TYROSINE–ALPHA-KETOGLUTARATE AMINOTRANSFERASE ACTIVITY IN RAT LIVER AFTER SPINAL CORD SECTION

Spinal cord section brings about early and late changes in rat liver tyrosine-alpha-ketoglutarate aminotransferase activity. Early effects (4 h after surgery): spinal cord section at C₇ level causes an unreactiveness of rat liver tyrosine-alpha-ketoglutarate aminotransferase both to endogenously and exogenously elevated plasma glucocorticoid levels. Induction of tyrosine–alpha-ketoglutarate aminotransferase by hydrocortisone administration is almost completely inhibited. This unreactiveness of the rat liver enzyme to hydrocortisone is not due to delayed resorption of hydrocortisone by the peritoneum as tested with [³H]hydrocortisone, to changes in the secretion of hypophyseal hormones or to changes in the levels of glucose in blood or liver. L₃ level section of the spinal cord or sham operation results in a stress-like enzyme pattern (an increase at 4 h with return to normal level at 24 h). The stress elevation of tyrosine–alpha-ketoglutarate aminotransferase at 4 h after the operation is absent in C₇ level sectioned rats. This effect is not due to a decreased plasma corticosterone level since it is 4.1-fold higher in C₇ level sectioned rats and 2.7-fold higher in sham-operated controls (as measured 2.5 h after the operation). Late effects (24 h after the surgery): C₇ level section of the spinal cord brings about a nine-fold increase in a tyrosine–alpha-ketoglutarate aminotransferase activity in animals with intact adrenals and three-fold increase in adrenalectomized rats at 24 h after the operation. This increase is abolished almost completely by cycloheximide, irrespective of the time of administration. Experiments with actinomycin D, injected at different times after C₇ level section have shown that there exists a period of higher sensitivity of the amino-transferase toward the antibiotic (lasting about 3 h), followed by a period of lower sensitivity (lasting 16 h or longer). These results can be explained by assuming the existence of two tyrosine-alpha-ketoglutarate aminotransferase mRNAs with different lifetime. A direct participation of the CNS in the changes in enzymic activity observed after section of the spinal cord above the segments innervating the liver is suggested.     

Studies on the mechanism of the stimulation of tyrosine aminotransferase activity in vivo by pyrimidine analogs: the role of enzyme synthesis and degradation

The pyrimidine analogs, 5-fluoroorotate and 5-azacytidine, have been shown to stimulate the basal level as well as the cortisone, tryptophan, and casein hydrolysate-induced levels of the rat liver enzyme, tyrosine aminotransferase. This stimulation was most marked in the case of dietary and hormonal induction when the analog was given 4–6 hr prior to the administration of the inducer. When tryptophan induced tyrosine aminotransferase, maximal stimulation by the analog occurred if it were given 2 hr prior to the administration of the amino acid. The optimal stimulatory dose of 5-azacytidine was 5 mg/kg body weight whereas 5-fluoroorotate gave its highest stimulation at a dose of 60 mg/kg. Of several orotic acid analogs tested, only the chloro-analog had an effect similar to the fluoro-congener.Utilizing quantitative immunochemical precipitation and pulse labeling in vivo, it was demonstrated that the administration of 5-fluoroorotate or 5-azacytidine at doses of 60 and 5 mg per kg, respectively, while causing a stimulation in the basal level of tyrosine aminotransferase, did not result in any change in the rate of enzyme synthesis. Furthermore, after cortisone induction of the enzyme, the delayed administration of these analogs caused either a further stimulation in the level of the enzyme or the maintenance of a high level while the enzyme activity decayed in animals not given the analogs. The rates of synthesis either showed no change or a decrease while the amount of enzyme was increasing. Prelabeling of the enzyme in vivo after induction with cortisone and followed by the administration of 5-fluoroorotate resulted in a marked decrease in the t$\text{1}\text{2}$ of the decay rate of the enzyme measured either by loss of radioactivity or by loss of enzyme activity. These studies suggest that these analogs act in some manner to prevent enzyme turnover by an inhibition of enzyme degradation.     

L-tryptophan inhibition of tyrosine aminotransferase degradation in rat liver in vivo

The administration of l-tryptophan to both intact and adrenalectomized animals results in a marked increase in the activity of tyrosine aminotransferase. Maximal increases in enzyme activity are stimulated by doses of l-tryptophan much lower than those required for maximal stimulation of tryptophan oxygenase activity in vivo. When l-tryptophan was administered to animals that had been given cortisone 5 hr earlier, a further sustained increase in enzyme activity was demonstrated. 5-Hydroxy-dl-tryptophan and indole administration in amounts equimolar to l-tryptophan also result in similar increases in activity whereas α-methyl-dl-tryptophan produces little or no increase.Utilizing pulse-labeling in vivo with quantitative immunochemical precipitation of tyrosine aminotransferase by specific antisera, it was demonstrated that the administration of tryptophan caused an increase in enzyme amount with no concomitant increase in the rate of enzyme synthesis. In animals given cortisone, subsequent injections of tryptophan caused the amount of enzyme to continue to increase while both the amount of enzyme in control animals, as well as the rates of synthesis in both tryptophan-treated and control animals, decreased in a parallel fashion. Prelabeling of tyrosine aminotransferase in vivo after the enzyme had been induced with cortisone demonstrated that the subsequent administration of tryptophan caused a marked inhibition in the decay of the radioactive enzyme, as well as in enzyme activity. These data support the proposal that the amino acid, tryptophan, has a special role both in the maintenance of hepatic protein synthesis and in the regulation of specific enzyme degradation in rat liver.     

Control of liver tyrosine aminotransferase expression: Enzyme regulatory studies on inbred strains and mutant mice

Studies on the genetic mechanisms in control of mouse liver tyrosine aminotransferase expression were of three general types: (1) studies on strain variance in endogenous enzyme activity and of various factors affecting the basal enzyme level, (2) purification of the enzyme and studies of its properties, and (3) studies of strain variance in enzyme regulation dealing primarily with glucocorticoid induction and with the starvation-induced enzyme adaptation. Tyrosine aminotransferase (l-tyrosine: 2-oxoglutarate aminotransferase, E.C. 2.6.1.5) was purified 400 to 600-fold from livers of C57BL/6J and DBA/2J inbred mice. Several of the properties of the mouse liver enzyme were similar to those known for the rat liver enzyme although the apparent K _m (l-tyrosine) was lower, calculated at 6.25×10^–4 M. Disc gel electrophoresis of the enzyme from 105,000 g supernatant fluid after induction by hydrocortisone indicated three bands of enzyme activity with strain variance in electrophoretic mobility between the C57BL/6J and DBA/2J mice. The administration of glucose to fasting C57BL/6J mice repressed the starvation-induced increase in enzyme activity, but did not prevent the hydrocortisone induction of enzyme activity. DEAE-cellulose chromatography of purified enzyme from fasting DBA/2J and C57BL/6J mice which had been labeled in vivo with C ¹⁴ -l-leucine revealed strain differences in the elution patterns for both enzyme activity and radioactivity. Two peaks of enzyme activity were detected in the enzyme preparations from fasting mice. The marked strain variance in the enzyme activity and the quantity of radioactivity associated with the first enzyme peak may indicate differential rates of protein turnover for different isozymic forms of tyrosine aminotransferase. Flumethasone, a potent difluoro synthetic glucocorticoid, was used in studies on the hormonal regulation of tyrosine aminotransferase in obese mutant mice of the C57BL/6J-ob strain. The obese mice are relatively insensitive to the action of adrenal glucocorticoids to cause liver enzyme induction.This paper was presented at a symposium entitled Genetic Control of Mammalian Metabolism held at The Jackson Laboratory, Bar Harbor, Maine, June 30–July 2, 1969. The symposium was supported in part by an allocation from NIH General Research Support Grant FR 05545 from the Division of Research Resources to The Jackson Laboratory.This investigation was supported in part by an allocation from the NIH General Research Support Grant FR 05545 from the Division of Research Resources to The Jackson Laboratory and in part by Institutional Grant IN-19 from the American Cancer Society to The Jackson Laboratory.     

Hormonal regulation of ornithine aminotransferase biosynthesis in rat liver and kidney.

The relative rates of ornithine aminotransferase (OAT) synthesis in vivo were studied by pulse-labeling rats with [4,5-³H]leucine, isolating the mitochondrial enzyme protein by immunoprecipitation with a monospecific antibody, dissociating the immunoprecipitates on sodium dodecyl sulfate-acrylamide gels, and determining the radioactivity in OAT. After 4 days of treatment with triiodothyronine (T₃), both the enzyme activity level and the relative synthetic rate of OAT in rat kidney were elevated over twofold. The level of hepatic OAT activity was unaffected by this treatment. Thyroidectomy caused a 50% drop in the basal level of OAT activity and synthesis in kidney but not in liver. Although the basal levels of activity and synthesis of both renal and hepatic OAT were unaffected by adrenalectomy, the glucagon induction of the enzyme in liver was enhanced by about one-third and the T₃ induction in kidney was suppressed 50% by this operation. After 4 days of treatment with estrogen, both the enzyme activity level and the relative synthetic rate of OAT in male rat kidney were elevated nearly 10-fold. Hepatic OAT activity and synthesis were unaffected by this regimen. Thyroidectomy almost completely abolished the estrogen induction of OAT in kidney. OAT induction by estrogen could be restored by treating thyroidectomized rats with T₃. Simultaneous administration of T₃ plus estrogen to intact rats produced a multiple effect, resulting in a striking 20-fold induction of renal OAT. Although administration of either T₃ or estrogen causes an increase in the synthesis of immunoprecipitable OAT protein in rat kidney, each of these hormones may induce OAT by a different mechanism.     

Induction of hepatic tyrosine aminotransferase mRNA by protein synthesis inhibitors.

Several protein synthesis inhibitors were as effective as the inducers hydrocortisone or cyclic AMP in elevating rat liver tyrosine aminotransferase mRNA levels when assayed in the wheat germ cell-free translational system. Cycloheximide, emetine, or puromycin increased this mRNA activity 6- to 7-fold within 4 h after in vivo administration. No increase in total hepatic mRNA levels or tryptophan oxygenase mRNA was found after treatment with these protein synthesis inhibitors. Furthermesults suggest that a short lived protein may specifically regulate the level of functional hepatic tyrosine aminotransferase mRNA or that ongoing translation of this mRNA is required for its degradation.     

Evidence for a dual effect of dibutyryl cyclic AMP on the synthesis of tyrosine aminotransferase in rat liver

A single injection of dibutyryl cyclic AMP (Bt2cAMP) into adrenalectomized rats results in rapid and proportionate increases in hepatic tyrosine aminotransferase catalytic activity and in the amount of functional mRNA coding for this enzyme. This effect is transient in that mRNATAT peaks at 0.065% of total poly(A)+RNA activity at 1 h and is back to the basal level of 0.012% in 2.5 h. Enzyme activity peaks at 2.5 h and is back to the basal level by 5 h. If Bt2cAMP is repeatedly injected (0, 1, 2.5, and 4 h), enzyme activity remains at maximal levels for 4 to 5 h, whereas changes in mRNATAT activity are identical with those observed in the single injected rats. The rate of tyrosine aminotransferase synthesis at 5.5 h in the multiply injected rats, a time when mRNATAT has already returned to the basal level, is 3 to 4 times greater than that in either control or singly injected rats at the same time (0.3% of total protein versus 0.07%) and is equivalent to the maximal rate seen 1 h after the initial injection of the cyclic nucleotide. Since the rate of synthesis is increased in proportion to the increase in enzyme catalytic activity, stabilization of the enzyme against degradation is excluded as an induction mechanism at this late time point. These responses are not due to differences in the metabolism of Bt2cAMP, and the effect depends on the presence of metabolically active derivatives of this nucleotide. It thus appears that Bt2cAMP induces the synthesis of tyrosine aminotransferase in rat liver in two distinct ways. One is pretranslational and involves a transient and rapid increase in mRNATAT activity. The second appears to involve a delayed but sustained increase in translation of a basal level of mRNATAT.     

Increase in hepatic tyrosine aminotransferase mRNA during enzyme induction by N6,O2'-dibutyryl cyclic AMP.

Tyrosine aminotransferase mRNA was quantitated by translation in a cell-free system derived from wheat germ followed by specific immunoprecipitation of the newly synthesized enzyme subunit. Hepatic poly(A)-containg RNA prepared from rats treated for 4 h with N6, O2'-dibutyryl cyclic AMP and theophylline was approximately 5.6 times more active in directing the synthesis of the tyrosine aminotransferase subunit relative to untreated controls. The overall template activity of the RNA prepared from control and cyclic AMP-treated animals was virtually identical, demonstrating that the cyclic nucleotide effect was specific for the tyrosine aminotransferase mRNA. At all times, after a single injection of dibutyryl cyclic AMP and theophylline, the increase in hepatic enzyme activity was accompanied by corresponding induction in the level of functional tyrosine aminotransferase mRNA. Other inducers of tyrosine aminotransferase, such as glucagon and hydrocortisone, also increased the level of tyrosine aminotransferase mRNA in proportion to their effect on enzyme activity. The RNA polymerase II inhibitor, alpha-amanitin, completely blocked the dibutyryl cyclic AMP-mediated increase in tyrosine aminotransferase mRNA activity. These studies demonstrate that, in intact animals, the induction of tyrosine aminotransferase activity by dibutyryl cyclic AMP can be completely accounted for by a corresponding increase in the level of functional mRNA coding for the enzyme.     

Liver proline oxidase activity and collagen synthesis in rats with cirrhosis induced by carbon tetrachloride

In rats treated with CCl₄ for 7 weeks, liver proline oxidase activity was drastically reduced 24 h after the initial administration of the toxic agent and remained low throughout the treatment period. This was accompanied by a larger accumulation of added proline in the incubation medium and a lesser release of ¹⁴CO₂ from [¹⁴C]proline during incubation.Collagen synthesis by liver slices of CCl₄-treated rats increased in proportion to proline concentration, a plateau being reached at 0.48 mM proline. The plateau did not occur within the range studied with liver slices of normal liver.Increased collagen synthesis in vitro was accompanied by increased deposition of collagen in vivo only during the first 3 weeks of CCl₄ treatment. No further increase in liver collagen content occurred thereafter. Discontinuance of CCl₄-administration was followed by a return to normal of proline oxidase activity and in vitro collagen synthesis within 2 weeks. Nevertheless, collagen content remained elevated.The results suggest that proline oxidase activity, together with the previously shown increased formation of proline from precursor amino acids, may control the amount of proline available for collagen biosynthesis; and that the rate of degradation of collagen, perhaps by collagenase, may determine the levels of collagen remaining after discontinuance of CCl₄-administration.     

Vitamin E up-regulates arachidonic acid release and phospholipase A2 in megakaryocytes

The alteration in calcium transport in the liver nuclei of rats orally administered carbon tetrachloride (CCl4) was investigated. Rats received a single oral administration of CCl₄(5, 10, and 25%, 1.0ml/100 g body weight), and 5, 24 and 48 h later the animals were sacrificed. The administration of CCl₄ (25%) caused a remarkable elevetion of calcium content in the liver tissues and the nuclei of rats. Liver nuclear Ca2+-ATPase activity was markedly decreased by CCl₄ (25%) administration. The presence of dibutyryl cyclic AMP(10^-4 and 10^-3 M) or inositol 1,4,5-trisphosphate (10^-6 and 10^-5 M) in the enzyme reaction mixture caused a significant decrease in Ca²⁺-ATPase activity in the liver nuclei obtained from normal rat, while the enzyme activity was significantly increased by calmodulin (1.0 and 2.0 g/ml). These signaling factor's effects were completely impaired in the liver nuclei obtained from CCl₄ (25%)-administered rats. DNA fragmentation in the liver nuclei obtained from CCl₄ -administered rats was significantly decreased by the presence of EGTA (2 mM) in the reaction mixture, suggesting that the endogenous calcium activates nuclear DNA fragmentation. The present study demonstrates that calcium transport system in the liver nuclei is impaired by liver injury with CCl₄ administration in rats.     

Activatory effect of regucalcin on hepatic plasma membrane (Ca2+-Mg2+)-ATPase is impaired by liver injury with carbon tetrachloride administration in rats

The alteration of the plasma membrane (Ca²⁺-Mg²⁺)-ATPase activity in the liver of rats administered orally carbon tetrachloride (CCl₄) solution was investigated. Rats received a single oral administration of CCl₄ (10, 25 and 50%, 1.0 ml/100 g body weight), and 3 or 24 h later they were sacrificed. CCl₄ administration caused a remarkable elevation of liver calcium content and a corresponding increase in liver plasma membrane (Ca²⁺-Mg²⁺)-ATPase activity, indicating that the increased Ca²⁺ pump activity is partly involved in calcium accumulation in liver cells. Moreover, the participation in regucalcin, which is an intracellular activating factor on the enzyme, was examined by using anti-regucalcin IgG. The plasma membrane (Ca²⁺-Mg²⁺)-ATPase activity increased by CCl₄ administration was not entirely inhibited by the presence of anti-regucalcin IgG (1.0 and 2.5 ug/ml) in the enzyme reaction mixture. However, the effect of regucalcin (0.25–1.0 uM) to activate (Ca²⁺-Mg²⁺)-ATPase in the liver plasma membranes of normal rats was not revealed in the liver plasma membranes obtained from CCl₄-administered rats. Also, the effect of regucalcin was not seen when the plasma membranes were washed with 1.0 mM EGTA, indicating that the disappearance of regucalcin effect is not dependent on calcium binding to the plasma membranes due to liver calcium accumulation. Now, the presence of dithiothreitol (5 mM) or heparin (20 ug/ml) caused a remarkable elevation of the plasma membrane (Ca²⁺-Mg²⁺)-ATPase activity in the liver obtained from CCl₄-administered rats. Thus, the regucalcin effect differed from that of dithiothreitol or heparin. The present study suggests that the impairment of regucalcin effect on Ca²⁺ pump activity in liver plasma membranes is partly contribute to hepatic calcium accumulation induced by liver injury with CCl₄ administration.     

Regulation of tyrosine aminotransferase messenger ribonucleic acid in rat liver. effect of cycloheximide on messenger ribonucleic acid turnover

Tyrosine aminotransferase messenger ribonucleic acid (mRNA) activity in rat liver was rapidly increased 3-6-fold following in vivo administration of hydrocortisone acetate, dibutyryladenosine cyclic 3',5'-phosphate, or the protein synthesis inhibitor cycloheximide. Treatment with the steroid hormone or cyclic nucleotide in combination with cycloheximide resulted in levels of tyrosine aminotransferase mRNA 10-20-fold greater than control values. These changes in mRNA activity were not accompanied by changes in albumin mRNA or total liver template activity. The rapid decline in tyrosine aminotransferase mRNA activity following cordycepin inhibition of de novo RNA synthesis was prevented by cycloheximide treatment. This protection was not observed when pactamycin was substituted for cycloheximide, demonstrating that the inhibition of protein synthesis per se was not responsible for the stabilization of tyrosine aminotransferase mRNA. Based upon the effects of cycloheximide and pactamycin on rat liver polysome structure, it is concluded that the cycloheximide-mediated increase in tyrosine aminotransferase mRNA activity is the result of stabilization of the mRNA molecule which renders the message less susceptible to inactivation and degradation in the cytoplasm. The action of cycloheximide is very specific for tyrosine aminotransferase, phosphoenolpyruvate carboxykinase, and probably several other mRNAs that code for minor liver proteins that turn over rapidly in response to hormonal or metabolic stimuli.     

Dibutyryl cyclic AMP increases the amount of functional messenger RNA coding for tyrosine aminotransferase in rat liver.

The administration of N6,O2-dibutyryl cyclic AMP and theophylline to adrenalectomized rats results in an increase in the amount of functional mRNA coding for tyrosine aminotransferase that can be isolated from liver. The induction of this specific mRNA, as quantitated in a mRNA-dependent reticulocyte lysate system, and using poly(A)+ mRNA extracted from total tissue and polysomes, is very rapid. Within an hour after the intraperitoneal injection of the cyclic AMP derivative there is a 5- to 7-fold elevation of functional mRNA coding for tyrosine aminotransferase (mRNATAT), and by 3 h this has returned to basal levels. In contrast, the 4- to 5-fold induction of tyrosine aminotransferase catalytic activity is maximal at 2 h and is still significantly greater than the basal level at 5 h. In the basal state, tyrosine aminotransferase mRNA codes for 0.019 +/- 0.003% of the protein synthesized in the in vitro system, whereas after cyclic nucleotide treatment this value 0.115 +/- 0.015%, hence the increase in mRNATAT activity is relatively specific. Cordycepin, at a concentration which prevents the accumulation in cytoplasm of poly(A)+ mRNA, completely blocks the increase in both the catalytic and mRNA activity of this enzyme. The marked increase in functional mRNA, the requirement for continued synthesis of poly(A)+ RNA, and the rapid induction and deinduction suggest that the cyclic nucleotide is enhancing specific mRNA synthesis and/or, processing, however an effect on mRNA degradation cannot be excluded.     

Translation of mRNA from rat-liver polysomes into tyrosine aminotransferase and tryptophan oxygenase in a protein-synthesizing system from wheat germ. Effects of cortisol on the translatable levels of mRNA for these two enzymes.

Messenger RNA was isolated from rat liver polysomes by phenol/chloroform extraction and subsequent oligo(dT)-cellulose chromatography. The mRNA was translated in a protein-synthesizing system in vitro derived from wheat germ. The system was optimized in respect to Mg2+ and K+. The presence of spermidine or spermine is necessary for the synthesis of polypeptides having molecular weights of over 20 000. In the absence of the bases only small molecular weight products are formed. The amount of protein synthesized is linearly dependent on the amount of mRNA added up to concentrations of 80 mug mRNA/ml. The synthesis of tyrosine aminotransferase and tryptophan oxygenase in the system in vitro has been demonstrated by specific immunoprecipitation and sodium-dodecylsulfate polyacrylamide gel electrophoresis of the precipitate with enzyme proteins as marker. The amount of specific product formed is linearly dependent on the amount of mRNA present. The amount of translatable tyrosine aminotransferase mRNA and tryptophan oxygenase mRNA increases after administration of hydrocortisone to adrenalectomized rats. At low doses of hormone (2 mg/100 g body weight) maximal values are observed at 4 h, control levels being reached at 6-8 h after hormone application. With higher doses of hydrocortisone (20 mg/100 g body weight) maximal values are attained at 6 h, tending to control levels 14 h after treatment. The enzyme activity curves are parallel to the mRNA curves, the peak of enzyme activity occurring 2 h after the peak of mRNA activity.     

Cationic liposomes-mediated plasmid DNA delivery in murine hepatitis induced by carbon tetrachloride

In order to elucidate the influence of hepatic disease stage on cationic liposomes-mediated gene delivery, we investigated the cationic liposomes-mediated plasmid DNA delivery with time in murine hepatitis induced by subcutaneous injection of CCl₄. Liver injury after injection of CCl₄ was confirmed by the determination of serum aspartate aminotransferase and alanine aminotransferase activities. Two kinds of liposomes constructed with N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethlylammoniumchloride and dioleylphosphatidylethanolamine (DOTMA-DOPE) or DOTMA and cholesterol (DOTMA-CHOL) were used for the gene-delivery vector. We determined luciferase activities in various organs after the intravenous administration of the lipoplexes. The CCl₄-treated mice administered with DOTMA-DOPE lipoplexes showed the more significant decreases of transgene expression in the liver and spleen at 18 hours after CCl₄ injection. On the other hand, the CCl₄-treated mice administered with DOTMA-CHOL lipoplexes showed a significant increase in the liver at 48 hours. In conclusion, our findings demonstrate that murine hepatitis induced by CCl₄ can influence cationic liposomes-mediated plasmid DNA delivery. The extent of influences was also affected by lipid contents. These results indicate the necessity of considering the timing and the formulation for gene therapy according to the disease stage.     

Hepatoprotective effect of Origanum vulgare in Wistar rats against carbon tetrachloride-induced hepatotoxicity

The effect of an aqueous extract of Origanum vulgare (OV) leaves extract on CCl₄-induced hepatotoxicity was investigated in normal and hepatotoxic rats. To evaluate the hepatoprotective activity of OV, rats were divided into six groups: control group, O. vulgare group, carbon tetrachloride (CCl₄; 2 ml/kg body weight) group, and three treatment groups that received CCl₄ and OV at doses of 50, 100, 150 mg/kg body weight orally for 15 days. Alanine amino transferase (ALT), alkaline phosphatase (ALP), and aspartate amino transferase (AST) in serum, lipid peroxide (LPO), GST, CAT, SOD, GPx, GR, and GSH in liver tissue were estimated to assess liver function. CCl₄ administration led to pathological and biochemical evidence of liver injury as compared to controls. OV administration led to significant protection against CCl₄-induced hepatotoxicity in dose-dependent manner, maximum activity was found in CCl₄?+?OV3 (150 mg/kg body weight) groups and changes in the hepatocytes were confirmed through histopathological analysis of liver tissues. It was also associated with significantly lower serum ALT, ALP, and AST levels, higher GST, CAT, SOD, GPx, GR, and GSH level in liver tissue. The level of LPO also decreases significantly after the administration of OV leaves extract. The biochemical observations were supplemented with histopathological examination of rat liver sections. Thus, the study suggests O. vulgare showed protective activity against CCl₄-induced hepatotoxicity in Wistar rats and might be beneficial for the liver toxicity.     

3-Alkynyl selenophene protects against carbon-tetrachloride-induced and 2-nitropropane-induced hepatic damage in rats

The aim of this study was to investigate the protective effect of 3-alkynyl selenophene (3-ASP) on acute liver injury induced by carbon tetrachloride (CCl₄) and 2-nitropropane (2-NP) in rats. On the first day of treatment, the animals received 3-ASP (25 mg/kg, p.o.). On the second day, the rats received CCl₄ (1 mg/kg, i.p.) or 2-NP (100 mg/kg, p.o.). Twenty-four hours after CCl₄ or 2-NP administration, the animals were euthanized, and their plasma and liver were removed for biochemical and histological analyses. The histological analysis revealed extensive injury in the liver of CCl₄-exposed and 2-NP-exposed rats, which was attenuated by 3-ASP. 3-ASP significantly attenuated (1) the increase in plasmatic aspartate and alanine aminotransferase activities and lipid peroxidation levels induced by CCl₄ and 2-NP; (2) the inhibition of δ-aminolevulinic dehydratase activity caused by 2-NP; and (3) the decrease in ascorbic acid (AA) levels and catalase (CAT) activity caused by CCl₄. AA levels and CAT activity remained unaltered in the liver of rats exposed to 2-NP. The protective effect of 3-ASP on acute liver injury induced by CCl₄ and 2-NP in rats was demonstrated.     

The role of messenger RNA in tyrosine aminotransferase superinduction: effects of camptothecin on hepatoma cells in culture

Camptothecin inhibited the hydrocortisone but not the insulin induction of tyrosine aminotransferase activity in hepatoma cells in culture. However, camptothecin did not cause “superinduction” of tyrosine aminotransferase activity even though it reportedly inhibits messenger RNA synthesis. In hydrocortisone pre-induced cultures, camptothecin treatment caused a rapid decline in tyrosine aminotransferase activity suggesting it did not block degradation of the enzyme. A comparison of actinomycin D with camptothecin indicated that some of the effects of actinomycin D on tyrosine aminotransferase activity may not be mediated through inhibition of messenger RNA synthesis.     

The effect of unilateral nephrectomy and sham operation on tyrosine content and activity of tyrosine aminotransferase in the rat

During the first four days after unilateral nephrectomy the free tyrosine content in plasma, liver and hypertrophic kidney was decreased by more than 50% as compared with the values observed in intact rat. After sham operation, the content of tyrosine was decreased to the same extent. The activity of tyrosine aminotransferase in liver was doubled two days after sham operation: no such increase was observed after unilateral nephrectomy. At the same time a decline of the enzyme activity in kidney was demonstrated after both types of surgery. Hydrocortisone in a single i.p. dose stimulated enzyme activity in the liver of intact rats three-fold, and more than four-fold after nephrectomy and sham operation. In kidney of intact rat, as a result of hydrocortisone treatment, the enzyme activity was doubled; it was, however, insensitive to this treatment after unilateral nephrectomy, and increased only by 20% after sham operation. It is suggested that the changes in tyrosine content and tyrosine aminotransferase activity observed after unilateral nephrectomy were not due to stress alone, but underwent regulation aimed at assuring a sufficient level of this amino acid for metabolism.     

Incorporation of radioactive- -aminolevulinic acid into microsomal cytochrome P 450 : selective breakdown of the hemoprotein by allylisopropylacetamide and carbon tetrachloride

Administration of allylisopropylacetamide (AIA) or CCl₄ to rats previously treated with phenobarbital leads to a rapid decrease in cytochrome P₄₅₀ within 1 hr. The amount of cytochrome b₅ and NADPH cytochrome c reductase in liver microsomes remains unchanged following AIA treatment. In contrast, CCl₄ administration causes a decrease in total microsomal protein thus leading to a net loss in cytochrome b₅ and NADPH cytochrome c reductase. By using ³H-δ-aminolevulinic acid to label microsomal cytochrome P₄₅₀ heme, the effect of AIA and CCl₄ on this cytochrome was shown to be caused by destruction of preexisting CO-binding pigment and not from inhibition of synthesis. In addition, the breakdown products of cytochrome P₄₅₀ heme accumulate in the liver after AIA or CCl₄ treatment.