Regulatory effects of corticosterone on ornithine decarboxylase activity during liver regeneration in rats

AIMS: The regulation of ornithine decarboxylase (ODC) gene expression and enzyme activity by corticosterone during rat liver regeneration induced by partial hepatectomy (PH) was evaluated. METHODS: Bilateral adrenalectomies were performed on ether-anesthetized rats 3 days before PH. Corticosterone in sesame oil was injected subcutaneously to adrenalectomized rats. ODC mRNA, ODC protein and enzyme activity were detected by in situ hybridization, Western blot and high performance liquid chromatography (HPLC), respectively. RESULTS: The ODC mRNA levels, protein accumulation and enzyme activity were lower in the intact liver compared to the regenerating liver. After PH, mRNA levels were remarkably enhanced in all groups and peaked at 5 h post-PH, and presented a persistent increase only in adrenalectomy rats during the regeneration process. Corticosterone treatment resulted in a dose-dependent decrease in ODC mRNA content after 5 h post-PH. ODC protein accumulation in adrenalectomy rats was higher than that in sham-adrenalectomy rats, but it decreased in corticosterone-treated (10 mg/kg) rats until 24 h post-PH, with a strong decline seen in 40 mg/kg corticosterone-treated rats. ODC activity was rapidly promoted, and the highest levels were observed at 6 h after PH in all groups. After corticosterone treatment, the activities declined significantly at 6 h post-PH, with the lowest value found in the 40 mg/kg group. CONCLUSIONS: Corticosterone treatment results in dose-dependent decreases in ODC mRNA and enzyme protein both in the intact liver and the regenerating liver. The change in ODC activity is partially related to alterations of ODC mRNA and protein accumulation.     

Effects of ethanol and acetaldehyde on myocardial ornithine decarboxylase activity.

Intraperitoneal ethanol or acetaldehyde had no effect on myocardial ornithine decarboxylase activity in the rat. When given with propranolol there was a decrease in enzyme activity.In the isolated, perfused heart, high concentrations of acetaldehyde inhibited the enzyme activity, while ethanol had no effect.Ethanol or acetaldehyde had no direct effect on the cytosolic enzyme activity.It is suggested that ethanol or its metabolites both directly inhibit myocardial ornithine decarboxylase activity and indirectly stimulate it by catecholamine release. The inhibitory effect appears to be mediated through a diminished rate of synthesis of the enzyme.     

Changes in rat liver ornithine decarboxylase activity during ageing and effect of stimulation by dexamethasone

We have studied the ornithine decarboxylase activity in the liver of 1, 3 and 24 months old rats: such activity has a dramatic diminuation in the age range from 1 to 3 months, but the activity at 24 months is significantly higher than that at 3 months. The treatment with Dexamethasone causes a very remarkable elevation in the activity of ornithine decarboxylase, up to rates that are not significantly different for the three ages.     

The effect of isoprenaline and propranolol on rat myocardial ornithine decarboxylase.

The intraperitoneal injection of isoprenaline in rats caused an increase in myocardial ornithine decarboxylase activity which reached a maximum of about four times the control value one hour after the injection. The intraperitoneal injection of dl-propranolol had no effect on myocardial ornithine decarboxylase activity. The injection of dl-propranolol 30 min before the injection of isoprenaline almost completely prevented the effect of isoprenaline.     

Effect of captopril on isoproterenol-induced myocardial ornithine decarboxylase activity.

Polyamines are thought to play an essential role in cellular hypertrophy and proliferation. Ornithine decarboxylase (ODC) catalyzes the first and probably the rate-limiting step in biosynthesis of polyamines. In this study, we evaluated the pathophysiological role of the renin-angiotensin system in isoproterenol-induced cardiac hypertrophy, using myocardial ODC activity as an indicator of cardiac hypertrophy. Isoproterenol caused an eight-fold increase of myocardial ODC activity in normotensive Wistar rats within 4 h after injection. Captopril suppressed the induction of ODC by isoproterenol to two-thirds of the control level. These results indicate that the renin-angiotensin system may participate in the induction of myocardial hypertrophy by isoproterenol.     

The effects of hypertrophy,hypobaric conditions and diet on myocardial ornithine decarboxylase activity

Myocardial ornithine decarboxylase activity has been measured in the right and left ventricles of rats subjected to hypobaric conditions. Control normobaric groups included both free-fed animals and animals whose diet was restricted to that chosen by the hypobaric group.In normal animals, left ventricular ornithine decarboxylase activity is higher than right ventricular. A diminution in the intake of food causes a decreased myocardial activity of the enzyme. Hypoxia also appears to cause a transient decrease in activity distinct from the effects of anorexia. Hypertrophy of the right ventricle due to hypoxic pulmonary hypertension is associated with an increased ornithine decarboxylase activity in that ventricle.     

Effects of prostaglandins on ornithine decarboxylase activity in rat small intestine

Role of prostaglandins on feeding-associated induction of ornithine decarboxylase in small intestine was studied. Rats received intraperitoneal injection of either saline, or 16,16-dimethyl prostaglandin E₂, or TRY-200 (a stable prostaglandin I₂ analog), or refeeding, after a 44 hr-fast. Four hours later, mucosae from duodenum, jejunum, and ileum were scraped for subsequent measurements of enzyme activity of ornithine decarboxylase by a radiometric technique. Refeeding resulted in a profound induction of enzyme activity throughout the small intestine. Parenteral administration of prostaglandin I₂ also led to a significant induction with the level similar to refeeding. The stimulatory effect of prostaglandin I₂ was completely abolished by a specific and irreversible enzyme inhibitor, difluoromethylornithine. Prostaglandin E₂ had a similar but lesser effect than prostaglandin I₂ on the induction of the enzyme activity. Pretreatment with indomethacin, a cyclooxygenase inhibitor had no effect on feeding-associated enzyme induction. These results indicate that although exogenous prostaglandin I₂ appears to be a potent stimulant for ornithine decarboxylase activity in rat small intestine, endogenous prostaglandins seem to play little or no role in feeding-associated induction of ornithine decarboxylase.     

Hepatoprotective effect of Geranium schiedeanum against ethanol toxicity during liver regeneration

AIM: To evaluate the effect of an extract of Geranium schiedeanum(Gs) as a hepatoprotective agent against ethanol(Et OH)-induced toxicity in rats. METHODS: Male Wistar rats weighing 200-230 g were subjected to a 70% partial hepatectomy(PH); they were then divided into three groups(groups 1-3). During the experiment, animals in group 1 drank only water. The other two groups(2-3) drank an aqueous solution of Et OH(40%, v/v). Additionally, rats in group 3 received a Gs extract daily at a dose of 300 mg/kg body weight intragastically. Subsequently, to identify markers of liver damage in serum, alanine aminotransferase, aspartate aminotransferase, albumin and bilirubin were measured by colorimetric methods. Glucose, triglyceride and cholesterol concentrations were also determined. In addition, oxidative damage was estimated by measuring lipid peroxidation [using thiobarbituric-acid reactive substances(TBARS)] in both plasma and the liver and by measuring the total concentration of antioxidants in serum and the total antioxidant capacity in the liver. In addition, a liver mass gain assessment, total DNA analysis and a morpho-histological analysis of the liver from animals in all three groups were performed and compared. Finally, the number of deaths observed in the three groups was analyzed.RESULTS: Administration of the Geranium shiedeanum extract significantly reduced the unfavorable effect of ethanol on liver regeneration(restitution liver mass: PHEt OH group 60.68% vs PH-Gs-Et OH group 69.22%). This finding was congruent with the reduced levels of hepatic enzymes and the sustained or increased levels of albumin and decreased bilirubin in serum. The extract also modified the metabolic processes that regulate glucose and lipid levels, as observed from the serum measurements. Lower antioxidant levels and the liver damage induced by Et OH administration appeared to be mitigated by the extract, as observed from the TBARs(PH-Et OH group 200.14 mmol/mg vs PH-Gs-Et OH group 54.20 mmol/mg; P 0.05), total status of antioxidants(PH-Et OH group 1.43 mmol/L vs PH-Gs-Et OH group 1.99 mmol/L; P 0.05), total antioxidant capacity values, liver mass gain and total DNA determination(PH-Et OH group 4.80 mg/g vs PH-Gs-Et OH 9.10 mg/g; P 0.05). Overall, these processes could be related to decreased mortality in these treated animals.CONCLUSION: The administered extract showed a hepatoprotective effect, limiting the Et OH-induced hepatotoxic effects. This effect can be related tomodulating oxido-reduction processes.     

Effects of feeding, fasting, and caerulein treatment on ornithine decarboxylase in rat pancreas

Ornithine decarboxylase (ODC) is the rate-limiting enzyme in polyamine biosynthesis. We examined circadian variations in pancreatic ODC activity and time-course effects of caerulein in fed and fasted rats. Significant circadian variations in amount of ODC activity were observed. The highest values were obtained during the dark period (1855 +/- 406 pmoles CO2/h), and the lowest during the light period (359 +/- 84 pmoles CO2/h). Caerulein treatment induced hypertrophy and hyperplasia of the pancreas in fed rats; increases in pancreatic ODC activity preceded the rise in protein and DNA contents (447 +/- 44 pmoles CO2/h and 5573 +/- 893 pmoles CO2/h, 6 and 12 h after the first injection of caerulein, respectively). In fasted rats, pancreatic ODC activity was very low (149 +/- 37 pmoles CO2/h) and caerulein treatment induced a transient increase in this activity 12 h after the first injection; hypertrophy but not hyperplasia of the pancreas was observed. In caerulein-treated fasted rats, refeeding during the night following a 48 h fasting period was not enough to increase either ODC activity or DNA content. These findings demonstrate that nutritional status is an important factor in the regulation of ODC activity and, thereby, in caerulein-induced pancreatic growth.     

Lipid peroxidation and antioxidant defense systems in rat liver after chronic ethanol feeding

The effects of chronic ethanol feeding on hepatic lipid peroxidation, ascorbic acid, glutathione and vitamin E levels were investigated in rats fed low or adequate amounts of dietary vitamin E. Hepatic lipid peroxidation was significantly increased after chronic ethanol feeding in rats receiving a low-vitamin E diet, indicating that dietary vitamin E is an important determinant of hepatic lipid peroxidation induced by chronic ethanol feeding. No significant change was observed in hepatic non-heme iron content, but hepatic content of ascorbic acid and glutathione was increased by ethanol feeding. Both low dietary vitamin E and ethanol feeding significantly reduced hepatic alpha-tocopherol content, and the lowest hepatic alpha-tocopherol was found in rats receiving a combination of low vitamin E and ethanol. Plasma alpha-tocopherol was elevated after ethanol feeding, probably because of the associated hyperlipemia. Both the ratio of plasma alpha-tocopherol/plasma lipid and the red blood cell alpha-tocopherol were reduced by ethanol feeding. Furthermore, ethanol feeding caused a marked increase of hepatic alpha-tocopheryl quinone, a metabolite of alpha-tocopherol by free radical reactions. Ethanol feeding caused little changes of alpha-tocopherol and alpha-tocopheryl quinone content in mitochondria, whereas a striking increase in alpha-tocopheryl quinone was observed in microsomes. These data suggest that ethanol feeding causes a marked alteration of vitamin E metabolism in the liver and that the combination of ethanol with a low-vitamin E intake results in a decrease of hepatic alpha-tocopherol content which renders the liver more susceptible to free radical attack.     

Testosterone suppression of ornithine decarboxylase activity in rat Sertoli cells

The effect of testosterone on the induction of Sertoli cell ornithine decarboxylase (ODC) activity was investigated in highly purified cultures derived from testes of 20-day-old rats. Sertoli cell cultures were maintained in serum-free Ham's F-10 medium, with refeeding on days 2 and 4. Before refeeding on day 4, ODC activity was 7.4 U (1 U = 1 pmol 14CO2 released/mg protein.60 min at 37 C). After a medium change, ODC activity increased (41.6 U at 10 h; 180.0 U at 24 h) and then returned to near-basal activity (26.3 U) after 48 h. Simultaneous addition of testosterone (150 ng/ml; 5.2 X 10(-7) M) with the day 4 medium change suppressed the increase in ODC induction (7.53 U at 10 h, 91.6 U at 24 h). Addition of testosterone 24 h before refeeding resulted in greater inhibition of ODC induction (6.9 U at 10 h; 45.4 U at 24 h) than when added simultaneously. Other androgens, 5 alpha-dihydrotestosterone, androsterone, and 5 alpha-androstane-3 alpha,17 beta-diol, also suppressed induction of ODC, whereas 17 beta-estradiol was ineffective, illustrating the steroid specificity of the effect. Coadministration of the antiandrogens hydroxyflutamide or cyproterone acetate partially blocked the testosterone effect. Induction of ODC activity by ovine FSH (10 ng/ml) was also suppressed when Sertoli cells were cultured in the presence of testosterone (150 ng/ml) from the time of isolation. However, induction of ODC activity by (BU)2cAMP was uncompromised by testosterone. These results suggest that testosterone may repress ODC activity and, hence, polyamine biosynthesis in the Sertoli cell, but that cAMP, acting through the trophic hormone FSH, can overcome this suppression of putrescine biosynthesis. Intratesticular and hypophyseal modulation of polyamine biosynthesis may influence not only cellular processes in the Sertoli cell itself but also its role in spermatogenesis.     

大戟对血吸虫细胞鸟氨酸脱羧酶活性的作用

目的：通过观察大戟水提取液对日本血吸虫成虫细胞鸟氨酸脱羧酶活性的影响，研究其对该种细胞转化、增殖的作用。方法：在细胞接种1周后分别用浓度为10、20、30、40g/L的大戟水提取液处理24h ,然后用RPMI－1640加10％小牛血清的培养基培养。用分光光度法测定细胞鸟氨酸脱羧酶活性。结果：浓度为30g/L的大戟水提取液处理后第2、3周时细胞鸟氨酸脱羧酶活性显著增高。结论：大戟水提取液有一定促进日本血吸虫成虫细胞增殖的作用。     

Hormonal regulation of renal ornithine decarboxylase activity in the rat.

The regulation of the activity of the renal enzyme ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) was examined in the rat. In the intact animal adapted to a light/dark cycle of 14 hours and 10 hours, respectively, the level of renal ornithine decarboxylase activity was rhythmical and paralleled the diurnal rhythm in plasma corticosteroid concentration. Renal ornithine decarboxylase activity and plasma corticosterone were highest during the early hours of darkness and lowest during the hours of light. Following hypophysectomy, the level of renal ornithine decarboxylase activity declined rapidly and remained low and without a demonstrable diurnal rhythm. When pituitary hormone levels were temporarily restored in the hypophysectomized rat by the injection of pituitary extract, renal ornithine decarboxylase activity increased rapidly, reached a peak within 8 hours, and returned toward pre-injection levels by 12 hours. Exogenous growth hormone, ACTH and cortisol each increased renal ornithine decarboxylase activity in the hypophysectomized rat, with the highest levels of activity being achieved with growth hormone. Other pituitary hormones (FSH, LH, TSH and prolactin) were ineffective. After bilateral adrenalectomy, renal ornithine decarboxylase activity retained a rhythmical pattern similar to that observed in the intact rat, but the levels were increased. Growth hormone and cortisol increased renal ornitine decarboxylase activity in the adrenalectomized-hypophysectomized animal to the same extent as in the hypophysectomized animal, but ACTH was almost totally ineffective. These data suggest that the pituitary plays a major role in the regulation of renal ornithine decarboxylase activity in the rat, primarily through the rhythmical secretion of growth hormone and ACTH.     

Stimulation of hepatic and renal ornithine decarboxylase activity by selected amino acids

The activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis, increases after a protein meal. The effect of amino acid mixtures on hepatic and renal ODC activity and polyamine content was studied in postabsorptive and 72-hour fasted rats. Fasting decreased ODC activity in liver and in kidney by approximately 50%. Hepatic ODC activity increased tenfold 4 hours after intraperitoneal injection of either 1 g/kg of a synthetic mixture of 17 amino acids or of casein hydrolysate to fed rats and about 20-fold in fasted rats. Renal ODC activity increased four- and tenfold respectively. A mixture of glutamate, aspartate, and alanine at concentrations given in the hydrolysate reproduced the full amino acid effect. No amino acid was effective when given alone, nor were mixtures of the other amino acid constituents of the hydrolysate. Glutamate + alanine was ineffective as were glucose or various combinations of arginine, ornithine, aspartate and NH₃. Ornithine + glutamate or aspartate + glutamate were active but stimulated less than aspartate + glutamate + alanine. Hepatic and renal putrescine content increased in parallel with ODC activity. The data suggest that specific amino acids possess the full ODC-stimulating capability of a high quality protein and that polyamine synthesis is linked to urea cycle activity.     

Enhancement of ornithine decarboxylase activity in Ambystoma liver slices by ovine prolactin: an evaluation of possible mediators

Prolactin has been shown to increase the activity of ornithine decarboxylase in a variety of mammalian tissues and in the pigeon crop sac. This study demonstrates a similar effect of ovine prolactin on ornithine decarboxylase activity in liver slices taken from larval tiger salamanders (Ambystoma tigrinum). An evaluation of potential mediators of prolactin action in liver slices revealed that the effect of the hormone on enzyme activity was not blocked by ouabain, an inhibitor of the sodium pump reported to block other actions of prolactin. Oxytocin, which inhibits prolactin actions in A. tigrinum, blocked the increase in ornithine decarboxylase activity induced by prolactin. Since previous results had implicated inositol phospholipid turnover in oxytocin action, the effects of the calcium ionophore, A 23187, and of synthetic diacylglycerol were examined. Both agents blocked the increase in enzyme activity when they were combined with prolactin treatment. Verapamil, a calcium channel blocker, had a prolactin-like effect on the activity of ornithine decarboxylase, and the combination of prolactin and verapamil produced a stimulation of the enzyme that was no greater than that observed with either the drug or prolactin alone, suggesting that both agents might be acting via a common cellular pathway. The tentative hypothesis that prolactin acts via a mechanism which lowers intracellular calcium is suggested.