Carbon tetrachloride hepatotoxicity in endotoxin tolerant and polymyxin B-treated rats

Gut-derived endotoxin has been implicated in the hepatotoxic effects of CCl4. The present study has investigated whether two procedures known to block LPS effects would alter the action of CCl4 to decrease hepatic cytochrome P-450 and microsomal drug-metabolizing activity. Administration of polymyxin B or induction of LPS tolerance were shown to attenuate the effect of CCl4 administration to increase SGOT and SGPT levels, signs of hepatic damage. Polymyxin B administration but not LPS tolerance caused a slight decrease in cytochrome P-450. In pretreated animals given CCl4, only those which had received polymyxin B showed a reduced effect of CCl4 to alter cytochrome P-450 level and activity. However, the apparent protective effect was of the same magnitude as the loss of cytochrome P-450 caused by polymyxin B itself. These results suggest that the ability of polymyxin B to ablate the CCl4 loss of P-450 might be due to a reduced metabolic activation of CCl4 by P-450 and not due to any anti-LPS activity. The results suggest that gut-derived LPS does not participate in the effect of CCl4 decreasing cytochrome P-450-mediated reactions. However, participation of LPS in other hepatotoxic effects of CCl4 is not excluded.     

Effect of endotoxin to differentially affect cytochrome P-450 monooxygenase activities of untreated rats and animals induced with phenobarbital or 3-methylcholanthrene

The effect of endotoxin in decreasing the cytochrome P-450-dependent metabolism of aniline, aminopyrine and ethoxycoumarin was examined in untreated rats, and in rats pretreated with either phenobarbital or 3-methylcholanthrene. Ethoxycoumarin metabolism was determined at two substrate concentrations (5 microM and 500 microM) to determine the effect of endotoxin on the high and low affinity enzyme activities. In untreated animals, endotoxin depressed both aniline and ethoxycoumarin metabolism by the high and low affinity enzymes by approximately 70%, but aminopyrine was decreased by only 47%. In phenobarbital pretreated rats, endotoxin decreased enzyme activities less than in untreated animals. Aniline metabolism and low affinity ethoxycoumarin metabolism were decreased by only 24%, and aminopyrine metabolism was decreased by 35%. The high affinity ethoxycoumarin metabolism was least affected, being decreased by only 12%. In 3-methycholanthrene pretreated rats, aniline and ethoxycoumarin (500 microM) metabolism were decreased by approximately 45%, but aminopyrine metabolism was only decreased by 20%. In these animals, endotoxin did not significantly affect the activity of ethoxycoumarin metabolism assayed with the low substrate concentration. Endotoxin decreased total cytochrome P-450 level of untreated rats by 32%, of phenobarbital pretreated rats by 39%, and in 3-methylcholanthrene pretreated animals the decrease was only 21%. Heme oxygenase activity of untreated animals was induced most by endotoxin administration and least in phenobarbital treated rats. The data suggest that endotoxin may differentially affect the various isozymes of cytochrome P-450 associated with the metabolism of aniline, aminopyrine and ethoxycoumarin. The results also suggest that the isozymes associated with these activities in untreated, phenobarbital or 3-methylcholanthrene pretreated rats may differ in their sensitivity to the effect of endotoxin.     

Role of interleukin-1 in the depression of liver drug metabolism by endotoxin.

Endotoxin-resistant C3H/HeJ mice were used to test the hypothesis that a macrophage product, possibly interleukin-1, might mediate the depression of liver cytochrome P-450-dependent drug metabolism in endotoxin-treated mice. Depression of liver drug metabolism by endotoxin was observed in normal mice (C3H/HeN) but not in C3H/HeJ mice. Serum transfer experiments demonstrated that a serum factor was responsible for the depression of liver drug metabolism. Experiments of passive transfer of peritoneal macrophages showed that this endotoxin-induced factor might be a macrophage product. In vitro experiments showed that endotoxin-stimulated monocytes produced a factor that depressed cytochrome P-450-dependent metabolism in cultured hepatocytes. Homogeneous human monocyte and recombinant interleukin-1 also depressed liver drug metabolism both in vivo and in vitro, suggesting that this macrophage product might be involved in the regulation of liver function by the immune system.     

Interactions between cyclosporin A, indomethacin and 16,16-dimethyl prostaglandin E2: effects on renal, hepatic and gastrointestinal toxicity in the rat

Rats were treated for 3 or 14 days with cyclosporin A (CsA, 50 mg/kg) or indomethacin (2 or 5 mg/kg) either alone or in combination, or with CsA plus 16,16-dimethylprostaglandin E2 (DMPGE2, 0.25 mg/kg). Hepatic and renal function were unaffected by treatment with indomethacin at either dose and only at the higher dose was severe intestinal ulceration observed. CsA caused renal and hepatic toxicity, evidenced by increased urine N-acetyl-beta-D-glucosaminidase activity, serum urea, creatinine and bilirubin and decreased serum albumin and total protein. In rats cotreated with CsA and either dose of indomethacin the increases in serum urea and creatinine and decreases in serum albumin and total protein were accentuated, but serum bilirubin was not further increased. Intestinal lesions were present in rats treated for 14 days with CsA plus the lower dose of indomethacin, but not in rats treated with either drug alone. In rats treated with DMPGE2 plus CsA, serum urea and creatinine were normal and urine N-acetyl-beta-D-glucosaminidase activity was reduced compared to rats treated with CsA alone, but DMPGE2 cotreatment had no effect on the CsA induced hyperbilirubinaemia. Hepatic microsomal cytochrome P-450 concentration and aminopyrine N-demethylase activity were lower in rats treated with CsA plus indomethacin than in untreated rats or those treated with either drug alone. Coadministration of indomethacin or DMPGE2 had no effect on serum trough CsA levels. The results are interpreted as showing an exacerbation by CsA of the intestinal toxicity of indomethacin, an increase by indomethacin in the renal toxicity of CsA and a protection by DMPGE2 against CsA renal toxicity. Possible mechanisms involving drug interactions and either hepatic cytochrome P-450, renal cyclooxygenase or other renal sites are discussed.     

Protective effect of interferon inducers against hyperoxic pulmonary damage

Interferon inducers, poly I:poly C, endotoxin, hepatic RNA, and Tilorone, were administered to rats at different time points in relation to the onset of hyperoxic exposure (O2 greater than 97%). All interferon inducers tested significantly reduced the mortality of rats when compared with the control groups. In hyperoxia alone, malondialdehyde, a product of lipid peroxidation, was significantly increased and the microsomal enzyme NADPH cytochrome c reductase decreased as measured in the whole lung. With the administration of either endotoxin or poly I:poly C these two parameters remained within the range of control values. These data suggest that the administration of interferon inducers protects against hyperoxic microsomal damage. After the administration of these interferon inducers with or without hyperoxia the increased activity of heme oxygenase and marked reduction of the heme content of microsomes were demonstrated. Since cytochrome P-450 and b5 are the major hemoproteins of microsomes and the known source of oxygen-free radical generation, the results obtained in this study appear to indicate that the depression of the hemoprotein of microsomes by the administration of interferon inducers may be largely responsible for the protective effects of these agents against hyperoxia.     

Effects of chlordane pretreatment on the hepatotoxicity of carbon tetrachloride.

Male albine rats weighing approximately 200 g received intraperitoneal injections of chlordane (25 mg/kg) in olive oil on each of three successive days. Controls included animals given only olive oil and untreated rats. Twenty-four hours after the last dose, augmented hepatic drug-metabolizing enzyme activity in chlordane-treated rats was reflected in vivo by a reduction in zoxazolamine-paralysis time and in vitro by an increased hepatic microsomal cytochrome P-450 level. The insecticide-treated animals did not, however, display any increase of hepatic microsomal NADPH-cytochrome c reductase activity. In chlordane-treated rats, electron microscopy revealed overt proliferation of smooth endoplasmic reticulum in the hepatocytes, particularly in those located in the central one-third to one-half of the liver lobules. Olive oil-treated controls showed no alterations in paralysis time, microsomal enzyme activity, or hepatocellular ultrastructure, when compared to the untreated animals.Identically prepared chlordane-treated and control rats then were challenged with an intraperitoneal injection of carbon tetrachloride (0.5 ml of a 25% solution of CCl₄ in olive oil). Some animals from each group were killed at 4 hr after the toxic challenge; and it was determined that, in each category, there was a sharp drop in hepatic microsomal cytochrome P-450 but no change in NADPH-cytochrome c reductase, as compared to prechallenge levels. The reduction in cytochrome P-450 was most striking in the insecticide-stimulated rats. The remaining animals from each CCl₄-injected group were sacrificed at 48 hr after the toxic challenge. Histologic slides prepared from their livers revealed more extensive hepatocellular necrosis in the chlordane-pretreated rats than was found in either the olive oil-pretreated rats or the animals with no treatment prior to CCl₄ administration.It was concluded that chlordane can induce smooth-membrane proliferation and can enhance drug-metabolizing enzyme systems in rat liver and that these changes are associated with an enhanced hepatotoxic response to CCl₄ administration. It was suggested that a sharp fall in hepatic microsomal cytochrome P-450 might serve as a relatively early indicator of toxic injury in an induced liver.     

Effect of acute and repeated chlordimeform treatment on rat hepatic microsomal drug metabolizing enzymes

The effect of chlordimeform treatment on the hepatic microsomal drug metabolizing enzymes was examined in male and female rats following either acute or repeated treatment. After acute administration of chlordimeform (100 mg/kg, ip one hr prior to sacrifice) differential effects were observed in various parameters of the hepatic microsomal mixed function oxidase system with significant decreases in ethylmorphine metabolism, cytochrome P-450 content, NADPH cytochrome c reductase, and in the spectral binding of hexobarbital and aniline while no changes were found in the metabolism of aniline or p-nitroanisole. Durations of zoxazolamine-induced paralysis and pentobarbital-induced hypnosis were increased significantly after acute chlordimeform administration. Following repeated administration of chlordimeform (75 mg/kg ip for four days) to adult male rats, a decrease was observed in zoxazolamine-induced paralysis time while pentobarbital-induced hypnosis was not altered. Metabolism studies using isolated hepatic microsomal fractions showed a decrease rate of biotransformation of ethylmorphine and aniline while the activity of p-nitroanisole O-demethylase was not changed. No differences were found in cytochrome P-450 levels whereas microsomal spectral binding of hexobarbital was reduced while that of aniline was not affected. Following acute or repeated administration of chlordimeform to adult female rats, decreases in the hepatic microsomal metabolism of aniline, but not ethylmorphine or p-nitroanisole, were observed. Addition of chlordimeform to microsomal suspensions yielded a Type I spectral binding curve.     

Effects of aging and caloric restriction on hepatic drug metabolizing enzymes in the Fischer 344 rat. I: The cytochrome P-450 dependent monooxygenase system

The effects of long-term caloric restriction on the hepatic cytochrome P-450 dependent monooxygenase system were investigated in the 22-month-old Fischer 344 rat. Caloric restriction decreased the age-related changes in hepatic testosterone metabolism, which are associated with demasculinization of the liver. Caloric restriction also increased hepatic microsomal testosterone 6 beta-hydroxylase, lauric acid 12-hydroxylase and 4-nitrophenol hydroxylase activities over corresponding values in both ad libitum fed 22-month and 60-day-old control male rats. This suggests that cytochrome P-450 isozymes, P-450 pcn1&2, P-452 and P450j may be induced by caloric restriction. Such changes in cytochrome P-450 isozyme profiles could result in altered carcinogen activation, radical formation or drug detoxication in the calorically restricted rat.     

Effect of PSK, a protein-bound polysaccharide from Coriolus versicolor, on drug-metabolizing enzymes in sarcoma-180 bearing and normal mice

The effects of PSK and Propionibacterium acnes (anaerobic Corynebacterium) on hepatic drug-metabolizing enzymes were studied using sarcoma-180 bearing and non-tumor bearing mice. PSK had no influence on aminopyrine N-demethylase and aniline hydroxylase activities, cytochrome P-450 concentration in hepatic microsomes, and the reductase activity of cytochrome c in normal mice. The content of cytochrome P-450 was not significantly reduced in S-180 bearing mice. On the other hand, P. acnes administration significantly decreased the amount of cytochromes P-450 and b5 and aminopyrine N-demethylase activity. When FT-207 (Tegafur) was administered orally to S-180 bearing mice combined with the immunoadjuvants, only P. acnes significantly reduced the 5-FU levels in the serum and some organs.     

Aberration of heme and hemoprotein in aged female rats

The magnitude and duration of drug action is determined partially by the activity of the drug metabolizing enzyme systems in the liver. The pharmacological effectiveness of many drugs is altered during the aging process. In this study, the regulation of heme metabolism and hemoprotein content was examined in livers of aged female rats. The activities of hexobarbital hydroxylase and aniline hydroxylase, indicators of mono-oxygenase function, were decreased in aged rats by 31% and 24%, respectively, as compared to values in young rats. This was accompanied by a proportional decrease in the level of cytochrome P-450 (26%). Additionally, the activity of delta-aminolevulinic acid synthetase (ALA-S), the rate-limiting enzyme in heme synthesis, and the microsomal concentration of heme were also decreased by 33% and 26%, respectively, in these animals. In contrast, the basal activity of microsomal heme oxygenase (MHO), the rate-limiting enzyme in heme degradation, and the percent heme saturation of tryptophan pyrrolase (TPO), a sensitive indicator of changes in the availability of heme in the "regulatory" heme pool, were increased by (87%) and (31%), respectively, in the aged rats. The serum concentration of bilirubin, an indicator of erythrocyte breakdown and/or liver function was likewise increased in these animals. In view of these findings, we suggest that the high activity of MHO and the low level of ALA-S may be a significant causative factor for the decreased microsomal concentration of heme, cytochrome-P-450 and its dependent monooxygenase activities in senescent female rats.     

Turnover of hepatic cytochrome P-450 in experimental cholestasis

In mechanical experimental chllestasis, hypertrophy of smooth microsomal membranes was observed. In contrast to typical induction, the membranes were deficient in cytochrome P-450. The total cytochrome P-450 content of the liver, however, as determined in the liver homogenate remained unchanged. To clarify the mechanism of the development of cytochrome P-450 deficient membranes in cholestasis, the half life of the heme portion of cytochrome P-450, and the initial rate of synthesis of cytochrome P-450 and b₅ hemes were compared in bile duct ligated rats and in control animals after labeling the heme by injection of the precursor δ-[4-¹⁴C]aminolevulinic acid. The half lives were not significantly different, which eliminates the possibility that selective destruction of cytochrome P-450 has occurred. Depression of cytochromal heme synthesis was not observed. During mechanical cholestasis, the relative cytochrome P-450 deficiency is probably caused by proliferation of components of the endoplasmic reticulum other than the hemoprotein.     

Thymus influences liver functions through hypothalamus-pituitary-gonad axis in rats

The aim of the review is to summarize our recent studies on the influence of the thymus on liver functions and its intermediary pathway in rats. Young adult thymectomized rats were used as a model in the experiments, and either thymic peptides or sex hormones were supplemented to these animals. Liver microsomal cytochrome P-450 and aminopyrine-N-demethylase (ADM) activities were decreased in thymectomized rats, and the change in the male was more significant than that in female rats. An increase of liver malondialdehyde (MDA) and a decrease of liver glutathione (GSH) and superoxide dismutase activity were observed in the female thymectomized rats, but not in the males. Accompanied by the increase of MDA, a decline of membrane fluidity of liver microsomes and mitochondria and a decrease of Ca²⁺ uptake by liver microsomes were exhibited in the female thymectomized rats. Subcutaneous injection of thymic peptides decreased MDA level, and increased GSH content, membrane fluidity and Ca²⁺ uptake by microsomes in the liver of thymectomized rats. On the other hand, male thymectomized rats showed a decrease of hypothalamic luteinizing hormone-releasing hormone (LHRH), plasma luteinizing hormone (LH) and testosterone levels. Subcutaneous injection of testosterone propionate to these animals restored their liver P-450 and ADM activities to normal levels. Female thymectomized rats exhibited a decline of hypothalamic LHRH and plasma estradiol levels. Supplementation of estradiol benzoate reversed the increase of liver MDA in these animals. The data suggest that the thymus may influence liver functions through the hypothalamus-pituitary-gonad axis. Thus, a new ‘thymus-neuroendocrine-liver pathway’ is proposed, which may account for the significance of the thymus in maintaining homeostasis and integrative functions in the body.     

Changes of the level of cytochrome P-450 and NADPH-cytochrome P-450 reductase in rats with hereditary degeneration of the retina

In animals with hereditary degeneration of the retina the level of cytochrome P-450 in the brain microsomal fraction is found to be higher than that in healthy animals. In rats with hereditary degeneration of the retina the activity of NADPH-cytochrome P-450 reductase is unchanged in all tissues examined except for the retina, where it is markedly higher than in healthy animals on postnatal day 90. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, N ^o 3, pp. 259–261, March, 1994     

Dexamethasone modulation of in vivo effects of endotoxin, tumor necrosis factor, and interleukin-1 on liver cytochrome P-450, plasma fibrinogen, and serum iron

Treatment of mice with endotoxin (lipopolysaccharide, LPS) and the two LPS-induced monokines, tumor necrosis factor (TNF) and interleukin-1 (IL-1), caused a depression of liver cytochrome P-450 and related drug-metabolizing enzymes, as well as other acute-phase changes including increase in plasma fibrinogen levels and hypoferremia. However, only IL-1, not TNF or LPS, depressed cytochrome P-450 in cultured hepatocytes, suggesting that the effect of TNF in vivo might be mediated by a second mediator. TNF- or LPS-stimulated monocytes released a factor capable of depressing cytochrome P-450 in cultured hepatocytes. This factor was inhibited by anti-IL-1 antiserum, and its synthesis, like that of IL-1, was inhibited by dexamethasone (DEX). Pretreatment of mice with DEX protected against the depression of liver cytochrome P-450 by LPS or TNF but not by IL-1, suggesting that IL-1 directly depresses cytochrome P-450 and that DEX acts by inhibiting IL-1 synthesis in vivo induced by LPS or TNF. However, DEX did not inhibit two other effects of LPS and TNF in vivo: increase of plasma fibrinogen levels and decrease of plasma iron, suggesting that these might not be mediated by IL-1. Therefore, the effect of DEX in vivo, although supporting the hypothesis that depression of liver cytochrome P-450 by LPS and TNF is mediated by IL-1, indicates the existence of IL-1-independent pathways in the acute-phase response.     

Regulation of heme metabolism during senescence: activity of several heme-containing enzymes and heme oxygenase in the liver and kidney of aging rats

The activities of several heme-containing enzymes plus succinate dehydrogenase, the content of mitochondrial cytochromes, the amount of microsomal cytochrome P-450, and the activity of heme oxygenase, the major enzyme of heme degradation, have been compared in young, mature and senescent rats. Measurements were made in liver, a tissue previously reported to have an age-related decrease in δ-aminolevulinic acid synthetase, and in kidney, a tissue previously reported to have no age-related change in this enzyme, the rate-limiting enzyme of heme biosynthesis (Paterniti, Lin and Beattie, Arch. Biochem. Biophys., 191 (1978) 792–797). The activity of cytochrome oxidase in liver mitochondria did not decrease with age while this activity in kidney mitochondria was highest in animals one year old and decreased in the two-year-olds. By contrast, succinate dehydrogenase of both kidney and liver mitochondria decreased markedly in the aging rats. No age-related change in the content of cytochromes b, c or aa₃ was observed in liver mitochondria; however, a marked age-related decrease in cytochrome aa₃ was observed in kidney mitochondria. Similarly no change in cytochrome P-450 levels was observed in either tissue obtained from aging animals. In the liver, catalase activity increased while in the kidney it decreased in senescent as compared to mature animals. Heme degradation does not decrease with age as the activity of heme oxygenase increased in both liver and kidney of two-year-old rats as compared to one-year-olds. These results suggest that the lower activity of δ-aminolevulinic acid synthetase observed in the aging rat may not be correlated with a decrease in the activity of heme-containing proteins and that the regulation of the heme pool used for the synthesis of various intracellular hemo-proteins may be complex.     

Induction of reversible shock by Escherichia coli lipopolysaccharide in rats. Changes in serum and cell membrane parameters

Reversible endotoxic shock was induced in adult rats by i.v. injection of Escherichia coli O111:B4 lipopolysaccharide (1.6 mg/100 g). The shock progression was evaluated by measuring serum glucose levels as well as activities of aspartate aminotransferase (GOT) and alkaline phosphatase in serum. A rapid increase of serum glucose levels occurs, after LPS injection, followed by hypoglycaemia (minimum values at 6 h) with progressive reversion to control values. Serum GOT activity increased (twofold) 6 h after endotoxin administration and returned to control values at 72 h. No appreciable changes occurred in serum alkaline phosphatase activity. Endotoxaemia produced a decrease in the cytochrome P-450 levels in all target organs considered: lung, adrenal glands and liver. The progressive decrease in the serum albumin concentration as well as changes of the physical properties of the plasma membranes observed in vivo, can not be explained only by direct interaction of endotoxin with the target organs, underlining the importance of serum mediators in the induction of the shock response.     

Induction of reversible shock by Escherichia coli lipopolysaccharide in rats. Changes in serum and cell membrane parameters.

Reversible endotoxic shock was induced in adult rats by i.v. injection of Escherichia coli O111:B4 lipopolysaccharide (1.6 mg/100 g). The shock progression was evaluated by measuring serum glucose levels as well as activities of aspartate aminotransferase (GOT) and alkaline phosphatase in serum. A rapid increase of serum glucose levels occurs, after LPS injection, followed by hypoglycaemia (minimum values at 6 h) with progressive reversion to control values. Serum GOT activity increased (twofold) 6 h after endotoxin administration and returned to control values at 72 h. No appreciable changes occurred in serum alkaline phosphatase activity. Endotoxaemia produced a decrease in the cytochrome P-450 levels in all target organs considered: lung, adrenal glands and liver. The progressive decrease in the serum albumin concentration as well as changes of the physical properties of the plasma membranes observed in vivo, can not be explained only by direct interaction of endotoxin with the target organs, underlining the importance of serum mediators in the induction of the shock response.     

Effect of traditional Chinese herbal medicines on the pharmacokinetics of western drugs in Sprague-Dawley rats of different ages (II): Aminophylline-huan shao tan and aminophylline-pu chung yi chi tang.

The effect of Chinese herbal medicines (Huan Shao Tan and Pu Chung Yi Chi Tang) and western drugs (sodium phenobarbital and cimetidine) on the serum concentration and pharmacokinetic parameters of theophylline and cytochrome P-450 of Sprague-Dawley (SD) rats of three different ages were examined. The older rats without pretreatment with Chinese herbal medicines and western drugs exhibited higher serum theophylline concentration and lower pharmacokinetic parameters of theophylline than middle-aged and younger rats (P < 0.05), but there was no difference in cytochrome P-450 activity among the three different ages of rats. All rats when pretreated with sodium phenobarbital showed lower serum theophylline concentration and higher pharmacokinetics parameters of theophylline. Also, the activity of cytochrome P-450 was higher (P < 0.05). When cimetidine was pre-administered in SD rats of three age groups, all rats exhibited lower serum theophylline concentration and higher pharmacokinetics parameters (P < 0.05), but the activity of cytochrome P-450 remained unchanged (P > 0.05). The results were opposite to other studies, probably because the dose and dosing intervals were different. No single effect occurred on the younger and middle-aged rats after pretreatment with Huan Shao Tan and Pu Chung Yi Chi Tang: their serum theophylline concentration, pharmacokinetics parameters and cytochrome P-450 activity were the same as the control group. However, the older rats after pretreatment with Huan Shao Tan or Pu Chung Yi Chi Tang showed lower serum theophylline concentration and higher pharmacokinetics parameters than the younger and middle-aged rats pretreated with similar Chinese herbal medicines. This indicates that Huan Shao Tan and Pu Chung Yi Chi Tang may perhaps improve the elimination of theophylline in older rats. This might be attributed to the increase in hepatic blood flow or in liver volume, since the activity of cytochrome P-450 was not affected by the administration of Chinese herbal medicines.     

Metabolic activation of aflatoxin B1 by liver tissue from male fischer F344 rats of various ages

The effect of aging on the ability of the liver to activate chemical procarcinogens was studied using 12-, 18-, and 27-month-old male Fischer F344 rats. The cytochrome P-450 content of the S9 and microsomal fractions of the liver decreased approximately 30% between 12 and 18 months of age. The structural conformation of cytochrome P-450 in microsomes from 12-, 18-, and 27-month-old rats was studied using electron-spin resonance spectroscopy. An age-related decrease in the amount of cytochrome P-450 ferric iron in the liver microsomes was observed. The conversion of the chemical procarcinogen aflatoxin B1 to mutagenic compounds by the S9 and microsomal fractions of liver was measured using the Salmonella typhimurium bioassay. A 40-50% decrease in the metabolic activation of aflatoxin B1 was observed between 12 and 18 months of age. However, the activation of aflatoxin B1 did not change after 18 months of age. The age-related decrease in the activation of aflatoxin B1 by liver appears to be due to a decrease in the metabolic activity of the mixed-function oxidase system.     

Morphological and biochemical effects of carbon disulfide on rat liver

The early biochemical and ultrastructural effects on the liver of CS₂ administration in vivo to fasted rats were compared in animals treated and not treated with phenobarbital, to ascertain whether these effects differed quantitatively and/or qualitatively. Ultrastructural examination showed that in phenobarbital-treated rats, the main lesion induced by CS₂ was an increase in the number and size of the lysosomes containing cell debris from other cell organelles such as mitochondria. The endoplasmic reticulum was unchanged compared to that of rats treated only with phenobarbital. In particular, there was no decrease in the rough endoplasmic reticulum. By contrast, in rats not treated with phenobarbital, the main effect of CS₂ was a decrease in the number of ribosomes bound to the rough endoplasmic reticulum, with little or no change in other cell organelles. Cytochrome P-450 decreased more in phenobarbital-treated than in untreated rats, and cytochrome b5 decreased in phenobarbital-treated rats only. CS₂ lowered aniline hydroxylase activity, expressed per nanomole of cytochrome P-450 in untreated rats, but increased this activity in phenobarbital-treated rats. The opposite was observed for microsomal peroxidase and cytosolic glutathione reductase activities. Liver catalase diminished more in phenobarbital-treated than in untreated rats. The effects of CS₂ on liver endoplasmic reticulum as well as on the respective activities of aniline hydroxylase, microsomal peroxidase, and glutathione peroxidase show that untreated and phenobarbital-treated rats respond to CS₂ administration in qualitatively different ways. It is suggested that in untreated rats, the effects observed are mainly due to CS₂ itself, whereas in phenobarbital-treated animals, the effects are mainly caused by reactive CS₂ metabolites formed by the mixed function oxidase microsomal system.