RNA Synthesis In Rat Liver Research Articles

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.

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.

Effect of cycloheximide on the nucleolar RNA synthesis in rat liver. Changes in RNA polymerase I and nucleolar template activity.

Effect of cycloheximide on the nucleolar RNA synthesis in rat liver. Changes in RNA polymerase I and nucleolar template activity.

Mitochondrial RNA synthesis in rat liver: Dependence on nuclear and cytoplasmic systems

The synthesis of mitochondrial RNA (mitRNA) in rat liver after inhibition of nuclear genome expression by actinomycin or of cytoplasmic protein synthesis by cycloheximide has been studied. Both drugs cause an inhibition of mitRNA synthesis. The suggestion is made that mitRNA synthesis is under nuclear control through the synthesis of some protein coded for by the nuclear genome.

Effect of allylisopropylacetamide on Nuclear Ribonucleic Acid synthesis in rat liver.

The porphyrogenic drug allylisopropylacetamide, a potent inducer of delta-aminolaevulinate synthetase, specifically increases nucleoplasmic RNA synthesis in rat liver. The drug-mediated increase in nucleoplasmic RNA synthesis is blocked by cycloheximide and haemin, which also inhibit the enzyme induction.

RNA synthesis in rat liver after cortisol treatment: a possible mitochondrial-nuclear relationship.

ABSTRACT Liver mitochondrial RNA synthesis (as measured by an RNA polymerase assay) in adrenalectomized ovariectomized rats increased (42 %) 1 h after injection of 0.5 mg cortisol/100 g b. wt. Nuclear RNA synthesis increased (130–171 %) 4 h after injection of 4 mg cortisol/100 g but did not increase after treatment with the lower dosage of cortisol after 4 h. There was no effect on the nuclei from either 0.5 or 4 mg cortisol after 1 h. If either ethidium bromide, rifampicin or actinomycin D were injected 10 min before the hormone injection, a complete inhibition of the hormonal action on mitochondrial RNA synthesis was found. On the other hand, nuclear RNA synthesis was partly inhibited if either ethidium bromide or rifampicin preceded the hormone injection. Actinomycin D inhibited nuclear RNA polymerase below the saline control level. Assuming that ethidium bromide and rifampicin act specifically on mitochondrial RNA synthesis, it would appear that there is a mitochondrial component to the RNA synthesis measured in the nucleus after cortisol treatment.

Circadian rhythm of rna synthesis in rat liver: effect of protein synthesis-inhibiting antibiotics at different times of day

1. 1. The content of free nucleotides and nucleosides, determined by u.v. measurement, did not change significantly during 24 hours. 2. 2. The antibiotics cycloheximide, pactamycin, puromycin and fusidic acid inhibited [ 3H]leucine incorporation into rat liver proteins by about 90%: in the case of cycloheximide and pactamycin the effect continued at least over 3 or 4 hours, whereas even high doses of puromycin and fusidic acid were effective not longer than 90–150 minutes. 3. 3. When protein synthesis was inhibited by these antibiotics, [ 3H]uridine incorporation into three RNA fractions at 0700 and 1100 hours was altered: at 0700 hours, the labeling of the 65° C fraction was increased in all cases. At 1100 hours a relative decrease in the labeling of the 65° C fraction and a relative increase in the 4° C fraction could be observed. Puromycin had no effect at that time of day. 4. 4. Two hours after an injection of cycloheximide at 0700 hours the content of RNA in the nucleus increased, but remained at the normal level at 1500 hours. In both cases a pronounced increase followed by a decrease of the nuclear RNA content occurred within the first 60 minutes. 5. 5. The results support the assumption that protein-associated transport processes or permeabilities are involved in the circadian pattern of RNA labeling.

Inhibition of Rat Liver RNA Synthesis by Aflatoxin B1

THE administration to rats of aflatoxin B1, a potent hepatotoxin and carcinogen, rapidly results in an inhibition of both hepatic RNA synthesis in vivo1 and Mg2+ and Mn2+—(NH4)2SO4 stimulated RNA polymerase activities, assayed in vitro2,3. Previous work has demonstrated that the RNA polymerase enzyme, isolated from hepatic nucleic whose in situ polymerase activity was inhibited by previous administration of aflatoxin B1 to the animals has an activity equal to that of enzyme isolated from control tissues3,4. The enzyme was solubilized by incubating the nuclei in a low-salt medium, which predominantly extracts the nuclear polymerase enzyme. We have now carried our further experiments using the more vigorous technique of ultrasonication in a high-salt medium5 which solubilizes both the nucleolar and nucleoplasmic enzymes, and have separated the enzymes by gel filtration6.

N-methyl- N-nitrosourea induced changes in the labeling by [ 14C]orotate of RNA and acid-soluble fractions in rat kidney and liver

A single dose of N-methyl- N-nitrosourea (NMU) (100 mg/kg) reduces the labeling by [ 14C]orotate of rat kidney RNA by 40%, the maximum effect being reached at 1.5–3 h. The analysis of the acid-soluble pool revealed that this effect is due to an inhibition of the uptake of [ 14C]orotate into rat kidney. The decrease in the labeling by [ 14C]orotate of liver RNA is less marked and could be shown to result from an interference of NMU with the synthesis of pyrimidine nucleotides in the precursor pool. It is concluded that sublethal doses of NMU, although depressing DNA and protein synthesis, do not affect RNA synthesis in rat liver and kidney.

Sequential stimulation of extranucleolar and nucleolar RNA synthesis in rat liver by cortisol

Sequential stimulation of extranucleolar and nucleolar RNA synthesis in rat liver by cortisol

Differential effects of growth hormone and hydrocortisone on nuclear RNA synthesis in rat liver.

RNA has been isolated and fractionated from rat liver nuclei by a sequence of salt extractions into four subfractions: namely nucleoplasmic, deoxyribonucleoprotein-associated, ribonucleoprotein-associated, and nucleolar fractions.Study of 14C-methyl-methionine labeling indicates that the nucleolar RNA fraction isolated by the present procedure is, in fact, of nucleolar origin while the other three fractions are essentially of extranucleolar origin.The effects of growth hormone and hydrocortisone on the nuclear RNA synthesis have been further studied using the present isolation and double-labeling techniques. Both hormones cause an increase in the incorporation of labeled orotic acid into all types of RNA in all four nuclear subfractions. However, the stimulatory effect of growth hormone is found mainly in the 18–28 S and 45–60 S regions of the nucleolar fraction and in regions of the entire gradient of the nucleoplasmic fraction, whereas the stimulatory effect of hydrocortisone is localized mainly in the 10–28 S regions of the nucleolar fraction and in the 4 S and 10–18 S regions of the ribonucleoprotein fraction.The present report suggests that there are qualitative as well as quantitative differences in the action of growth hormone and hydrocortisone on the synthesis of RNA in liver nucleus. The mode of action of the two hormones is discussed.

Effects of cortisone on orotic acid transport and RNA synthesis in rat liver

The present studies evaluated hormonal effects upon cellular transport processes and upon pyrimidine nucleotide and RNA metabolism. Adrenalectomized rats which had received a single dose of 5 mg cortisone acetate per 100 g body weight intraperitoneally were sacrificed at various times thereafter; in each instance, radioactive orotic acid was administered 20 min prior to sacrifice and the total radioactivities as well as the specific activities of the total acid-soluble UMP fraction, RNA, and RNA-uracil were determined. It was found that, in addition to glucocorticoidal acceleration of nucleotide incorporation into RNA (representing RNA synthesis), over half of the hormonally enhanced incorporation into RNA reflect the increased specific activities of the uracil precursors of the acid-soluble pool. Furthermore, indirect evidence indicates that the hormonally induced increase in the specific activities of the acid-soluble uridine nucleotides was due neither to a change in the size of the pool nor to an increased rate of conversion of 3H-orotate to uracil nucleotides, but rather was due to an hormonally enhanced transport of the 3H-orotate precursor into the liver. Studies on the rate of disappearance of various labeled RNA precursors from the acid-soluble fraction indicate that the radioactivity of orotic acid had a half-life of about 8 hr for cortisone-treated animals, and 12 hr for controls. On the other hand, the half-life for the disappearance of radioactivity of uridine and guanine were only 30 and 70 min respectively, and were independent of hormone treatment. Orotic acid is, therefore, most useful in long-term incorporation studies; whereas, uridine and guanine, essentially pulse-labeling in nature, are best utilized for RNA turnover studies. With identical 20-min pulse-labeling incorporation periods, the incorporation efficiency into RNA for orotic acid was 15-fold that of uridine and 5-fold that of guanine.

Effect of cycloheximide on the nucleolar RNA synthesis in rat liver

Within 15 minutes of administration of cycloheximide, an inhibitor of protein biosynthesis, the synthesis of nucleolar 45 s RNA in rat liver begins to be suppressed. The suppression increased almost linearly up to 60 minutes, when the synthesis is inhibited by approximately 70%. The inhibition, however, does not exceed 80% even after three hours. The synthesis of extranucleolar nuclear RNA, on the other hand, is not inhibited at least up to 60 minutes, after which time gradual inhibition occurs. The intranucleolar pool of 45 s RNA decreases rapidly followed by the decrease of the 35 s † † This RNA species is most probably the same entity as the 32 s RNA described for HeLa cells (Penman, Smith & Holtzman, 1966). Since the S value varies depending upon the ionic strength and pH (Fujisawa & Muramatsu, 1968), and the position is apparently closer to 35 s in our system, we have used in this paper the terminology as originally described by Scherror & Darnell (1962). intermediate pool, suggesting that the processing of the 45 s RNA is not appreciably decelerated for some time after the cessation of protein synthesis. In vitro study revealed the inhibition of DNA-dependent RNA polymeraso activity in the nucleolar preparation isolated from rats treated with cycloheximide but little inhibition was noted for the activity of the extranucleolar nuclear fraction from the same sources. These observations suggest the presence of some short-lived protein(s) required for the normal level of transcription of the nucleolar genes.

Effects of cortisone on ribosomal RNA synthesis in rat liver.

The early and long-term effects of cortisone on rat liver ribosomal RNA synthesis have been studied. Because of difficulties in estimating precursor pool sizes, methods have been employed which do not require estimation of rates of synthesis from rates of radioactive precursor incorporation. It is shown that a single large dose of cortisone—even in animals with intact adrenal glands—results in at least a doubling of the rate of ribosomal RNA synthesis over the ensuing 16 hr. In contrast to the effects of a single dose, repeated administration of the hormone does not result in a sustained stimulation of ribosomal RNA synthesis; the rates of turnover of liver ribosomal RNA in normal animals and in animals receiving large doses of hormone daily over a 2-week period are not appreciably different. (Endocrinology 86: 1033, 1970)

Zn 2+-Induced stimulation of nuclear RNA synthesis in rat liver

Zn 2+-Induced stimulation of nuclear RNA synthesis in rat liver

Effects of Prednisolone on Growth and Nucleic Acid Metabolism of Pekin Ducks

INTRODUCTIONTHE adrenal corticosteroids are being used extensively for many therapeutic purposes. Although many gross effects are well known, their primary site or sites of action have not been elucidated. The results of numerous in vivo and in vitro experiments in recent years indicate rapid changes in nucleic acid metabolism after corticosteroid treatment.It has been established that corticosteroids stimulate protein synthesis within the liver (Weber et al., 1965), but depress protein synthesis and increase protein catabolism in extrahepatic tissues (Bethell et al., 1965). Effects of Cortisol treatment on increased RNA synthesis in rat liver was observed within 2–3 hours, followed 4–10 hours by increased protein synthesis (Lang and Sekeris, 1964). In tissues known to involute in response to glucocorticoids, e.g., the spleen and thymus, the synthesis of RNA was depressed (Feigelson, 1964). The rate of DNA synthesis was depressed by glucocorticoids to a greater degree than RNA…

Effects of aflatoxin B 1 on polysomal profiles and RNA synthesis in rat liver

1. Aflatoxin B 1, a known hepatocarcinogen, is found to induce polysomal disaggregation in rat liver. 2. The entry of [ 14C]orotic acid into liver RNA is also inhibited by this toxin. A significant inhibition is obtained at a dose as low as 6.5 μg per 100 g body weight and the inhibition seems to be almost complete at 150 μg per 100 g body weight. At lower doses the ribosomal RNA's showed greater susceptibility to inhibition than the smaller RNA species. 3. Aflatoxin B 1 did not inhibit an in vitro RNA synthesizing system containing rat-testicular RNA polymerase (nucleoside triphosphate: RNA nucleotidyltransferase, EC 2.7.7.6). 4. These results suggest that a metabolite of aflatoxin B 1 rather than the toxin itself is a binding inhibitor of DNA-dependent RNA synthesis.

The Rapid Acceleration of Hepatic Nuclear Ribonucleic Acid Breakdown by Actinomycin But Not by Ethionine

Abstract The effects of two different inhibitors of rat liver RNA synthesis, actinomycin D and ethionine, upon liver RNA metabolism have been studied and compared. Whereas ethionine administration leads to a relatively slow loss of about 30% of total nuclear RNA over a period of 12 to 16 hours involving the molecular species representative of the total pool, the administration of actinomycin D is followed by a rapid loss of recently labeled moieties of nuclear RNA. The pretreatment of animals with ethionine had no significant effect upon the loss of nuclear RNA induced by actinomycin D. The labeling of cytoplasmic RNA with orotic acid-6-14C was inhibited by each agent. It is considered probable that the different patterns of response of hepatic nuclear RNA to these two agents are a reflection of the different mechanisms whereby they inhibit RNA synthesis. It is concluded that compounds which bind to DNA, such as actinomycin D, have effects on nuclear RNA metabolism in addition to those resulting from the inhibition of RNA synthesis.

Stimulation of Rat Liver RNA Synthesis by Borate.

SummaryYoung rats on a diet containing not more than 0.001 ppm boron were used to study the effect of administered boric acid on the synthesis of nuclear liver RNA. A 30-min pulse of [6-14C]-orotic acid resulted in a higher incorporation of 14C in liver RNA when borate was given intraperitoneally. This increased incorporation was diminished when the diet contained 1 ppm boron as boric acid. An attempt to determine the effect of borate on the synthesis of liver DNA, using [6-3H]-thymidine, gave unsatisfactory results. It is apparent that borate increases the rate of synthesis of nuclear liver RNA.

Nuclear RNA synthesis in rat liver during the early stages of chemical carcinogenesis.

Nuclear RNA synthesis in rat liver during the early stages of chemical carcinogenesis.