Effect of phenobarbital pretreatment on benzene biotransformation in the rat

Factors responsible for different quantitative effect of phenobarbital (PB) pretreatment (sodium phenobarbital, 50 mg kg^–1 day^–1 for 3 days) on benzene metabolism to phenol in vivo and in vitro were studied in male Wistar rats. A more than 4-fold increase of benzene metabolism was observed with 9,000 g supernatant of liver homogenate, 2.8- to 4-fold increase with isolated perfused liver; phenol formation in vivo after oral benzene was increased by PB 2-fold, but only shortly following benzene administration and the enhancement rapidly diminished to 1.15-fold increase in the total excreted phenol. Benzene concentrations in 9,000 g supernatant incubations were 2 mM, those with isolated perfused livers were up to 4 mM, but those in blood in vivo were below 0.3 mM; the effect of PB induction in vivo disappeared along with decreasing benzene and increasing phenol blood concentrations which surpassed benzene 2–3 h after oral benzene administration. The effect of benzene concentration on the manifestation of PB induction is also supported by almost a 2-fold increased phenol formation in PB rats over controls in vivo after repeated administration of benzene. The elimination of radioactive metabolites of orally administered benzene-¹⁴C, 3 mmoles kg^–1, in urine was markedly inhibited by intraperitoneal administration of phenol (1.2 mmole kg^–1), but not by pyrocatechol, resorcinol or hydroquinol (0.6 mmole kg^–1, respectively) suggesting that phenol might inhibit benzene metabolism in vivo especially when its concentration exceeds that of benzene.     

Effect of phenobarbital or 3-methylcholanthrene pretreatment on carbon tetrachloride-induced lipid peroxidation in rat liver.

The enhancement of carbon tetrachloride hepatotoxicity following phenobarbital pretreatment is associated with an increase in lipid peroxidation in vivo when CCl₄ is administered orally or by inhalation. However, pretreatment with 3-methylcholanthrene did not increase in vivo lipid peroxidation following CCl₄ administration by the oral or inhalation route. CCl₄ stimulated lipid peroxidation, as determined by malonaldehyde formation in vitro, and was increased by phenobarbital pretreatment but not by 3-methylcholanthrene pretreatment. These data support a relationship between microsomal drug metabolizing activity and alterations in hepatic injury and lipid peroxidation following CCl₄ administration.     

Lipid peroxidation in acrylonitrile-treated rats, evidenced by elevated ethane production

The intraperitoneal administration of acrylonitrile (greater than 25 mg kg-1) to rats is associated with an increased production of ethane and a rise of the serum activity of the cytosolic enzyme, sorbitol dehydrogenase. These effects are prevented by pretreatment with vitamin E and the microsomal enzyme inhibitor SKF 525A, but are exacerbated by pretreatment with the microsomal enzyme inducer, phenobarbital. Repeated intraperitoneal administration of acrylonitrile (40 mg kg-1) for four weeks also increases ethane production and serum SDH activity, and produces various morphological changes in liver parenchymal cells (necrosis, increased mitotic activity, increased nucleolar size and myelinic figures in mitochondria) and inhibits the growth of the animals. All these effects are prevented by the administration of vitamin E (190 mg kg-1 i.p., daily) during the last two weeks of treatment. A dose of sodium cyanide (2.5 mg kg-1 i.p.) which leads to a urinary excretion of thiocyanate similar to that found after the intraperitoneal administration of 25 mg kg-1 acrylonitrile, does not stimulate ethane production. This study suggests that the hepatoxicity of acrylonitrile may, at least partly, result from a lipoperoxidation process and is linked with its microsomal oxidative biotransformation.     

Toxicity-Related Changes in Benzene Metabolism in vivo

1. The influence of microsomal enzyme inducers and inhibitors on the metabolism of [U-¹⁴C]benzene in the rat was examined.

2. Pre-treatment of animals with the inhibitors piperonyl butoxide and cobaltous chloride tended to reduce the urinary excretion of metabolites in 24?h but increase the overall urinary excretion. Piperonyl butoxide tended to increase expired benzene.

3. Pre-treatment of animals with the inducer phenobarbital tended to increase urinary excretion of metabolites but decrease expired benzene, as did pretreatment with benzene itself.

4. All pre-treatments appeared to increase the excretion of phenolic glucu-ronides, particularly benzene pre-treatment. Phenobarbital and benzene pre-treatment tended to increase phenylmercapturic acid excretion and benzene pre-treatment markedly increased excretion of quinol.

5. The results are discussed in relation to the effect of microsomal enzyme inhibitors and inducers on benzene-induced bone marrow toxicity.     

Acrylonitrile biotransformation in rats,mice, and chinese hamsters as influenced by the route of administration and by phenobarbital,SKF 525-A,cysteine, dimercaprol,or thiosulfate

Female Wistar rats, conventional albino mice, and Chinese hamsters were given a single dose of acrylonitrile, 0.5 or 0.75 mM/kg body weight. The elimination in the urine of thiocyanate, which is the main metabolite of acrylonitrile, indicated a decreasing proportion of biotransformation after oral (over 20 %), intraperitoneal, or subcutaneous (2 to 5 %), and intravenous (1 %) administration in rats. Oral administration of acrylonitrile in hamsters and mice was also followed by higher biotransformation than intraperitoneal administration. Pretreatment of rats with phenobarbital, SKF 525 A, cysteine, or dimercaprol did not significantly influence elimination of thiocyanate in the urine after the administration of acrylonitrile, but simultaneous administration of thiosulfate significantly increased the metabolized portion of acrylonitrile given intraperitoneally in rats (almost twice) and mice (more than three times). Acrylonitrile was found to be strongly bound in blood. The study confirmed the marked effect of distribution (first-pass metabolic phenomenon) on the metabolic fate of foreign compounds. The strong acrylonitrile binding and cyanoethylation are apparently responsible for the unusually high influence of the different routes of administration on the metabolic fate of acrylonitrile. Acrylonitrile was more effectively metabolized to thiocyanate in mice than in rats after oral, intraperitoneal, and intravenous administration. A greater response of acrylonitrile to thiocyanate metabolism and a larger decrease in its acute toxicity after thiosulfate in mice than in rats indicate possible differences in the mechanism of acrylonitrile toxicity in these animals. Cyanide apparently plays a minor role in the acrylonitrile toxicity in rats, but may play quite an important one in mice.     

Effect of propranolol on urinary prostaglandin E2 excretion and renal interlobar arterial blood flow after furosemide administration in patients with hepatic cirrhosis

Summary The effect of propranolol on furosemide-stimulated urinary prostaglandin E₂ (PGE₂) excretion and renal blood flow was evaluated in 12 patients with alcoholic liver cirrhosis. Plasma and urine were collected before and 60 min after furosemide 20 mgI with or without propranolol pretreatment, and plasma renin activity (PRA), plasma aldosterone concentration (PAC), urinary excretion of PGE₂ and sodium were determined. The renal interlobar arterial Pulsatility Index (PI), as an index of resistance to blood flow, was also determined before and 60 min after furosemide administration with and without propranolol pretreatment, by using a duplex Doppler ultrasound (Hitachi EUB 565).Urine volume and sodium excretion after furosemide administration were not influenced by the propranolol pretreatment. Furosemide administration significantly increased urinary PGE₂ excretion, PRA and PAC, and these effects were significantly reduced by propranolol. Furosemide administration with or without propranolol significantly reduced renal interlobar arterial PI, the average reduction in PI being significantly lower after furosemide administration with propranolol pretreatment.The results demonstrate that propranolol pretreatment significantly influenced the furosemide-induced increase in urinary PGE₂ excretion and renal interlobar arterial blood flow in cirrhotic patients.     

Toxic effects of methylcyclopentadienyl manganese tricarbonyl (MMT) in rats: Role of metabolism

The toxicity of methylcyclopentadienyl manganese tricarbonyl (MMT) has been investigated in relation to its in vivo biotransformation in the rat. The LD₅₀ dose of MMT was found to be 50 mg/kg for oral administration and 23 mg/kg for ip administration. Death appeared to be caused by severe pulmonary hemorrhagic edema. Histological studies of MMT-treated animals revealed pathologic changes in lungs, liver, and kidney. Phenobarbital pretreatment protected rats from the lethal effects of 2.5 times the LD₅₀ dose of MMT, it shifted the site of tissue injury from the lungs to the liver, and it caused a doubling of the rate of biliary excretion of MMT metabolites. The possibility is discussed that MMT per se is toxic without bioactivation, and that the protective effect of phenobarbital pretreatment is due to a first-pass effect preventing toxic concentrations of orally administered MMT from reaching the systemic circulation.     

Influence of P-4502E1 induction on benzene metabolism in rat hepatocytes and on biliary metabolite excretion.

The influence of P-4502E1 induction on the metabolite pattern of benzene was studied in hepatocytes in vitro and in bile in vivo, and compared with that obtained with phenol (the major benzene metabolite). Eight metabolites from benzene and four from phenol (including conjugates) represented over 90% of total metabolites. Benzene metabolism (0.1 mM) in hepatocytes from isopropanol-treated rats (2.5 ml/kg, orally) was 3-fold higher than in corresponding cells from control rats, primarily because of increased formation of hydroquinone and phenylglutathione. Immunoblotting of microsomes revealed a parallel induction of P-4502E1 in hepatocytes from isopropanol-treated rats. In contrast, treatment with 3-methylcholanthrene or phenobarbital caused a decrease of P-4502E1, together with reduced benzene metabolism at 0.01 mM benzene. Addition of isoniazid (5 mM) resulted in a strong inhibition of benzene and phenol metabolism. Benzene metabolites were determined in bile following intraperitoneal administration of benzene (2.5 and 150 mg/kg). Biliary benzene metabolites were increased 2- to 3-fold after isopropanol treatment. Hydroquinone sulfate was identified as a major biliary metabolite of phenol. The results suggest that treatment with inducers of P-4502E1 leads, even at low benzene exposure, to an increased release of potentially myelotoxic metabolites from liver into the systemic circulation.     

Potentiation of CCl4-induced hepatotoxicity in the dog by chronic exposure to phenobarbital

Carbon tetrachloride (CCl₄) hepatotoxicity was studied in normal and in phenobarbital-pretreated beagle dogs. The liver content of triglycerides (TG) and lipid peroxides, and activities of microsomal enzymes as well as serum glutamicoxaloacetic (SGOT) and glutamic-pyruvic (SGPT) transaminases were monitored for periods up to 24 hr after CCl₄ administration. CCl₄ alone produced no consistent changes in the parameters studied. Phenobarbital pretreatment produced significant increases in liver TG content, microsomal enzyme activities and SGPT activity. Phenobarbital pretreatment had no effect on CCl₄-induced changes in glucose-6-phosphatase activity, but produced an immediate increase in lipid peroxide content, which declined to normal by 24 hr after treatment. The TG content of livers from phenobarbital-pretreated dogs began to increase by 3 hr after CCl₄ administration and continued to increase as the time after administration increased. Activities of SGOT and SGPT were strikingly increased 3 hr after administration of CCl₄ and were still apparently increasing 24 hr after treatment. CCl₄ administration to phenobarbital-treated dogs eliminated the increase in activities of all microsomal drug-metabolizing enzymes that were seen with phenobarbital pretreatment alone. It was concluded that phenobarbital produced a true potentiation of the toxicity of CCl₄ by apparently decreasing the threshold at which the hydrocarbon becomes toxic. The results produced no definitive evidence to explain the mechanism by which phenobarbital produces the increase in CCl₄ toxicity.     

Effects of phenobarbital and 3-methylcholanthrene pretreatment on the plasma half-life and urinary excretion profile of theophylline and its metabolites in rats

The effects of the inducers of the hepatic microsomal enzyme system, phenobarbital and 3-methylcholanthrene, on theophylline plasma half-life and on the elimination of theophylline and its metabolites in urine and feces have been examined. The results indicate that induction of the hepatic microsomal drug-metabolizing enzyme system significantly decreases plasma theophylline half-life. In this respect, 3-methylcholanthrene was more effective than phenobarbital. Control theophylline half-life was 3.5 hr. After phenobarbital or 3-methylcholanthrene pretreatment, the theophylline half-life was 2.6 and 0.8 hr respectively. Thin-layer Chromatographie analysis of the urine showed three radioactive peaks corresponding to 1,3-dimethyluric acid, 1-methyluric acid and unchanged theophylline. Both inducing agents significantly increased the urinary elimination of 1,3-dimethyluric acid above that seen in control animals throughout the 24-hr collection period, but only 3-methylcholanthrene increased the total amounts of 1-methyluric acid excreted. Urinary elimination of unchanged theophylline was decreased from control values by both agents. A small, but not statistically significant, increase in the fecal elimination of radioactive material was also noted in the animals pretreated with phenobarbital. The results indicate that alteration in hepatic drug-metabolizing activity may markedly affect the in vivo biotransformation of theophylline.     

Effect of microsomal enzyme inducers on biliary and urinary excretion of acetaminophen metabolites in rats. Decreased hepatobiliary and increased hepatovascular transport of acetaminophen-glucuronide after microsomal enzyme induction

Treatment of rats with phenobarbital (PB), 3-methylcholanthrene, and pregnenolone-16 alpha-carbonitrile increased the total (biliary plus urinary) excretion of thioether and glucuronic acid conjugates of acetaminophen (AA) without influencing AA-sulfate excretion, suggesting that these microsomal enzyme inducers enhance both cytochrome P-450-mediated toxication and UDP-glucuronosyltransferase-mediated detoxication of AA. However, induction with transstilbene oxide (TSO) did not increase the total excretion of AA-thioethers or AA-glucuronide and decreased AA-sulfate excretion. In addition, all inducers increased the ratio of AA metabolites excreted into urine over that excreted into bile. The extent of this shift from biliary to urinary excretion was dependent on both the AA metabolite and the inducer. The largest shift in the excretory route was seen with AA-glucuronide and induction with PB and TSO as inducers. Specifically, PB and TSO treatments decreased biliary excretion of AA-glucuronide by 70 and 89%, respectively, and increased its blood concentration up to 6- and 11-fold and urinary excretion 3- and 3.6-fold, respectively. Galactosamine depletes UDP-glucuronic acid from the liver only, thereby inhibiting hepatic but not extrahepatic glucuronidation. Galactosamine treatment prevented the PB-induced increase in AA-glucuronide in blood and urine. This suggests that the PB-induced increases in AA-glucuronide in blood and urine originated from the liver. Thus, microsomal enzyme inducers not only influence xenobiotic biotransformation, but may also after the contribution of the excretory routes (i.e. bile and urine) in the elimination of xenobiotic metabolites by changing the direction of hepatic transport.     

On the Aromatic Hydroxylation of Amphetamine in Rat Liver Microsomes and Perfused Liver Preparations: Effects of Long-term Administration

Abstract The liver microsomal p-hydroxylation of amphetamine to parahydr-oxyamphetamine (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 administration 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.     

Induction of cytochrome P-450 and related drug-oxidizing activities in muscone (3-methylcyclopentadecanone)-treated rats

In the present study, we investigated the effects of muscone on both in vitro and in vivo parameters of the hepatic microsomal drug-metabolizing enzyme system and other enzyme activities in rats. In the in vivo study, the serum dimethadione (DMO)/trimethadione (TMO) ratios at 2 hr after oral administration of TMO (100 mg/kg) were significantly increased in both male and female rats treated with 75 and 150 but not 40 mg muscone/kg. Antipyrine metabolite profile in 24 hr urine of rats pretreated with muscone (150 mg/kg) was examined. The results showed that the excretion of norantipyrine was significantly increased as compared to the control group. In the in vitro study, we found that the content of cytochrome P-450, and activities of aminopyrine, N-demethylase, aniline hydroxylase and delta-aminolevulinic acid (ALA) synthetase were significantly increased as compared to the controls in both male and female rats treated with muscone (75 and 150 mg/kg). This type of induction of the hepatic metabolizing enzymes was similar to that seen after treatment with a prototype drug, phenobarbital.     

Effects of phenobarbital and beta-naphthoflavone on the in vivo toxicity and in vitro metabolism of aflatoxin in an aflatoxin-resistant and control line of chickens

The in vivo toxicity of aflatoxin and the in vitro microsomal metabolism of aflatoxin B1 (AFB1) were investigated in a population of chickens previously selected for resistance to aflatoxin (AR line) and a corresponding control population (NS line) after in vivo pretreatment with saline, sodium phenobarbital (PB), or beta-naphthoflavone (BNF) solutions. PB pretreatment increased survival and BNF pretreatment increased mortality in both the NS and AR lines when a single oral dose of aflatoxin was administered. The rate of in vitro metabolism of AFB1 was greater with microsomes from saline pretreated AR chicks than with microsomes from similarly treated NS chicks. In vivo pretreatment with PB increased AFB1 metabolism by NS and AR microsomes. After BNF pretreatment of vivo, AR microsomes metabolized more AFB1 than NS microsomes, and there was a dramatic decrease in AFB1 metabolism in NS microsomes. AFB1-dihydrodiol was the major metabolite produced by both lines, with aflatoxin M1 and aflatoxin Q1 recovered in small quantities from BNF-pretreated AR microsomal incubations only. These data indicate that increased in vivo resistance of the AR line to acute aflatoxicosis may be related to increased hepatic AFB1 metabolism and that genetic selection has resulted in altered in vitro quantitative and qualitative metabolism of AFB1 in the AR line.     

Absorption,distribution, metabolism and excretion of telmesteine,amucolitic agent,in rat

1. The metabolism and disposition of telmesteine, a muco-active agent, have been investigated following single oral or intravenous administration of ¹⁴C-telmesteine in the Sprague–Dawley rat.

2. ¹⁴C-telmesteine was rapidly absorbed after oral dosing (20 and 50mg kg^-1) with an oral bioavailability of > 90% both in male and female rats. The C_max and area under the curve of the radioactivity in plasma increased proportionally to the administered dose and those values in female rats were 30% higher than in male rats.

3. Telmesteine was distributed over all organs except for brain and the tissue/plasma ratio of the radioactivity 30min after dosing was relatively low with a range of 0.1–0.8 except for excretory organs.

4. Excretion of the radioactivity was 86% of the dose in the urine and 0.6% in the faeces up to 7 days after oral administration. Biliary excretion of the radioactivity in bile duct-cannulated rats was about 3% for the first 24 h. The unchanged compound mainly accounted for the radioactivity in the urine and plasma.

5. Telmesteine was hardly metabolized in microsomal incubations. A glucuronide conjugate was detected in the urine and bile, but the amount of glucuronide was less than 6% of excreted radioactivity.     

Effect of pretreatment with sodium phenobarbital on the toxicity of soman in mice

Pretreatment with sodium phenobarbital induces hepatic microsomal enzymes which are responsible for the metabolic breakdown of a large number of endogenous and exogenous chemical compounds. A previous study [K. P. DuBois and F. K. Kinoshita, Proc. Soc. exp. Biol. Med.129, 699 (1968)]reported that phenobarbital pretreatment reduced the toxicity of various organophosphorus anticholinesterases; however, the exact mechanism for the increased detoxification was not investigated. In this study, the effect of phenobarbital pretreatment on the toxicity of soman was investigated. Male mice were injected daily for 4 days with sodium phenobarbital (100 mg/kg, i.p.) and used in the various experiments 24 hr after the last injection. Phenobarbital pretreatment produced a significant increase in liver weight and decreased the sodium pentobarbital (75 mg/kg, i.p.) induced sleep-time to 41 min compared to 141 min in controls. The lethality of soman was reduced following phenobarbital pretreatment. In control mice, the soman 24hr LD₅₀ values (μg/kg) were 130, 393 and 42 following s.c., i.p. and i.v. administration, respectively, whereas in phenobarbital-pretreated mice the soman 24 hr LD₅₀ values (μg/kg) were 261, 746 and 63 following s.c., i.p. and i.v. administration respectively. Acetylcholinesterase activity was increased in the plasma (90%) but not in brain or diaphragm following phenobarbital pretreatment. Liver somanase activity was not affected. Liver aliesterase and serum aliesterase were both increased significantly following phenobarbital pretreatment. An increase in the amount of nonspecific binding sites for soman (esterases in liver and plasma) and not an increase in the metabolism of soman in vivo probably accounts for the protection afforded by phenobarbital pretreatment in mice.     

In Vitro Metabolism of p-Xylene by Rabbit Lung and Liver

1. Optimum conditions for metabolism in vitro of p-xylene by rabbit liver or lung microsomal enzymes have been studied. Reactions were linear with time for at least 30?min at a microsomal protein concentration of 1?mg/ml. Addition of cytosol fraction to incubation mixtures of microsomes, NADPH, and substrate increased enzyme activity but the increase was independent of amount of cytosol added (over range of 0.1 ml to 0.5 ml). The pH optimum for the lung and liver microsomal system was 7.3 and 7.8, respectively, using Hepes buffer. The apparent K_m and V_max for the liver and lung systems were determined. The NAD⁺ and NADP⁺ requirements were studied.

2. The major metabolite of p-xylene in vitro, as determined by t.l.c., of liver and lung microsomal incubation mixtures was p-toluic acid.

3. Phenobarbital pre-treatment of rabbits (multiple doses, intraperitoneal or intravenous) induced the liver microsomal xylene-metabolizing system approximately 3-fold, whereas there was no change in activity of the lung enzyme. Maximum induction of liver microsomal metabolism after a single intraperitoneal dose of phenobarbital (100?mg/kg) was reached in 2–3 days and declined slowly thereafter; during this same period lung xylene-metabolizing activity remained unchanged or increased only slightly. Chlorpromazine pre-treatment, intraperitoneal (but not intravenous), of rabbits stimulated hepatic microsomal xylene-metabolizing activity. Administration of 1,2,3,4-dibenzanthracene or 3-methylcholanthrene to rabbits resuited in decreased xylene metabolism in vitro by liver and lung microsomes.     

Study on in vivo and in vitro metabolism of dimethylformamide in male and female rats

The study of dimethylformamide (DMF) metabolism by rat tissues in vitro indicates that formaldehyde is not a metabolic product as previously reported [1]. Furthermore, no other monocarbon derivative (CO, CH₃OH, HCOOH, CH₄) was detected when DMF was incubated with a fortified liver preparation. One metabolic product is methylhydroxymethylformamide (DMF- OH) measured as N-methylformamide (NMF) due to the breakdown of the hydroxymethyl group during gas chromatography. It was usually believed that the main metabolite excreted in urine following administration of DMF to male and female rats was N.M.F. The results of this study indicate that DMF-OH constitutes the main metabolite in vivo. A quantitatively less inmportant urinary metabolite, hydroxymethylformamide (NMFOH), is determined as formamide (F) by gase chromatography, In male and female rats, partial hepatectomy reduces markedly the in vivo biotransformation of DMF. Following administration of DMF or NMF, the total amount of metabolites (DMFOH and/or NMFOH) excerted in urine is identical in both sexes, but female rats excrete more unchanged parent compound than male rats. The rate of NMFOH excretion in urine following high doses of DMF supports the hypothesis that DMP may inhibit its own bioransformation.     

治疗血吸虫病新药硝硫氰胺的代谢研究

硝硫氰胺是一非锑类治疗血吸虫病的新药。在动物和人体研究了该药的代谢。家兔口服给药后4小时达到高峰血浓度。由二室模型对血浓度数据作药物动力学参数计算,得t_1/2ka、t_1/2)α和t_(1/2)β分别为0.815,0.924和105.8小时,Kel、K₂₁和K₁₂分别为0.0127、0.398和0.356小时^-1,V_f为0.934升。大鼠口服给药后4小时药物在各组织的浓度大小依次为:肝、肾、脾、肺、肌肉、心、脑和血。血吸虫浓度高于肝和血浓度,而且雌虫高于雄虫。该药由尿和胆汁排泄,大鼠一次口服的尿排泄持续3天以上,人连服三次排泄持续超过19天。尿代谢产物由层析、高速液相色谱、紫外光谱和化学方法检测,硝硫氰胺转化成氨基物再转化成N-葡萄糖醛酸甙,这种代转变化是其生物转化途径之一。     

The relation between the oxidative biotransformation of hexachlorobenzene and its porphyrinogenic activity

The relation between the major toxic effect of hexachlorobenzene, hepatic porphyria, and its oxidative biotransformation was studied in vivo, by observing the effect of modulating its biotransformation on the expression of porphyria. This modulation was achieved by selective in vivo inhibition of the major cytochrome P450 isoenzyme involved in both the hydroxylation of hexachlorobenzene and its primary oxidative metabolite, pentachlorophenol. The involvement of this isoenzyme, cytochrome P450p, was established by in vitro biotransformation studies using microsomes derived from rats treated with various inducers of cytochrome P450 isoenzymes and selective in vitro inactivation of cytochrome P450p by triacetyloleandomycin (TAO), resulting in a strong inhibition of the microsomal conversion of hexachlorobenzene and pentachlorophenol. In vivo inactivation of cytochrome P450p was achieved by coadministration of hexachlorobenzene and TAO. Female rats which were treated with this diet for 10 weeks showed a strongly diminished urinary excretion of the major oxidative metabolites, pentachlorophenol and tetrachloro-1,4-hydroquinone, as compared to rats treated with hexachlorobenzene alone. The TAO coadministration was found to result in complexation of 70% of the total amount of hepatic microsomal cytochrome P450. The group treated with hexachlorobenzene alone displayed a 600-fold increase in the amount of hepatic porphyrins, whereas an almost complete absence of hepatic porphyrins was observed after administration of hexachlorobenzene together with TAO. The urinary excretion of porphyrins was also significantly lowered by cotreatment with TAO. A strong correlation was found to exist between the amount of porphyrins excreted and the amount of oxidative metabolites excreted, as a function of exposure time. Glucuronidation of pentachlorophenol was observed to an average extent of 30%. This percentage was not influenced by either TAO or phenobarbital. These results suggest that oxidative biotransformation, and thus the formation of the very reactive tetrachloro-1,4-benzoquinone, is directly related to the porphyrinogenic action of hexachlorobenzene.