Metabolic activation of 1,1-dichloroethylene by mouse lung and liver microsomes

1,1-Dichloroethylene (1,1-DCE) causes lung and liver necrosis in mice. Covalent binding of [14C]1,1-DCE to isolated lung and liver microsomes from CD-1 mice required NADPH and was strongly inhibited by carbon monoxide. Lung and liver microsomes isolated from animals treated with phenobarbital demonstrated no changes in covalent binding of [14C]1,1-DCE compared with those from vehicle-treated animals. While 3-methylcholanthrene caused no alterations in binding to lung microsomes, the same pretreatment resulted in significantly increased levels of binding to liver microsomes. Piperonyl butoxide caused significant decreases in covalent binding to lung and liver microsomes; SKF 525-A significantly inhibited binding to liver microsomes but had no effect on lung microsomes. The incubation of liver microsomes with inhibitors required more NADPH than those performed with lung microsomes. The results demonstrate that reactive metabolites of 1,1-DCE can be formed by lung and liver microsomes, and suggest the involvement of cytochrome P-450 isozymes in the lung and liver injury induced by the halocarbon. However, metabolic activation by lung and liver microsomes may additionally involve non P-450 dependent mechanisms as evidenced by relatively high levels of nonspecific binding of 1,1-DCE.

Effects of methylmercury on the spontaneous and potassium-evoked release of endogenous amino acids from mouse cerebellar slices

The effects of methylmercury on the spontaneous and potassium-evoked release of endogenous amino acids from mouse cerebellar slices have been examined. Methylmercury induced a concentration-dependent increase in the spontaneous release of glutamate, aspartate, gamma-aminobutyric acid, and taurine from mouse cerebellar slices. Glycine release was slightly increased, but not in a concentration-dependent manner. The spontaneous release of glutamine from mouse cerebellar slices was not altered by any concentration of methylmercury examined (10, 20, and 50 microM). The tissue content of glutamate, gamma-aminobutyric acid, glutamine, and taurine decreased after exposure to methylmercury. Exposure of cerebellar slices to 20 microM methylmercury resulted in a significant enhancement in glutamate release during stimulation with 35 mM K+. This increase could be accounted for by the methylmercury-induced increase in spontaneous glutamate release. The increase in spontaneous release of glutamate and gamma-aminobutyric acid was independent of the availability of extracellular calcium. These results suggest that methylmercury increases the release of neurotransmitter amino acids, particularly gamma-aminobutyric acid and glutamate, by acting at intracellular sites to increase release from a neurotransmitter pool. The increase in the potassium-stimulated release of glutamate may reflect an increased sensitivity of the cerebellar granule cell to the effects of methylmercury. It is suggested that alterations in amino acid neurotransmitter function in the cerebellum may contribute to some of the neurological symptoms of methylmercury intoxication.

Furosemide toxicity in isolated mouse hepatocyte suspensions

Incubation of freshly isolated mouse hepatocytes with 0.5 or 1.0 mM furosemide caused a depletion of cellular acid soluble sulfhydryls to approximately 20-30% of control over the course of 4.5 h. The depletion was accompanied by a reduction in cell viability (indicated by the lactate dehydrogenase latency test) which was significant (P less than 0.05) for 0.5 mM but not for 1.0 mM furosemide at 4.5 h. Ultrastructurally, 0.5 or 1.0 mM furosemide caused cytoplasmic changes including loss of glycogen, disaggregation of polyribosomes, vesiculation of endoplasmic reticulum, and occasional appearance of lamellar bodies consisting of concentric arrays of paired smooth membranes. These concentrations of furosemide also caused cell surface changes, including loss of microvilli, development of an irregular shape compared to the spherical appearance of untreated hepatocytes, and the development of occasional blebs. The appearance of pale staining hydropic cells was indicative of the final stages of cell death. N-Acetylcysteine (6.0 mM) was effective at preventing the depletion of soluble sulfhydryls, the loss of viability, and the ultrastructural effects of 0.5 or 1.0 mM furosemide, suggesting a role for soluble sulfhydryls in the pathogenesis of furosemide hepatotoxicity.

Effects of mercury compounds on the spontaneous and potassium-evoked release of [3H]dopamine from mouse striatal slices

The effects of mercury compounds on the spontaneous and potassium-evoked release of [3H]dopamine from mouse striatal slices have been examined. All mercury compounds examined produced concentration-dependent increases in the spontaneous release of [3H]dopamine, with an order of potency of methylmercury greater than mercuric (Hg2+) mercury greater than p-choloromercuribenzene sulfonic acid. Methylmercury had no effect on the 25 mM potassium evoked release of [3H]dopamine in the presence of 1.3 mM calcium. However, in calcium-free conditions, methylmercury significantly increased the potassium-evoked release of [3H]dopamine. Mercuric mercury significantly reduced the 25 mM potassium evoked release of [3H]dopamine in the presence of 1.3 mM calcium, and this response was not reversible with brief washing of the tissue. In calcium-free conditions, mercuric mercury significantly elevated the evoked release of [3H]dopamine, similar to the result obtained with methylmercury. It is suggested that mercury compounds alter dopaminergic synaptic function, possibly by disrupting calcium homeostasis or calcium-dependent processes, and that methylmercury and mercuric mercury can have differential effects to alter dopaminergic neurotransmission.

Properties of 17- to 19-day-old chick embryo liver microsomes. Induction of cytochrome P-450, effect of storage at low temperature, and resistance to lipid peroxidation

Maximal hepatic cytochrome P-450 levels were induced in the 17-day-old chick embryo (four to five times control) with a dose of sodium phenobarbital of 6 mg/egg/day for 2 days. Similar levels of hepatic cytochrome P-450 were induced with a dose of propylisopropylacetamide of 4 mg/egg/day for 1 day. Chick embryo hepatic microsomes from phenobarbital-pretreated or from untreated chick embryos could be stored for periods of 14 days at -70 degrees C without a decrease in cytochrome P-450 levels. Moreover, no significant differences was discerned between the degree of suicidal inactivation of chick embryo hepatic cytochrome P-450 by 3,5-diethoxycarbonyl-1,4-dihydro-2,6-dimethyl-4-ethylpyridine in fresh and stored microsomes. Unlike rat hepatic microsomes, chick embryo hepatic microsomes do not undergo lipid peroxidative loss of cytochrome P-450 and heme when incubated in the presence of NADPH.

Effects of administration of metabolic inducers and inhibitors on pulmonary toxicity and covalent binding by 1,1-dichloroethylene in CD-1 mice

The administration of 1,1-dichloroethylene (1,1-DCE, 125 mg/kg ip) to CD-1 mice caused bronchiolar necrosis, which was accompanied by substantial covalent binding of radiolabeled compound and/or metabolite to lung. Lung injury and covalent binding were not modified by phenobarbital pretreatment. However, 3-methylcholanthrene provided a protective influence but failed to alter covalent binding to lung macromolecules. Prior administration with the metabolic inhibitors, piperonyl butoxide and SKF 525-A, produced differential effects. While piperonyl butoxide exacerbated bronchiolar injury by 1,1-DCE, covalent binding remained unaltered. In contrast, SKF 525-A protected from lung damage and significantly decreased covalent binding. Hepatic necrosis was relatively mild, and was not observed in all animals treated with 1,1-DCE. Although the hepatic lesion was not modified by phenobarbital, liver injury was slightly diminished by 3-methylcholanthrene. The inducers, piperonyl butoxide and SKF 525-A, enhanced liver necrosis, with the latter eliciting more severe effects than the former agent. Covalent binding to liver tissues was not significantly changed by pretreatment with either inducers or inhibitors. These results indicate that lack of an unequivocal correlation of cellular injury with covalent binding, but suggest that metabolism may be involved in the pneumotoxicity by 1,1-DCE. The influence and modification of lung injury by the liver, however, remain to be further elucidated.

Differential effects of methylmercuric chloride and mercuric chloride on the L-glutamate and potassium evoked release of [3H]dopamine from mouse striatal slices

The effects of CH3HgCl and HgCl2 on the evoked release of 3H from mouse striatal slices prelabelled with [3H]dopamine have been examined. CH3HgCl (10 microM) was observed to increase the L-glutamate-evoked release of [3H]dopamine, while HgCl2 (10 microM) had no effect. In contrast, CH3HgCl at concentrations up to 100 microM had no effect on the 25 mM K+-stimulated release of [3H]dopamine, whereas HgCl2 (100 microM) significantly reduced the 25 mM K+-stimulated release of [3H]dopamine. Thus CH3HgCl and HgCl2 have differential effects on the L-glutamate- and K+-stimulated release of [3H]dopamine from mouse striatal slices, suggesting that these compounds may have different sites and (or) mechanisms of action in altering neurotransmitter release. It is suggested that CH3HgCl may act predominantly at intracellular sites or at the level of the L-glutamate receptor, whereas the major site of action of HgCl2 may be the voltage-operated calcium channel.

Effects of N-acetylcysteine on the disposition and metabolism of acetaminophen in mice

N-acetylcysteine is the drug of choice for the treatment of acetaminophen poisoning, yet the mechanism of protection in vivo is unknown. Prevention of liver injury could result from decreased production of the toxic intermediate(s), from increased capacity to detoxify the toxic intermediate(s) or from increased ability of the tissue to withstand or even repair the molecular damage caused by the toxic species. Treatment of mice with N-acetylcysteine (1200 mg/kg p.o.) was found to prevent the hepatic damage caused by 1000 mg/kg p.o. of acetaminophen. Possible mechanisms for this hepatoprotective effect were examined by measurement at different time points of acetaminophen and its metabolites in plasma, urine, bile and whole-body homogenates and by evaluation of the changes in these parameters caused by treatment with N-acetylcysteine. A high-pressure liquid chromatographic method was developed to measure the majority urinary metabolites of acetaminophen and was validated by desorption chemical ionization mass spectral analysis of individual metabolites. Minimal differences in the concentration of unchanged acetaminophen and metabolites in whole-body homogenates at 4, 6 and 24 hr postdose were noted for N-acetylcysteine-treated vs. vehicle-treated mice. These results are incompatible with a decreased formation of the toxic species secondary to delayed acetaminophen absorption from the gastrointestinal tract or with an increased clearance of acetaminophen via nontoxic pathways such as sulfation as plausible mechanisms for the observed hepatoprotection.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaminophen-induced hepatotoxic congestion in mice

Acetaminophen-induced (750 mg per kg p.o.) hepatotoxicity in mice is characterized by hepatomegaly and massive centrilobular congestion which precede the appearance of necrosis. The vascular changes are correlated with the morphologic features using liver hemoglobin content to quantitate erythrocyte sequestration, and hematocrit measurements and 125I-albumin injections to determine plasma and blood volume. The initial increase in liver size was a result of plasma accumulation due to endocytic vacuolation of hepatocytes and Disse space enlargement in centrilobular regions. Further increases in liver size after 3 hr were a consequence of erythrocyte and additional plasma sequestration within the damaged liver. These events occurred without any increase in intrahepatic or portal venous pressure. Hepatic hemoglobin and plasma levels increased 10- and 5-fold, respectively, by 4.5 to 6 hr after administration of acetaminophen. There are two major consequences of acetaminophen-induced hepatotoxic congestion. First, blood and plasma volumes fell significantly, and we suggest that hypovolemic shock contributes to early mortality after acetaminophen. Second, impaired circulation within the congested liver, as manifested by reduced 125I-albumin entry into the liver when 125I-albumin was injected after congestion had developed, probably aggravates the initial injury. Early lesions were always evenly distributed around central veins. However, the pattern of damage at 24 hr could be variable. Occasional large confluent areas of necrosis were always congested, which is consistent with the concept that secondary ischemic damage can develop. Congestion and hypovolemia are reversible and can be largely prevented by administration of the protective compound N-acetylcysteine (1,200 mg per kg p.o.) 3 hr after acetaminophen.

Effects of N-acetylcysteine on acetaminophen covalent binding and hepatic necrosis in mice

Experiments were designed to test whether the protective effect of N-acetylcysteine against acetaminophen hepatotoxicity precedes arylation of tissue or whether protection occurs after arylation of tissue. Investigation of potential postarylation actions showed that N-acetylcysteine was unable to attenuate the liver necrosis caused by acetaminophen or several other hepatotoxins that act through chemically reactive metabolites. Furthermore, varying the time and route of N-acetylcysteine treatment indicated that the late protection against acetaminophen mortality probably was a consequence of pharmacokinetic factors rather than postarylation intervention in the process of cell death. The antidote was found to inhibit covalent binding of acetaminophen by about 70% when N-acetylcysteine protected against liver necrosis. Treatment regimens that had no effect upon covalent binding also had no effect on acetaminophen hepatotoxicity. Previous failures to detect this relationship apparently occurred because of a failure to consider biological events important in the pathophysiology of acetaminophen-induced necrosis, particularly the marked intrahepatic hemorrhage and vascular congestion with liver engorgement by protein and fluid. These results support the hypothesis that sulfhydryl nucleophiles such as N-acetylcysteine act primarily through prearylation mechanisms to decrease the amount of reactive metabolite available for initiation of hepatic injury.

The disposition and the liver and thymus gland toxicity of 3,3',4,4'-tetrachlorobiphenyl in the female rat

3,3',4,4'-Tetrachlorobiphenyl (TCBP) was administered orally to adult female Sprague--Dawley rats in the oral dosage regimen, 5 mg X kg-1 X day-1 for 21 days, followed by a 22-day postdosing period. Control animals received either the corn-oil vehicle (1 mL X kg-1 X day-1) or no treatment. 3,3',4,4'-TCBP distributed preferentially into the adipose tissue and liver, and apparent steady-state xenobiotic concentrations were attained in the adipose tissue (8 micrograms/g) and liver (300 ng/g) prior to the cessation of dosing. The 3,3',4,4'-TCBP concentrations in the serum, brain, kidneys, and thymus gland were lower and more variable than those in the adipose tissue and liver. During the postdosing period, 3,3',4,4'-TCBP was eliminated from the adipose tissue and liver by apparent first-order kinetics with elimination half-life values of 2.5 days and 0.8 day, respectively. The major route of excretion of unmetabolized 3,3',4,4'-TCBP was via the feces, and the amount excreted over 24 h did not exceed 8% of the dose administered on any given day. Throughout the experiment, there were no differences in the body weight or food and water intake for the 3,3',4,4'-TCBP-treated animals compared with the corn-oil-treated and nontreated rats. There was a significant increase in liver weight and a significant decrease in thymus gland weight for the 3,3',4,4'-TCBP-treated rats compared with the corn-oil-treated rats at the cessation of dosing and at 11 days thereafter, but there were no observable histological changes in these organs as assessed by light microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Methylmercury distribution, metabolism, and neurotoxicity in the mouse brain

Methylmercury distribution, biotransformation, and neurotoxicity in the brain of male Swiss albino mice were investigated. Mice were orally dosed with [203 Hg]methylmercury chloride (10 mg/kg) for 1 to 9 days. Methylmercury was evenly distributed among the posterior cerebral cortex, subcortex, brain stem, and cerebellum. The The anterior cerebral cortex had a significantly higher methylmercury concentration than the rest of the brain. The distribution of methylmercury's inorganic mercury metabolite was found to be uneven in the brain. The pattern of distribution was cerebellum greater than brain stem greater than subcortex greater than cerebral cortex. The order of the severity of histological damage was cerebral cortex greater than cerebellum greater than subcortex greater than brain stem. There was no correlation between methylmercury distribution in the brain and structural brain damage. However, there was a relationship between the distribution of methylmercury's inorganic mercury metabolite and structural damage in the anterior cerebral cortex (positive correlation) and the anterior subcortex (negative correlation). There was also a positive correlation between the fraction of methylmercury's metabolite of the total mercury present and structural brain damage in the anterior cerebral cortex. This study suggests that biotransformation may have a role in mediating methylmercury neurotoxicity.

Scanning electron microscopic examination of acetaminophen-induced hepatotoxicity and congestion in mice

Acetaminophen-induced hepatotoxicity and associated hepatic congestion were investigated by scanning and correlative transmission electron microscopy. Acetaminophen (750 mg/kg orally) causes changes in cell surface morphology and the relationship between hepatocytes and sinusoidal lining cells. There is endocytic vacuolation at lateral and sinusoidal margins of centrilobular hepatocytes, loss of microvilli, Disse space enlargement, dilation of bile canaliculi, and disappearance of the studlike projections from hepatocyte lateral surfaces. Erythrocytes enter the enlarged Disse space and endocytic vacuoles via enlarged pores in sinusoidal lining cells, thereby collapsing the sinusoids. Lining cells are not lost, but apparently held in position by preservation of intercellular junctions, cytoplasmic projections from hepatocytes, and anchorage by fat-storing cells within the Disse space. Congestion can abate by 24 hours, indicating that erythrocytes can return to the general circulation from the Disse space.

Increased acetaminophen-induced hepatotoxicity after chronic ethanol consumption in mice

The effect of chronic ethanol consumption on acetaminophen (200, 400, and 600 mg/kg) toxicity was determined by maintaining mice for 10 days on diets consisting of chow and one of the following drinking solutions: 10% ethanol + 10% sucrose, 8% sucrose, or tap water. Toxicity as manifested by mortality, liver enlargement, and liver congestion was greatest in the ethanol-treated group. We suggest that the greater mortality was a result of the increased liver congestion and consequent hypovolemia. Despite the increased levels of cytochrome(s) P-450, covalent binding of [3H]acetaminophen reactive metabolite(s) to liver protein was not higher in ethanol-treated animals. This can be explained by the higher initial glutathione concentration and/or ability to replenish glutathione in the ethanol-treated group. We suggest that the enhancement of acetaminophen toxicity by ethanol is the result of an effect of ethanol on hepatocyte membranes which renders the cells more susceptible to toxic injury.

Ultrastructural effects of acetaminophen in isolated mouse hepatocytes

The ultrastructure of isolated mouse hepatocytes shows good correlation with that of cells from intact liver. Incubation of isolated mouse hepatocytes with 1.0 mM acetaminophen causes a variety of cytoplasmic and cell surface lesions, as well as cell death. The changes are similar or equivalent to those caused by acetaminophen in vivo. The most prominent feature of damage in isolated hepatocytes is bleb formation, which is also seen occasionally in control incubations. The protective compound alpha-mercaptopropionylglycine and the antidote N-acetylcysteine both prevented the acetaminophen-induced changes. It is suggested that the in vivo counterpart to the blebs are endocytic vacuoles which form at cell margins due to the intravascular pressure of the sinusoids. It is suggested that the cell surface changes both in vivo and in isolated hepatocytes are caused by some dysfunction to the microfilament component of the cytoskeleton.

Gas-liquid chromatographic determination of the distribution of 3,3',4,4'-tetrachlorobiphenyl in the adult female rat following short-term oral administration

A gas-liquid chromatographic assay using electron-capture detection was developed for the quantitation of 3,3',4,4'-tetrachlorobiphenyl (TCBP) in the serum, urine, brain, liver, adipose tissue, and feces of the rat. The sample preparation involves extraction of 3,3',4,4'-TCBP with hexane under neutral or alkaline conditions (and washing with concentrated acid for feces only). Aqueous standards are used for calibration of the assay, except for adipose tissue. The lower limit of quantitative sensitivity of the assay for 3,3',4,4'-TCBP is 25 ng/mL for serum and urine and 125 ng/g for brain, liver, adipose tissue, and feces, which can be extended to 5 ng/mL and 25 ng/g, respectively, by analyzing a larger aliquot of the hexane extract. The overall accuracy is greater than 95% for serum, urine, brain and feces and 86% for liver, and the within-day coefficient of variation does not exceed 8.6%. 3,3',4,4'-TCBP was administered orally to adult, female, Sprague-Dawley rats in the dosage regimens: 0.2, 0.5 and 2 mg X kg-1 X day-1 for 10 days and 5 mg X kg-1 X day-1 for 4 days. 3,3',4,4'-TCBP distributed preferentially into adipose tissue and liver, where the xenobiotic concentration was greater in adipose tissue. The adipose tissue and hepatic 3,3',4,4'-TCBP concentrations were dependent on both the absolute dose and dosing schedule of the xenobiotic. Only trace concentrations, usually below the lower limit of quantitation, were detected in the serum, brain and kidney. Fecal excretion of 3,3',4,4'-TCBP was greater than urinary excretion for the 5 mg X kg-1 X day-1 X 4-day regimen.

Metal ion – biomolecule interactions. IV. Methylmercury(II) complexes of l-methylimidazoline-2-thione (methimazole), a potentially useful protective agent in organomercurial intoxication

Two 1:1 methylmercury(II)-1-methylimidazoline-2-thione (methimazole, MeImSH) complexes, [MeHg(MeImSH)]NO3 and [MeHg(MeImS)], have been isolated from aqueous solution under acidic and basic conditions, respectively. 1H nmr and ir spectroscopy, as well as analytical data, were used to characterize the complexes. The nmr data, in particular, lead to the conclusion that the principal binding mode under both sets of conditions involves the sulfur atom at C2. However, under conditions of 2:1 (MeHgII:MeImSH) stoichiometry, binding to N3 is also found to occur. These interpretations have necessitated a reexamination of the 1H nmr spectrum of the free ligand, in particular with respect to assignment of NH and SH resonances corresponding to the two possible tautomeric forms. It has been found in this work that 1-methylimidazoline-2-thione shows a high affinity for MeHgII binding, which may be pertinent with respect to a previous report concerning the protective nature of this compound in organomercurial intoxication.

Perspectives on the central nervous system toxicity of methylmercury

Methylmercury is a widespread and highly toxic environmental pollutant. The source of the substance in the environment is industrial and agricultural use. Chronic methylmercury poisoning is characterized by peripheral and central nervous system damage. The rate of absorption and distribution of this organomercurial into neural tissue determines the rate of development and the severity of the neural lesion. Furthermore, the rate of metabolism and excretion of an organomercurial will greatly influence its neural toxicity. There are differences in the accumulation of methylmercury in different regions of the brain, as well as by the different cell types in these regions. The significance of this variable accumulation of methylmercury is not known. Methylmercury influences a large number of neurocellular functions ranging from inhibition of membrane integrity to alteration in the synthesis and release of transmitter substances.

Acetaminophen toxicity in fed and fasted mice

Acetaminophen (750 mg/kg) toxicity and its modification by N-acetylcysteine (NAC, 1200 mg/kg) have been compared in fed and fasted mice. There was no significant difference between fed and fasted animals with respect to microsomal protein content, cytochrome(s) P-450 content, and aryl hydrocarbon hydroxylase activity. Glucuronyl transferase activity was significantly higher in fasted mice. Hepatotoxicity, as determined histologically and by liver enlargement was greater in fasted than fed mice. Covalent binding of [3H]acetaminophen metabolite(s) to liver proteins was also greater in fasted animals. NAC administration prevented acetaminophen-induced microscopic changes and liver enlargement and reduced the magnitude of covalent binding of acetaminophen metabolites. Fasting caused a marked fall in liver reduced sulfhydryl concentration. The incidence of acetaminophen-induced hypothermia was greater in fasted than in fed animals. NAC administration reduced hypothermia in fasted mice and abolished it in fed animals. It is concluded that enhanced acetaminophen toxicity in fasted mice compared with fed mice is unlikely to be a consequence of increased reactive metabolite formation, but rather a result of reduced inactivation of reactive metabolite(s) due to reduced hepatic glutathione stores in fasted mice.

Acetaminophen-induced hypothermia in mice: evidence for a central action of the parent compound

Pretreatment of mice with phenobarbital, an inducer of oxidative drug metabolism, had no effect on the early hypothermic effect of a toxic dose of acetaminophen, while pretreatment with metyrapone, SKF-525A, or piperonyl butoxide (inhibitors of mixed-function oxidase) enhanced the hypothermia. In mice treated with acetaminophen alone, brain parent drug levels correlated with the degree of hypothermia, while liver drug levels did not. Also, intracerebroventricular injection of acetaminophen resulted in significant hypothermia within 20 min. These results indicate that the early hypothermia caused by acetaminophen in mice is due to the parent drug, not to its toxic reactive metabolite, and that the effect is mediated centrally. The observation that piperonyl butoxide and SKF-525A themselves caused significant hypothermia indicates that the use of these compounds should be avoided when body temperature is being followed in drug metabolism experiments.

Effects of porphyrin-inducing drugs on ferrochelatase activity in isolated mouse hepatocytes

The effects of several concentrations of griseofulvin and 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) on ferrochelatase activity in suspensions of isolated mouse hepatocytes were examined. In agreement with previous findings in the intact chick embryo liver and chick embryo liver cell culture, DDC, but not griseofulvin, inhibited the enzyme in the isolated mouse hepatocyte suspension. These results indicate that the difference between the effects of griseofulvin on hepatic ferrochelatase in rodents in vivo (inhibition), the intact chick embryo (no effect), and the chick embryo liver cell culture (no effect) cannot be attributed solely to species differences.

Drug interactions of amitriptyline and nortriptyline with warfarin in the rat

Treatment of rats with amitriptyline or nortriptyline for 6 days at 6, 15 and 30 mg/kg produced no increases in the activities of aniline hydroxylase and aminopyrine N-demethylase or the content of microsomal protein and cytochrome P-450. Significant decreases in aminopyrine N-demethylase activity and cytochrome P-450 content were observed at 30 mg/kg. This inhibition of activity appeared to be at the level of cytochrome P-450 and not a cytotoxic effect in liver cells. Concomitant administration of amitriptyline or nortriptyline (6, 15 and 30 mg/kg)with warfarin to rats produced a dose dependent increase in the prothrombin time. At high doses of the tricyclic antidepressants, these increases in prothrombin time correlated with increases observed in the plasma half-life of warfarin. In vitro studies suggested that amitriptyline and nortriptyline inhibited the metabolism of warfarin. A double-reciprocal plot (Lineweaver-Burk method) showed this inhibition to be competitive. Nortriptyline produced greater inhibition of warfarin metabolism than amitriptyline and correspondingly greater enhancement of the anticoagulant effect.