Decrease In Cytochrome P-450 Content Research Articles

Ascorbic acid deficiency decreases hepatic cytochrome P-450, especially CYP2B1/2B2, and simultaneously induces heme oxygenase-1 gene expression in scurvy-prone ODS rats.

The mechanisms underlying the decrease in hepatic cytochrome P-450 (CYP) content in ascorbic acid deficiency was investigated in scurvy-prone ODS rats. First, male ODS rats were fed a diet containing sufficient ascorbic acid (control) or a diet without ascorbic acid (deficient) for 18 days, with or without the intraperitoneal injection of phenobarbital. Ascorbic acid deficiency decreased hepatic microsomal total CYP content, CYP2B1/2B2 protein, and mitochondrial cytochrome oxidase (COX) complex IV subunit I protein, and simultaneously increased heme oxygenase-1 protein in microsomes and mitochondria. Next, heme oxygenase-1 inducers, that is lipopolysaccharide and hemin, were administered to phenobaribital-treated ODS rats fed sufficient ascorbic acid. The administration of these inducers decreased hepatic microsomal total CYP content, CYP2B1/2B2 protein, and mitochondrial COX complex IV subunit I protein. These results suggested that the stimulation of hepatic heme oxygenase-1 expression by ascorbic acid deficiency caused the decrease in CYP content in liver.

Cisplatin induced toxicity in rat tissues: The protective effect of Lisosan G

The protective effect of a powder of grain (Lisosan G) against cisplatin-induced toxicity in rats was studied. Male rats were fed with Lisosan G before injection of cisplatin and four days later they were killed and blood was collected along with hepatic, renal and testicular tissues. The results showed that cisplatin treatment increased plasma blood urea nitrogen, creatinine and hydrogen peroxide and decreased cytochrome P450 content in renal and hepatic tissues. It also reduced the plasmatic testosterone level and caused a depletion of testicular 17α-progesterone hydroxylase activity. In the group fed with Lisosan G and treated with cisplatin blood urea nitrogen and creatinine returned to the control level indicating a protective effect of Lisosan G. It was also observed that the ones fed with Lisosan G were able to attenuate the decrease in the P450-dependent activities and the activities of antioxidant enzymes as well. Lisosan G protected the testicular 17α-progesterone hydroxylase activity and increased the plasma testosterone level compared to animals treated only with cisplatin. Our results showed a protective effect of Lisosan G against the cisplatin induced toxicity. The protective effect of Lisosan G could be associated mainly with the attenuation of the oxidative stress and the preservation in antioxidant enzymes.

Phenotype of hepatic xenobiotic metabolizing enzymes and CYP450 isoforms of sanguinarine treated rats: Effect of P450 inducers on its toxicity

Catalytic and immunochemical activities of cytochrome P450 (CYP) isoforms were investigated in argemone alkaloid, sanguinarine (SAN) intoxicated rats, pre-treated with different CYP inducers. SAN treated control (CON) and ethanol (ET), 3- methylcholantherene (MC) or dexamethasone (DEX) pre-exposed rats, resulted in 48, 64, 47 and 33% decrease in CYP content. SAN exposure to CON, and DEX, MC or ET pre-treated animals caused a decrease (22-37%) in glutathione-S-transferase (GST) activity, however, quinone reductase (QR) activity decreased (26–45%) in the MC pre-exposed group. Similarly, western-blot analysis of hepatic CYP1A1 and CYP1A2 showed a decrease (27–37%) in MC pre-treated SAN exposed animals. Further, a decrease in mortality in the SAN+MC (25%) group compared to SAN treated animals was also observed. The results suggest that inhibition of CYP 1A1, 1A2, 2D1, 2E1, 3A1, and Phase II enzymes by SAN augments its toxicity, whereas attenuation of SAN toxicity by MC may be due to removal of parent compound/metabolites from the body.

Effect of berberine on hepatocyte proliferation, inducible nitric oxide synthase expression, cytochrome P450 2E1 and 1A2 activities in diethylnitrosamine- and phenobarbital-treated rats

This study investigated the effect of berberine on the early phase of hepatocarcinogenesis stimulated by diethylnitrosamine (DEN, 150 mg/kg, 4 weeks) plus phenobarbital (PB, 75 mg/kg, 7 days) in rats. The expressions of proliferating cell nuclear antigen (PCNA) and inducible nitric oxide synthase (iNOS) were evaluated by immunohistochemistry. The activities of CYP isoenzymes were analyzed using different probe drugs including chlorzoxazone (CYP2E1) and phenacetin (CYP1A2) by high-performance liquid chromatography (HPLC) in vivo or in vitro. Results showed that the expressions of PCNA and iNOS were induced by DEN plus PB in liver tissues. Oral administration of berberine (50 mg/kg) inhibited the hepatocyte proliferation and iNOS expression, decreased cytochrome P450 content, inhibited activities of CYP2E1 and CYP1A2 in DEN-plus-PB-treated rats in vivo. Moreover, berberine (10, 50 and 100 μM) inhibited the activities of CYP2E1 and CYP1A2 in microsomes isolated from DEN-plus-PB-treated rats in vitro, suggesting that anti-hepatocarcinogenetic potential of berberine might be due to inhibiting oxidative metabolic activities of CYP 2E1 and CYP1A2, and decreasing NO production in rats.

The beneficial effect of trolox on sepsis-induced hepatic drug metabolizing dysfunction

Trolox is a hydrophilic analogue of vitamin E. The aim of this study was to investigate its effects on hepatic injury, especially alteration in cytochrome P450 (CYP)-dependent drug metabolism during polymicrobial sepsis. Rats were subjected to polymicrobial sepsis by cecal ligation and puncture (CLP). The rats were treated intravenously with Trolox (2.5 mg/kg) or vehicle, immediately after CLP. Serum aminotransferases and lipid peroxidation levels were markedly increased 24 h after CLP. This increase was attenuated by Trolox. Total CYP content and NADPH-P450 reductase activity decreased significantly 24 h after CLP. This decrease in CYP content was attenuated by Trolox. At 24 h after CLP, there was a significant decrease in the activity of these CYP isozymes: CYP1A1, 1A2, 2B1, and 2E1. However, Trolox differentially inhibited the decrease in CYP isozyme activity. Trolox had little effect on the decrease in CYP1A1 activity but Trolox significantly attenuated decreases in CYP1A2 and 2E1 activities. In fact, Trolox restored CYP2B1 activity to the level of activity found in control rats. Our findings suggest that Trolox reduces hepatocellular damage as indicated by abnormalities in hepatic drug-metabolizing function during sepsis. Our data also indicates that this protection is, in part, caused by decreased lipid peroxidation.

Repeated dose toxicity of alfa-cypermethrin in rats

The present study was performed to investigate the subacute effect of alpha-cypermethrin (alpha-CP) in rats. Alfacypermethrin a synthetic pyrethroid insecticide, dissolved in dimethyl sulfoxide (DMSO) and oral LD50 was investigated after administering orally different doses in rats and was determined as 145 mg/kg. Other groups of rats were given repeated daily oral dose (1/10 LD50) of alpha-CP for 30 days. The animals were sacrificed on 31st day. Activities of various enzymes, cytochrome P450 and b5 contents in liver, hepatic antioxidant status, tissue residue concentration, haemogram and pathological changes were studied. It increased the serum aminotransaminases (AST, ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH) activities and blood glucose level significantly. alpha-CP decreased RBC count, PCV and Hb level significantly. It significantly decreased cytochrome P450 in liver. Residues were present in different tissues. It increased malondialdehyde (MDA) level, while decreased the activities of catalase (CAT), superoxide dismutase (SOD) and glycogen level in liver significantly. Mild to moderate histological alterations were observed in lungs, liver, stomach, kidneys, testes and cerebellum. So repeated daily oral doses of alpha-CP at 1/10LD50 altered the biochemical parameters, decreased cytochrome P450 content, antioxidant status, which correlated with histopathological changes of tissues.

Regulation of heme oxygenase activity in rat liver during oxidative stress induced by cobalt chloride and mercury chloride.

Activities of heme oxygenase and tryptophan-2,3-dioxygenase and cytochrome P450 content in liver as well as absorption of the Soret band and optical density at 280 nm in serum were determined 2 and 24 h after administration of HgCl(2) and CoCl(2) and after co-administration of the metal salts with alpha-tocopherol. Administration of HgCl(2) and CoCl(2) increased the contents of hemolysis products in the serum, induced heme oxygenase, and decreased cytochrome P450 content in the liver. Injection of HgCl(2) increased the activity of tryptophan-2,3-dioxygenase holoenzyme and enzyme saturation with the heme, but administration of CoCl(2) decreased these parameters. Pretreatment with alpha-tocopherol completely blocked the changes induced by HgCl(2) after 24 h. Induction of heme oxygenase induced by CoCl(2) was not blocked by alpha-tocopherol, but this antioxidant normalized the increase in the level of hemolysis products in the serum and decrease in tryptophan-2,3-dioxygenase holoenzyme activity and cytochrome P450 content. Mechanisms of regulation of heme oxygenase by mercury and cobalt ions are discussed.

Genotoxic and mono-oxygenase system effects of the fungicide maneb.

The in vivo effects of a commercial preparation of maneb on mono-oxygenase activities of hepatic microsomes of basal and induced rats were examined. In vitro experiments with the D7 strain of yeast Saccharomyces cerevisiae were also performed. In both basal and induced rats maneb caused a decrease in cytochrome P-450 content and aniline hydroxylase. Immunoblotting analysis using anti-P-450 IIE1 antibodies confirmed the data obtained for aniline hydroxylase activity. Maneb was toxic in cells of S. cerevisiae. On the basis of in vivo and in vitro experiments it can be concluded that maneb possesses a toxic activity attributable to its main metabolite ethylene thiourea. Immunoblotting analysis indicates that maneb biotransformation influences the IIEI P-450 isoform.

Dose-related increase in liver heme catabolism during rabbit aflatoxicosis

Aflatoxin B1 (AFB1) has been reported to decrease microsomal hepatic cytochrome P450 (P450) content and increase both total plasma bilirubin concentration and liver heme oxygenase activity. The purposes of this study were to determine whether liver hemoproteins contents and heme catabolizing enzymes were affected by the mycotoxin and whether these alterations were linked to hyperbilirubinemia. Male New Zealand rabbits were divided into three groups of five animals, each receiving for 5 days either arabic gum as vehicle or AFB1 at a daily oral dose of 0.05 or 0.10 mg/kg. These treatments affected neither cytochrome b5 content nor NADPH-cytochrome reductase activity. A linear dose-dependent decrease in cytochrome P450 content and increases in both heme oxygenase and biliverdin reductase activities were observed. Bilirubin UDP-glucuronyltransferase activity was dramatically decreased at both doses, whereas cholestasis occurred only at 0.10 mg/kg. An exponential dose-dependent increase in plasma bilirubin concentration was also observed. Both the simultaneous exponential increase in bilirubinemia associated to a reduced bilirubin UDP-glucuronyltransferase activity and the absence of cholestasis at 0.05 mg/kg, suggested that the hyperbilirubinemia is more probably related to an increased heme catabolism than to an altered bile duct permeability.

EFFECTS OF p-CHLOROTOLUENE (PCT) ON RAT LUNG AND LIVER BENZO[a]PYRENE METABOLISM AND MICROSOMAL MEMBRANE STRUCTURE AND FUNCTION

Treatment of rats with p-chlorotoluene (PCT, 1 g/kg, ip) resulted in peak PCT blood and lung concentrations at 4 h, which declined to very low levels at 12 h. The concentration of PCT in the liver attained its highest value at 1 h and also declined to low levels at 12 h. In the dose-response study, PCT significantly decreased hepatic and pulmonary AHH activities at 0.5 g/kg, 1 h. Maximum inhibition was attained at 1 g/kg, 1 h, and further increase in the dose did not enhance the enzyme inhibition. In the time-course investigation, PCT (1 g/kg) maximally inhibited hepatic and pulmonary arylhydrocarbon hydroxylase (AHH) activities at 1 h and the decrease in enzyme activity was sustained through 12 h. Administration of PCT (1 g/kg, 1 h) also markedly decreased pulmonary cytochrome P-450 content, while hepatic cytochrome P-450 content was only slightly reduced. The partial decrease in cytochrome P450 content indicated altered levels of the P-450 isozymes, which may have profound effects on the metabolic disposition of benzo[a]pyrene [BaP]. BaP is regioselectively metabolized by two major isoforms of P-450 to toxic dihydrodiols and nontoxic phenol derivatives and there is a balance between these two metabolite groups. PCT (1 g/kg, 1 h) significantly inhibited the phenolic 3-OH BaP formation in both lung (52%) and liver (56%). The formations of BaP 7,8-dihydrodiol (146%) and 9,10-dihydrodiol (90%) were significantly elevated in the lung. The toxication to detoxication ratios were significantly elevated in both organs. Total quinone formation was markedly enhanced in the liver. Since PCT inhibited phenolic metabolite formation and increased dihydrodiol production, the activities of the isozymes that are responsible for their formations were determined. PCT (1 g/kg, 1 h) significantly inhibited cytochrome P-4502B1 in the lung (50%) and 2B1/2B2 in the liver (40%), while cytochrome P-4501A activity was not altered in either lung or liver. PCT increased phospholipid (PL) levels (45%) and conjugated diene (CD) formation (58%) in lung but not in liver, while membrane fluidity was increased [phospholipid/cholesterol (PL/CL) ratio; diphenylhexatriene (DPH) and trimethylammonium DPH (TMA-DPH) fluorescence polarization] in both organs. There was no apparent relationship between these membrane changes and alterations in MFO activity. Taken together the results suggest that PCT is capable of nonselectively inactivating the hepatic and pulmonary isozymes of P-450 that are responsible for the detoxication of BaP. The observed shift in the metabolism of BaP toward potentially more toxic metabolites suggests that concurrent exposure to BaP and PCT may result in greater toxicity, compared to exposure to BaP alone.

Oxidative Stress Produced by Drugs and Chemicals and the Induction of Heme Oxygenase.

Evidence has been accumulating that oxidative stress plays important roles in pathogenesis of various acute and chronic diseases. A wide variety of drugs and chemicals have been shown to produce reactive oxygen species by their oxidative metabolism in the body, thus may cause oxdative stress and lead to cellular and tissue damages. In order to response to such oxidative insults, many antioxidative defense systems are constitutively expressed in mammalian cells the body. Of these antioxidative defense systems, heme oxygenase-1 (HO-1), a first and rate-limiting enzyme of heme degradation, has recently been shown to be highly responsible enzyme against oxidative stress. HO oxidatively cleaves heme into carbon monoxide (CO), Fe2+ and biliverdin, the latter is readily reduced to bilirubin. These degradative byproducts of heme by HO has currently been characterizing their physiological importance. Namely, CO, as just like NO, may play as a gaseous messenger; bilirubin acts as an antioxidant; Fe2+ is a modulator of ferritin. Therefore, the induction of HO-1 produced by physiological and pathophysiological states, and by drugs and chemicals may play vital roles in the adaptive and/or protective response to oxidative stress as a whole. Accumulated evidence demonstrates that HO-1 is induced by not only the substrate heme but also a wide variety of divergent drugs and chemicals, such as hormones, heavy metals, organic compounds including glutathione depletors, cytokines, prostaglandins and so on. Although a detailed mechanism of the induction of HO-1 by these compounds remains to be determined, most of them produce the enzyme induction through oxidative stress. Additionally, it is well established that HO-1 induction in liver or kidney is generally followed by the decrease in cytochrome P-450 content, important enzyme(s) which metabolizes endogenous substances and exogenous drugs and chemicals. This review will describe partly on the current understanding of physiological and/or pathophysiological significance of HO-1, and mainly focus on the significance of this enzyme induction in response to oxidative stress produced by drugs and chemicals. I hope that this review will stimulate interest and understandings in HO-1 and its potential roles in response to oxidative stress.

Cytochrome P-450 and free radical generation in rat liver microsomes under the influence of prostaglandin E1.

There is evidence to suggest that the mechanism of antioxidant effect of prostaglandin E1 (PGE1) is due to decrease of radical species generation by cytochrome P-450 in rat liver microsomes. Chronic alcohol intoxication increased NADPH oxidation, cytochrome P-450 content and NADPH-stimulated chemoluminiscence of microsomes. Ethanol also raised superoxide dismutase (SOD) activity in microsomes. PGE1 decreased cytochrome P-450 content, normalized NADPH oxidation, NADPH-induced chemoluminiscence and SOD activity in the liver of alcohol-treated rats. PGE developed the similar effect after microsomal induction by both acetone combined with starvation and phenobarbital normalizing all the above parameters. Therefore, PGE1 affects on both, ethanol-inducible IIE1 and phenobarbital-inducible IIB1 isoforms.

Interactions between calvatic acid and related compounds with rat liver microsomes.

In this study we examined the interactions of liver microsomes with the antibiotic calvatic acid and with structural analogues, some of which had shown antimicrotubular properties. These drugs decreased cytochrome P-450 content differently according to the substitutions on the azoxy function and the ethoxycarbonyl derivatives were found to be the most effective ones. The decrease in cytochrome P-450 could be prevented by addition of cysteine or GSH, suggesting an involvement of sulphydryl groups. Furthermore, chromatographic analyses showed that ethoxycarbonyl derivatives were completely metabolized, and this would explain the different behaviour of these compounds towards microtubular protein when they were incubated with purified bovine brain protein or with liver or hepatoma extracts.

The influence of aging on dimethylnitrosamine-demethylase enzyme kinetics in rat liver microsomes

To investigate the observed age-related increased susceptibility to chemically-induced carcinogenesis, liver microsomes from 12- or 36-month-old rats either untreated or maximally induced with phenobarbital or isoniazid were used to determine the V max and K m for dimethylnitrosamine-demethylase (DMNA-d). A decrease in cytochrome P450 content between young and old animals was observed in the untreated group, but no change was seen in the treated animals. Inducer-related increases were observed after phenobarbital treatment and in the 36-month-old isoniazid-treated group. The V max for DMNA-d did not change between 12 and 36 months of age in all experimental groups, but significant changes between the young and old age-group and inducer-related differences were observed in the K m,app for DMNA-d. A high correlation was found between the Cl int (= V max K m,app ) of DMNA-d and the V max of p-nitrophenol-hydroxylation, indicating a major role for CYP2E1 in the metabolism of DMNA-d. The observed changes in the cytochrome-P450 levels and the reduced affinity in DMNA-d metabolism in the untreated group in this study is another indication that aging predominately affects the activity of some constitutive cytochrome P450 enzymes but not the activity of the inducible types of P450.

Influence of growth hormone on the hepatic mixed function oxidase and transferase systems of rainbow trout

The effect of GH treatment on hepatic cytochrome P450 content, aryl hydrocarbon hydroxylase (AHH), aminopyrine-N-demethylase (AND), testosterone hydroxylase, testosterone 5α- and 5β-reductase, UDP-glucuronyl transferase (UDPGT) and glutathione S-transferase (GST) activities in immature rainbow trout were investigated. Hepatic cytochrome P450 content, AHH and GST activities were measured in both GH implanted and GH injected animals whereas other activities were assayed in GH implanted trout only.GH implants significantly decreased cytochrome P450 content at 15 days compared to the control but no significant effect was observed at 15 or 30 d when GH was injected biweekly. In both cases, AHH activity was significantly decreased by GH treatment compared to the control whereas GST remained unchanged. Compared to the control, GH implanted fish exhibited a pronounced inhibition of AND, a decreased 6β and 16β-testosterone hydroxylation, an inhibition of UDPGT with testosterone as substrate and an enhanced 17β-testosterone oxidation.

Effect of cadmium on hepatic microsomal monooxygenase activities in guinea pigs with low and high ascorbic acid intake

The influence of in vivo administration of cadmium on hepatic microsomal cytochrome P-450 and cytochrome b 5 content, aniline hydroxylase, p-nitroanisole O-demethylase, and NADPH-cytochrome c reductase activities was investigated in guinea pigs with low (2 mg/animal/day) and high (100 mg/animal/day) ascorbic acid intake. Male guinea pigs received 10 mg Cd/L drinking water for 5 and 12 weeks. Cadmium administration resulted in significant decreases in cytochrome P-450 content and NADPH-cytochrome c reductase activity in the group of guinea pigs with low ascorbic acid intake, while the decreases were less evident in guinea pigs with high ascorbic acid intake. The activities of aniline hydroxylase and O-demethylase were not apparently changed by Cd administration, except for the group of guinea pigs with high ascorbic acid intake in 12th week of cadmium treatment, when increased activities were observed. These findings suggest that hepatotoxic effect of cadmium manifested by inhibition of hepatic microsomal metabolism may be in part beneficially moderated by enhanced ascorbic acid intake.

The effects of age on the pharmacokinetics and biotransformation of theophylline in vivo and in vitro in the Mongolian gerbil ( Meriones unguiculatus)

The effect of post maturational aging on the in vivo disposition of theophylline was examined in the Mongolian gerbils ( Meriones unguiculatus) aged 30–39 (old), 12–18 (middle-aged) and 3 (young) months following a 20 mg/kg i.p. dose. Biotransformation of theophylline was also examined in liver microsomes from non-induced and 3-methylcholanthrene induced gerbils. Analysis of theophylline plasma kinetics showed decreased clearance, increased half-life and increased volume of distribution in old vs. young animals. Clearance to the 1,3-dimethyluric acid metabolite was similar for all age groups, while clearance to the 1-methyluric acid metabolite was significantly lower in the middle-aged group compared to that of young and old gerbils. Urinary recovery of 1-methylurate was increased in old vs. young and middle-aged animals while recovery of theyphylline was decreased. 3-Methylcholanthrene inductions resulted in decreased recovery of theophylline and increased recovery of 1,3-dimethylurate and 1-methylurate in young and middle-aged gerbils compared to non-induced controls. Decreased microsomal protein content was observed in old vs. young and middle-aged gerbils and an age-related decrease in cytochrome P-450 content (nmol P-450/ g liver) was also observed. The rate of dimethylurate formation was decreased 37% in microsomes fromold vs. young and middle-aged gerbils. increase in the rate of 1,3-dimethylurate formation in young and middle-aged gerbils, respectively. The results of these experiments indicate that the Mongolian gerbil may be useful for the study of the biochemical mechanisms underlying age-related changes in the biotransformation and kinetics of theophylline.

Modification of DENA-induced hepatocarcinogenesis by CCl4 cirrhosis. Comparison of the marker enzyme patterns.

The modifying action of chronic liver injury on the process of hepatocarcinogenesis was investigated. To induce cirrhosis or fibrosis F344 rats received CCl4 alone or in combination with phenobarbital, either before (model 1) or after (model 2) the application of initiator, diethylnitrosamine (DENA). In these models, morphology, tumor incidence as well as polysubstrate monooxygenase system, gamma-glutamyltransferase (GGT) and glucose-6-phosphatase (G-6-Pase) were studied. The data presented show that in model 1 the tumor incidence was much lower than in rats treated with DENA alone. This reduction appeared to be associated with the decrease in cytochrome P450 content occurring in model 1 after DENA administration. Promotion of the hepatocarcinogenic process was observed when CCl4 injury followed the application of DENA (model 2). Comparison of marker enzymes in cirrhotic livers and in tumors either with or without cirrhosis indicated that changes in cytochrome P450 and G-6-Pase were rather the results of parenchymal damage, while GGT was elevated only in tumorous livers. In tumorous livers none of the xenobiotic metabolizing activities decreased as much as the cytochrome P450 content of the same samples. Thus conceivably the cytochrome P450 operates more rapidly in tumors than in normal livers.

Regulation of cholesterol and bile acid homoeostasis in bile-obstructed rats

We examined how total blockage of biliary excretion, the major pathway through which cholesterol and bile acids are removed from the body, affects liver function, cholesterol and bile acid metabolism and homoeostasis. After 4 weeks of bile-duct ligation, rats showed impaired liver function, as documented by elevations in serum bilirubin and alkaline phosphatase activity. Moreover, bile-duct ligation decreased by about 30% both the amount of microsomal cytochrome P-450 in the liver and the elimination of aminopyrine in vivo, a reliable index in vivo of microsomal mixed-function oxidase activity. Cholesterol and bile acid contents in livers of bile-duct-ligated rats were doubled compared with sham-operated controls. Despite the increase in the contents of cholesterol and bile acids in liver, activities of the respective rate-limiting enzymes, 3-hydroxy-3-methylglutaryl-CoA reductase and cholesterol 7 alpha-hydroxylase, were doubled. Serum concentrations of bile acids and free cholesterol increased 25- and 4-fold respectively. The large increase in serum bile acids was associated with a 380-fold increase in the urinary excretion of bile acids. Although there is a general decrease in cytochrome P-450 content and drug metabolism involving cytochrome P-450-containing hydroxylases, the activity of cholesterol 7 alpha-hydroxylase, also a cytochrome P-450-containing enzyme, is actually increased. These data show that complete obstruction of the bile duct results in the selective impairment of microsomal cytochrome P-450. Increased activity of 7 alpha-hydroxylase, bile acid synthesis and urinary excretion provides an alternative excretory pathway that helps to maintain cholesterol homoeostasis when the biliary excretory pathway is eliminated.

Morphological and biochemical analyses of trichloroethylene hepatotoxicity: Differences in ethanol- and phenobarbital-pretreated rats

The histological and biochemical differences between ethanol- and phenobarbital (PB)-potentiated hepatotoxicity of trichloroethylene (TRI) in Wistar strain male rats were investigated. Both ethanol (2 g in daily liquid diet for 3 weeks) and PB (80 mg/kg/day for 4 days, ip) pretreatments enhanced TRI (inhalation exposures of 500 ppm for 8 hr, 2000 ppm for 2 or 8 hr, and 8000 ppm for 2 hr)-induced hepatic damage as judged by increases in plasma transaminase activities. Livers from PB-treated rats exposed to TRI displayed centrilobular necrosis, whereas livers from ethanol-treated rats exposed to TRI were characterized by ballooning degeneration mainly in midzonal areas. TRI exposure decreased the in vitro metabolism of TRI, high- K m benzene aromatic hydroxylase (BAH) activity, and cytochrome P450 content in livers of PB-treated rats with severe hepatic damage. In ethanol-treated rats, TRI exposure increased both the in vitro metabolism of TRI and the low- K m BAH activity but did not cause an apparent decrease in cytochrome P450 content even in animals with severe hepatic damage. These results suggest that TRI caused necrosis of centrilobular hepatocytes in PB-pretreated rats, which was accompanied by loss of xenobiotic metabolizing functions, whereas ballooning degeneration of hepatocytes mainly in midzonal areas occurred in ethanol-pretreated rats without loss of xenobiotic metabolizing functions.