Ornithine Decarboxylase Activity In Liver Research Articles

Effect of different thyroid state on ornithine decarboxylase activity and receptors of T3 in rat liver.

The effects of thyreoidectomy, of the administration of 3,5,3'-triiodothyronine (T3), of thyroxine (T4) together with the inhibitor of iodothyronine 5'-deiodinase activity 6-propyl-2-thiouracil (PTU) and of PTU alone on rat liver ornithine decarboxylase (ODC) activity was studied. 28 days after thyroidectomy there was a decrease in ODC activity, whereas T3 treatment of normal rats increased enzyme activity. PTU decreased ODC activity in intact rats and inhibited ODC activity in animals treated with T4. Neither thyroidectomy T3, T4 given in vivo nor the polyamines spermine and spermidine added in vitro influenced the binding of 125I-T3 to its receptor in liver nuclei. Only addition of PTU increased Ka significantly (P less than 0.01). It is concluded that ODC activity in the liver is directly correlated with the thyroid state but not to parameters of thyroid hormone receptor in liver nuclei.

Dietary inclusion of crystalline D - and L -methionine: effects on growth, feed and protein utilization, and digestibility in small and large Atlantic salmon (Salmon salar L.)

Use of crystalline methionine to optimize amino acid profiles in feeds for Atlantic salmon (Salmo salar L.) was studied in three experiments. A basic experimental diet with 25% of dietary protein from marine origin and the remaining 75% from soya protein concentrate was used either with or without supplementation of L-methionine, D-methionine or DL-methionine. A fishmeal-based diet was used as control. In experiment 1, growth performance of 100 g salmon in seawater was improved by supplementation with the different methionine products. Growth performance was, however, inferior to that of fish fed the control. Feed conversion ratios (FCR) exhibited similar trends to specific growth rate (SGR) with methionine supplementation, but again not as the control. Protein retention, measured as productive protein value (PPV), was significantly better in the control and D-methionine groups as compared with either L-methionine or the nonsupplemented group. These trends were confirmed in experiment 2, using fish of the same size, where an absorption and digestibility study of D- and L-methionine clearly indicated that D-methionine was absorbed as well as L-methionine. Results indicated that racemization of D- into L-methionine occurs in liver and kidney in Atlantic salmon. Ornithine decarboxylase (ODC) activity in liver was significantly affected by dietary treatment and there was a good correlation with growth and feed utilization data. In experiment 3, a growth study with large salmon (1 kg) was performed using increasing supplementation of DL-methionine to the basic diet. Results indicated a methionine requirement for maximum growth of 9.2 g kg–1 feed dry matter (DM) kg–1 growth. This is slightly higher than that reported in the literature. The present study clearly shows that optimizing the amino acid profile by inclusion of a single crystalline amino acid (crystalline methionine) does not give the same protein utilization as that of a diet in which the amino acids are mainly protein bound. D-methionine was found to result in better protein utilization than L-methionine when measured as PPV.

Suppression of Chemical Carcinogenesis by Water-Soluble Organosulfur Compounds

The chemopreventive effects of five water-soluble organosulfur compounds, S-methylcysteine (SMC) and four analogs, were examined on the promotion stage of diethylnitrosamine hepatocarcinogenesis in male F344 rats, using the medium-term bioassay (Ito test), which is based on the two-step model of hepatocarcinogenesis. In addition, we investigated the modifying effects of SMC and cysteine on the initiation stage of rat hepatocarcinogenesis. Carcinogenic potential was scored by comparing the numbers and areas of a putative neoplastic lesion, glutathione S-transferase placental form (GST-P)--positive hepatocellular foci. SMC and cysteine significantly decreased the number and area of GST-P--positive foci when given in the promotion stage of the Ito test. When given during the initiation stage, these two organosulfur compounds also significantly inhibited focus formation. Liver ornithine decarboxylase activity after two thirds partial hepatectomy and the proportion of hepatocytes positive for proliferating cell nuclear antigen significantly decreased the number of aberrant crypt foci in the colon in a multiorgan carcinogenesis bioassay of rats. These results support SMC and cysteine as chemopreventive agents for hepatocarcinogenesis and colon carcinogenesis. Their intake may be of importance for cancer.

Some aspects of hepatic function in feral brown trout, Salmo trutta, living in metal contaminated water.

Brown trout, Salmo trutta, exposed to heavy metals (mainly Cd and Zn) for at least 2 years in the Eagle River, Colorado, were examined for liver size and activity of the growth-promoting enzyme, ornithine decarboxylase (ODC) and compared to trout living in an uncontaminated site. Liver-somatic index (LSI) was greater for trout living in the uncontaminated site with the LSI of females being significantly greater than that of males. The LSI for females at the uncontaminated site was greater than that of females at the contaminated site, but males were not different statistically. ODC activity in the livers of both males and females was lower at the contaminated site. However, males and females did not differ with respect to ODC activity. These data suggest that chronic exposure to heavy metals may have important implications for growth and reproduction and possibly survival. The activity of ODC in liver might serve as a useful biomarker when assessing chronic toxicity of metals to naturally reproducing fish populations.

Glucocorticoid regulation of ornithine decarboxylase in the postnatal rat lung

Ornithine decarboxylase (ODC) is thought to play a critical role in pulmonary development. The purpose of this study was to characterize the effects of dexamethasone on ODC gene expression and enzyme activity in the lung of rat pups. Subcutaneous administration of dexamethasone (10 mg kg ) was shown to suppress ODC activity in 2-, 6- and 10-day-old rats for as long as 24 h after injection. In contrast, dexamethasone treatment stimulated liver ODC activity indicating that the inhibition of lung ODC is tissue specific. Contrary to expectation, the glucocorticoid enhanced lung ODC expression as indicated by an increased accumulation of ODC mRNA transcripts. The latter effect was associated with an heightened expression of c-myc and max mRNAs, the encoded proteins of which act as transactivators of the ODC gene. Dexamethasone did not alter lung levels of “antizyme” (AZ), an inducible protein that specifically promotes the degradation of the ODC protein enzyme. However, the lack of AZ induction does not necessarily mean that ODC degradation is not the mechanism for the decrease in lung ODC activity of dexamethasone-treated animals. The results obtained indicate that glucocorticoids can downregulate lung ODC activity, and that the effect is mediated by post-transcriptional rather than transcriptional mechanisms. These findings are consistent with the idea that endogenous glucocorticoids play an important role in the modulation of ODC activity and early pulmonary development.

Ornithine decarboxylase activity in muscle, liver, and intestinal tissue of turkeys during a short-term feed withdrawal and following refeeding

The activity of ornithine decarboxylase (ODC), an enzyme associated with cellular growth and protein synthesis, was examined in breast muscle, liver, and intestinal tissues of turkeys during a short-term period of feed withdrawal (FW) and following refeeding. Turkeys from a randombred control line were reared under standard management practices to 3 wk of age in battery brooders. Feed was then withdrawn from FW birds for a 48-h period, after which feed was consumed ad libitum. Control birds consumed feed ad libitum throughout the test period. Tissues were collected from 12 birds per treatment following 24 and 48 h of FW and at 6, 12, 24, and 48 h following refeeding for later determination of tissue ODC activity. Activity of ODC was greater in tissue from the small intestine than in liver tissue and both had greater activity than that exhibited by breast muscle. Short-term FW and refeeding produced differential responses in ODC activity of the three tissues examined. Feed withdrawal resulted in a reduction of ODC activity in intestinal tissue, whereas activity was unaffected for liver or breast muscle tissues. Compensatory increases in ODC activity were observed in liver and intestinal tissues; however, the increase was both more rapid and transitory in small intestine than in liver tissue. The ODC activity in breast muscle was largely unaffected by short-term FW and refeeding. Patterns of ODC activity in liver during FW and refeeding closely resembled patterns observed for absolute and relative liver weight. Thus, the results of the present experiment demonstrate that short-term FW and refeeding influence underlying growth mechanisms of supply organs, such as hepatic and intestinal tissue, in addition to affecting overall growth and muscle development.

Dietary conjugated linoleic acid induces peroxisome-specific enzyme accumulation and ornithine decarboxylase activity in mouse liver

Previous studies have shown that the dietary fatty acids, conjugated linoleic acids (CLA), inhibit carcinogenesis in the colon, mammary gland, forestomach, and skin. Several properties of this chemoprotective polyunsaturated fatty acid suggest it will act as an hepatic peroxisome proliferator. This study evaluated the effect of dietary CLA on the accumulation of enzymes associated with peroxisome proliferation in rodent liver. Female SENCAR mice were fed one of four semipurified diets containing 5% corn oil without CLA (“control diet”) or supplemented with incremental levels of CLA (0.5%, 1.0% or 1.5% by weight of diets) for 6 weeks. Hepatic mRNA levels of several enzymes known to be induced during peroxisome proliferation [i.e., acyl-CoA oxidase (ACO), cytochrome P4504A1 (CYP4A1), and liver fatty acid binding protein (FABP)] were measured by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Diets containing 0.5%, 1.0% or 1.5% CLA were associated with approximately 6-, 9-, and 9-fold increases in ACO mRNA, respectively, compared with mRNA levels in mice fed the control diet. The steady state levels of FABP and CYP4A1 mRNA accumulation were maximal in animals fed 1.0% CLA diets and less magnified in mice fed 1.5% CLA diets. Western blot analysis revealed that the relative abundance of ACO protein in livers of mice fed CLA-containing diet groups (0.5%, 1.0%, and 1.5% CLA) were 2.5, 3.0, and 3.0 times the level ACO protein of mice fed the control diet (0.0% CLA). Because most peroxisome proliferators are considered nongenotoxic hepatocarcinogens in rodents, the effect of dietary CLA on ornithine decarboxylase (ODC) activity, a measure of cell proliferation and tumor promotion, was quantified. Activity on hepatic ODC was increased by approximately 10-fold for mice fed 1.0% and 1.5% diets, respectively, compared with those fed the control or 0.5% CLA diets. These data suggest that CLA displays the typical peroxisome proliferation response, i.e., induction of ACO, CYP4A1 and FABP accumulation and cell proliferation in rodent liver.

Central administration of morphine inhibits brain and liver ornithine decarboxylase activity in neonatal rats: Involvement of transcription- and non-transcription-dependent mechanisms

This study examined whether the developmental deficits usually observed in infants born to opiate addicted mothers could involve effects on ornithine decarboxylase, a growth-controlling enzyme. Intracerebroventricular (i.c.v.) injection of a single dose of morphine (2 μg) to 6-day-old rats markedly decreased basal brain and liver ornithine decarboxylase activity as well as the increases in hepatic ornithine decarboxylase activity produced by subcutaneously (s.c.) administered insulin, an important trophic hormone. Centrally applied morphine acts supraspinally to downregulate peripheral ornithine decarboxylase activity, since s.c. administration of the same dose as used i.c.v. decreased neither basal liver ornithine decarboxylase levels nor tissue responsiveness to insulin. This does not imply that the opiate is unable to affect ornithine decarboxylase when applied systemically. In fact, a robust inhibition of both basal and induced liver ornithine decarboxylase activity was obtained in rat pups given 20 μg of morphine s.c. This larger dose is able to trigger the hepatic ornithine decarboxylase effects presumably by stimulating opiate receptors located at central sites after crossing the blood–brain barrier and penetrating into the brain. Concomitant administration of naloxone plus morphine i.c.v. prevented morphine from downregulating ornithine decarboxylase activity, confirming the participation of supraspinal opioid receptors in morphine ornithine decarboxylase actions. Finally, as was the case for insulin induced stimulation of ornithine decarboxylase activity, i.c.v. injection of morphine markedly diminished insulin induced stimulation of hepatic ornithine decarboxylase mRNA accumulation. In turn, contrary to the inhibition of basal ornithine decarboxylase activity, morphine did not lower basal hepatic ornithine decarboxylase mRNA levels when given alone. Thus, CNS morphine can apparently suppress tissue ornithine decarboxylase expression through both transcriptional and posttranscriptional mechanisms. The evidence obtained suggest that postnatal exposure to opiate drugs might detrimentally affect development by altering normal tissue ornithine decarboxylase ontogeny.

Effects of eicosanoids on lipopolysaccharide-induced ornithine decarboxylase activity and polyamine metabolism in the mouse liver

Background/Aims: During endotoxic shock, arachidonic acid is released from the inflammatory cell membranes and is metabolized to form eicosanoids, which modify the deleterious effects of lipopolysaccharide (LPS) on liver function, However, it is not known which protaglandins (PGs) or leukotrienes (LTs) are produced or how they affect the LPS-treated liver. As LPS treatment elevates hepatic ornithine decarboxylase (ODC) activity and affects the polyamine levels of the mouse liver, this study was carried out to examine the effects of eicosanoids and their inhibitors on the induction of ODC activity and polyamine levels in the LPS-treated mouse liver.Methods: LPS in the presence or absence of other drugs was intraperitoneally administered to 6-week-old mice and the livers were then removed. The hepatic ODC activity, polyamine levels, and level of ODC mRNA were determined.Results: The levels of LPS-induced ODC activity, the putrescine (PUT) and N1-acetylspermidine (A-SPD) were reduced by the administration of PGE1. ODC activity was enhanced by the administration of corticosteron, AA-2414 (an antagonist of thromboxane (TX) A2) and TXB2, whereas the A-SPD level was reduced by corticosterone and AA-2414 treatment. The level of ODC mRNA changed in parallel with the change in OdC activity.Conclusions: PGE1 may reduce the LPS-induced production of inflammation-accelerating cytokines and reduce the level of ODC activation. Corticosterone and AA-2414 treatment may attenuate the LPS-induced production of eicosanoids, and enhance the LPS-induced ODC activation. It is possible that the eicosanoids produced by LPS treatment inhibit ODC activation during endotoxic shock.

Effects of chronically elevated growth hormone levels on polyamine metabolism in elderly transgenic mice

The polyamines are ubiquitous, multifunctional aliphatic amines with roles in cell growth, proliferation, differentiation, and malignant development. After growth stimulation, rapid and transient changes occur in polyamine regulatory enzymes. In this respect, acute effects of growth hormone (GH) injection on polyamine metabolic enzymes have earlier been shown. The present investigation comprises studies of the effects on polyamine metabolism of constitutively elevated levels of circulating GH in elderly transgenic (tg +) mice, overexpressing bovine GH. Polyamine levels were found to be constitutively altered in the liver and kidney of tg + mice. Less changes were found in the spleen and none in the brain. The cellular uptake of polyamines in the liver from tg + mice showed an increase and considerable changes were observed in the activity of ornithine decarboxylase (ODC) in the liver and kidney and S-adenosylmethionine decarboxylase (AdoMetDC) in the liver. A conspicuous finding was the distribution pattern of ODC protein in the liver in both tg − and tg + animals. The results show that the effects of chronically elevated GH levels are organ-dependent and complex, and differ from acute GH effects. Despite high ODC activity and polyamine levels in liver, these mice did not display any malignant transformation even at an advanced age, indicating that high ODC activity is not sufficient to induce tumorigenesis in vivo.

Inhibitory effect of chlorophyllin on diethylnitrosamine and phenobarbital-induced hepatocarcinogenesis in male F344 rats.

Modifying effects of chlorophyllin (CHL) on the diethylnitrosamine (DEN)‐phenobarbital (PB) hepatocarcinogenesis model were examined in rats. Five‐week‐old male F344 rats were divided into 8 groups. Groups 1 through 5 were given i.p. injections of DEN (100 mg/kg body weight) once a week for 3 weeks beginning one week after the start of the experiment, while groups 6 through 8 received vehicle treatment. Groups 1, 2, 3 and 7 received drinking water with 500 ppm PB from one week after the end of carcinogen or vehicle treatment. CHL‐containing diet (2000 ppm) was given to group 2 during the initiation phase and to groups 3 and 5 during the promotion and the post‐initiation phase, respectively. Group 6 was given the experimental diet alone throughout the experiment (24 weeks). Liver neoplasms were present in DEN‐treated groups and PB treatment promoted liver tumorigenesis. The incidences of adenoma in groups 2 and 3 were significantly smaller than in group 1 (P<0.05 and P<0.02), although the reductions in the incidences of liver cell cancer were not significant. The average numbers of liver neoplasms/rat in group 2 were significantly smaller than in group 1 (P<0.05‐P<0.005), Glutathione S‐transferase placental form‐positive foci were also significantly decreased by CHL treatment (P<0.05 and P<0.001). DEN and PB exposure increased liver ornithine decarboxylase activity and this increase was significantly inhibited by feeding of CHL during the initiation phase (P<0.001). These results suggest that CHL is a chemopreventive agent for liver neoplasia.

Ornithine decarboxylase activity in rat intestinal mucosa and liver is stimulated by central administration of 2-deoxy- d-glucose but not of 2,5-anhydro- d-mannitol

It has been shown that 2-deoxy- d-glucose (2-DG) inhibits glucose utilization and elicits feeding through the lateral hypothalamus. In contrast, 2,5-anhydro- d-mannitol (2,5-AM), blocking glycogenolysis and/or gluconeogenesis, elicits feeding through the ventromedial hypothalamus. The aim of the present study was to determine whether ornithine decarboxylase (0130 activity in the rat small intestine is stimulated by infusion into the third ventricle of 2-DG or of 2,5-AM. Under anesthesia, a cannula was implanted into the third ventricle one week before the experiment. Each rat was infused with 6, 12, and 24 μmol 2-DG or 2,5-AM into the third ventricle without disturbing the behavior. Ingestive behavior was observed for one h after the infusion. ODC activity in the intestinal mucosa and the liver was measured 2 h after the infusion. Additionally, ODC activity was measured in vagotomized rats. Both test solutions elicit feeding at 24 μmol/rat. Infusion of 2-DG into the cerebroventricle significantly increased ODC activity in the duodenal and jejunal mucosa and the liver. In contrast to 2-DG, infusion of 2,5-AM did not increase ODC activity in the intestinal mucosa or liver. Truncal vagotomy attenuated the increase of ODC activity in the intestinal mucosa and liver induced by 2-DG. The present study showed that 2-DG, but not 2,5-AM, increased ODC activity in the peripheral organs, indicating that glucose-metabolism at specific sites of the central nervous system, including the lateral hypothalamus, is important for stimulatory signals to ODC activity. It is also indicated that the stimulatory signals from the central nervous system are mediated, at least in part, via the efferent vagal nerve.

Transgenic mice expressing the human ornithine decarboxylase gene under the control of mouse metallothionein I promoter

We have generated a transgenic mouse line harbouring the human ornithine decarboxylase gene under the control of mouse metallothionein I promoter. Even in the absence of an exposure to heavy metals, ornithine decarboxylase was over-expressed in heart, testis, brain, and especially in liver, of the transgenic animals. An exposure of the transgenic mice to zinc further enhanced the enzyme activity to a level which in liver represented up to 8000-fold increase in comparison with non-transgenic animals. The striking stimulation of liver ornithine decarboxylase activity upon treatment of the transgenic mice with zinc was accompanied by a nearly 150-fold increase in the hepatic putrescine content as compared with similarly treated non-transgenic animals. Even though the liver putrescine concentration reached that of spermidine and spermine in the transgenic animals, the contents of the higher polyamines only transiently increased upon zinc administration and then returned to the basal level. These findings once again indicate that mammalian cells possess extremely powerful regulatory machinery to prevent an over-accumulation of spermidine and spermine in non-dividing cells, and that very high tissue putrescine concentrations can be tolerated, at least for periods of a few days, with seemingly no phenotypic changes.

Arsenite, but not cadmium, induces ornithine decarboxylase and heme oxygenase activity in rat liver: relevance to arsenic carcinogenesis

Sodium arsenite and cadmium chloride, were administered orally to adult female rats at 21 and 4 h prior to sacrifice. Liver, lung, skin and urinary bladder were the tissues studied. DNA damage, cytochrome P450, glutathione content (GSH), ornithine decarboxylase (ODC), serum alanine aminotransferase and heme oxygenase activity were measured. Sodium arsenite increased rat hepatic ODC activity at 1.6 and 24.6 mg/kg and hepatic heme oxygenase activity at 8.2 and 24.6 mg/kg, but did not cause any DNA damage. Cadmium chloride did not affect any of the six parameters tested. These findings suggest that sodium arsenite may be a promoter rather than an initiator of carcinogenesis.

Persistent chemopreventive effect of S-adenosyl-L-methionine on the development of liver putative preneoplastic lesions induced by thiobenzamide in diethylnitrosamine-initiated rats.

S-Adenosyl-L-methionine (SAM) is a strong chemopreventive agent of rat liver carcinogenesis. Examination was made to determine whether inhibition by SAM of the development of preneoplastic liver lesions persists to SAM withdrawal in diethylnitrosamine-initiated F344 rats promoted with thiobenzamide (TB). The rats were subjected, 2 weeks after initiation, to 5 weeks feeding with a 0.1% TB diet followed by a TB-free diet for 6 weeks and then a second TB treatment for 3 weeks. SAM (384 micromol/kg/day) was injected i.m. during the first TB cycle (treatment A) or for 6 weeks after the first TB cycle (treatment B). Many gamma-glutamyltranspeptidase (GGT)-positive lesions developed in initiated rats after the first TB cycle. They decreased in number after TB withdrawal, while partial recovery of lesion number and a great increase in volume occurred after the second TB cycle. Liver ornithine decarboxylase (ODC) activity and c-myc and c-Ha-ras mRNAs increased during the TB cycles and returned to normal liver values after TB withdrawal. Number and size of GGT-positive lesions, DNA synthesis of GGT-positive cells, liver ODC activity and c-myc and c-Ha-ras mRNA levels decreased as a consequence of SAM treatment A. The recovery of these parameters, induced by a second TB cycle in rats not treated with SAM, was prevented by SAM treatment B. These results suggest that SAM causes a persistent decrease in growth capacity of preneoplastic liver lesions in rats subjected to a diethylnitrosamine/TB protocol.

Arsenite, but not cadmium, induces ornithine decarboxylase and heme oxygenase activity in rat liver: relevance to arsenic carcinogenesis

Sodium arsenite and cadmium chloride, were administered orally to adult female rats at 21 and 4 h prior to sacrifice. Liver, lung, skin and urinary bladder were the tissues studied. DNA damage, cytochrome P450, glutathione content (GSH), ornithine decarboxylase (ODC), serum alanine aminotransferase and heme oxygenase activity were measured. Sodium arsenite increased rat hepatic ODC activity at 1.6 and 24.6 mg/kg and hepatic heme oxygenase activity at 8.2 and 24.6 mg/kg, but did not cause any DNA damage. Cadmium chloride did not affect any of the six parameters tested. These findings suggest that sodium arsenite may be a promoter rather than an initiator of carcinogenesis.

Different patterns of expression of ornithine decarboxylase mRNAs in rat liver after acute administration of hepatocarcinogens.

In the present study, we have evaluated the induction of ornithine decarboxylase (ODC) activity in rat liver after acute in vivo administration of different hepatocarcinogens, and correlated the ODC activity peaks with the accumulation of the three ODC-related mRNA species in rat liver at different times after the intraperitoneal injection of different hepatocarcinogens. ODC activity peaked 16 h after 2-acetylaminofluorene (2-AAF) treatment, while accumulation of the three ODC-mRNAs, starting 4 h after the injection, was maximal 6 h later. Thioacetamide (TAA) administration caused a single peak of ODC activity 20 h after treatment, while there had been the maximum increases of the three ODC-mRNAs 4-h earlier. The first ODC activity peak occurred 20 h after treatment with 3'-methyl-4-(dimethylamino)azobenzene (MDAB), at the same time that accumulation of the ODC-mRNAs was maximum. There was no increase in ODC-mRNA accumulation at 28 h or 36 h after MDAB treatment, the time at which ODC activity once again peaked. All the ODC-related transcripts accumulated after MDAB treatment, although to different degrees. The 1.7 kilobase (kb) transcript accumulated the most after 2-AAF treatment. After TAA treatment, the 2.2 kb mRNA was the most abundantly expressed. In neonatal liver, in which ODC activity is physiologically high, the 1.7 kb mRNA is expressed more abundantly than the other two ODC-related transcripts. These results demonstrate that the peak of ODC enzyme activity does not always correspond in time with the peak of ODC-mRNA accumulation; that different hepatocarcinogens induce different patterns of accumulation of the ODC-related transcripts; and that the minor ODC-related transcript (1.7 kb) in rat liver seems to be expressed not only constitutively but is also inducible.

The inhibition of ornithine decarboxylase activity in developing rat tissues by central nervous system β-endorphin is mediated by μ-opioid receptors, but not by δ- or ϵ-opioid receptors

Our laboratory has previously shown that intracerebroventricular (i.c.v.) administration of β-endorphin suppresses brain and liver ornithine decarboxylase activity (ODC; a growth regulatory enzyme) in preweanling rats. This investigation examined, in 6-day-old rats, the relative participation of brain μ-, δ- and ϵ-opioid receptors in β-endorphin's ODC effects, by comparing tissue ODC responses to β-endorphin given alone i.c.v. and in the presence of d-Phe-Cys-Tyr- d-Trp-Orn-Thr-Pen-Thr-NH 2 (CTOP; μ-opioid receptor antagonist), N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI-174,864; δ-opioid receptor antagonist) or β-endorphin-(1–27) (ϵ-opioid receptor antagonist). Administration of 0.5 μg of β-endorphin alone significantly decreased brain and liver ODC activity 4 h after injection, and the effect was completely blocked by coinjection of CTOP (0.075 μg) but not by ICI-174,864 (0.75 or 3.75 μg) or β-endorphin-(1–27) (3.75 or 7.5 μg). The blockade of endogenous opioid:opioid receptor interactions by either CTOP (at doses > 0.075 μg) or ICI-174,864 alone was accompanied by increased levels of basal ODC activity. The results obtained demonstrate that i.c.v. β-endorphin downregulates ODC expression in central as well as in peripheral tissues by interacting with brain μ-opioid receptors, but not with δ- or ϵ-opioid receptors or μ/δ-opioid receptor complexes. Also, they indicate that endogenous opioid systems have a tonic inhibitory influence on ODC activity which is mediated, at least in part, by μ- and δ-opioid receptors.

Modulation of Expression of fos and Ha-ras Oncogenes and Ornithine Decarboxylase Activity in Mammary Gland and Liver of Young Female Rats by the Absence of Dietary Lipotropes

There is evidence that diets deficient in lipotropes [methionine, choline, pteroylmonoglutamic acid (folic acid), and cyanocobalamin (vitamin B12)] induce and enhance hepatocarcinogenesis. This research examined the extent to which dietary lipotropes modify cellular oncogene expression and ornithine decarboxylase activity in mammary gland and liver of rats. Eighteen female Sprague-Dawley rats (8 wk old) were fed 3 wk on one of three diets: 1) a control synthetic diet; 2) a methyl-deficient diet lacking choline, methionine, pteroylmonoglutamic acid, and cyanocobalamin; or 3) a diet supplemented with twice the amount of each lipotrope as in the control synthetic diet. The group fed the methyl-deficient diet gained less body weight than groups fed the control or methyl-supplemented diet. The group fed the methyl-deficient diet had approximately 5– and 11-fold greater fos transcription in mammary gland and liver, respectively, than did the control group. The expression of the Ha-ras gene in mammary gland and liver of the group fed the methyl-deficient diet was increased by 4- and 6-fold compared with that of the control. Ornithine decarboxylase activity, considered to be a developmental marker, was higher in liver and mammary gland of the group fed the methyl-deficient diet than in either the group fed control synthetic diet or the group fed the methyl-supplemented diet. The methyl-deficient diet may have caused activation of the transcription factor fos and thus the activation of the transcription regulatory complex, AP-1. In turn, AP-1 may regulate genes, such as ornithine decarboxylase, which are responsible for cell proliferation and differentiation.

Binding of the anti-inflammatory steroid deflazacort to glucocorticoid receptors in brain and peripheral tissues. In vivo and in vitro studies

Deflazacort (DFC) is a heterocyclic glucocorticoid with anti-inflammatory activity but with decreased side effects. In this study, we have evaluated the capacity of DFC and other glucocorticoids to reach the central nervous system (CNS) in vivo by measuring changes of [ 3H]dexamethasone (DEX) binding to glucocorticoid receptors (GR) in vitro. GR occupation was effected by DEX in the cerebral cortex, hippocampus, pituitary, liver and thymus, with DFC showing a similar profile except for the cerebral cortex. In contrast, corticosterone weakly occupied GR in the thymus, pituitary and hippopocampus and methyl-prednisolone was active only in peripheral tissues. Furthermore, IC 50 for DEX in vitro amounted to 15–17 nM in the hipopocampus and liver, wheras IC 50 the active metabolite 21-deacetyl-DFC (21-OH-DFC) was 4 times higher. 21-OH-DFC bound to type II and was absent from type I GR. When tested in equipotent doses based on IC 50 analysis, DFC and DEX similarly induced in vivo ornithine decarboxylase activity in hippopocamus and liver, although body weight loss after chronic treatment was significantly less for DFC. The results show that DFC distributes on the CNS similarly to DEX, induces ornithine decarboxylase activity but presents less intensive catabolic effects, making it suitable for use as an anti-inflammatory steroid during chronic therapeutic regimes.