[Regulation of RNA synthesis in the rat heart in L-thyroxine toxicosis and hypothyroidism; the role of RNA-polymerases and the template activity of chromatin]. / Reguliatsiia sinteza RNK v serdtse krysy pri L-tiroksinovom toksikoze i gipotireoze; rol' RNK-polimeraz i matrichnoi aktivnosti khromatina.

It is shown that L-thyroxin applied to rats has induced in them development of pronounced cardiac hypertrophy accompanied by an increase in the total amount of nucleic acids in the myocardium (per organ) and enhancement of the RNA synthesis rate. It is confirmed by a considerable rise of the intensity of the labelled uridine incorporation into RNA without alteration of the specific radioactivity in a pool of free nucleotides and by the growth of the RNA-polymerase I activity. When L-thyroxin toxicosis lasts for four weeks and heart weight has not already increased the content of nucleic acids remains high, the rate of the label incorporation into RNA lowering down to the normal level. The activity of RNA-polymerase I is almost twice as low as that under thyrotoxicosis lasting for a week. In this case the matrix activity of chromatin tested by exogenous RNA-polymerase III of the rat gets lower. Under mercasolyl-induced hypothyrosis the heart weight decreases as well as the amount of nucleic acids, RNA synthesis intensity (by 40%) and RNA-polymerase I activity in it. The data obtained testify to the versatile effect of the thyroid hormones on RNA biosynthesis in the cardiac muscle and on the activity of both the RNA-polymerases and chromatin matrix.

[RNA synthesis and modifications of heart nuclear proteins during thyroid hormone deficiency]. / Sintez RNK i izemeneniia iadernykh belkov serdtsa pri nedostatke tireoidnykh gormonov.

RNA synthesis, correlation of various histones and acetylation and phosphorylation of the chromatin proteins were studied in the rat heart during monthly hypothyroidism. It was shown that [3H]uridine incorporation into heart RNA decreases considerably at hypothyrosis. The alteration in relative amounts of the histone H4 subfractions, which does not depend on the method of hypothyrosis reproduction (inhibition of thyroid function by 1-methyl-2-mercaptoimidazole, thyroidectomy) was detected by the method of analytical electrophoresis in 15% polyacrylamide gels containing 3.125 M urea and 0.9 N acetic acid. Increased incorporation of [32P]phosphate into histone fraction H2b and total fraction of acidic chromatin proteins was observed in vivo. Increased incorporation of labeled acetate into the total histone fraction and reduced incorporation into acidic nuclear proteins were obtained. It was shown that the increased incorporation of acetate into the total histone fraction was due to the increased acetylation of histones H3, H2b, H4 and acid-soluble chromatin proteins characteristic of tissues with a low level of replication. It is assumed that the observed changes of nuclear proteins reflect the process of chromatin reorganization caused by a prolonged deficiency of thyroid hormones.