Metabolic effects of acetaminophen. Studies in the isolated perfused rat liver

Toluidine blue O directly and photodynamically impairs the bioenergetics of liver mitochondria: a potential mechanism of hepatotoxicity

Toluidine blue O (TBO) is a phenothiazine dye that, due to its photochemical characteristics and high affinity for biomembranes, has been revealed as a new photosensitizer (PS) option for antimicrobial photodynamic therapy (PDT). This points to a possible association with membranous organelles like mitochondrion. Therefore, here we investigated its effects on mitochondrial bioenergetic functions both in the dark and under photostimulation. Two experimental systems were utilized: (a) isolated rat liver mitochondria and (b) isolated perfused rat liver. Our data revealed that, independently of photostimulation, TBO presented affinity for mitochondria. Under photostimulation, TBO increased the protein carbonylation and lipid peroxidation levels (up to 109.40 and 119.87%, respectively) and decreased the reduced glutathione levels (59.72%) in mitochondria. TBO also uncoupled oxidative phosphorylation and photoinactivated the respiratory chain complexes I, II, and IV, as well as the F_oF₁-ATP synthase complex. Without photostimulation, TBO caused uncoupling of oxidative phosphorylation and loss of inner mitochondrial membrane integrity and inhibited very strongly succinate oxidase activity. TBO's uncoupling effect was clearly seen in intact livers where it stimulated oxygen consumption at concentrations of 20 and 40 μM. Additionally, TBO (40 μM) reduced cellular ATP levels (52.46%) and ATP/ADP (45.98%) and ATP/AMP (74.17%) ratios. Consequently, TBO inhibited gluconeogenesis and ureagenesis whereas it stimulated glycogenolysis and glycolysis. In conclusion, we have revealed for the first time that the efficiency of TBO as a PS may be linked to its ability to photodynamically inhibit oxidative phosphorylation. In contrast, TBO is harmful to mitochondrial energy metabolism even without photostimulation, which may lead to adverse effects when used in PDT.

The Hepatic Mitochondrial Pyruvate Carrier as a Regulator of Systemic Metabolism and a Therapeutic Target for Treating Metabolic Disease

Pyruvate sits at an important metabolic crossroads of intermediary metabolism. As a product of glycolysis in the cytosol, it must be transported into the mitochondrial matrix for the energy stored in this nutrient to be fully harnessed to generate ATP or to become the building block of new biomolecules. Given the requirement for mitochondrial import, it is not surprising that the mitochondrial pyruvate carrier (MPC) has emerged as a target for therapeutic intervention in a variety of diseases characterized by altered mitochondrial and intermediary metabolism. In this review, we focus on the role of the MPC and related metabolic pathways in the liver in regulating hepatic and systemic energy metabolism and summarize the current state of targeting this pathway to treat diseases of the liver. Available evidence suggests that inhibiting the MPC in hepatocytes and other cells of the liver produces a variety of beneficial effects for treating type 2 diabetes and nonalcoholic steatohepatitis. We also highlight areas where our understanding is incomplete regarding the pleiotropic effects of MPC inhibition.

Metabolic network-based predictions of toxicant-induced metabolite changes in the laboratory rat

In order to provide timely treatment for organ damage initiated by therapeutic drugs or exposure to environmental toxicants, we first need to identify markers that provide an early diagnosis of potential adverse effects before permanent damage occurs. Specifically, the liver, as a primary organ prone to toxicants-induced injuries, lacks diagnostic markers that are specific and sensitive to the early onset of injury. Here, to identify plasma metabolites as markers of early toxicant-induced injury, we used a constraint-based modeling approach with a genome-scale network reconstruction of rat liver metabolism to incorporate perturbations of gene expression induced by acetaminophen, a known hepatotoxicant. A comparison of the model results against the global metabolic profiling data revealed that our approach satisfactorily predicted altered plasma metabolite levels as early as 5 h after exposure to 2 g/kg of acetaminophen, and that 10 h after treatment the predictions significantly improved when we integrated measured central carbon fluxes. Our approach is solely driven by gene expression and physiological boundary conditions, and does not rely on any toxicant-specific model component. As such, it provides a mechanistic model that serves as a first step in identifying a list of putative plasma metabolites that could change due to toxicant-induced perturbations.

Hepatoprotective effect of Lycopodium clavatum 30CH on experimental model of paracetamol-induced liver damage in rats

INTRODUCTION

Homeopathic Lycopodium clavatum is indicated for disorders of the digestive system and its accessory organs, including atony of the liver and liver tissue failure. Tis suggests that it may have action on drug-induced hepatitis, as occurs in paracetamol overdose.

PURPOSE

To evaluate the effectiveness of Lycopodium clavatum 30C (Lyc) as a hepatoprotector against liver damage experimentally induced by paracetamol (Pct) in Wistar rats.

METHODOLOGY

Thirty animals subdivided into 6 groups were used. Animals from the treated groups were pretreated for 8 days with Lyc 30c (0.25 ml/day), receiving a dose of 3 g/kg of Pct on the 8th day. A positive control group received similar treatment, replacing Lyc 30c with 30% ethanol and a negative control received only 30% ethanol. After 24 and 72 h, the animals were sacrificed for tissue and blood sample collection. Subsequently, enzyme serum measurements indicative of liver damage (aspartate-aminotransferase (AST) and Alanine-aminotransferase (ALT)) and liver histological and morphometric analyses were performed.

RESULTS

Pretreatment with Lyc 30c reduced hepatic lesions produced by Pct overdose as evidenced by a significant reduction (p < 0.05) in ALT levels in the LyP 24h-group (901.04 ± 92.05 U/l) compared to the respective control group (1866.28 ± 585.44 U/l), promoted a significant decrease in the number of acinar zone 1 affected by necrosis and inflammatory infiltration (15.46 ± 13.86 clr/cm(2) in LyP72 for 73.75 ± 16.60 clr/cm(2) in PC72), and inhibition of 1,2-glycol (glycogen) depletion in zone 3 (a significant reduction in Lyc 72 h group animals in comparison to the control group). Significant changes concerning the development of fibrosis or alterations in transaminase levels were not observed after 72 h.

CONCLUSION

Lyc 30c exerted a moderate hepatoprotective effect on acute Pct-induced hepatitis, mainly shown by a histological decrease in necrosis and inflammatory foci, preserved glycogen and other 1,2-glycols in zone 3 and reduced serum levels of ALT and AST.

Effects of an Agaricus blazei aqueous extract pretreatment on paracetamol-induced brain and liver injury in rats

The action of an Agaricus blazei aqueous extract pretreatment on paracetamol injury in rats was examined not only in terms of the classical indicators (e.g., levels of hepatic enzymes in the plasma) but also in terms of functional and metabolic parameters (e.g., gluconeogenesis). Considering solely the classical indicators for tissue damage, the results can be regarded as an indication that the A. blazei extract is able to provide a reasonable degree of protection against the paracetamol injury in both the hepatic and brain tissues. The A. blazei pretreatment largely prevented the increased levels of hepatic enzymes in the plasma (ASP, ALT, LDH, and ALP) and practically normalized the TBARS levels in both liver and brain tissues. With respect to the functional and metabolic parameters of the liver, however, the extract provided little or no protection. This includes morphological signs of inflammation and the especially important functional parameter gluconeogenesis, which was impaired by paracetamol. Considering these results and the long list of extracts and substances that are said to have hepatoprotective effects, it would be useful to incorporate evaluations of functional parameters into the experimental protocols of studies aiming to attribute or refute effective hepatoprotective actions to natural products.

Prooxidant activity of fisetin: effects on energy metabolism in the rat liver

Flavonols, which possess the B-catechol ring, as quercetin, are capable of producing o-hemiquinones and to oxidize NADH in a variety of mammalian cells. The purpose of this study was to investigate whether fisetin affects the liver energy metabolism and the mitochondrial NADH to NAD+ ratio. The action of fisetin on hepatic energy metabolism was investigated in the perfused rat liver and isolated mitochondria. In isolated mitochondria, fisetin decreased the respiratory control and ADP/O ratios with the substrates α-ketoglutarate and succinate. In the presence of ADP, respiration of isolated mitochondria was inhibited with both substrates, indicating an inhibitory action on the ATP-synthase. The stimulation of the ATPase activity of coupled mitochondria and the inhibition of NADH-oxidase activity pointed toward a possible uncoupling action and the interference of fisetin with mitochondrial energy transduction mechanisms. In livers from fasted rats, fisetin inhibited ketogenesis from endogenous sources. The β-hydroxybutyrate/ acetoacetate ratio, which reflects the mitochondrial NADH/NAD+ redox ratio, was also decreased. In addition, fisetin (200 μM) increased the production of (14)CO2 from exogenous oleate. The results of this investigation suggest that fisetin causes a shift in the mitochondrial redox potential toward a more oxidized state with a clear predominance of its prooxidant activity.

Dose-dependent hepatoprotective effect of emodin against acetaminophen-induced acute damage in rats

Protective effect of emodin (1,3,8-trihydroxy-6-methyl anthraquinone), an active compound of Ventilago madraspatana Gaertn., was evaluated against acetaminophen-induced biochemical and histological alterations in rats. Acetaminophen (2g/kg, po) administration caused significant elevation in the release of serum transaminases, alkaline phosphatase, lactate dehydrogenase, serum bilirubin and serum protein with concomitant decrease in hemoglobin and blood sugar after 24h of its administration. Toxicant exposure intensified the lipid peroxidation and altered glutathione status, activities of adenosine triphosphatase, acid phosphatase, alkaline phosphatase as well as major cellular constituents i.e., protein, glycogen and total cholesterol in liver and kidney. Treatment of emodin (20, 30 and 40 mg/kg, po) significantly lessened the toxicity by protecting acetaminophen-induced alterations in various blood and tissue biochemical variables after 24h of its administration. Acetaminophen administration initiated histological damage in liver. Some degree of protection was seen after emodin therapy in a dose-dependent manner. Emodin at doses of 30 and 40 mg/kg effectively reversed toxic events induced by acetaminophen as same as silymarin (50mg/kg, po). Thus, the study concluded that emodin at a dose of 30 mg/kg (po) possesses optimum hepatoprotective ability against acetaminophen-induced toxicity.

Reversal of acetaminophen induced subchronic hepatorenal injury by propolis extract in rats

The ethanolic extract of propolis (200mg/kg, p.o.) was evaluated against acetaminophen (APAP; 20mg/kg, p.o.) induced subchronic hepatorenal injury in rats. Administration of APAP significantly increased the release of serum transaminases, alkaline phosphatase, lactate dehydrogenase, γ-glutamyl transpeptidase, bilirubin and serum proteins, whereas concomitantly decreased hemoglobin, blood sugar and albumin. Hepatorenal reduced glutathione and activities of superoxide dismutase and catalase, hepatic CYPs i.e., aniline hydroxylase and amidopyrine-N-demethylase were significantly decreased after APAP intoxication. Lipid peroxidation showed significant elevation in both organs significantly after APAP assault. Total proteins, glycogen contents and the activities of certain metabolic enzymes i.e., adenosine triphosphatase, alkaline phosphatase and acid phosphatase were altered after APAP administration. Propolis extract exhibited curative effects by reversing APAP induced alterations in blood biochemical variables, CYP enzymes and markers of oxidative stress. Histopathological analysis of liver and kidney was consistent with the biochemical findings and led us to conclude the curative potential of propolis against APAP induced hepatorenal injury.

Metabolic effects of carbenoxolone in rat liver

The action of carbenoxolone on hepatic energy metabolism was investigated in the perfused rat liver and isolated mitochondria. In perfused livers, carbenoxolone (200-300 microM) increased oxygen consumption, glucose production and glycolysis from endogenous glycogen. Gluconeogenesis from lactate or fructose, an energy-dependent process, was inhibited. This effect was already evident at a concentration of 25 microM. The cellular ATP levels and the adenine nucleotide content were decreased by carbenoxolone, whereas the AMP levels were increased. In isolated mitochondria, carbenoxolone stimulated state IV respiration and decreased the respiratory coefficient with the substrates beta-hydroxybutyrate and succinate. The ATPase of intact mitochondria was stimulated, the ATPase of uncoupled mitochondria was inhibited, and the ATPase of disrupted mitochondria was not altered by carbenoxolone. These results indicate that carbenoxolone acts as an uncoupler of oxidative phosphorylation and, possibly, as an inhibitor of the ATP/ADP exchange system. The inhibitory action of carbenoxolone on mitochondrial energy metabolism could be contributing to induce the mitochondrial permeability transition (MPT), a key phenomenon in apoptosis. The results of the present study can explain, partly at least, the in vivo hepatotoxic actions of carbenoxolone that were found in a previous clinical evaluation.

The action of extracellular NAD+ on gluconeogenesis in the perfused rat liver

In the rat liver NAD+ infusion produces increases in portal perfusion pressure and glycogenolysis and transient inhibition of oxygen consumption. The aim of the present work was to investigate the possible action of this agent on gluconeogenesis using lactate as a gluconeogenic precursor. Hemoglobin-free rat liver perfusion in antegrade and retrograde modes was used with enzymatic determination of glucose production and polarographic assay of oxygen uptake. NAD+ infusion into the portal vein (antegrade perfusion) produced a concentration-dependent (25-100 microM) transient inhibition of oxygen uptake and gluconeogenesis. For both parameters inhibition was followed by stimulation. NAD+ infusion into the hepatic vein (retrograde perfusion) produced only transient stimulations. During Ca2+-free perfusion the action of NAD+ was restricted to small transient stimulations. Inhibitors of eicosanoid synthesis with different specificities (indo-methacin, nordihydroguaiaretic acid, bromophenacyl bromide) either inhibited or changed the action of NAD+. The action of NAD+ on gluconeogenesis is probably mediated by eicosanoids synthesized in non-parenchymal cells. As in the fed state, in the fasted condition extracellular NAD+ is also able to exert two opposite effects, inhibition and stimulation. Since inhibition did not manifest significantly in retrograde perfusion it is likely that the generating signal is located in pre-sinusoidal regions.

Effects of the Kielmeyera coriacea extract on energy metabolism in the rat liver

Kielmeyera coriacea Mart is a medicinal plant of the Clusiacea (Guttiferae) family used by the native population of Brazil in the treatment of several tropical diseases such as malaria, schistosomiasis, leishmaniasis, and fungal or bacterial infections. Kielmeyera coriacea is also effective as an antidepressant drug. Extracts of the plant are rich in xanthones. Compounds of this class have been reported to inhibit mitochondrial energy metabolism. For this reason the action of the Kielmeyera coriacea extract on hepatic energy metabolism was investigated in the present work, using isolated rat liver mitochondria and the perfused rat liver. In perfused livers the extract (20-80 microg/ml) caused stimulation of oxygen consumption, inhibition of gluconeogenesis and stimulation of glycogenolysis and glycolysis. In isolated mitochondria the Kielmeyera coriacea extract (5-20 microg/ml) stimulated state IV respiration, reduced the ADP/O ratio and decreased the respiratory coefficient. The activities of succinate-oxidase, NADH-oxidase, NADH dehydrogenase and succinate dehydrogenase were inhibited. The ATPase of intact mitochondria was stimulated and the ATPase of uncoupled mitochondria was inhibited. The results of this investigation suggest that the Kielmeyera coriacea extract impairs the hepatic energy metabolism by acting as mitochondrial uncoupler and inhibitor of enzymatic activities linked to the respiratory chain. The impairment of mitochondrial energy metabolism could lead to adverse metabolic effects by the use of the crude extract, but it could equally be the basis of its antiprotozoan and antifungal effects.

Metabolic effects ofp-coumaric acid in the perfused rat liver

The p-coumaric acid, a phenolic acid, occurs in several plant species and, consequently, in many foods and beverages of vegetable origin. Its antioxidant activity is well documented, but there is also a single report about an inhibitory action on the monocarboxylate carrier, which operates in the plasma and mitochondrial membranes. The latter observation suggests that p-coumaric acid could be able to inhibit gluconeogenesis and related parameters. The present investigation was planned to test this hypothesis in the isolated and hemoglobin-free perfused rat liver. Transformation of lactate and alanine into glucose (gluconeogenesis) in the liver was inhibited by p-coumaric acid (IC50 values of 92.5 and 75.6 microM, respectively). Transformation of fructose into glucose was inhibited to a considerably lower degree (maximally 28%). The oxygen uptake increase accompanying gluconeogenesis from lactate was also inhibited. Pyruvate carboxylation in isolated intact mitochondria was inhibited (IC50 = 160.1 microM); no such effect was observed in freeze-thawing disrupted mitochondria. Glucose 6-phosphatase and fructose 1,6-bisphosphatase were not inhibited. In isolated intact mitochondria, p-coumaric acid inhibited respiration dependent on pyruvate oxidation but was ineffective on respiration driven by succinate and beta-hydroxybutyrate. It can be concluded that inhibition of pyruvate transport into the mitochondria is the most prominent primary effect of p-coumaric acid and also the main cause for gluconeogenesis inhibition. The existence of additional actions of p-coumaric acid, such as enzyme inhibitions and interference with regulatory mechanisms, cannot be excluded.

Metabolic effects of propofol in the isolated perfused rat liver

Inhibitory effects of the intravenous anaesthetic propofol on mitochondrial energy metabolism have been reported by several authors. Impairment of energy metabolism is usually coupled to reduction in ATP production, which in turn is expected to lead to several alterations in cell metabolism such as stimulation of glycolysis and inhibition of gluconeogenesis. The present work aimed at finding an answer to the question of how propofol affects energy metabolism-linked parameters in the isolated perfused rat liver. In the fed state, propofol increased glycogenolysis (glucose release), glycolysis (lactate and pyruvate production) and oxygen uptake in the range between 10 and 500 microM. In the liver of fasted rats, propofol up to 100 microM increased oxygen uptake but decreased gluconeogenesis from three different substrates: lactate, alanine and glycerol. When lactate was the substrate 50% inhibition occurred at a propofol concentration of 50 microM. Propofol (100 microM) decreased the ATP content of the liver (-33.3%), increased the AMP content (+25%) and decreased the ATP/ADP and ATP/AMP ratios (49 and 45%, respectively). Most effects of propofol are probably due to impairment of oxidative phosphorylation. Particularly, the combined differential action on oxygen uptake (stimulation) and gluconeogenesis (inhibition) is strongly suggestive of an uncoupling action also under the conditions of the intact cell. This effect, in turn, is consistent with the reported high affinity of the cellular hepatic structure, especially membranes, for propofol.

The action of oxybutynin on haemodynamics and metabolism in the perfused rat liver

The present study was planned to investigate the possible action of oxybutynin on liver haemodynamics and its influence on metabolic variables. The isolated liver perfused either bivascularly or monovascularly in the non-recirculating system was used for the experiments and Krebs/Henseleit-bicarbonate buffer (pH 7.4) as a perfusion fluid. Oxybutynin (25-200 microM) was infused, the infusion time for each concentration being 14 min. Portally infused oxybutynin increased the perfusion pressure starting at 100 microM. Oxygen uptake was diminished, also starting at 100 microM. Arterially infused oxybutynin also increased the perfusion pressure in the hepatic artery. Lactate and pyruvate releases were considerably diminished by oxybutynin. Glucose release showed a small initial stimulation, then returned to values slightly below the basal ones. Cessation of oxybutynin infusion resulted in progressive stimulation of glucose release. When Ca2+ was omitted all effects of oxybutynin vanished. The hepatic contents of glucose, glucose 6-phosphate and lactate in the presence of 200 microM oxybutynin increased 7.8-, 4.6- and 5.1 times, respectively. The pyruvate content was not changed. The ATP content was diminished by 26.6% in the presence of 200 microM oxybutynin, but the AMP content was increased by 64.3%. The ADP content was not changed. Apparently, upon administration of oxybutynin, a considerable fraction of the liver parenchyma ceased to be irrigated or almost so, which is apparent from the concomitant inhibition of oxygen uptake, pressure increase and inhibition of glucose, lactate and pyruvate release together with the simultaneous intracellular accumulation of glucose, lactate and glucose 6-phosphate.

Modulation of paracetamol metabolism by Kupffer cells: a study on rat liver slices

Recent studies support the hypothesis that non parenchymal cells (mainly macrophages) may play a role in the metabolism and cellular effects of paracetamol. In order to investigate this hypothesis, male Wistar rats were intravenously injected with either 7.5 mg/kg gadolinium chloride (Gd+) or NaCl 0.9% (Gd-). The treatment with GdCl3 decreased the number and the function of Kupffer cells in liver tissue, as assessed by the histological examination of the liver after colloidal carbon injection in the portal vein. Precision-cut liver slices (PCLS) were prepared from both groups of rats and cultured for 8h in Waymouth's medium in the presence and absence of 5 mM paracetamol. Interestingly, PCLS obtained from Gd+ rats exhibited a lower release of tumor necrosis factor (TNF-alpha) and a better viability than PCLS from control (Gd-) rats. Incubation with paracetamol led to a decreased glycogen level in liver slices from Gd+ or Gd-, without modifying neither liver morphology nor ATP level nor LDH release. A higher proportion of paracetamol glucuronide, was secreted from the slices obtained from Gd+ rats. These data suggest that Kupffer cells could affect the viability of PCLS in culture and are involved in the regulation of phase II metabolism in the adjacent hepatocytes. We propose that PCLS in culture is a suitable model to elucidate the biochemical mechanism underlying the modulation of metabolism occurring through hepatocytes-Kupffer cells interactions.

Uncoupling effects of diclofenac and aspirin in the perfused liver and isolated hepatic mitochondria of rat

Gluconeogenesis, glycolysis and glycogenolysis were studied in rat perfused liver following the infusion of various concentrations of diclofenac and aspirin, two non-steroidal anti-inflammatory drugs (NSAIDs). Glucose synthesis was measured in livers isolated from 48-h fasted rats perfused with Krebs-Henseleit bicarbonate buffer containing L-lactate (2 mM) and pyruvate (0.1 mM) as precursors. Both diclofenac (0.01-0.1 mM) and aspirin (1-10 mM) had an inhibitory effect on gluconeogenesis (GNG). The inhibition was dose-dependent and reversible. For the estimation of glycogenolysis and glycolysis, the rates of glucose release and of lactate and pyruvate production were measured in livers of well-fed rats perfused with substrate-free buffer. Infusion of diclofenac (0.1 mM) or aspirin (5 mM) strongly stimulated glycogenolysis and glycolysis (GGL/GL). In general, an increased oxygen consumption by the liver tissue was also noted in both types of experiments, as deduced from the continuous monitoring of oxygen concentration changes in the effluent. Such a pattern of response can be attributed to the uncoupling effects of the two drugs on oxidative phosphorylation. Measurements of respiration rates and membrane potential in isolated liver mitochondria submitted to various concentrations of diclofenac and aspirin confirms this assumption. Thus, 0.01 to 0.2 mM diclofenac stimulates state-4 respiration and slightly inhibits state 3, decreasing the respiratory control ratio, while the membrane potential is decreased or collapsed (depending on the drug concentration). Similar effects are recorded for aspirin at higher concentrations (0.2-5 mM), even though state 3 is not affected in this case. Arguments are presented that the concentrations of the drugs used largely correspond to the pharmacological doses employed in antipyretic and anti-inflammatory treatments. Therefore, a greater consideration should be given to the uncoupling effect, at least from the toxicological viewpoint.

Protective effect of nifedipine against cytotoxicity and intracellular calcium alterations induced by acetaminophen in rat hepatocyte cultures

Alteration of calcium homeostasis has been proposed to play a major role in cell necrosis induced by a variety of chemical agents such as acetaminophen (APAP). In this study, a potential protective effect of the dihydropyridine calcium channel blocking agent, nifedipine, was investigated in vitro on acetaminophen-induced hepatocyte damage. Rat hepatocytes were exposed during 20 hours to various concentrations of APAP (0.50 to 4.00 mM). The following metabolic and functional parameters were investigated: -lactate dehydrogenase (LDH) release as an indicator of plasma membrane integrity, -cell viability evaluated by the colorimetric MTT assay, and intracellular calcium concentration as evaluated by two fluorimetric methods: a scanning laser cytometer using indo-1-AM as fluorescent probe and a fluorescence plate reader using fluo-3-AM as calcium indicator. Incubation of hepatocytes with APAP alone in the range 0.50 to 4.00mM resulted in a dose-response relationship with regard to LDH release (243% to 750% of control) and to the loss of cell viability (0 to 67% of control). Moreover these results were correlated with a significant increase in cytosolic calcium content (189 to 406 nM). Nifedipine treatment prior to APAP exposure, partially prevented LDH release, the plasma membrane blebbing, and thereby the loss of viability. In addition, intracellular calcium level progressively returned within the limits of the control values with increasing concentrations of nifedipine. It can be concluded that, in vitro conditions, nifedipine pretreatment exhibits a preventive effect against acetaminophen hepatocyte injury.

The toxicological relevance of paracetamol-induced inhibition of hepatic respiration and ATP depletion

In order to elucidate the role of mitochondrial dysfunction in paracetamol-induced hepatotoxicity, the effects of paracetamol on the oxygen consumption and ATP content of the isolated perfused rat liver were correlated with parameters of hepatic viability and hepatotoxicity. Paracetamol at 5 g/L reduced the oxygen consumption of the livers by about 80% and hepatic ATP content by 96%. Hepatotoxicity was evident from the nearly complete interruption of bile secretion, a marked release of enzymes [glutamate-pyruvate transaminase (GPT), lactate dehydrogenase (LDH)] in the perfusate, a depletion of hepatic glutathione and an accumulation of calcium in the liver. Paracetamol-induced hepatotoxicity could be prevented completely by using livers from non-fasted rats as well as by addition of fructose to the perfusate of livers from fasted animals. Both treatments resulted in an increased energy supply from anaerobic glycolysis as evidenced by a large release of lactate and pyruvate into the perfusate, but did not inhibit paracetamol-induced decline of oxygen consumption. The decrease in hepatic oxygen consumption depended on the dose of paracetamol and occurred first at a concentration of 0.2 g/L (-10%). LDH and GPT release, on the other hand, was elevated at 2 and 5 g/L and calcium accumulation occurred at 5 g/L paracetamol only. Inhibition of mixed-function oxidases by dithiocarb did not prevent the decrease in oxygen consumption and the resulting hepatic injury induced by paracetamol. The oral administration of the high dose of 5 g/kg paracetamol in vivo to rats exerted strong hepatotoxicity but produced maximal serum levels of 800 mg/L paracetamol only and did not decrease hepatic oxygen consumption as measured in vitro. Our results show that in the isolated perfused rat liver in vitro, only high concentrations of paracetamol can produce "chemical hypoxia" by attacking mitochondria so as to cause hepatic injury. Such high concentrations of paracetamol are not attained in vivo, however. "Chemical hypoxia", thus, seems not to be relevant to the well-known hepatotoxic action of paracetamol.