Abstract
Cardiac hypertrophy was induced in normal and hypophysectomized male Long Evans rats by triiodothyronine treatment. Polyadenosine-diphosphoribose polymerase activity of cardiocyte nuclei was reduced about 50% after hypophysectomy as compared to controls, whereas RNA polymerase activity was not influenced by hypophysectomy. Treatment with triiodothyronine produced a profound (∼80%) decrease in polyadenosine-diphosphoribose synthetase activity in cardiocyte nuclei of both normal and hypophysectomized rats. Simultaneously RNA synthesis was significantly augmented in cardiocyte nuclei isolated from triiodothyronine-treated animals which also showed significant cardiac hypertrophy. The simultaneous and opposite response of the two enzyme systems that is induced by triiodothyronine is consistent with a regulatory function of covalent modification of nonhistone proteins by polyadenosine-diphosphoribosylation on RNA synthesis.
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