scholarly journals Effects of γ-irradiation on biosynthesis of different types of ribonucleic acids in normal and regenerating rat liver

1975 ◽  
Vol 146 (1) ◽  
pp. 41-51 ◽  
Author(s):  
G G Markov ◽  
G N Dessev ◽  
G C Russev ◽  
R G Tsanev
Keyword(s):  
Partial Hepatectomy ◽  
Rat Liver ◽  
Cellular Response ◽  
Specific Radioactivity ◽  
Regenerating Liver ◽  
Γ Irradiation ◽  
Ribonucleic Acids ◽  
New Genes ◽  
Regenerating Rat Liver ◽  
Different Types

1. The effect of γ-irradiation (4000rd) on the synthesis of ribosomal (pre-rRNA) and heterogeneous nuclear RNA (pre-mRNA) in normal and in regenerating rat liver was studied by using 40 min labelling with [6(-14)C]orotic acid. 2. Partial hepatectomy caused a sharp transient increase in the specific radioactivity of the endogenous low-molecular-weight RNA precursors in the livers of both normal and irradiated rats. Irradiation of intact animals did not affect the pool. 3. Irradiation enhanced the synthesis of pre-rRNA for at least 12h. The synthesis of pre-mRNA was also enhanced, but only in the first 3h after irradiation. 4. Partial hepatectomy strongly stimulated the synthesis of both pre-rRNA and pre-mRNA. 5. The synthesis of pre-rRNA was enhanced also in regenerating liver of animals irradiated before or after the operation. The conclusion can be drawn that the early increase in the synthesis of ribosomal RNA is a non-specific cellular response to different injuring factors. 6. The only case where irradiation caused an early inhibition of RNA synthesis was that of pre-mRNA in regenerating liver. This supports the hypothesis that ionizing radiation does not suppress the transcription per se but affects the mechanisms of activation of new genes (cellular programming).

DEOXYCYTIDYLATE DEAMINASE LEVELS IN REGENERATING RAT LIVER

1961 ◽  
Vol 39 (6) ◽  
pp. 1043-1054 ◽  
Author(s):  
D. K. Myers ◽  
C. Anne Hemphill ◽  
Constance M. Townsend
Keyword(s):  
Dna Synthesis ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Deoxyribonucleic Acid ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
High Level ◽  
Early Regeneration

Deoxycytidylate deaminase activity and net synthesis of deoxyribonucleic acid (DNA) in vivo were found to increase at approximately the same time during the early stages of liver regeneration. However, deaminase activity in the regenerating liver remained at a high level for 1 day after DNA synthesis had slowed down again during the later stages of regeneration. The increase in deaminase activity was restricted as a result of exposure to 600 r X radiation during early regeneration, but this effect only became evident 11–16 hours after the irradiation. Irradiation on the second day after partial hepatectomy, when deaminase levels in control regenerating livers were relatively constant, failed to affect the deaminase activity immediately but did produce a 40–50% decrease in activity 11–16 hours later. Other antimitotic agents, e.g., colchicine, had little effect on deaminase activity.

scholarly journals Increased synthesis of low-molecular-weight nuclear ribonucleic acids of rat liver after γ irradiation and hepatectomy

1975 ◽  
Vol 146 (2) ◽  
pp. 357-360 ◽  
Author(s):  
A Fónagy ◽  
E J Hidvégi
Keyword(s):  
Molecular Weight ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Orotic Acid ◽  
Low Molecular Weight ◽  
Polyacrylamide Gels ◽  
Γ Irradiation ◽  
Ribonucleic Acids

Incorporation of [3H]orotic acid into low-molecular-weight nRNA of rat liver, fractionated on polyacrylamide gels, increased 6-12h after partial hepatectomy and 6h after γ-irridation at 2000 R. The incorporation of orotic acid was particularly increased into the 4.5S, 5S and approx. 10S nRNA fractions. If the irradiation was given after 6h of regeneration and RNA was isolated from the nucleus 12h after hepatectomy then the incorporation of orotic acid into these low-molecular-weight nRNA components was greater than after hepatectomy or irradiation alone.

Cholesterol metabolism in regenerating liver of the rat

1985 ◽  
Vol 249 (6) ◽  
pp. G679-G684 ◽  
Author(s):  
F. J. Field ◽  
S. N. Mathur ◽  
D. R. LaBrecque
Keyword(s):  
Dna Synthesis ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Cholesterol Synthesis ◽  
Cholesterol Metabolism ◽  
Reductase Activity ◽  
Plasma Cholesterol ◽  
Regenerating Liver ◽  
Acyltransferase Activity ◽  
Regenerating Rat Liver

The regenerating rat liver was used as a model to investigate the necessity for new cholesterol synthesis prior to the onset of cell division. Plasma cholesterol levels in partially hepatectomized rats were significantly decreased 24 and 48 h after surgery compared with levels in sham-operated animals. Hepatic cholesteryl ester content was also significantly increased in livers from partially hepatectomized animals, but the hepatic content of unesterified cholesterol was not affected. Hepatic triglyceride content was significantly increased within 6 h after surgery in the regenerating liver. The triglyceride levels reached a peak at 24 h, and by 72 h they had decreased back to levels that were no different from control. In the regenerating liver, microsomal 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase activity was increased 12 h after surgery. The activity of this enzyme remained significantly elevated throughout the 72-h period after surgery. In contrast, 12 h after partial hepatectomy the rate of hepatic cholesterol synthesis was significantly lower than that observed in livers from sham-operated rats. An increase in the rate of cholesterol synthesis was not observed until 48 h after partial hepatectomy, some 32 h after the start of DNA synthesis. Microsomal acyl-CoA:cholesterol acyltransferase activity was unchanged except for a 28% decrease at 72 h after partial hepatectomy. The data suggest that new cholesterol synthesis is not a requirement prior to the initiation of DNA synthesis in the regenerating rat liver.(ABSTRACT TRUNCATED AT 250 WORDS)

RIBONUCLEASE ACTIVITY IN REGENERATING RAT LIVER

1967 ◽  
Vol 45 (7) ◽  
pp. 1021-1026 ◽  
Author(s):  
D. J. S. Arora ◽  
G. de Lamirande
Keyword(s):  
Enzymatic Activity ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Ribonucleic Acid ◽  
Ribonuclease Activity ◽  
Regenerating Liver ◽  
Early Stages ◽  
Regenerating Rat Liver ◽  
Ribonucleoprotein Particles

Ribonucleoprotein particles were isolated from sham-hepatectomized and partially hepatectomized animals. The levels of ribonucleic acid and of proteins, as well as the ribosomal ribonuclease activity, have been studied in regenerating liver at periods of 4, 8, 16, 36, and 72 hours after partial hepatectomy. The results showed that the amount of ribosomes in regenerating rat liver was not affected as compared with the level observed in sham-operated rats. However, a decrease of ribonuclease activity was noticed in the early stages of liver regeneration. The ribonuclease activity was practically negligible at 16 and 36 hours. Less than 50% of the enzymatic activity was regained at the 72-hour period after partial hepatectomy.Results show that the ribosomes from regenerating liver are more stable and the stabilizing factor seems to be the absence of ribonuclease.

scholarly journals Quantitative alterations in the nucleolar and nucleoplasmic ribosomal ribonucleic acids in regenerating rat liver

1982 ◽  
Vol 204 (1) ◽  
pp. 179-183 ◽  
Author(s):  
Mariana D. Dabeva ◽  
Kalin P. Dudov
Keyword(s):  
Quantitative Analysis ◽  
Rat Liver ◽  
Rrna Processing ◽  
Regenerating Liver ◽  
Ribonucleic Acids ◽  
Regenerating Rat Liver ◽  
Rrna Species ◽  
The Absolute ◽  
Pool Sizes

A quantitative analysis of the nuclear pre-rRNA (precursor to rRNA) and rRNA in normal and 12h-regenerating rat liver was carried out, and the absolute amounts of the identified pre-rRNA and rRNA species in the nucleolus and nucleoplasm were determined. Characteristic changes in the pre-rRNA and rRNA pool sizes in regenerating liver are found which reveal alternations in both pre-rRNA processing and nucleocytoplasmic transition of ribosomes.

Upregulation of Escherichia coli heat-stable enterotoxin receptor in regenerating rat liver

1994 ◽  
Vol 266 (5) ◽  
pp. G899-G906 ◽  
Author(s):  
D. W. Laney ◽  
J. A. Bezerra ◽  
J. L. Kosiba ◽  
S. J. Degen ◽  
M. B. Cohen
Keyword(s):  
Escherichia Coli ◽  
Mrna Expression ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Acute Phase ◽  
Chloride Secretion ◽  
Hepatocyte Proliferation ◽  
Heat Stable ◽  
Hepatocyte Regeneration ◽  
Regenerating Rat Liver

Guanylate cyclase C (GC-C) is a transmembrane protein that serves as a receptor for the recently characterized endogenous ligand guanylin and for Escherichia coli heat-stable toxin (STa). Binding of either guanylin or STa to intestinal GC-C results in net chloride secretion. Although GC-C is expressed in the rat intestine throughout life, its expression in the rat liver has previously been shown to occur only during the perinatal period. As a step toward elucidating the role of this receptor in the liver, we tested the hypothesis that GC-C mRNA expression could be induced in the adult rat liver following 1) partial hepatectomy, a stimulus for hepatocyte proliferation; 2) intraperitoneal carbon tetrachloride injection, a model of hepatocyte regeneration in the presence of inflammatory changes; and 3) subcutaneous turpentine injection, which generates an acute phase response without hepatocyte proliferation. We demonstrated expression of GC-C mRNA in the regenerating rat liver following either partial hepatectomy or CCl4-induced hepatic necrosis. We have also shown that GC-C mRNA expression occurred in association with an acute phase reaction. Coordinate with the expression of GC-C mRNA, there was upregulation of radiolabeled STa binding to liver plasma membranes prepared from turpentine-treated rats. Maximal expression of GC-C occurred in preparations enriched for the canalicular domain. Although the function of GC-C in the liver is unknown, localization to the canalicular domain would be consistent with a role for GC-C in hepatic chloride secretion, especially in the perinatal liver and during hepatocyte regeneration.

scholarly journals Post-transcriptional regulation of ribosome formation in the nucleus of regenerating rat liver

1983 ◽  
Vol 210 (1) ◽  
pp. 183-192 ◽  
Author(s):  
K P Dudov ◽  
M D Dabeva
Keyword(s):  
Rat Liver ◽  
Ribosome Biogenesis ◽  
Rrna Processing ◽  
Regenerating Liver ◽  
Regenerating Rat Liver ◽  
Rrna Species ◽  
Rrna Maturation ◽  
The Individual ◽  
Post Transcriptional Regulation

Kinetic experiments on RNA labelling in vivo with [14C]orotate were performed with normal and 12h-regenerating rat liver. The specific radioactivities of nucleolar, nucleoplasmic and cytoplasmic rRNA species were analysed by computer according to the models of rRNA processing and nucleo-cytoplasmic migration given previously [Dudov, Dabeva, Hadjiolov & Todorov, Biochem. J. (1978) 171, 375-383]. The rates of formation and the half-lives of the individual pre-rRNA and rRNA species were determined in both normal and regenerating liver. The results show clearly that the formation of ribosomes in regenerating rat liver is post-transcriptionally activated: (a) the half-lives of all the nucleolar pre-rRNA and rRNA species are decreased by 30% on average; (b) the pre-rRNA processing is directed through the shortest maturation pathway: 45 S leads to 32 S + 18 S leads to 28 S; (c) the nucleo-cytoplasmic transfer of ribosomes is accelerated. As a consequence, the time for formation and appearance of ribosomes in the cytoplasm is shortened 1.5-fold for the large and 2-fold for the small subparticle. A new scheme for endonuclease cleavage of 45 S pre-rRNA is proposed, which explains the alterations in pre-rRNA processing in regenerating liver. Its validity for pre-rRNA processing in other eukaryotes is discussed. It is concluded that: (i) the control sites in the intranucleolar formation of 28 S and 18 S rRNA are the immediate precursor of 28 S rRNA, 32 S pre-rRNA, and the primary pre-rRNA, 45 S pre-rRNA, respectively; (ii) the limiting step in the post-transcriptional stages of ribosome biogenesis is the pre-rRNA maturation.

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