Effect of urethan on polyamine and DNA synthesis in the regenerating rat liver

When a single dose of urethan was injected into the peritoneal cavity of rats immediately after partial hepatectomy, DNA synthesis was delayed by 12 h. The induction of ornithine decarboxylase which was induced biphasically following partial hepatectomy was also reduced and delayed by 14–15 h by the administration of urethan. S-Adenosylmethionine decarboxylase activity in urethan-treated rat liver at 20 h and 29 h after operation was significantly lower than that of untreated animals. This enzyme activity was shown to increase thereafter, reaching a higher level than in untreated rats at 37–42 h. Hepatic spermidine content changed biphasically in a manner similar to DNA synthesis. These results suggest that the activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase may correlate with DNA synthesis and that an increase of spermidine concentration is necessary to DNA synthesis.     

Effect of colchicine and vincristine on DNA synthesis in regenerating rat liver

The increases in the activities of hepatic thymidylate synthetase and thymidine kinase were significantly suppressed at 24 h after 70% partial hepatectomy in rats which had been administered a microtubule disrupter, colchicine or vincristine. The decrease of these enzymic activities was accompanied by a reduction of DNA content in 24 h regenerating liver. The immunoblotting assay showed that the depression of the thymidylate synthetase activity by the injection of colchicine or vincristine was due to the decrease of the enzyme protein. These results indicate that colchicine and vincristine inhibit the DNA synthesis during liver regeneration by inhibiting the induction of the key enzyme in DNA synthesis.     

DNA synthesis in the mono- and binuclear cells of regenerating rat liver after x-ray irradiation

The effect of X-irradiation on the dynamics of DNA synthesis during the S-period in bi- and mononucleated of regenerating rat liver was studied autoradiographically and microphotometrically. Rats were treated with X-rays at doses 3.84 X 10(-2), 15.48 X 10(-2), and 30.96 X 10(-2) Kl/kg 23 hours after a partial hepatectomy, and were sacrificed one hour after irradiation. In the control liver the rate of DNA synthesis was the lowest at the beginning of the S-period and the highest at the last quarter of this period in both mono- and binucleated cells. The irradiation results in the inhibition of DNA synthesis mainly at the end of the S-period depending on doses employed. This inhibition was the same in bi- and mononucleated cells. In addition, the increase of correlation of the 3H-thymidine incorporation rate and DNA content was found between nuclei of binucleated cells after irradiation.     

Effect of an exogenous energy source and amino acids on DNA synthesis in regenerating rat liver

Rats on a protein-free diet synthesized less DNA after partial hepatectomy than rats on a normal diet. In regenerating livers of animals on the protein-free diet, induction of several enzymes involved in the DNA precursor synthetic pathway, and especially ribonucleotide reductase, were depressed. When young rats were maintained solely by parenteral nutrition after partial hepatectomy, exogenous amino acids were more important than the exogenous energy source for induction of enzymes involved in synthesis of DNA and its pyrimidine nucleotide precursors. In particular, induction of ribonucleotide reductase appeared to be controlled by exogenous amino acids. Tryptophan, methionine, phenylalanine, leucine, valine, isoleucine and threonine seemed to stimulate the induction of this enzyme most after partial hepatectomy.     

Stimulating effect of histones on DNA synthesis in the regenerating rat liver]

Effect of exogenous histones, nuclear globulins and acid proteins on DNA synthesis is studied in regenerating liver of rats in which the synthesis of their own proteins and thus DNA replication are inhibited by cycloheximide. In these conditions histones from regenerating rat liver are found to stimulate 3H-thymidine incorporation into DNA of hepatectomyzed rat liver. Nuclear globulins and acid proteins from regenerating liver, and histones from intact liver produced no stimulating effect on DNA sythesis.     

Synchrony between DNA synthesis and thymidine incorporation into DNA in regenerating rat liver

DNA synthesis in regenerating liver was studied to determine whether the onset of stimulated DNA synthesis preceded the onset of increased incorporation of thymidine into DNA. Thymidine incorporation into hepatic DNA was not stimulated 15 h after operation, but was stimulated after 18 h; peak stimulation occurred 30 h after operation. Thymidine kinase activity was stimulated 24 h after operation; highest kinase activity was observed at 36 h. The onset of stimulated DNA synthesis was estimated by following the incorporation of labeled aspartic acid, sodium formate, adenine or orotic acid into appropriate DNA bases, viz., thymine, adenine, adenine or cytosine, respectively. Incorporation of adenine and orotic acid was stimulated between 15 h and 18 h after operation; incorporation of aspartic acid and sodium formate was stimulated between 18 h and 21 h after operation.The incorporation of thymidine into DNA was accelerated by stress stimulus and was inhibited by hydrocortisone. Changes in thymidine kinase activity also were correspondingly accelerated or delayed. Incorporation of labeled thymidine, adenine, formate, orotic acid or thymine into appropriate DNA bases, viz., thymine, adenine, adenine, cytosine or thymine, respectively, was stimulated by stress stimulus or was inhibited by hydrocortisone.It was concluded from these data that stimulation of DNA synthesis and of thymidine incorporation into DNA was essentially synchronized in regenerating rat liver. Results from this study were compared with results from similar studies in 2 other tissues, and the limitations, attendant with using thymidine incorporation into DNA as an indicator of stimulated DNA synthesis, were discussed.     

Effect of realimentation after several days' pure carbohydrate intake on DNA synthesis in regenerating rat liver

The authors studied the effect of realimentation after several days' isolated glucose or fructose intake on DNA synthesis in liver regenerating after partial hepatectomy (PH) (65-70%) or after carbon tetrachloride (CCl4) poisoning 1.5 ml/kg. Two days before PH or the administration of CCl4 and two days after, the experimental rats were given glucose (50% solution) of fructose (50% solution) as the only source of energy. Rats with PH were then fed for one day on a standard laboratory diet (25 cal% protein) or a high protein diet (81 cal% protein). Rats with CCl4 liver damage were fed for one day on the standard laboratory diet only. In the rats given glucose, liver DNA synthesis and the total amount of these nucleic acids in the liver 48 hours after CCl4 administration was lower than in the controls or the rats given fructose. In all the experimental groups (PH and CCl4), stimulation of liver DNA synthesis was observed after one day's realimentation. The total DNA content of the liver of rats with PH rose markedly during realimentation. The experiments indicate that the regenerative activity of damaged liver can be influenced by the nutritional regimen.     

Influence of clofibrate administration on the rate of synthesis of macromolecules in regenerating rat liver

Administration of the antihypercholesterolaemic drug clofibrate stimulates the rates of synthesis of nucleic acids and proteins in rat liver. The biosynthesis of mitochondrial proteins also is enhanced by the drug. In drug-fed animals, the rates of incorporation in vivo of radioactive precursors into DNA, RNA and proteins are stimulated even when the liver undergoes regeneration following partial hepatectomy. The rate of synthesis of mitochondrial proteins in the regenerative phase is higher in clofibrate-fed animals. These effects are consistent with the hepatomegalic and mitochondria-proliferating property of the drug.     

Effect of triiodothyronine or etiroxate on DNA synthesis in intact and regenerating liver

An increase in liver DNA synthesis (p less than 0.01) was found in rats with an intact liver 24 h after the administration of a single dose of triiodothyronine (200 micrograms/kg i.g.) Statistically significant stimulation of DNA synthesis was also found in rats given triiodothyronine (p less than 0.01) or etiroxate (p less than 0.05) for 3 days at 24-hour intervals. When a single dose of triiodothyronine was administered immediately after partial hepatectomy (65-70% resection of the liver), increased stimulation of DNA synthesis (p less than 0.01) was found 24 h after the operation. Etiroxate partly inhibited DNA synthesis (p less than 0.05). In rats given triiodothyronine at 24-h intervals, starting at the time of partial hepatectomy, DNA synthesis 72 h after the operation was double the value in the control group. Marked stimulation of DNA synthesis by triiodothyronine (p less than 0.01) and an increase in the total DNA content of the liver (p less than 0.05) were likewise found 48 h after partial hepatectomy if the hormone was administered once, 24 h after the operation. The increase in the two indicators after the administration of etiroxate was not statistically significant.     

Potential neural progenitor cells in fetal liver and regenerating liver

From unfractionated embryonic mice liver cells, appreciable amount of spherical bodies containing nestin-positive cells were generated in the presence of neuronal growth factors. Following cultivation on poly-d-lysine/laminin-coated slips, approximately 70% of the cells expressed neuronal markers, and 16% had long processes. Functional analysis of these long-process-bearing cells with the whole-cell patch clamp method showed an inward current in response to glutamate, GABA, and serotonin as the neuronal characteristics. Furthermore, regenerating liver in adult mice also contained nestin-positive cells to the same extent as fetal liver. Regenerating liver could have potential as a source of neural cells for autologous transplantation.     

Influence of cyclic AMP on DNA synthesis in slices of regenerating rat liver.

DNA synthesis in slices of regenerating rat liver is inhibited by adenosine cyclic 3',5'-monophosphate [cAMP]. The number of cells synthesizing DNA as assayed by 2-14C-thymidine incorporation is reduced by 65% in the presence of 10(-3) M cAMP. The inhibition of cAMP is not specific; other adenosine compounds, N6,O2,-dibutyryl adenosine 3',5'-monophosphate, 5'AMP and adenosine have the same effect. Moreover, the concentration of cAMP in the cell required for this inhibition is much higher than the normal levels of cAMP in liver cells.     

DNA synthesis in nuclei and nuclear matrices of regenerating rat liver: Effect of whole-body gamma irradiation

Summary Partial hepatectomy (PH) of rats (Wistar strain) resulted in acceleration of DNA synthesis in liver which reached a maximum at 36 h after PH. Whole-body radiation exposure (10 Gy) of the rats at 12 h after PH completely arrested this stimulation in DNA synthesis. The elevation of DNA synthetic rate in response to PH and complete obliteration of this stimulation by whole-body radiation exposure were found to be the reflection of levels of DNA polymerase-alpha in nuclei and nuclear matrices isolated from the rat livers. Studies based on assays of DNA polymerase in nuclei and nuclear matrices, with and without exogenous DNA template (activated calf thymus DNA), revealed that whole-body irradiation blocked induction of DNA polymerase-alpha and, in turn, assembling of DNA polymerizing apparatus. Irradiation of nuclei (suspended in buffer) in vitro at doses as high as 500 Gy did not have any inhibitory effect on DNA polymerase-alpha activitiy.     

Effect of an inhibiting factor isolated from rat liver on DNA polymerases in regenerating rat liver.

We partially purified an inhibitory factor (LIFE), isolated from 105,000 g supernatant of a saline adult rat liver homogenate. LIF stopped in vitro cell multiplication by blocking the G1--S transition, and reduced in vivo [3H]thymidine incorporation into liver DNA in two-thirds hepatectomized rats. This reduction in DNA synthesis was observed at 24 hr after hepatectomy, even when the LIF was injected before the beginning of the S phase, 10 hr after hepatectomy, i.e. when DNA polymerase activity had not yet increased. Under these experimental conditions, LIF in vivo treatment prevented alpha DNA polymerase activity from increasing after partial hepatectomy, so that enzyme activity at 24 hr in LIF-treated rats decreased compared to the controls. No direct inhibitory effect of LIF on alpha DNA polymerase was detected. LIF did not affect beta DNA polymerase. These results suggest that LIF plays a part in controlling liver growth.     

Inhibition of in vivo DNA synthesis in regenerating rat liver following thermal injury

Hepatic repair and regeneration which is extremely important after thermal injuries can be inhibited by the acute inflammatory reaction. Since thermal injury initiates this acute inflammatory reaction, DNA synthesis was studied in the regenerating liver following this injury. In vivo incorporation of [3H]-thymidine into hepatic DNA, autoradiographic determination of a labeling index, and thymidine kinase activity were determined. Incorporation of [3H]-thymidine into hepatic DNA and labeling indices were markedly diminished at 24 hours if partial hepatectomy and thermal injury were carried out concurrently. After partial hepatectomy, the expected elevations in thymidine kinase activity were inhibited by the thermal injury (p less than 0.01) and elevation of serum fibrinogen, a marker of the acute phase reaction that normally follows thermal injury, was blunted by the partial hepatectomy (p less than 0.05). The combination of thermal injury and partial hepatectomy resulted in a greatly diminished DNA replicative response as compared to partial hepatectomy alone and suggests that multiplicative injury is more likely to result in multi-system failure.     

DNA synthesis and mitotic activity in cells of regenerating rat liver following x-irradiation in stages GO and Gl]

Effect of X-rays on DNA synthesis and mitotic activity of regenerating liver cells has been studied. The irradiation was performed at a dose of 630 rad before hepatectomy and 2.5 and 6 hours after the stimulation of liver. With the stimulated liver being irradiated, the number of cells synthetizing DNA and entering into mitosis was seen reduced almost twice, whereas DNA synthesis and entering into mitosis were delayed, resp., by 4 and 6 hours. Irradiation of liver before the stimulation brings about a delay in DNA synthesis and in start of mitosis by 2 and 4 hours, resp., without reducing the numbers of cells capable to synthesize DNA and to enter mitosis.