Effects of adrenocortical hormones on RNA metabolism in rat kidney and liver

The turnover of RNA in various subcellular fractions of kidney and liver of normal, adrenalectomized and adrenalectomized plus adrenocortical hormone treated rats was investigated. The turnover rates were measured by the injection of a single dose of ¹⁴C-orotic acid and then following the loss of radioactivity from purified nuclei, mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, free polysomes, total ribosomes and sRNA. Single exponential decay patterns were observed in all the subcellular fractions of both tissues. The half-lives (t½) of the RNA for above fractions of normal kidneys were 7.4, 5.8, 5.1, 5.0, 5.4, 4.1, and 4.6 days, respectively, The t½ values for adrenalectomized rat kidneys were 9.2, 7.3, 6.1, 6,0, 5.8, 6.0, and 4.9 days, respectively. The half-lives (t½) of the RNA of normal rat liver nuclei, mitochondria, rough endoplasmic reticulum, smooth endoplasmic reticulum, polysomes, total ribosomes and sRNA were 8.7, 6.5, 5.4, 6.4, 4.4, 4.9, and 4.8 days, respectively, The corresponding values for adrenalectomized rat livers were 12.0, 8.5, 6.9, 6.5, 5.8, 6.1, and 5.9 days, respectively. -- The slower turnover rate of RNA in adrenalectomized rat kidney and liver suggests a slower rate of RNA synthesis (steady state approximation) . Daily administration of aldosterone or deoxycorticosterone to adrenalectomized rats restored the turnover rates to normal in kidney and daily administration of corticosterone or hydrocortisone reversed the effects of adrenalectomy in liver indicating a tissue specificity of mineralocorticoids and glucocorticoids. -- Aggregate DNA-dependent RNA polymerase activity in nuclei of both tissues was decreased by adrenalectomy and restored by administration of aldosterone or deoxycorticosterone in kidney and by corticosterone or hydrocortisone in liver. To further investigate the mechanism of RNA polymerase stimulation by aldosterone in kidney, the polymerases were purified from various groups of rats and activity was determined using different sources of DNA. It was found that the DNA from aldosterone treated rats was transcribed more efficiently than from other sources. Fractionation of (¹⁴C-aldosterone injected) kidney chromatin revealed the presence of radioactivity in the non histone acidic protein and DNA fractions suggesting the possible binding of aldosterone, or aldosterone-receptor complex or metabolite(s) of aldosterone to these chromatin fractions which may result in enhanced template activity of DNA