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.

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.

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)

scholarly journals Loss and reappearance of gap junctions in regenerating liver.

1978 ◽  
Vol 78 (2) ◽  
pp. 554-564 ◽  
Author(s):  
A G Yee ◽  
J P Revel
Keyword(s):  
Gap Junctions ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Close Association ◽  
Freeze Fracture ◽  
Regenerating Liver ◽  
Bile Canaliculi ◽  
Zonulae Occludentes ◽  
Fracture Study

Changes in intercellular junctional morphology associated with rat liver regeneration were examined in a freeze-fracture study. After a two-thirds partial hepatectomy, both gap junctions and zonulae occludentes were drastically altered. Between 0 and 20 h after partial hepatectomy, the junctions appeared virtually unchanged. 28 h after partial hepatectomy, however, the large gap junctions usually located close to the bile canaliculi and the small gap junctions enmeshed within the strands of the zonulae occudentes completely disappeared. Although the zonulae occludentes bordering the bile canaliculi apparently remained intact, numerous strands could now be found oriented perpendicular to the canaliculi. In some instances, the membrane outside the canaliculi was extensively filled with isolated junctional strands, often forming very complex configurations. About 40 h after partial hepatectomy, very many small gap junctions reappeared in close association with the zonulae occludentes. Subsequently, gap junctions increased in size and decreased in number until about 48 h after partial hepatectomy when gap junctions were indistinguishable in size and number from those of control animals. The zonulae occludentes were again predominantly located around the canalicular margins. These studies provide further evidence for the growth of gap junctions by the accretion of particles and of small gap junctions to form large maculae.

scholarly journals A comparison of isometallothionein synthesis in rat liver after partial hepatectomy and parenteral zinc injection

1984 ◽  
Vol 217 (1) ◽  
pp. 85-92 ◽  
Author(s):  
K Cain ◽  
B L Griffiths
Keyword(s):  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Half Life ◽  
Intraperitoneal Injection ◽  
Time Course ◽  
Regenerating Liver ◽  
Unequal Distribution ◽  
Post Operation ◽  
Zinc Levels

The time course of hepatic zinc-isometallothionein synthesis was studied in the regenerating liver and compared with that produced after the parenteral injection of zinc (6 mg of Zn2+/kg). In the regenerating liver, zinc levels rose rapidly after partial hepatectomy and reached a maximum at approx. 14h before declining to approximately normal levels at 48h post-operation. During this 48h period most of the zinc was incorporated into metallothionein. Purification of the latter into the charge-separable isometallothioneins (i.e. MT1 and MT2) showed that, in the regenerating liver, there was an unequal distribution of zinc between the two isoproteins. Thus at operation the endogenous thionein had an MT2/MT1 ratio of 1; after regeneration this ratio increased, and all times during the time course there was more MT2 than MT1. In contrast, the intraperitoneal injection of zinc produced a biphasic uptake of zinc into the liver with maxima at 10h and 32h. During the first phase of zinc uptake, metallothionein synthesis increased rapidly and, unlike the regenerating liver, the MT2/MT1 ratio of 1 remained constant. Thereafter, this ratio increased in a manner analogous to that exhibited by the regenerating liver. Half-life determinations for thionein disappearance/degradation shows that MT2 and MT1 were degraded with half-lives (t1/2) of 26.18h and 16.44h respectively in the regenerating liver and 14.75h and 9.3h after zinc injection. Thus thionein disappearance/degradation in the regenerating liver was slower than that seen after zinc injection. However, in both situations MT2 was always removed at a slower rate than MT1. Calculation of the rates of thionein synthesis (assuming the above disappearance rates were constant throughout the time course) showed that, in the regenerating liver, the rate of MT2 synthesis was approximately twice that of MT1. This was not the case after zinc injection, where both isometallothioneins were synthesized in equal amounts. These results demonstrate that the rates of synthesis of MT2 and MT1 can be altered according to the metabolic status of the cell and suggest a specific role for MT2 during liver regeneration.

Turnover of ribosomal 28S and 18S rRNA during rat liver regeneration

1983 ◽  
Vol 3 (8) ◽  
pp. 781-788 ◽  
Author(s):  
Emil N. Nikolov ◽  
Mariane D. Dabeva
Keyword(s):  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
18S Rrna ◽  
Regenerating Liver ◽  
Experimental Procedure ◽  
Rat Liver Regeneration ◽  
Synthesis And Degradation

The turnover of 28S and 18S rRNA was studied in the course of 12 d after partial hepatectomy, including the proliferative (1st to 5th d) and post-proliferative (6th to 12th d) phases of liver regeneration. Turnover data, as the day-to-day rates of synthesis and degradation of 28S and 18S rRNA, were obtained by employing a suitable experimental procedure for the estimation of the increase of the amount of rRNA in the regenerating liver. It was found that 28S and 18S rRNA are accumulated into the cytoplasm and degraded at identical rates both in the proliferative and post proliferative phases. The turnover of both rRNA moieties is markedly slower during the first 3 d of liver regeneration.

Effects of methotrexate on rat liver regeneration after partial hepatectomy

1992 ◽  
Vol 82 (2) ◽  
pp. 181-184 ◽  
Author(s):  
Ikuyo Tsukamoto ◽  
Shosuke Kojo
Keyword(s):  
Liver Regeneration ◽  
Thymidine Kinase ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Dihydrofolate Reductase ◽  
Thymidylate Synthase ◽  
Liver Weight ◽  
Regenerating Liver ◽  
Dna And Rna ◽  
Immunoblotting Assay

1. Methotrexate was administered immediately after partial (70%) hepatectomy, resulting in complete inhibition of dihydrofolate reductase in 24 h-regenerating liver. 2. At 48 h and 72 h after partial hepatectomy, thymidylate synthase activity was increased, whereas thymidine kinase was inhibited, by the injection of methotrexate. The DNA and RNA contents and the liver weight were also reduced in methotrexate-treated rats. 3. The immunoblotting assay showed that methotrexate stimulated the synthesis of thymidylate synthase protein in 48 h-regenerating liver. At the same time, thymidylate synthase activity was directly inhibited by methotrexate. The mechanisms of inhibition of these enzymes by methotrexate appeared to be different.

scholarly journals Regulated transcription of c-Ki-ras and c-myc during compensatory growth of rat liver.

1984 ◽  
Vol 4 (8) ◽  
pp. 1493-1498 ◽  
Author(s):  
M Goyette ◽  
C J Petropoulos ◽  
P R Shank ◽  
N Fausto
Keyword(s):  
Dna Synthesis ◽  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Compensatory Growth ◽  
Chemical Injury ◽  
Regenerating Rat Liver ◽  
Regenerative Growth ◽  
Cellular Oncogenes

We examined the transcription of six cellular oncogenes during the process of compensatory growth in rat liver after partial hepatectomy. We have previously reported that transcripts of c-rasH are elevated during regenerative growth of the liver. We now report that transcripts of c-rasK and c-myc genes are significantly elevated after partial hepatectomy, whereas transcripts of c-abl and c-src are essentially unchanged and transcripts of c-mos are undetectable in either normal or regenerating rat liver. In liver regeneration after partial hepatectomy or chemical injury, changes in c-myc transcripts occur before DNA synthesis. The elevation of c-myc and c-ras transcripts is sequential in that highest levels of c-myc transcripts were detected 12 to 18 h after partial hepatectomy, whereas the levels of c-rasH and c-rasK were maximal by 36 to 48 h. Transcripts of all three activated oncogenes returned to their basal levels by 96 h.

NUCLEODEPOLYMERASE ACTIVITY IN REGENERATING RAT LIVER

1952 ◽  
Vol 30 (3) ◽  
pp. 180-184
Author(s):  
Roger Daoust ◽  
Gaston de Lamirande ◽  
Antonio Cantero
Keyword(s):  
Liver Injury ◽  
Enzymatic Activity ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Azo Dye ◽  
Time Intervals ◽  
Constant Amount ◽  
Average Cell ◽  
Regenerating Rat Liver

The desoxyribonucleodepolymerase and ribonucleodepolymerase activity has been estimated in rat liver at various time intervals following partial hepatectomy. When expressed per a constant amount of nitrogen of the tissue, as routinely done, the activity of these enzymes shows significant variations in regenerating rat liver. However, these variations are no longer evident when the enzymatic activity is recalculated “per cell” and it is concluded that they do not reflect actual variations of enzymatic activity in the average cell of the regenerating rat liver. Presumably, the increase in activity of the two nucleode-polymerases, previously observed in liver of rats fed p-dimethylaminoazobenzene, should be attributed to the liver injury by the azo dye rather than to the ensuing regeneration with ultimate hepatoma formation.

Enhanced production of dolichol, but not dolichyl phosphate, in the earliest stages of rat liver regeneration

1986 ◽  
Vol 6 (4) ◽  
pp. 409-413 ◽  
Author(s):  
M. Marino ◽  
G. Bruscalupi ◽  
S. Spagnuolo ◽  
S. Leoni ◽  
M. T. Mangiantini ◽  
...  
Keyword(s):  
Liver Regeneration ◽  
Partial Hepatectomy ◽  
Rat Liver ◽  
Physiological Significance ◽  
Regenerating Liver ◽  
Rat Liver Regeneration ◽  
Enhanced Production ◽  
Dolichyl Phosphate

The regenerating liver presents a changed ability to use mevalonate 16 hr after partial hepatectomy. The dolichol content and its synthesis from mevalonate is increased, while no variation of dolichyl-P and ubiquinone parameters are detectable. The greater amount ofmevalonate utilized to form dolichol, but not dolichyl-P, in this proliferating system, raises some questions about the physiological significance of these isoprenoid compounds and about their biosynthetic sequence.

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