Abstract  Simultaneous administration of trichloroethylene (TCE), at an oral dose of 0.5 ml/kg, resulted in a marked potentiation of liver injury caused by an oral dose of carbon tetrachloride (CCl4, 0.05 ml/kg). Hepatic glutathione levels were depressed at 24 hr only in the rats given TCE and CCl4. Using serum enzyme (ALT and SDH) as indicators of hepatotoxicity, potentiation of CCl4-injury was most apparent at 24 hr. Upon histological examination of H&E stained liver sections, the differences between livers obtained from TCE and CCl4-treated rats versus CCl4-treated rats were most apparent at later time points (48 and 72 hr). At 48 hr after CCl4, livers showed a distinctive and uniform pattern of injury with regeneration features predominating over necrosis. At this time, livers from TCE and CCl4-treated rats were characterized by extensive zone 3 coagulative necrosis. Inflammatory infiltrations were less prominent. At 72 hr, morphological features of livers from TCE and CCl4 rats were similar to those from rats given CCl4 alone at 48 hr. From the results obtained, it appears that the regenerative activity of the liver may be delayed in rats simultaneously administered TCE and CCl4 as compared to rats administered only CCl4.

Abstract  Rats, guinea pigs, dogs, rabbits, and monkeys were exposed to trichloroethylene, carbon tetrachloride, 1,1,1-trichloroethane, dichlorodifluoromethane, and 1,1-dichloroethylene. Two types of inhalation experiments were conducted: continuous exposure for 90 days and 8-hour exposures, 5 days a week, for a total of thirty exposures. The parameters studied included mortality, visible signs of toxicity, and hematologic, biochemical, pathologic, and body weight changes. Throughout this entire study which encompassed 17 separate exposures over a period of nearly four years, no visible signs of toxicity were noted in any species exposed to these materials. Significant mortality was found in both the repeated (515 mg/m3) and continuous (61 mg/m3) exposures to carbon tetrachloride as well as in the continuous exposures to 1,1-dichloroethylene at 189, 101, and 61 mg/m3. Growth depression in varying degrees was found in all continuous exposures involving trichloroethylene, carbon tetrachloride, and 1,1-dichloroethylene and in the repeated exposures to carbon tetrachloride. No significant hematologic alterations were noted in any of the studies. No biochemical studies were done in the earlier years and hence no biochemical data were obtained from the animals exposed to trichloroethylene and dichlorodifluoromethane. Serum urea nitrogen levels were within control limits in all of the exposures to carbon tetrachloride, 1,1-dichloroethylene, and 1,1,1-trichloroethane in which determinations were made. Liver lipid contents in guinea pigs were found to be significantly elevated following repeated exposure to 515 mg/m3 of carbon tetrachloride. Significant elevations of serum glutamic-pyruvic transaminase and liver alkaline phosphatase activities were found in rats and guinea pigs following continuous exposure to 189 mg/m3 of 1,1-dichloroethylene. Histopathologic study revealed liver damage following continuous exposures to high levels of dichlorodifluoromethane (3997 mg/m3), and to lower levels of carbon tetrachloride (61 mg/m3), and 1,1-dichloroethylene (189 mg/m3). Similar liver damage was also found in the repeated exposures to the two latter materials at 515 mg/m3 and 395 mg/m3, respectively.

Abstract  The present research was conducted to evaluate the effect of mitogen pre-exposure on CCl4-induced hepatotoxicity. Male Wistar rats were administered a single i.p. injection of CCl4 (0.3 ml kg-1 in corn oil) 48 h following either a single dose of lead nitrate (0.33 mg kg-1) or distilled water via i.v. injection. Hepatotoxicity, as measured by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, was monitored 6, 24, 48, 72 and 120 h after CCl4 exposure. The lead nitrate-pretreated rats displayed markedly lower serum ALT and AST levels at 24, 48 and 72 h than rats pretreated with distilled water. However, treatment with the antimitotic agent colchicine did not alter the lead-induced protection. These findings suggest that the lead-induced protection is not associated with the major mitogenic response of lead, despite its strong temporal association. A critical review of the available toxicological data also argues against the lead protection being a function of its capacity to inhibit cytochrome P-450.

Abstract  A series of halogenated compounds was tested by oral intubation in 200 Osborne-Mendel rats and 200 B6C3F1 mice of both sexes. Carbon tetrachloride, used as a positive control, induced liver and adrenal tumors in mice and neoplastic nodules in the livers of rats. 1,2-Dibromoethane and 1,2-dibromo-3-chloropropane caused stomach tumors with many metastases in both rats and mice. Chloroform, known to cause hepatocellular carcinomas in mice, led in addition to kidney tumors in male rats. 1,2-Dichloroethane was much weaker than the analog, 1,2-dibromoethane, and induced only a few stomach tumors in rats. It increased liver and lung tumors in mice. Most of the compounds, namely, trichloroethylene, 1,1-dichloroethane, 1,1,2-trichloroethane, hexachloroethane, and tetrachloroethylene, increased hepatocellular carcinomas in mice but had little or no action in rats. Iodoform tended to increase thyroid tumors in male rats and hepatocellular carcinomas in male mice. The action of 3-chloropropene was questionable. No tumors could be attributed to 1,1,1-trichloroethane (methylchloroform).

Abstract  Studies were carried out to compare the effects of CCl4 in vivo and in vitro on adrenal and hepatic microsomal metabolism in guinea pigs. CCl4 administration in vivo decreased adrenal and hepatic microsomal cytochrome P-450 concentrations and lowered benzphetamine (BZ) demethylase and benzo(a)pyrene (BP) hydroxylase activities in both tissues. NADPH-cytochrome c reductase activity was decreased in hepatic but not in adrenal microsomes. Addition of CCl4 to adrenal or hepatic microsomes in vitro produced a type 1 difference spectrum suggesting binding of CCl4 to cytochrome(s) P-450; its magnitude was greater in adrenal than in liver. Incubation of adrenal or hepatic microsomes in vitro with CCl4 alone had little or no effect on mixed-function oxidase activity or on lipid peroxidation. When microsomes were incubated with CCl4 + NADPH, the rates of BZ and BP metabolism decreased, cytochrome P-450 concentrations decreased and lipid peroxidation was increased. The effects of CCl4 + NADPH on enzyme activities were greater in adrenal than in hepatic microsomes. Addition of 1.0 mM EDTA or 0.1 mM MnCl2 to the incubation medium blocked the effects of CCl4 + NADPH on lipid peroxidation in adrenal and liver but had no effect on the decreases in mixed-function oxidase activities. The adrenal cortex in the guinea pig was an active site of CCl4 metabolism. CCl4 metabolism resulted in a loss of microsomal enzyme activities in the adrenal and liver. Lipid peroxidation was not obligatory for CCl4-mediated destruction of microsomal enzymes.

Abstract  Presently, there are many uncertainties in risk assessment of volatile organic compounds VOCs, due to a paucity of data relevant to human exposure situations. It is unclear whether the relatively large VOC inhalation toxicity data base can be used qualitatively or quantitatively to forecast the consequences of ingestion of the chemicals in food or water. It is also unclear whether the existing VOC oral toxicity data base, which largely consists of bolus gavage studies, is applicable to drinking water hazard evaluation. The objective of our study was to evaluate the influence of route and pattern of exposure on the pharmacokinetics and target organ toxicity of carbon tetrachloride CCl4. Male Sprague-Dawley rats of 350-400 g inhaled 100 or 1000 ppm CCl4 for 2 hr through a one-way breathing valve.

Abstract  The effects of starvation and protein-deficient diet on the acute carbon tetrachloride (CCl4)-induced hepatotoxicity of the mice were studied histologically and histochemically. A total of 69 male mice (C57BL/6) were used and carbon tetrachloride was administered by a single subcutaneous injection at a dose of 0.1 mg/10 g body weight after starvation for 24 hours and feeding with protein-deficient diet for one month. The changes were examined consecutively. It was shown the the CCl4-induced hepatotoxicity was exaggerated by starvation and that the regeneration after centrilobular necrosis due to CCl4 administration was retarded under this condition. In the CCl4-treated group on protein-deficient diet, the centrilobular liver cells seemed to be less responsive to CCl4.

Abstract  Liver damage was investigated in rat using serum enzyme activities measurements. Responses were recorded 24 h after whole body inhalation exposure to vapors of bromobenzene, carbon tetrachloride, chloroform, o-dichlorobenzene, 1,2-dichloroethane and dimethylformamide as model toxicants. First, rats were exposed during a single 4 h period to different concentrations of each solvent and the minimally active concentration was determined. Second, repeated exposures to chemicals at this concentration level (6 h daily, 2 or 4 days) were used in order to examine whether hepatotoxicity was enhanced. GLDH and SDH are more sensitive and more constant indices than GOT and GPT. It appears that a single exposure period induced more marked serum activities enhancement than repeated exposures

Abstract  The relationship was investigated between biochemical and morphological changes in chloroform (CHCl3)- and carbon tetrachloride (CCl4)-induced liver damage. The time courses of hepatic microsomal cytochrome P450 (CYP) content, hepatic microsomal CYP2E1 activity, hepatic reduced glutathione (GSH) content, plasma alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities were examined in relation to the liver morphology in rats orally treated with CHCl3 or CCl4 (3.35 mmol/kg). The CYP content and the activity of CYP2E1 markedly decreased in the CCl4-treated rats 3 h after treatment compared to much lower decreases in the CHCl3-treated rats. The hepatic GSH content was decreased to a similar extent in both groups of rats at 3 h after treatment; in the CCl4-treated rats, the GSH content continued to decrease, reaching a minimum at 24 h and without attaining the normal level at 72 h after treatment. By contrast, hepatic GSH content in the CHCl3-treated rats began to increase from 6 h, attaining complete recovery 48 h after treatment. Plasma ALT and AST activities were significantly elevated by CCl4 as early as 3 h after treatment, while the activities in the CHCl3-treated rats did not increase until 6 h after treatment. In both groups of rats, ALT and AST activities reached a maximum at 24 h, and gradually decreased, remaining at abnormal levels at 72 h. Hepatic cells in the CCl4-treated rats were found to be necrotic as early as 3 h post-treatment, whereas few or no morphological changes appeared in the liver of CHCl3-treated rats. The extent of necrosis was at a maximum 24 h after treatment in both CHCl3- and CCl4-treated rats. In addition, some necrotic cells remained in the liver of CCl4-treated rats 72 h after treatment, while the necrosis in the CHCl3-treated rats was almost negligible. The present results indicate that almost the same time-courses of biochemical and morphological changes were followed in rats of both the CHCl3- and CCl4-treated groups.

Abstract  The in vivo-in vitro DNA repair and DNA replication assay in mouse hepatocytes has promise as a short-term test for detecting potential mouse liver carcinogens. In addition, this assay may provide information on the mode of action of known hepatic carcinogens. The induction of DNA repair is clearly a response to hepatic DNA damage. However, it is unclear whether induction of replicative DNA synthesis (S phase) represents regenerative hyperplasia in response to hepatotoxicity or is a result of direct mitogenic stimulation of the hepatocytes by the test compound. The objective of the present study was to examine the relationship between hepatotoxicity, which was assessed by measuring serum concentrations of glutamic-oxalacetic transaminase (SGOT), glutamic-pyruvic transaminase (SGPT), alkaline phosphatase (AP), and gammaglutamyl transferase (GGT), and induction of S phase following either single or multiple doses of the model mouse hepatocarcinogen carbon tetrachloride (CCl4). Under the experimental conditions in this study, CCl4 elevated SGPT and SGOT but did not affect serum concentrations of AP or GGT. CCl4 did not induce DNA repair. An increase in the percentage of hepatocytes in S phase followed the appearance of elevated SGOT and SGPT in all single-dose studies. The results from the multiple-dose studies showed a similar relationship except that with 20 mg/kg X d the concentrations of SGOT and SGPT decayed to control values after 14 d of dosing whereas the percentage of hepatocytes in S phase remained markedly elevated (greater than 10 X control). The daily dose of CCl4 that gave a no-observed-effect level for induction of S phase was lower with multiple administrations than it was following a single exposure. A single administration of CCl4 at 25 mg/kg did not increase S phase, SGOT, or SGPT, but if 20 mg/kg X d was given for 7 d the number of hepatocytes in S phase and the concentrations of SGOT and SGPT increased more than 10-fold. These data support the hypothesis that induction of replicative DNA synthesis in the mouse liver following CCl4 administration is related to hepatotoxicity. In single-dose studies elevation in S phase was always associated with elevation of SGOT and SGPT. However, in the multidose studies, SGOT and SGPT declined after 14 d of administering 20 mg/kg X d while S phase remained elevated.(ABSTRACT TRUNCATED AT 400 WORDS)

Abstract  CD-1 mice received carbon tetrachloride daily by gavage for 14 or 90 consecutive days. Corn oil was the vehicle used. The 14-day study involved doses of 625, 1250, and 2500 mg/kg; the 90-day subchronic study involved doses of 12, 120, 540, and 1200 mg/kg. The 14-day study revealed a dose-dependent mortality and decreased body weight in males, whereas females demonstrated mortality only at the high dose. Other dose-dependent findings included decreased fibrinogen and lymphocytes; increased LDH, SGPT (ALT), and SGOT (AST); increased liver weights and ratios in both sexes; and decreased lung, thymus, and kidney weights in males only. There were no compound-related deaths in the 90-day study. There were no consistent compound-related effects on any of the hematological or urinary parameters evaluated. LDH, SGPT (ALT), SGOT (AST), ALP, cholesterol, and bilirubin were increased in an apparent dose-dependent manner while blood glucose levels decreased at all dosage levels. Liver, spleen, and thymus weights and ratios were increased at all dosage levels in both sexes. Histopathology revealed no kidney damage, but liver damage was observed at all doses in both sexes. A no-observable-adverse-effect level was not obtained in these studies.

Abstract  Electron spin resonance spectroscopy has been used to monitor free radicals formed during CCl4 metabolism by perfused livers from phenobarbital-treated rats. Livers were perfused simultaneously with the spin trap phenyl N-t-butylnitrone and with either 12CCl4 or 13CCl4. Perfusate samples and CHCl3:CH3OH extracts of perfusate and liver samples were analyzed for phenyl N-t-butylnitrone radical adducts of reactive free radicals. In the organic extracts, hyperfine coupling constants and 13C isotope effects observed in the ESR spectra indicated the presence of the radical adduct of the trichloromethyl radical. Surprisingly, an additional free radical signal about two orders of magnitude more intense than that of the phenyl N-t-butylnitrone/CCl.3 radical adduct was observed in the aqueous liver perfusate. This adduct was also detected by ESR in rat urine 2 h after intragastric addition of spin trap and CCl4. This radical adduct had hyperfine coupling constants and 13C isotope effects identical with the radical adduct of the carbon dioxide anion radical (CO2-.). Analysis of the pH dependence of the coupling constants yielded a pK alpha of 2.8 for the CO2-. radical adduct formed either in the perfused liver or chemically. Carbon tetrachloride is converted into CCl.3 by cytochrome P-450 through a reductive dehalogenation. The trichloromethyl free radical reacts with oxygen to form the trichloromethyl peroxyl radical, CCl3OO., which may be converted into .COCl and then trapped. This radical adduct would hydrolyze to the carboxylic acid form, which is detected spectroscopically. Alternatively, the carbon dioxide anion free radical could form through complete dechlorination and then react with the spin trap to give the CO2-. radical adduct directly.

Abstract  The 1,N2-propanodeoxyguanosine adducts of trans-4-hydroxy-2-nonenal (HNE-dGp-adducts) were quantitated in tissues of rats treated with trans-4-hydroxy-2-nonenal (HNE) or carbon tetrachloride, respectively, using a 32P-postlabeling method. The method development was based on chemically synthesized HNE-1,N2-propanodeoxyguanosine adduct standard, which was characterized by NMR and mass spectra. The adducts were enriched by Nuclease P1. They were subsequently reacted with γ-32P-ATP to give the respective 3′-5′-bisphosphates, which were two-directionally separated on PEI-cellulose-TLC and quantitated by autoradiography. The labeling efficiency for the adduct standard was 27%, and the recovery of spiked amounts of adduct standard in the enzymatical procedure was about 80%. Internal standard was used to eliminate methodological variations. The determination of the limit of quantitation in DNA from rat tissues by spiking of HNE-dGp-adduct standard revealed a sensitivity of about 20 HNE-dGp-adducts/109 normal nucleotides. Background levels of HNE-dGp-adducts in tissues of rats including liver, kidney, lung, colon and forestomach were found in the range of 18–158 adducts/109 nucleotides with relatively high adduct levels in the liver and low adduct levels in kidney, lung and colon. These background levels were statistically significantly increased by the factor of 2 in liver, lung, colon and forestomach after induction of lipid peroxidation by carbon tetrachloride. The finding that background HNE-dGp-adduct levels may be in context with different metabolic activities of the tissues and the increase of HNE-dGp-adduct levels after application of carbon tetrachloride indicate that HNE-dGp-adducts are an endogenous lesion and that they are probably formed from radical initiated lipid peroxidation.

Abstract  Carbon tetrachloride-mediated hepatotoxicity in mice was influenced by two standard, commercially available diets and by a corn oil treatment vehicle. Animals maintained on Purina 5001 diet were less sensitive than animals maintained on Teklad LM-485 diet to hepatic intoxication by carbon tetrachloride (CCl4). Lower sensitivity of the Purina group was evidenced by significantly lower plasma alanine aminotransferase (ALT) levels and higher hepatic cytochrome P-450 levels at all dosages of CCl4. In addition to the diets, the nature of the corn oil vehicle affected toxicological responses of mice to CCl4. When the vehicle from which tocopherols had been extracted was used, CCl4 elicited about twice the levels of plasma ALT than when nonextracted corn oil was used. In conclusion, the nature of the animal diet and treatment vehicle not only can influence toxicological response, but also can be important considerations in the interpretation of toxicological data.

Abstract  In vivo exposure of B6C3F1 mice to the hepatotoxic chlorinated hydrocarbon, CCl4, suppresses T-cell-dependent humoral immune responses to sRBC. In the present studies, separation-crossover-reconstitution experiments with spleen cell subpopulations isolated from vehicle and CCl4-treated mice (500 mg/kg/day for 7 days) indicate that T-cells are the primary immunologic cell-type altered following CCl4 exposure. Despite suppression of T-cell activity, Con A-activated spleen cell supernatants from CCl4-treated mice produced greater amounts of biologically active IL-2 than untreated spleen cells. Furthermore, Con A-induced upregulation of the p55 subunit of the IL-2 receptor was not altered in spleen cells from CCl4-treated mice. The mediator of immune suppression is a serum-borne factor induced 48 hr following a single exposure to CCl4. Sera isolated from mice treated with CCl4 for 7 days (500 mg/kg/day) or 48 hr following a single exposure (1000 mg/kg) were found to possess high concentrations of TGF-beta 1. Direct addition studies demonstrated that T-cell-dependent AFC responses are more sensitive to suppression by TGF-beta 1 than are T-cell-independent responses. Finally, incubation of sera from CCl4-treated mice with TGF-beta 1-neutralizing mAb reversed the immune suppression associated with this serum. These results demonstrate that CCl4-induced immune suppression is at least partially mediated by induction of TGF-beta 1.

Abstract  The chlorinated methanes, particularly carbon tetrachloride and chloroform, are classic models of liver injury and have developed into important experimental hepatoxicants over the past 50 years. Hepatocellular steatosis and necrosis are features of the acute lesion. Mitochondria and the endoplasmic reticulum as target sites are discussed. The sympathetic nervous system, hepatic hemodynamic alterations, and role of free radicals and biotransformation are considered. With carbon tetrachloride, lipid peroxidation and covalent binding to hepatic constituents have been dominant themes over the years. Potentiation of chlorinated methane-induced liver injury by alcohols, aliphatic ketones, ketogenic compounds, and the pesticide chlordecone is discussed. A search for explanations for the potentiation phenomenon has led to the discovery of the role of tissue repair in the overall outcome of liver injury. Some final thoughts about future research are also presented.

Abstract  A simplified method for the quantitation of DNA damage in nonlabeled hepatocytes, using a fluorometric technique for the quantitation of DNA in conjunction with a modification of the alkaline elution technique of Kohn et al [1976], following chemical treatment in vitro and in vivo, is described. Freshly isolated hepatocytes were treated in vitro with 2-acetylaminofluorene, aflatoxin B1, and dimethylnitrosamine, then examined for DNA damage. Exposure to each of these compounds resulted in DNA damage. Hepatocytes isolated from rats treated with the hepatocarcinogens 2-acetylaminofluorene, benzidine, azoxymethane, dimethylhydrazine, dimethylnitrosamine, and diethylnitrosamine sustained DNA damage as evidenced by increased alkaline elution. DNA damage in hepatocytes was also observed as a result of treatment with methylmethanesulfonate and azaserine. The hepatotoxin carbon tetrachloride did not induce DNA damage in hepatocytes isolated from treated animals. A comparison of the induction of DNA damage and of unscheduled DNA synthesis in hepatocytes from the same animals revealed that in most cases the extent of elution of DNA from filters was proportional to the induction of DNA repair.

Abstract  Abstract: super(1) super(4)C from super(1) super(4)CCl sub(4) irreversibly bind in vivo) to liver DNA from strain A/J mice and Sprague-Dawley rats. Binding of super(1) super(4)CCl sub(4) to DNA was also observed in vitro) in incubation mixtures containing microsomes and a NADPH-generating system as well as in tissue slices. Chemically induced multiplied by CCl sub(3) (CCl sub(4) + benzoyl peroxide system) intensively binds to DNA. Liver nuclear proteins also irreversibly bind CCl sub(4) metabolites. Nuclear protein fractionation studies revealed that deoxyribonucleoproteins, acidic proteins, histones, and residual proteins are the favorite targets of metabolite interaction. Nuclear sap proteins are less intensively labeled. Nuclear lipids were markedly labeled by CCl sub(4) reactive metabolites. Most of the label is in the phospholipid fraction and diphosphatidylglycerol is most intensively labeled; phosphatidylethanolamine, phosphatidylcholine, lysophosphatidylcholine, and sphingomyeline are also labeled by metabolites. ds: carbon tetrachloride evised - 2006-11-01 e field[29]: 1,4-Dioxane

Abstract  The effect of age and peroxidative stress on the concentration of a deoxyguanosine malondialdehyde adduct (dG-MDA) in rat tissues was investigated. Vitamin E deficiency had no effect on the dG-MDA content of liver DNA in rats fed a diet containing 10% corn oil. When 2% cod liver oil was added to this diet, the dG-MDA content of liver DNA doubled in the positive controls fed a high level of vitamin E (100 ppm dl-alpha-tocopherol), and there was a further increase when vitamin E was deleted. Neither iron nitrilotriacetate administration nor choline deficiency had any effect on the dG-MDA content of liver DNA. Carbon tetrachloride had a lowering effect. The failure of iron or carbon tetrachloride administration and of vitamin E deficiency to increase liver dG-MDA is consistent with their failure in previous experiments to affect the urinary excretion of dG-MDA. In contrast, these forms of peroxidative stress produce large increments in the urinary excretion of MDA adducts with lysine, reflecting increased formation and degradation of MDA-modified proteins. DNA appears to be protected from modification by MDA produced at extranuclear sites. The frequency of dG-MDA in different tissues of 4-month-old rats varied markedly: brain >> liver > kidneys and testes. Higher concentrations of dG-MDA were found in the liver and kidneys, but not the testes, of 25-month-old rats. The determinants of the concentration of dG-MDA in DNA merit further investigation.

Abstract  Pretreatment of rats with large doses of vitamin A (VA) potentiates the hepatotoxicity of CCl4. Because our previous studies indicate that VA treatment does not enhance CCl4 metabolism but does enhance CCl4-induced lipid peroxidation and activates liver Kupffer cells to release increased amounts of oxygen-centered free radicals, the current studies were designed to determine if VA treatment potentiates CCl4-induced liver injury through increased release of reactive oxygen species. Plasma clearance of colloidal carbon, an index of Kupffer cell phagocytic activity, was enhanced two- to threefold in rats treated for 7 days with VA (retinol, 250,000 IU/kg per day). Accordingly, VA treatment alone caused Kupffer cell activation. To determine if these activated Kupffer cells could potentiate hepatic injury through release of reactive oxygen species upon CCl4 challenge, polyethylene glycol coupled-superoxide dismutase (PEG-SOD, 10,000 IU/kg) or -catalase (PEG-CAT, 40,000 IU/kg) was given iv 2 hr after CCl4 (0.15 ml/kg, ip) to control or VA-pretreated rats to quench any released reactive oxygen. PEG-SOD and PEG-CAT effectively blocked VA potentiation of CCl4 liver injury as assessed at 24 hr by change in plasma ALT. Methylpalmitate (MP, 2 g/kg), an inhibitor of Kupffer cell phagocytosis and related oxygen burst, also blocked the potentiation of liver injury when given iv 24 hr before CCl4 to VA-pretreated rats. At the doses used, PEG-SOD or PEG-CAT did not influence CCl4 toxicity in control rats (at 0.15 or 2 ml CCl4/kg). Importantly, SOD, CAT, and MP blocked the enhanced lipid peroxidation induced by CCl4 in VA-pretreated rats. From these findings we conclude that the potentiation of CCl4 liver injury by VA pretreatment is mediated, at least in part, by active oxygen species released from Kupffer cells and possibly other macrophages that are activated by VA. Supporting this conclusion is the failure of VA pretreatment to increase the release of LDH from suspension of hepatocytes incubated with CCl4.