr after aortic constriction and remained high for a two weeks' observation period, suggesting an increased RNA synthesis and enlargement of nuclei. The apparent activity of polymerase of the control hearts measured in the presence of Mn²⁺ and (NH₄)₂ SO₄ was 2·5-fold higher than that measured in the presence of Mg²⁺ . The activity in the sham-operated rats was elevated in the first three days. The increase in RNA polymerase activity after aortic banding was biphasic in that an early, transient increase was observed at 4 hr after the operation and a later and greater increase appeared at approximately 24 hr and remained at a high level for several days. The early increase in the Mg²⁺ activated system was 109% and the Mn²⁺ system 169%, whereas at the peak that appeared on the third-fourth day the respective increases were 618% and 310%. The results suggest a predominant synthesis of messenger RNA at the early stage of hypertrophy followed later by an increased synthesis of ribosomal RNA.