RNA Synthesis In Liver Research Articles

Adriamycin-induced hepatic and myocardial lipid peroxidation and DNA damage, and enhanced excretion of urinary lipid metabolites in rats

Adriamycin produces clinically useful responses in a variety of human cancers including lymphomas, leukemias, and solid tumors. However, the toxicity of adriamycin has limited its usefulness. Iron-catalyzed free radical reactions as the peroxidation of membrane lipids, inactivation of critical enzymes, and the inhibition of DNA, RNA and protein synthesis in heart, liver and kidney have been implicated in the toxicity of adriamycin. In order to further assess the role of oxidative stress in the toxicity of adriamycin, the effects of adriamycin were examined on the urinary excretion of lipid metabolites at 0, 6, 12, 24, 48 and 72 h post-treatment, and on myocardial and hepatic lipid peroxidation and nuclear DNA single strand breaks at 24 h post-treatment following single oral and intravenous (i.v.) doses of 10 mg/kg adriamycin. Urinary malondialdehyde (MDA), formaldehyde (FA), acetaldehyde (ACT) and acetone (ACON) excretion was significantly increased at all time points examined. Following the oral administration of adriamycin, maximum excretion of MDA, FA, ACT and ACON of 6.2-, 2.7-, 3.7- and 2.2-fold relative to control values, respectively, occurred 24 h after treatment. However, following the i.v. administration of adriamycin, greatest increases in excretion of MDA, FA and ACT reaching 6.9-, 3.3- and 6.3-fold relative to control values, respectively, were observed 6 h after treatment, while the greatest increase in ACON excretion of 4.2-fold relative to control values occurred 12 h post-treatment. Following oral and i.v. administration of adriamycin, significant increases were observed in myocardial and hepatic lipid peroxidation in mitochondrial and microsomal membranes, and myocardial and hepatic nuclei DNA single strand breaks 24 h after treatment. The results indicate that adriamycin administration induces myocardial and hepatic lipid peroxidation which may be responsible for enhanced excretion of urinary lipid metabolites as a result of membrane damage, and also induces enhanced DNA damage. These effects may be due to adriamycin-induced production of reactive oxygen species.

Effect of gastric distention on RNA synthesis in neonatal chick liver

RNA synthesis in the nuclei of liver from newly hatched chicks was enhanced 1.25 fold at 10 min after intragastric administration of water. Differential inhibition of RNA synthesis by α-amanitin indicated that the enhancement mainly represented rRNA synthesis; the synthesis of mRNA and tRNA was scarcely affected. Enhanced RNA synthesis was accompanied by greater susceptibility of nuclei to digestion by micrococcal nuclease, indicating that the chromatin structure was modified. It was further shown that the “water effect” was mimicked by distention of the stomach by raising the pressure in the intragastric balloon. Since the prior administration of atropine abolished the “water effect”, the enhancement of hepatic RNA synthesis may be mediated by hepatic nervous system.

In vitro effect of profenofos, fenvalerate and dimilin on protein and RNA biosynthesis by rabbit liver and muscle tissues

The present study was carried out to investigate the effect of Curacron (profenofos), Sumicidin (fenvalerate) and Dimilin (difluobenzuron) on the in vitro rate of protein and RNA synthesis by rabbit liver and muscle tissues. The synthesis of protein and RNA were significantly stimulated in the liver and inhibited in the muscle by graded doses of these insecticides. Profenofos showed maximum effect on protein synthesis in both tissues at a dose of 0.2 microgram/mL, while the maximum effect on RNA synthesis occurred at 0.2 microgram/mL, while the maximum effect on RNA synthesis occurred at 0.2 microgram mL in the liver and at 2 micrograms/mL in the muscle. Fenvalerate caused maximum stimulation in both liver protein and RNA synthesis at a dose of 2 micrograms/mL, and maximum inhibition in the muscle at 10 and 0.2 micrograms/mL for protein and RNA synthesis respectively. The maximum effect of Dimilin on both tissues was reached at 5 micrograms/mL for protein synthesis and at 0.2 microgram/mL for RNA synthesis. The effect of Dimilin on RNA synthesis was more pronounced in both tissues than its effect on protein synthesis, but this trend was reversed in the case of profenofos and fenvalerate. Present data also showed antagonism between these insecticides on the rate of protein and RNA synthesis.

Alteration of RNA synthesis in vitro in intact cerebral cortex nuclei induced by convulsions in seizure-susceptible el mice

We examined the effects of convulsive seizures on in vitro RNA synthesis by cerebral cortex nuclei in El mice. The rate of incorporation of [ 3H]uridine-5′-triphosphate by intact nuclei during seizures was decreased to 47.4% compared with the rate during the interictal period, but gradually recovered. During the 30-min period after onset of seizures, the rate of RNA synthesis was significantly lower in El mice than in identically stimulated ddY mice. Seizures in El mice had no effect on liver RNA synthesis, suggesting that the alteration of RNA polymerase activity is specific to the brain. Analysis of gel electrophoresis of polyadenylated RNA synthesized in the presence of ammonium sulphate revealed a marked decrease in high-molecular weight RNA species 15 min after seizures in El mice compared with the pattern in nonstimulated ddY mice. This shift from high- to low-molecular weight RNA species was not attributable to RNase activity, but it appeared to be related RNA polymerase.

Mitochondrial DNA, RNA and protein synthesis in normal and hypothyroid developing rat liver

Mitochondrial DNA, RNA and protein synthesis in normal and hypothyroid rat liver between the ages of −3 and 21 days were followed. In normal rats DNA polymerase activity and protein synthesis behaved similarly, showing two peaks of activity, one at −3 and the other at 21 days of age. RNA polymerase activity did not change between days · and 14, whereas it increased by 21 days of age. Hypothyroidism delayed the developmental pattern of DNA polymerase activity, affected RNA polymerase activity only at 21 days, whereas it inhibited protein synthesis at birth and in the third week of life. The cytochrome aa 3 content appeared to be affected by hypothyroidism at birth and at 21 days of age.

Effects of starvation on rat liver mRNA translation products.

The synthesis of rat liver protein and RNA decreases with starvation. It is not yet known whether such decreases are regulated strictly at a transcriptional level, or if post-transcriptional controls are also involved. In this study we investigate the effects of 0, 2, or 4 days starvation on the levels of specific, abundant mRNAs in total and polysomal RNA populations. The mRNAs were analyzed by translation in vitro in mRNA-dependent, cell-free, protein synthesizing systems. The resulting polypeptide products were separated by gel electrophoresis and visualized with fluorography. The amount of albumin translated from both polysomal and total cellular mRNA decreased 20-40% with fasting. In contrast, a specific peptide having a molecular mass of approximately 30 kDa increased two- to three-fold in total cellular RNA with a smaller increase observed in polysomal RNA. These changes were maximal at 2 days of starvation. Since starvation is known to cause alterations in liver metabolism the 30-kDa polypeptide may be related to enzymes or other proteins involved in this homeostatic response.

Effect of Chlorpromazine on Protein, Phospholipid and RNA Synthesis or Degradation in Rat Liver

Chlorpromazine (CPZ) administration to rats (25 mg/kg ip) significantly stimulated (14C)-leucine incorporation to liver microsomal proteins, (14C)-orotic acid incorporation to liver RNA and (32P) incorporation to liver microsomal lipids. CPZ administration did not modify the decay of radioactivity of liver microsomal lipids prelabeled with (32P) or that of microsomal proteins prelabeled with [(14C)-guanidino]-arginine. Results suggest that CPZ administration stimulates protein, phospholipids and RNA synthesis but does not affect their degradation. The relation of these findings with CPZ preventive effects on CCl4-induced liver injury is discussed.

Stimulating actions on ribonucleic acid biosynthesis of aconitines, diterpenic alkaloids of Aconitum roots

Mesaconitine (MA) significantly stimulated the incorporation of 5-[ 3H]orotic acid into liver nuclear RNA 16h after its administration. MA exhibited the strongest activity among the aconitine alkaloids. This stimulatory effect of MA was inhibited by actinomycin D, but the incorporation ratio of 5-[ 3H]orotic acid in the combined treatment group with MA and actinomycin D was significantly higher than that in the single treatment group with actinomycin D. MA also increased the incorporation of 5-[ 3H]orotic acid into polysomal RNA in mouse liver. When MA was added to the RNA polymerase (EC 2.7.7.6) preparation obtained from rat liver, the increase of the enzyme activity was weak. While RNA polymerase preparation from the liver of rats, which were previously treated with MA, elicited increased incorporation of [ 3H]cytidine monophosphate into RNA as compared with that from the livers of normal rats. Accumulated data indicate that aconitine alkaloids, in particular MA, accelerate liver RNA synthesis mainly by the increase of RNA polymerase.

Mechanism of enhanced RNA synthesis in acute-phase rat liver and its relationship to chromatin structure.

Nuclei isolated from the liver of rats undergoing an acute inflammatory reaction induced by turpentine treatment show increased RNA synthesis. This increase is essentially determined by a faster polyribonucleotide-elongation rate while the number of transcribing polymerase molecules is unchanged. The sensitivity of chromatin to micrococcal-nuclease digestion and the composition of chromosomal proteins are not affected by the acute-phase process. Therefore the increased RNA synthesis by liver nuclei from acutely inflamed rats does not seem to correlate with major changes in chromatin structure.

Ribosomal RNA synthesis in liver of adrenalectomized rats after partial hepatectomy

The ribosome formation in four experimental groups: normal, adrenalectomized, partially hepatectomized and adrenalectomized — partially hepatectomized rats was studied. Ribosomal RNA was labelled for different intervals and the transfer of the radioactivity from 45 S pre-rRNA through the nucleolar pre-rRNA and rRNA pools into cytoplasmic 28S and 18S rRNA was followed. The results show that there are at least two ways of positive control of rRNA synthesis, one of them being glucocorticoid-dependent. The acceleration of the pre-rRNA processing through the shortest maturation pathway in regenerating liver is reduced in the absence of the hormone. Glucocorticoids do not influence nucleo-cytoplasmic rRNA transport.

Enhancement of ribonucleic acid synthesis by chromium(III) in mouse liver

The effect of Cr(III) administration on hepatic RNA synthesis in mice was studied. It was found that Cr accumulated in mouse liver. Forty-eight hours after intraperitoneal injection of CrCl 3 (0.005–5 mg Cr/kg body weight) approximately 10% of the administered dose perg of tissue remained. The accumulated Cr was still retained 64 days after administration (5 mg Cr/kg) with only a slight decrease. Approximately 20% of the hepatic Cr was detected in the nuclei. By administering CrCl 3, RNA synthesis in mouse liver was markedly enhanced without altering the pool size of nucleotides. This enhancement was dose-dependent and statistically significant at doses of 0.05 ( p < 0.05), 0.5 ( p < 0.01), and 5 mg Cr/kg ( p < 0.01), and remained so for at least 16 days after administration of 5 mg Cr/kg. The syntheses of DNA and protein in mouse liver were not significantly changed by CrCl 3 administration. On the other hand, Cr(VI) administration did not enhance but rather inhibited RNA synthesis in mouse liver. These results suggest that Cr(III) specifically enhances RNA synthesis in mouse liver.

Effects of bovine growth hormone on RNA synthesis in brain and liver of neonatal hypothyroid rats.

The action of growth hormone upon RNA synthesis was studied in isolated nuclei from cerebrum and liver of hypothyroid rats. The acute administration of bovine growth hormone (bGH) to cretinoid rats, 10 days after birth, stimulated the endogeneous activity of RNA polymerase I and II in both organs. The transcription of ribosomal RNA in cerebrum and hnRNA in liver increased 40 min. after the injection and continued to be higher than in controls until 14 hrs. An increase in the synthesis of hepatic ribosomal RNA occurred 5 hrs. after treatment, the effect persisting during the whole period studied. The activity of cerebral RNA polymerase II displayed a bimodal curve with an early stimulation at 40 min. and a second one at 14 hrs. The results give evidence in favour of the action of growth hormone during the postnatal development of rat brain.

Effect of Chromium (III) on RNA Synthesis in Mouse Liver and Regenerating Rat Liver (Regular Presentations) (Proceedings of the 9th Symposium on Environmental Pollutants and Toxicology)

Effect of Chromium (III) on RNA Synthesis in Mouse Liver and Regenerating Rat Liver (Regular Presentations) (Proceedings of the 9th Symposium on Environmental Pollutants and Toxicology)

Thyroid hormones effects on RNA synthesis in brain and liver of neonatal hypothyroid rats.

The effect of replacement therapy with thyroid hormones upon RNA transcription was studied in isolated nuclei of cerebrum and liver from hypothyroid rats. The chronic administration of T4 to hypothyroid rats, from the 5th day of life, during ten days, corrected the RNA synthesis in isolated nuclei from cerebrum and liver. The injection of a single dose of T3 to neonatally thyroidectomized rats, ten days after birth, enhanced the endogeneous activity of RNA polymerase I and II of cerebrum and liver. In cerebrum the transcription of ribosomal RNA increased 40 minutes after T3 injection, this activity being constant during the whole period studied. On the other hand, the synthesis of heterogeneous RNA showed an increase only 5 hrs. after the beginning of the treatment. In liver, the lag period is higher for both enzymes, being the maximal response achieved 5 hs. after the hormonal administration.

Temporal studies of factors associated with changes in transcription during Q fever.

Temporal studies were made of factors associated with increased RNA synthesis in guinea pig liver during Q fever. DNA-dependent RNA polymerase activities increased immediately after infection. The major distribution of RNA polymerase classes shifted from class II to class I during infection. Ornithine decarboxylase activity was induced or stimulated soon after infection and remained elevated throughout the four-day period studied. S-Adenosylmethionine decarboxylase activity increased on the first day after infection and subsequently declined. Concomitantly elevated concentrations of the polyamines putrescine, spermidine and spermine reached a maximum on the first day after infection and then decreased. A model is presented to integrate these and other results to explain how RNA synthesis may be regulated during infection.

Effect of polychlorinated biphenyls (Phenoclor DP6) on in vivo protein and RNA synthesis in rat liver.

The results obtained from this study indicate that DP6 ingestion increases the protein synthesis in microsomal membrane fraction from rat liver. However, the nature of the relation between DP6 and RNA metabolism is still not clear, Our experimental procedure does not study all types of RNA involved in the protein synthesis mechanism. However, the increased incorporation of3H-orotic acid into the soluble RNA from DP6 fed rats suggests that this fraction participates in the stimulatory effect of DP6 ingestion.

Anabolism versus catabolism of [5-3H]uridine and its relationship to ribonucleic acid labelling in mouse liver after partial hepatectomy

The balance between anabolism and catabolism of [5-(3)H]uridine was studied in the mouse after partial hepatectomy. Labelling of RNA and UDP-glucose was determined and evaluated in relation to changes in the specific radioactivity of UTP. The amounts of labelled catabolic products of uridine were increased several-fold in liver and blood after partial hepatectomy. The specific radioactivity of RNA decreased to about 60% of the control value at 6h and was in the same range as that of control liver at 24h after operation. Decreased labelling of RNA and UDP-glucose was attributable to decreased specific radioactivity of UTP. No changes in the size of the UTP pool or in the balance between uridine anabolism and catabolism were found that could explain the decreased specific radioactivity of UTP. Rather, the alterations in the labelling of this metabolite induced by the partial hepatectomy may be related to decreased phosphorylating capacity in the liver cells and/or dilution of the labelled precursor in an expanded uridine pool. The enhanced amounts of uridine catabolic products in liver and blood were probably a consequence of accumulation and altered incorporation of the metabolites from the blood into the liver cells. Despite the increased amounts of labelled catabolic products and the decreased labelling of RNA, the results reported here actually suggest decreased uridine catabolism and slightly increased RNA synthesis in mouse liver after partial hepatectomy. The results stress the importance of proper controls in determination of nucleic acid synthesis and in metabolic studies by use of labelled precursors.

The Role of Cortisone Acetate in Liver RNA Synthesis of Gamma-irradiated Rats

The possible role of induced endogenous glucocorticoid levels stimulated by ionizing radiation and their subsequent effect on rat-liver RNA was investigated in adrenalectomized rats using an intraperitoneal injection of cortisone acetate immediately prior to exposure to gamma-radiation (1800 rad). Adrenalectomized rats were divided into four groups: (1) control rats, (2) irradiated rats, (3) nonirradiated rats treated with cortisone acetate (10 mg/rat), and (4) irradiated rats which received cortisone acetate immediately before irradiation. Newly synthesized RNA was measured by an intraperitoneal injection of 8 muCi (6-14C) orotic acid either immediately after irradiation or 40 min prior to killing. All the rats were killed 6 hours post-irradiation. The results of these investigations indicate that (1) newly synthesized (40 min labelling) RNA increased in irradiated adrenal-intact rats, but not in adrenalectomized animals; (2) cortisone acetate by itself stimulated RNA synthesis whether the radioactive precursor was administered 6 hours of 40 min prior to killing; and (3) irradiation of adrenalectomized rats pre-treated with cortisone acetate induced more RNA synthesis than did cortisone alone. The results of this study support the suggestion that ionizing radiation may induce rat-liver RNA synthesis, at least in part, via stimulated adrenal secretion of glucocorticoids.

Inhibitory by d,1-methadone of RNA and protein synthesis in neonatal mice: Antagonism by naloxone or naltrexone

Neonatal mice were injected once daily with d,1-methadone in a dosage of 2 mg/kg. The remaining half of the litter was injected with saline. After one week the incorporation of labeled uridine and labeled leucine was significantly (P < 0.05) reduced in skeletal muscle. Longer treatment with methadone impaired RNA and protein synthesis in liver, heart, skeletal muscle and brain. The percentage reduction in RNA was log-dose related. When methadone was discontinued for 1 week following 4 weeks of treatment, incorporation of precursors into RNA and protein was found to be normal. A specific opioid effect is suggested by the finding that naltrexone or in part, nalaxone, given concomitantly with the methadone prevents development of the biochemical lesion.

RNA metabolism and poly(A) distribution in mouse liver following administration of dimethylnitrosamine

Dimethylnitrosamine (DMNA) strongly inhibited RNA synthesis in mouse liver under conditions when the nucleotide pattern, rate of nucleotide synthesis and phosphorylation ratio were unaffected. (An unidentified, probably non-nucleotide, component in the acid-soluble liver fraction was selectively reduced.) The inhibition of RNA synthesis was associated with a decrease in the RNA polymerase activity of isolated liver nuclei, well established already 45 min after DMNA administration. The reduced activity included both Mg 2+- and Mn 2+/(NH 4) 2SO 4-stimulated polymerase functions. The inhibition in vivo involved the whole complement of RNA, including poly(A)-containing RNA and isolated poly(A) sequences. The transfer of labelled RNA from the nucleus to the cytoplasm was not impaired. There was no detachment of poly(A)-containing RNA from the microsomes, and the proportion of tightly membrane-bound microsomal RNA and poly(A) sequences was not reduced as determined by use of a flotation technique. No breakage or shortening of the poly(A) chains was indicated by sedimentation analysis.