Metabolism of the dyestuff intermediate 2,4-diaminoanisole in the rat

1. 2,4-Diamino[ring-U-¹⁴C] administered intraperitoneally to rats is excreted chiefly via the urine (79 and 85% of the dose in 24 and 48h, respectively). The isotope in the faeces was 2·1 and 8·9% of the dose at 24 and 48 h.

2. The major metabolic pathway was acetylation of the amine group(s), resulting in 4-acetylamino-2-aminoanisole and 2,4-diacetylaminoanisole.

3. Oxidative pathways yielded 2,4-diacetylaminophenol (O-demethylation), 5-hydroxy-2,4-diacetylaminoanisole (ring hydroxylation), and 2-methoxy-5-(glycolamido)acetanilide or its isomer (ω-oxidation).

4. These major metabolites were excreted in the urine both as free and glucuronic acid conjugates.

1. A single oral dose of desmethylimipramine (80mg/kg) administered to rats inhibited the hepatic microsomal hydroxylation of thiabendazole (45%), aniline (30%), biphenyl (30%) and ethylmorphine (15%) in vitro at 5 h after dosage; there was no decrease in cytochrome P-450 or b₅.

2. A single oral dose of ethoxyquin (200mg/kg) to rats inhibited the hepatic microsomal hydroxylation of thiabendazole (65%), aniline (40%) and biphenyl (40%) in vitro at 1 h after dosage; inhibition was less at 5 h. There were no changes in the contents of cytochromes P-450 and b₅.

3. The max. plasma concn. of thiabendazole occurred 2-4h after oral dosing (50-200mg/kg) to rats. Thiabendazole (100mg/kg) administered orally 30min after oral ethoxyquin (400 mg/kg) or thiabendazole (200 mg/kg) administered orally 30 min after oral desmethylimipramine (80 mg/kg) delayed absorption of the thiabendazole and resulted in markedly decreased plasma concentration of the anthelmintic.

4. Simultaneous administration of ethoxyquin (300 mg/kg) potentiated the anthelmintic effect of thiabendazole (750 mg/kg) on the helminth parasite, Nematospiroides dubius, the mouse. Desmethylimipramine showed no similar potentiation.

1. The α-isomer of 1,2,3,4,5,6-hexachlorocyclohexane (HCH) is converted, on incubation with the 100 000g supernatant fraction (cytosol) of rat liver homogenates, to four positional isomers of S-(dichlorophenyl)glutathione (DCPG).

2. Radiochemical evidence shows that primary conjugates formed are subject to rapid aromatization.

3. The GSH-conjugates produced from γ-HCH (lindane), Δ-HCH, and three stereoisomers of 1,3,4,5,6-pentachlorocyclohex-1-ene (PCCH) have been characterized by g.l.c. of their aromatic moieties. All compounds were exclusively converted to at least two positional isomers of DCPG. An isomer of HCH and its trans-dehydrochlorination product yielded DCPG of almost identical composition.

4. β-HCH was not entirely unreactive, but the identity of the product remained uncertain.

5. DCPG-formation from HCH-d₆ exhibited a significant deuterium isotope effect (5·8 at 310 K for the α-configuration), while none was found for the conversion of PCCH-d₅ (1·2 at 298 K for the 3,4,6/5-isomer).

6. In the absence of GSH, liver cytosol protein mediated a trans-dehydrochlorination of lindane and of α-HCH to PCCH with a catalytic factor of 15 and 25, respectively. Addition of GSH raised HCH conversion by a factor of 3 to 4 and resulted in the formation of DCPG.

7. GSH-conjugation of PCCH is shown to be enzymic.

8. It is concluded that the rate of formation of DCPG from HCH in rat liver cytosol depends on gradual monodehydrochlorination, and that the enzymic transfer of GSH onto PCCH is not preceded by a second dehydrochlorination. The transfer and elimination reactions involved in DCPG formation from PCCH are considered taking into account (a) differences between stereoisomers in reaction rate and product composition and (b) the observation that a purified soluble GSH-S-transferase (E.C. 2.5.1.18) converted 3,4,6/5-PCCH-and α-HCH-to the same set of four isomeric DCPGs as did the entire cytosol fraction.

9. In corroboration of earlier evidence, transferase activity associated with liver microsomes and mitochondria also converts α-HCH and 3,4,6/5-PCCH each to four positional isomers of DCPG.

10. The result of the study is discussed with reference to earlier work in mammals and in insects and in relation to HCH-biotransformation by rats in vivo.

1. The disposition of spirohydantoin mustard (SHM) has been examined in rats and dogs after i.v. administration of [hydantoin-4-¹⁴C] SHM and [2-chloroethyl-U-¹⁴C] SHM.

2. Four hours after dosing to rats and dogs, renal clearance of the ethyl-¹⁴C moiety (14-21%) is lower than that of the hydantoin-¹⁴C moiety (29-35%). In contrast, biliary excretion of the ethyl-¹⁴C in rats is greater, and there appears to be enterohepatic circulation of the ethyl-¹⁴C.

3. Less than 1% of the radioactivity appearing in rat bile is unchanged SHM. Two major metabolites containing the ethyl-¹⁴C moiety are conjugates of glutathione or cysteine.

4. Levels of ¹⁴C in plasma decline in a biphasic manner. No difference in the initial plasma disappearance of the two labelled moieties is observed, but disappearance of the ethyl-¹⁴C during the second phase is slower.

5. Concentrations of ethyl-¹⁴C and hydantoin-¹⁴C in the brains of rats and dogs, 4h after i.v. administration, are equivalent to those in plasma.

6. Radioactivity is also distributed to the brain of rats after oral administration of [2-chloroethyl-U-¹⁴C]SHM, but at a concn. less than half that of plasma.     

Studies on the metabolism of d-Limonene (p-Mentha-1,8-diene). III. Effects of d-Limonene on the lipids and drug-metabolizing enzymes in rat livers.

1. After a single oral dose of d-limonene (200-1200 mg/kg) no effects were observed on liver triglyceride, microsomal protein, cytochrome b5, and the drug-metabolizing enzymes. Glycogen content was slightly decreased at doses higher than 800 mg/kg, and cytochrome P-450 and delta-aminolaevulinic acid synthetase activity was slightly increased at 1200 mg/kg. 2. After repeated treatment (400 mg/kg/day) for 30 days, the relative liver weight and hepatic phospholipid content were only slightly increased, and liver and serum cholesterol were decreased 49 and 8%, respectively. Of the phospholipid fatty acids, palmitic, linoleic and arachidonic acids were increased, and stearic acid was decreased. Aminopyrine demethylase and aniline hydroxylase were increased 26 and 22%, respectively, and cytochrome P-450 and b5 were likewise increased 31 and 30%.     

Effect of malotilate (diisopropyl 1,3-dithiol-2-ylidenemalonate) on drug metabolizing activity in rat liver microsomes

The effect of malotilate (diisopropyl 1,3-dithiol-2-ylidenemalonate) on drug metabolizing activity in rat liver microsomes was examined. Malotilate (500 mg/kg/day) was administered orally to rats for 3 days. The contents of cytochrome P-450 (P-450) and cytochrome b5 (b5), the activity of NADPH-cytochrome c reductase, and the metabolization of aniline, aminopyrine, benzo(a)pyrene (B(a)P) and 7-ethoxycoumarin (7-EC) in the microsomal fraction were examined 24 hr after the final administration of malotilate. The content of b5 and the activity of NADPH-cytochrome c reductase were increased by the malotilate treatment, but the content of P-450 was not significantly affected. 7-EC O-deethylation was markedly and aminopyrine N-demethylation was moderately enhanced; in contrast, aniline hydroxylation was significantly and B(a)P hydroxylation was slightly reduced. Such different effects of malotilate among the four substrate-metabolizing activities may be due mainly to the increase in the content of b5, which participates in the transport of the second electron required for P-450 function to various extents. It is also possible that malotilate affects the population of P-450 subtypes, each having a different substrate specificity and a different affinity for b5.     

Contrasting effects of ethylenethiourea on hepatic monooxygenases in rats and mice

The effects of ethylenethiourea (ETU) on the hepatic xenobiotic metabolizing system in rats and mice were investigated. Male rats and male mice were given oral doses of 50 and 75, or 50, 75, 100, 500, and 1,000 mg/kg for 3 days. The microsomal enzymes studied were aminopyrine N-demethylase, aniline hydroxylase, and cytochrome P-450. In rats, the activity of aminopyrine N-demethylase was reduced to values between 60 and 70% of controls 24 h after treatment. A decrease in aniline hydroxylase activity and cytochrome P-450 content was observed on the 3rd day after exposure. In mice, treatment with ETU resulted in an increase of cytochrome P-450 at all dose levels. The activity of aniline hydroxylase was significantly elevated in the groups receiving doses of 100 mg/kg and higher. Aminopyrine N-demethylase was unaffected by the treatment. The results suggest that there are qualitative differences between rats and mice after ETU exposure with respect to the response of the hepatic monooxygenases.     

Early, selective and reversible suppression of cytochrome P-450-dependent monooxygenase of liver microsomes following the administration of low doses of carbon disulfide in mice

The effects of carbon disulfide (CS2) on the liver microsomal drug-metabolizing enzyme system and other enzyme activities were studied 1 hr after the oral administration of 3-300 mg/kg of CS2 in mice. Considerable decreases in drug-metabolizing enzyme activities (such as hydroxylation of aniline, O-dealkylation of p-nitroanisole, 7-ethoxycoumarin and 7-ethoxyresorufin, and N-demethylation of N,N-dimethylaniline), NADPH-cytochrome P-450 reductase (but not NADPH-cytochrome c reductase), and P-450-associated peroxidase activities were already observed at 3 and 30 mg/kg of CS2, dose dependently. At the same dosage levels, the magnitudes of microsomal spectral changes induced by aniline and nicotinamide (type 2 substrates), but not those induced by hexobarbital and SKF-525A (type 1 substrates), were also reduced to a considerable extent. The degrees of these alterations were all greater than that of the measurable loss of P-450 content, i.e. the loss of functional activity of P-450 was much greater than simply expected from the apparent decrease in the hemoprotein content. Cytochrome b5 content and NADH-ferricyanide reductase activity were unchanged at 30 and 300 mg/kg of CS2, although NADH-cytochrome c reductase activity was increased at the latter dose. The following enzyme activities did not change significantly at up to 300 mg/kg of CS2: flavin-containing monooxygenase, UDP-glucuronyl transferase, glucose-6-phosphatase and heme oxygenase in microsomes, and glutathione S-transferases in the soluble fraction. Microsomal conjugated diene levels and liver glutathione content were also unchanged. These observations support the theory that P-450 is a sensitive and selective site for CS2 action, where CS2 itself is bioactivated. It was also shown that the loss of P-450 was reversible after a single, or repeated, administration of CS2.     

Induction of hepatic microsomal drug-metabolizing enzymes by inhibitors of 5-lipoxygenase (5-LO): studies in rats and 5-LO knockout mice.

The effect of 5-lipoxygenase (5-LO) inhibitors on the hepatic microsomal mixed-function oxidase (MFO) system of rodents was investigated. After establishing the relative in vitro and in vivo potencies of the 3 test compounds, male Crl:CD (SD) BR rats received CJ-11,802 (0, 10, 50, or 200 mg/kg/day), zileuton (0, 10, 60, or 300 mg/kg/day) or ZD2138 (0 or 200 mg/kg/day) once daily by oral gavage for 14 (zileuton and ZD2138) or 30 (CJ-11,802) consecutive days. Controls were given an equivalent volume of 0.5% methylcellulose vehicle. At necropsy, all livers were weighed, and sections from representative animals (control and highest dose for each compound) were utilized to prepare hepatic microsomal fractions, which were assayed for cytochrome P-450 (CYP) content and the activities of cytochrome c reductase (CRed), para-nitroanisole O-demethylase (p-NOD), ethoxyresorufin O-deethylase (EROD), and pentoxyresorufin O-dealkylase (PROD). A dose-related increase in liver weight occurred in rats given CJ-11,802 and zileuton, while animals administered ZD2138 were unaffected. Rats given CJ-11,802 (200 mg/kg/day) and zileuton (300 mg/kg/day) had increases in CYP, EROD, PROD, CRed and p-NOD compared to corresponding controls, while only the latter two activities were elevated in animals administered ZD2138. To determine if induction of the hepatic microsomal MFO system was related to 5-LO inhibition, male DBA wild-type and 5-LO knockout mice were administered either CJ-11,802 (200 mg/kg/day) or vehicle by oral gavage for 14 consecutive days. At necropsy, liver weight, CYP content, and CRed activity were measured and all were increased similarly in the treated wild-type and knockout mice compared to corresponding controls, indicating that induction was not related to inhibiting 5-LO.     

Comparison of the effects of piperine administered intragastrically and intraperitoneally on the liver and liver mixed-function oxidases in rats

Piperine, a major pungent constituent of black and red peppers, was administered to rats intragastrically and intraperitoneally to study whether it alters the activities of hepatic mixed-function oxidases (MFO) and serum enzymes as specific markers of hepatotoxicity. An intragastric dose of 100 mg/kg of piperine to adult, male Sprague-Dawley rats caused an increase in hepatic microsomal cytochrome P-450 and cytochrome b5, NADPH-cytochrome c reductase, benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase 24 h following treatment. On the other hand, a 10 mg/kg dose given i.p. exhibited no effect on the activities of the aforementioned parameters of the hepatic drug-metabolizing enzyme system. However, when the intragastric and intraperitoneal doses were increased to 800 mg/kg and 100 mg/kg, respectively, the black pepper alkaloid produced a significant decrease in the levels of cytochrome P-450, benzphetamine N-demethylase, aminopyrine N-demethylase and aniline hydroxylase 24 h after treatment. None of the treatments significantly elevated the activities of serum sorbitol dehydrogenase (SDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and isocitrate dehydrogenase (ICD), suggesting that piperine is not a hepatotoxic agent.     

Toxicity of carbon disulfide in developing rats: LD50 values and effects on the hepatic mixed-function oxidase enzyme system

The 24-hr LD50 values of carbon disulfide (CS2) were estimated in 1-, 5-, 10-, 20-, 30-, and 40-day-old rats. CS2 was least toxic to 20-day-old rats (LD50 1545 mg/kg, ip) and most toxic to 1-day-old rats (LD50 583 mg/kg, ip). Twenty-four hours after administration of CS2 (375 mg/kg, ip) to 1-, 5-, 10-, 20-, 30-, and 40-day-old rats, significant inhibition of cytochrome P-450 and aniline hydroxylation was observed in rats of all ages studied except the 1-day-old rats. Following incubation of hepatic microsomes isolated from 1-, 5-, 10-, 20-, 30-, and 40-day-old rats with CS2, decreases in activity of the hepatic mixed-function oxidase enzyme system and/or concentration of cytochrome P-450 were observed when an NADPH-generating system was present during incubation. When hepatic microsomes isolated from rats of all ages studied were incubated with C35S2, 35S was covalently bound to microsomal protein in the presence of an NADPH-generating system. Also, more 35S than 14C was covalently bound to microsomal membranes after incubation of microsomes isolated from rats of all ages studied with C35S2 or 14CS2 in the presence of an NADPH-generating system. The results of this research demonstrated the LD50 of CS2, the effects of CS2 on the hepatic mixed-function oxidase enzyme system, and that the conversion of CS2 to a covalently binding sulfur-containing biotransformation product varied with age in developing rats.     

Toxicologic studies of N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (captan): its metabolism by rat liver drug-metabolizing enzyme system

The degree of toxicity caused in rats by captan (N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide) administered intraperitoneally is greater than that induced by orally administered captan. With regard to its effect on the drug-metabolizing enzymes of rat liver, the activity of aniline hydroxylase and the level of cytochrome P-450 were found to decrease in the treated rats 24 h after a single oral dose (650 mg/kg). The loss was even greater in the animals receiving diethyl maleate 1 h prior to captan. Furthermore, usual increase in the activity of drug biotransformation enzymes seen after phenobarbital treatment appears to decrease in rats dosed with this funaicide. In vitro incubations of rat liver microsomes with captan resulted in a profound loss of cytochrome P-450 and the acitivty of benzphetamine N-demethylase as well as aniline hydroxylase. Although the inhibition of drug-metabolizing enzyme activity by captan was observed in microsomal incubations with or without NADPH, a detectable amount of carbonyl sulfide (COS) was found only in the incubations that contained captan plus NADPH. Carbonyl sulfide appears to arise from a captan-derived metabolite, thiophosgene (CSCl2), which decomposes to COS in aqueous solutions and in the presence of NADPH inhibits the activity of drug biotransformation enzymes.     

Effect of repeated oral doses of a novel immunosuppressive macrolide lactone on hepatic mixed-function oxidase system in the rat. Comparative study with ciclosporin.

Effect of pretreatment of rats with FK506((-)-(1R,9S,12S,13R,14S,17R,18E,21S,23S,24R,25S,27R)-17-allyl-1,14- dihydroxy-12-[(E)-2-[(1R,3R,4R)-4-hydroxy-3methoxycyclohexyl]-1- methylvinyl]-23,25-dimethoxy-13,19,21,27-tetramethyl-11,28-dioxa-4- azatricyclo-[22.3.1.0(4.9)]octacos-18-ene-2,3,10,16-tetrone hydrate, CAS 104987-11-3) on microsomal cytochrome P-450 system and oxidations of the administered drug and other model substrates were studied and compared with those of a pharmacologically related drug, ciclosporin (cyclosporin A). Oral treatment of male Sprague-Dawley rats with FK506 (0.4, 2 or 10 mg/kg/d) for 7 days did not decrease microsomal content of total cytochrome P-450 in livers, but rather increased the content in groups with the dose of 0.4 or 10 mg/kg to the levels of 126-130% of the control. Microsomal NADPH-cytochrome c reductase activities were decreased up to 67% of the control with the increasing dose of FK506 and to 62% in a group treated orally with cyclosporin A (25 mg/kg/d for 7 days), although another microsomal electron-transport component, cytochrome b5, was rather increased in all the treated groups. Treatment with FK506 or cyclosporin A did not reduce but slightly increased microsomal activities of aniline hydroxylation, p-nitroanisole O-demethylation and O-ethoxyresorufin O-deethylation. Microsomal depropylation of 7-propoxycoumarin, a typical P-450IIIA-substrate, was also not reduced in all dose groups of FK506, while it was decreased by the treatment with 25 mg/kg cyclosporin A.(ABSTRACT TRUNCATED AT 250 WORDS)     

Age-dependent toxicity of acorn extract in young and old male rats

Intraperitoneal administration of acorn extract of dosage levels of 200, 400 and 600 mg/kg body weight did not produce significant change in the hepatic microsomal cytochrome P-450 levels and the activities of NADPH-cytochrome c reductase, benzphetamine N-demethylase and aniline hydroxylase in young, adult rats (weighing 200-250 g), with the exception of the activity of benzphetamine N-demethylase at the 600 mg/kg dose which was decreased significantly. On the other hand, a dose of only 100 mg/kg body weight ip to old rats (weighing 400-450 g) caused significant decreases in the microsomal cytochrome P-450, benzphetamine N-demethylase and NADPH-cytochrome c reductase activities. However, there was no significant change in the activity of aniline hydroxylase in these rats, indicating selective inhibition of the microsomal enzymes and higher susceptibility of old rats than young ones to acorn toxicants. When the serum samples from the treated young rats were analyzed for sorbitol dehydrogenase (SDH), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities as markers of liver toxicity, these activities were significantly higher in the treated rats than the corresponding control values. Similar changes were noted for old rats receiving a dose of 100 mg/kg body weight of acorn extract. The results indicate that acorn extract affects old rats more than young rats as measured by its effect on liver and liver microsomal enzymes.     

Effect of monensin on liver glutathione, glutathione S-transferase and monooxygenases in rats.

Monensin administered ip to male rats at a dosage of 2.5 mg/kg/d for 3 consecutive days did not change the liver levels of glutathione, but depressed significantly the amount of cytochrome P-450 and the activities of aniline hydroxylase and a cytosolic CDNB-specific glutathione S-transferase. There was a marked decrease in the aminopyrine N-demethylase activity and a significant increase in the pentobarbital sleeping time in rats treated with monensin. In contrast, no change in these parameters was found 2 h after a single ip dose (7.5 mg/kg) of monensin. The results suggest that monensin-induced inhibition of the liver cytosolic glutathione S-transferase and microsomal monooxygenases is non-specific.     

Effect of acute and repeated selenium treatment on hepatic monooxygenase enzyme activity in male rats

The effect of sodium selenite administered acutely or repeatedly on the biochemical components of the hepatic microsomal monooxygenase enzyme system was examined in male rats. 72 h following acute administration of selenium (2.4 mg Se/kg, i.p.), there was a significant decrease in ethylmorphine-N-demethylase activity and cytochrome P-450 levels but no change in aniline hydroxylase or NADPH cytochrome c reductase activity. Following repeated administration of selenite in the drinking water (1, 2, or 4 ppm Se) for 30 days, there was no alteration in any of the parameters measured. Following the in vitro additions of selenite to microsomes obtained from untreated rats, ethylmorphine-N-demethylase and aniline hydroxylase activities were inhibited at selenium concentrations of 10(-4) M or greater, but the inhibition achieved was less than 50%. No alterations in cytochrome P-450 levels were observed. These results indicate that selenium is a rather weak, indirect, and substrate-specific inhibitor of the hepatic monooxygenase enzyme system.     

The effects of cyclosporin A (CsA) on hepatic microsomal drug metabolism in the rat

The effects of cyclosporin A (CsA), a powerful immunosuppressant, on the hepatic microsomal mixed function oxidase (MFO) system was studied in male rats. Difference spectroscopy studies indicated that CsA binds to cytochrome P-450 producing a type I spectral change. To investigate potential interactions with the MFO system, CsA was administered orally at doses of either 25 mg/kg or 50 mg/kg once daily for 9 days. Various metabolic parameters were examined, including: levels of microsomal protein, cytochrome P-450, and cytochrome b5, NADPH-cytochrome c reductase activity, N-demethylation of ethylmorphine (ETM), and p-hydroxylation of aniline (ANL). Rats treated with 50 mg/kg showed a 25% or greater decrease over controls in all parameters examined except microsomal protein and cytochrome b5 levels. Rats treated with 25 mg/kg showed a 28% or greater decrease in all parameters except microsomal protein, cytochrome b5, and cytochrome P-450. Kinetic studies of ETM-N-demethylase and ANL-hydroxylase activities were conducted either with microsomes prepared from CsA-treated animals (50 mg/kg/day for 5 days) or with pooled microsomes prepared from untreated animals to which CsA was added directly. Enzyme reaction velocities were measured and apparent KM and apparent Vmax were determined. Studies with CsA-treated animals revealed a 57% decrease in both KM and Vmax for ETM-N-demethylase, and a 46% decrease in KM and a 32% decrease in Vmax for ANL-hydroxylase. Studies involving direct addition of CsA to microsomes at final concentrations of 0.01 mM and 0.10 mM revealed no significant changes in apparent KM or Vmax for either enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of cimetidine on hepatic biochemical changes, liver toxicity and major urinary metabolite excretion of trichloroethylene in rats

The effects of cimetidine (CIM) (an inhibitor of the hepatic microsomal monooxygenase system) on the metabolism and hepatotoxicity of trichloroethylene (TRI) were studied in male Sprague-Dawley rats. Rats were given three doses of 120 mg/kg i.p. (low-dose regimen) of CIM at 0, 6 and 11 h for 1 day, or ten doses of 200 mg/kg (high-dose regimen) at 8, 11, 14 and 17 h for 2 days and 8 and 11 h on 3rd day. Trichloroethylene (0.5 or 0.65 ml/kg) was administered i.p. 1 h after 2nd dose (low-dose regimen) or 9th dose (high-dose regimen) of CIM. In the low-dose regimen study, the activity of hepatic microsomal aminopyrine N-demethylase was decreased 1 and 5 h after the second dose and 7 h after the third dose of CIM, but became normal 20 h after the last dose. The cytochrome P-450 content and the activities of aniline hydroxylase and epoxide hydratase remained unchanged. Trichloroethylene at both dose levels produced liver toxicity, as verified by increase in activities of SDH and SGPT as well as by liver histology. Cimetidine alone had no such effect. An apparent reduction in TRI toxicity by CIM (at both dose regimens) could be observed histologically. The biochemical tests (SDH and SGPT) corroborated the histological changes only when TRI was given at a dose of 0.5 ml/kg combined with a high-dose regimen of CIM. Cimetidine at both dose regimens had a tendency to decrease the in vivo metabolism of TRI.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of chronic acetone administration on ethanol-inducible monooxygenase activities in the rat

Liver microsomal monooxygenase activities known to be ethanol-inducible were determined in female Sprague-Dawley rats after 2-week treatment with 1% (v/v) acetone. Daily acetone intake was in the order of 1.2 g/kg. The final body weight, liver weight and microsomal protein content of acetone-treated rats were identical to those of untreated controls. Microsomal NADPH-cytochrome c reductase activity was also unaffected, while cytochrome P-450 content was only increased 12-18%. Ethanol-inducible p-nitrophenol hydroxylation, aniline hydroxylation and 7-ethoxycoumarin O-deethylation activities were enhanced 5.3-, 4.4- and 2.6-fold, respectively, by chronic acetone treatment. The sex-dependent inducing effect of ethanol on benzphetamine N-demethylation activity in female rats was not observed however, after acetone. Addition of acetone in vitro had a stimulatory effect on aniline hydroxylation by microsomes from control and acetone-induced rats. Acetone, however, was found to be a competitive inhibitor of p-nitrophenol hydroxylation activity (apparent Ki = 1.8 mM), an observation suggesting that p-nitrophenol is a more selective substrate than aniline for rat liver ethanol- and acetone-inducible cytochrome P-450j. Interruption of the chronic acetone treatment for 24 hr resulted in the almost complete disappearance of its inducing affects, this treatment apparently reproducing only the rapidly reversible preferential inducing effects of chronic ethanol administration. This experimental model of induction by acetone in the rat, when compared to chronic ethanol administration, would thus permit a more selective look at the consequences of these common inducing effects in particular, with respect to drug metabolism and toxicity in vivo, and this, in the absence of the hepatotoxic effects of ethanol itself.     

Metabolic fate and disposition of [14C]hydroquinone given orally to Sprague-Dawley rats

Hydroquinone (HQ) is used widely in industry and in commerce and is considered to have a low degree of toxicity. Although the metabolism of HQ has been studied elsewhere, a complete materials balance has not been reported. We investigated the metabolism of HQ in naive and HQ pretreated male Sprague-Dawley rats. [14C]HQ was administered by gavage in single doses of 5, 30, or 200 mg/kg to naive rats. HQ was given repeatedly by gavage to male rats at 200 mg/kg for 4 consecutive days followed by a single dose with 200 mg/kg of [14C]HQ. In separate studies rats were fed 5.6% unlabeled HQ in the diet for 2 days or were dosed by gavage with 311 mg/kg [14C]HQ. The excretion patterns of [14C]HQ and its metabolites were similar for rats dosed singly or repeatedly. Rats given a single dose of 200 mg/kg of [14C]HQ excreted 91.9% of the dose in the urine within 2-4 days; 3.8% was excreted in the feces, about 0.4% was excreted in expired air, and 1.2% remained in the carcass. Radioactivity was widely distributed throughout the tissues with higher concentrations in the liver and kidneys. A decrease in 14C tissue concentrations occurred from 48 to 96 h. The only radiolabeled compounds in the urine were HQ (1.1-8.6% of the dose), hydroquinone monosulfate (25-42%), and hydroquinone monoglucuronide (56-66%). Similar findings were observed for rats given HQ in the feed. There were no significant increases from controls for absolute or relative liver weights, liver microsomal protein concentrations, cytochrome b-5, cytochrome P-450 or cytochrome c reductase activity in rats dosed repeatedly with 200 mg/kg HQ. Cytochrome P-450 values were slightly but significantly decreased in rats dosed repeatedly with HQ compared with controls.     

2,3,7,8-Tetrachlorodibenzo-p-dioxin-induced changes in the hydroxylation of biphenyl by rat liver microsomes

Biphenyl 2- and 4-hydroxylase activities and cytochrome P-450 concentrations in microsomes were increased by oral doses of less than 1 μg TCDD/kg. Female rats were more sensitive than male rats to the inductive effects of TCDD. since highly significant increases in biphenyl-hydroxylating activities were observed at the dose level of 0.2 μg TCDD/kg in female but not in male rats. The inductive effect was very persistent: biphenyl 2- and 4-hydroxylases remained stimulated even after 73 days following a single oral dose of 25 μg TCDD/kg. The levels to which the hydroxylases were stimulated in female rats were the same as in male rats. Rats of all ages from 10 to 335 days responded to hepatic microsomal effects of TCDD to approximately the same degree. The enzyme inductive effect was diminished by the simultaneous administration of actinomycin D. The K_m of biphenyl 2-hydroxylase (1.42 mM) was not altered significantly by TCDD treatment, but the K_m of biphenyl 4-hydroxylase (0.62 mM) was increased to approximately the same value (1.6 mM) as that of the 2-hydroxylase. The V_max of biphenyl 4-hydroxylase was increased 4.5-fold but that of biphenyl 2-hydroxylase was increased 16.5-fold. Rates of 2β- and 16α-hydroxylation of testosterone were suppressed by TCDD but rates of 7α- and 6β-hydroxylation were unaffected. It would appear that the hepatic microsomal mixed-function oxidases responsible for the hydroxylation of biphenyl and testosterone are different.     

On the aromatic hydroxylation of amphetamine in rat liver microsomes and perfused liver preparations: effects of long-term administration.

The liver microsomal p-hydroxylation of amphetamine to parahydroxyamphetamine (pOHA) was dependent on NADP and inhibited by carbon monoxide indicating the involvement of cytochrome P-450, SKF 525-A, fenfluramine and desmethylimipramine were the most effective inhibitors of this pathway of amphetamine metabolism. Repeated administraion of phenobarbital resulted in reduced p-hydroxylation of amphetamine in vitro. Chronic administration of amphetamine reduced the microsomal p-hydroxylation of amphetamine without apparent changes in the cytochrome P-450 levels or in the activity of NADPH-cytochrome c reductase. The aromatic hydroxylation of aniline and the demethylation of ethylmorphine was not affected by this treatment. However, the 455 nm complex formed during the microsomal metabolism of N-hydroxy-amphetamine was increased by the long-term administration of amphetamine. These results indicate some pecularities of the in vitro hydroxylation of amphetamine by rat liver microsomes. Amphetamine disappeared from the perfusate of the perfused liver at the same rate in rats given a single dose of amphetamine and in rats given amphetamine orally for four weeks. The excretion of pOHA and its conjugate increased at 60 and 90 min. and 30, 60 and 90 min. respectively in the perfusate of the same experiment as compared to the controls. The total excretion of radioactive amphetamine metabolites at the end of the perfusion was increased in the perfusate and reduced in the bile compared to the control experiment.     

Comparative incidence of oral ochratoxicosis and aflatoxicosis on the activity of drug-metabolizing enzymes in rat liver

Mycotoxicosis has been produced in the rat by daily oral administrations of ochratoxin A (1.5 mg/kg/day) or aflatoxin B1 (1 mg/kg/day). Hepatic microsomal cytochrome P-450 and b5 contents and many phase I and II biotransformation systems have been measured in the course of ochratoxicosis (4 to 15 dosings) and aflatoxicosis (1 to 8 dosings). In case of ochratoxicosis, decreases in cytochrome P-450 level, aminopyrine demethylase and aniline hydroxylase activities were observed in rats receiving 15 administrations of the toxin. Aflatoxicosis induced more severe decreases in cytochrome P-450, aminopyrine demethylase and ethoxycoumarin deethylase following 8 daily gavages. In the two studies, there was no significant change in activities of liver phase II biotransformation enzymes.