Chloroform-induced multiple forms of ornithine decarboxylase: differential sensitivity of forms to enhancement by diethyl maleate and inhibition by ODC-antizyme

The role of glutathione (GSH) and ornithine decarboxylase-antizyme (ODC-AZ) in the regulation of the chloroform-mediated stimulation of rat hepatic ornithine decarboxylase (ODC) was investigated. We have previously implicated roles for each while examining the chloroform effect on crude cytosolic enzyme preparations. In this study we examined the effect of pretreatment with diethyl maleate (DEM), a GSH-depleting agent, on the chloroform stimulation of the two forms of the rat hepatic ODC enzyme and the sensitivity of these two forms to inhibition by the ODC-AZ. While the pretreatment with DEM provided a greater amount of the two forms of the ODC enzyme, it also resulted in a differential stimulation of each form when compared to chloroform alone. Additionally, Peak II was 20-25% more sensitive to the same amount of ODC-AZ then Peak I ODC activity.     

Effect of chloroform on hepatic and renal DNA synthesis and ornithine decarboxylase activity in mice and rats

Chloroform administered intraperitoneally (i.p.) to male mice and rats resulted in a dose-dependent increase in hepatic ornithine decarboxylase (ODC) activity. Maximal induction of the enzyme in mice was 10-fold and occurred at 375 mg/kg chloroform; in rats it was 52-fold and occurred at 750 mg/kg chloroform. Chloroform increased in mice and decreased in rats the rate of hepatic and renal DNA synthesis. Therefore, the induction of ODC activity in rat liver was not followed with an increase in DNA synthesis. The implications of these results to the proposed nongenetic mechanism of chloroform induction of hepatocellular carcinoma in mice and renal tumors in rats are discussed.     

Effect of diethyl maleate on the biliary excretion rate of infused sulfobromophthalein-glutathione

Diethyl maleate (DEM) was given intraperitoneally to rats in a dose (4.3 mmoles/kg) known to markedly decrease glutathione levels in liver. DEM induced a choleresis previously shown to be due to the osmotic activity of DEM conjugates (DEM-glutathione and subsequent metabolic products) excreted into bile. Coincident with the choleresis, the biliary excretory Tm for the infused glutathione conjugate of sulfobromophthalein (BSP-GSH) was depressed significantly. The data are interpreted as indicating that DEM-GSH conjugates compete with BSP-GSH conjugates for a canalicular carrier mechanism.     

Impairment of bromosulfophthalein hepatic transport and cholestasis induced by diethyl maleate in the rabbit

The present study was designed to investigate the effect of hepatic glutathione depletion induced by intraperitoneal administration of diethyl maleate (DEM) on the maximum biliary transport (Tm) and on the biliary excretion of bromosulfophthalein (BSP) in anaesthetized rabbits when the dye was perfused endovenously at doses exceeding Tm. The Tm of total BSP (BSPt) and that of conjugated BSP (BSPc) were significantly reduced after DEM administration whereas that of unconjugated BSP (BSPu) was markedly increased. A reduction in the biliary excretion of BSPt and BSPc, in the percentage of BSPc, in the cumulative excretion of BSPt and in the percent-dose recovery were also observed. However, no change in hepatic glutathione S-transferase activity was noted after DEM. The cholestasis observed following DEM administration coursed with falls in the biliary secretion of sodium, chloride and bicarbonate.     

Effect of fasting,diethyl maleate,and alcohols on carbon tetrachloride-induced hepatotoxicity

The effect of fasting, diethyl maleate treatment, and methanol, ethanol, iso-propanol, or tert-butanol treatment on carbon tetrachloride (CCl₄)-induced hepatotoxicity in male Sprague-Dawley rats was studied. A 24-hr fast and the administration of diethyl maleate were found to be equipotent and not additive in potentiating CCl₄-induced hepatotoxicity; this potentiation appeared to be due to a depletion of hepatic glutathione (GSH) levels. Concomitant diurnal variations in hepatic GSH content and in CCl₄-induced hepatotoxicity also suggested hepatic GSH involvement in CCl₄-induced hepatic damage. Whereas ethanol has been reported to potentiate CCl₄-induced hepatotoxicity and to lower hepatic GSH levels, the present study suggested that these effects are due to an ethanol-induced loss of body weight. Methanol, iso-propanol, and tert-butanol, on the other hand, show the same maximal potentiation of CCl₄-induced hepatotoxicity and do so without inducing a depletion of hepatic GSH content or producing a loss of body weight. In contrast to a previous report, however, methanol was found to be markedly less effective on an equimolar basis than either iso-propanol or tert-butanol in potentiating CCl₄-induced hepatotoxicity. The study suggests that GSH is an important modulator of CCl₄-induced hepatotoxicity and also suggests that methanol, iso-propanol, and tert-butanol, but not ethanol, potentiate CCl₄-induced hepatotoxicity by a mechanism that does not involve altered hepatic GSH levels.     

Induction of metallothionein by diethyl maleate.

Metallothionein (MT) is a sulfhydryl-rich protein whose levels are increased by administration of a variety of agents including metals, cytokines, and oxidative stress agents. Recent studies have suggested that MT is involved in protecting against various forms of oxidative stress, but little is known about the induction of MT by oxidative stress agents. Diethyl maleate (DEM) causes oxidative stress by depleting glutathione levels and is quite effective at increasing hepatic concentrations of MT. The purpose of the current study was to learn more about the relationship between induction of MT and oxidative stress by characterizing this increase in hepatic MT levels produced by DEM. Administration of DEM (3 to 9 mmol/kg, sc) increased hepatic MT concentration in mice as much as 37-fold to 213 micrograms MT/g liver, which is similar to the hepatic MT level seen after administration of other effective MT inducers, such as Cd. The maximal increase of hepatic MT took place 12 to 24 hr after administration of 5 mmol DEM/kg. This rise in MT was preceded by a 60% depletion of hepatic glutathione 3 hr after DEM and increases in both MT-I and MT-II mRNA, which reached a peak 6 to 9 hr after DEM. Administration of DEM (3-5 mmol/kg, sc) also increased MT levels in Sprague-Dawley rats. Pretreatment with DEM protected against Cd-induced hepatotoxicity in a fashion which suggested that a functional MT was being synthesized. In summary, DEM is a highly effective inducer of MT which increases MT at the mRNA level.     

Effect of adrenergic stimulation on ornithine decarboxylase activity in the rat spleen

The effect of a single administration of catecholamines on ornithine decarboxylase activity and polyamine biosynthesis in the rat spleen was investigated. Isoproterenol elicited a dose-dependent increase in spleen ODC activity which reached a maximum 4 hr after the administration of the drug. Putrescine content was also found to increase within a few hours, whereas S-adenosylmethionine decarboxylase activity and spermidine and spermine levels did not change significantly. Adrenaline and noradrenaline proved to be even more effective in increasing splenic ODC activity than isoproterenol. alpha- and beta-adrenergic antagonists prevented the ODC increase by catecholamines to a different extent.     

Effect of trimethyltin on ornithine decarboxylase in various regions of the mouse brain

Male C57B1/6N mice, 8-10 weeks old were given a single oral dose of 0, 1.0 or 3.0 mg/kg body weight of trimethyltin hydroxide (TMT). Levels of ornithine decarboxylase (ODC) activity were measured in several brain areas, 1, 2 and 7 days later. The lower dose of TMT produced a decrease of ODC in the caudate nucleus and hippocampus at all time points studied. Hypothalamus, cerebellum and brain stem levels of this enzyme were unaltered. At the higher dose of TMT, ODC activity in hippocampus, cerebellum and brain stem were increased relative to controls at 1 and 2 days after treatment, while other regions were not significantly affected. These elevated ODC levels returned to control values within 7 days. Thus, trimethyltin treatment causes changes in ODC activity in a region and dose-specific manner.     

Effect of maternal ethanol ingestion on neonatal rat brain and heart ornithine decarboxylase

Perinatal exposure of developing rats to ethanol caused an alteration in the developmental pattern of ornithine decarboxylase (ODC) activity in heart and brain which was different for the two tissues. In brain, an initial decrease in ODC activity was followed by normal or Supranormal levels before declining again, whereas heart ODC activity initially was increased but then declined to the low levels of activity characteristic of adult heart tissue. Withdrawal from ethanol at birth or at 3 and 5 days postnatally produced alterations in brain and heart ODC activity that were different from those seen in pups exposed to ethanol continuously throughout development, indicating that the biochemical changes are dependent on the duration of exposure as well as the time at which withdrawal is initiated. The altered ODC developmental patterns in the brain and heart are consistent with the hypothesis that maternal ethanol administration exerts significant effect on fetal polyamine metabolism and ultimately upon the growth and development of these tissues.     

Disulfiram-like effect of diethyl maleate on barbiturate-induced hypnosis and 5-hydroxytryptamine metabolism

Diethyl maleate (DEM, 600 mg kg^?1 i.p.) significantly potentiated hexobarbitone hypnosis and lowered plasma hexobarbitone level on awakening. Sleeping time following intra-cerebroventricular (i.c.v.) injection of phenobarbitone was also prolonged by DEM treatment. When administered to DEM-treated rats, L-tryptophan (50 mg kg^?1 i.p.) significantly potentiated hexobarbitone hypnosis, although alone it had no effect in control rats. DEM markedly diminished the activity of brain low-Km aldehyde dehydrogenase (AlDH) and the formation of 5-hydroxyindoleacetic acid from 5-hydroxytryptamine (5-HT) without affecting MAO activity in various areas of the brain. Conversely, the protein-bound radioactivity derived from i.c.v. [¹⁴C]-5-HT was increased by DEM treatment. These results showed that DEM is comparable with disulfiram, a brain AlDH inhibitor, in terms of its effect on 5-HT metabolism and barbiturate hypnosis.     

Postnatal methyl mercury exposure: effects on ontogeny of renal and hepatic ornithine decarboxylase responses to trophic stimuli

The effects of postnatal methyl mercury exposure on the ontogeny of renal and hepatic responsiveness to trophic stimuli were examined. Increased ornithine decarboxylase (ODC) activity was used as an index of tissue stimulation. In the rat, renal ODC responsiveness to growth hormone, angiotensin, vasopressin, isoproterenol, and serotonin was absent at birth and matured 3 to 4 weeks later. However, pups exposed to methyl mercury showed marked, ODC responses to these same agents as early as 10 to 19 days of postnatal age, accompanied by a significant renal hypertrophy. In contrast to the kidney, the liver of normally developing rats was responsive to trophic factors even in the neonate. In this tissue, there was no consistent effect of neonatal methyl mercury treatment on ODC responses at any developmental stage tested; although absolute liver weights were reduced, liver/body weight ratio was not affected. These results demonstrate that postnatal methyl mercury exposure causes a precocious onset of ODC responses to trophic agents specifically in the kidney. Altered responsiveness may mediate some of the effects of this organomercurial on overall renal development and function.     

Effect of apomorphine, piribedil and haloperidol on adrenal ornithine decarboxylase activity of the rat

The administration of the dopaminergic drugs, apomorphine and piribedil to rats resulted in an increase in the activity of ornithine decarboxylase of the adrenal medulla and cortex. Pretreatment of the rats with the dopamine-receptor antagonist haloperidol caused a partial blockade of the apomorphine-induced effect at 4 hr in both medulla and cortex. At 6 hr, however, haloperidol did not block the effect of apomorphine and produced an increase in ornithine decarboxylase activity of both structures when administered alone. Hypophysectomy abolished the cortical ornithine decarboxylase response to apomorphine and haloperidol and the medullary response to haloperidol. The results suggest that the response of cortical ornithine decarboxylase activity to apomorphine and haloperidol is entirely mediated by the hypophysis and that the effect of apomorphine and the antagonistic action of haloperidol towards apomorphine in regard to the induction of adrenal medullary ornithine decarboxylase must be taking place at some central site independent of the hypothalamic-hypophyseal system.     

Effect of alpha-difluoromethylornithine, an irreversible ornithine decarboxylase inhibitor, on formation of GGTase-positive foci

The importance of the induction of ornithine decarboxylase to the development of GGTase foci is examined in the classic initiation-promotion assay. This was accomplished by examining the complete foci system in the presence and absence of alpha-DFMO, an irreversible inhibitor of ornithine decarboxylase, at concentrations capable of inhibiting both phenobarbital stimulated and control levels of the enzyme. Although the hepatic enzyme was inhibited by the alpha-DFMO, there was no decrease in the progression of formation of the GGTase foci.     

Ontogeny of stress effects on ornithine decarboxylase activity in rats

This study demonstrates that “stress” elicits a specific pattern of organ response in developing rats that is determined by the particular “stress” and by the age of the animal. Maternal deprivation (MD) of preweanling rat pups decrease ornithine decarboxylase (ODC) activity in many tissues, as reported previously, while immobilization (IMM) and cold stress increase ODC activity in liver and heart of neonatal rat. Serum GH is decreased by MD and by IMM, but is not affected by cold stress. Stress-induced ODC elevation increases with age, while MD effects disappear at weaning. IMM and cold increase ODC activity in kidney, liver and heart of adult rats. These effects of IMM are blocked by the ganglionic antagonist chlorisondamine in adult but not in neonatal rats. The results of this study suggest that MD and the “classical” stress paradigms IMM and cold evoke different patterns of organ ODC response in neonatal rats. Furthermore, these findings suggest that the mechanism by which immobilization increases ODC activity changes from a hormonal to a neural mechanis, during ontogeny.