Effect of total flavonoids of epimedium on liver microsomal CYP 1A2,CYP3A4 and CYP2E 1 activities in rats

To assess the potential effect of total flavonoids of epimedium （TFE） on cytochrome P450 and activity of its main isoforms in rat liver microsomes. TFE （300 mg/kg） was administered once daily to male Sprague-Dowley rats by gavage for fifteen days. The total cytochrome P450 content and its main isoforms CYP1A2, CYP3A4 and CYP2E1 activities in rat liver microsomes were detected. The activity of CYP1A2 was measured by fluorometry and the activities of CYP3A4 and CYP2E1 were determined by measuring the amount of methanal and p-aminophenol formed using UV/Vis spectrophotometer, respectively. Administration of TFE significantly increased the total CYP450 content and activities ofCYP1A2, CYP3A4 and CYP2E1 in rat liver microsomes, compared with the control group. Particularly, the activities of CYP1A2 and CYP2E1 were enhanced significantly （P〈0.01）. TFE induced the increase in total CYP450 content and its main isoforms CYP1A2, CYP3A4 and CYP2E1 activities in rat liver microsomes.

Polymorphisms of microsomal triglyceride transfer protein in different hepatitis B virus-infected patients

AIM: To identify the two polymorphisms of microsomal triglyceride transfer protein (MTP) gene in the Chinese population and to explore their correlation with both hepatitis B virus (HBV) self-limited infection and persistent infection. METHODS: A total of 316 subjects with self-limited HBV infection and 316 patients with persistent HBV infection (195 subjects without familial history), matched with age and sex, from the Chinese Han population were enrolled in this study. Polymorphisms of MTP at the promoter region -493 and at H297Q were determined by the allele specific polymerase chain reaction (PCR). RESULTS: The ratio of males to females was 2.13:1 for each group and the average age in the self-limited and chronic infection groups was 38.36 and 38.28 years, respectively. None of the allelic distributions deviated significantly from that predicted by the Hardy-Weinberg equilibrium. There was a linkagedisequilibrium between H297Q and -493G/T (D’ = 0.77). As the χ2 test was used, the genotype distribution of MTP -493G/T demonstrated a significant difference between the self-limited infection group and the entire chronic group or the chronic patients with no family history (χ2 = 8.543, P = 0.015 and χ2 = 7.199, P = 0.019). The allele distribution at the MTP-493 position also demonstrated a significant difference between the study groups without family history (χ2 = 6.212, P = 0.013). The T allele emerged as a possible protective factor which may influence the outcomes of HBV infection (OR: 0.59; 95% CI: 0.389-0.897). CONCLUSION: The polymorphism of the MTP gene, T allele at -493, may be involved in determining the HBV infection outcomes, of which the mechanism needs to be further investigated.

Pluronic L-81 ameliorates diabetic symptoms in db/db mice through transcriptional regulation of microsomal triglyceride transfer protein

AIM: To test whether oral L-81 treatment could im-prove the condition of mice with diabetes and to investigate how L-81 regulates microsomal triglyceride transfer protein (MTP) activity in the liver. METHODS: Genetically diabetic (db/db) mice were fed on chow supplemented with or without L-81 for 4 wk. The body weight, plasma glucose level, plasma lipid profile, and adipocyte volume of the db/db mice were assessed after treatment. Toxicity of L-81 was also evaluated. To understand the molecular mecha-nism, HepG2 cells were treated with L-81 and the effects on apolipoprotein B (apoB) secretion and mRNA level of the MTP gene were assessed.RESULTS: Treatment of db/db mice with L-81 sig-nificantly reduced and nearly normalized their body weight, hyperphagia and polydipsia. L-81 also markedly decreased the fasting plasma glucose level, improved glucose tolerance, and attenuated the elevated levels of plasma cholesterol and triglyceride. At the effective dosage, little toxicity was observed. Treatment of HepG2 cells with L-81 not only inhibited apoB secretion, but also signif icantly decreased the mRNA level of the MTP gene. Similar to the action of insulin, L-81 exerted its effect on the MTP promoter. CONCLUSION: L-81 represents a promising candidate in the development of a selective insulin-mimetic mol-ecule and an anti-diabetic agent.

The Hydroxylation of Vitamin D on C25 in Thyrotoxicosis The Role of the Activity of Microsomal Liver Enzymes

Vitamin D3 after its entrance in the organism undergoes hydroxylation on C-25 carbon atom by the action of microsomal liver enzymes giving the metabolite 25 hydroxyvitamin D3 (25OHD3). The function of microsomal liver enzymes is influenced in some specified states by hormones or drugs. It has approved that thyroxin is a potent stimulator of these enzymes while allopurinol suppresses their function. The aim of this issue is to examine 25OHD3 plasma levels in thyrotoxic subjects and in those pretreated with allopurinol on the base of the afford mentioned data. In a first phase 25OHD3 plasma levels were estimated in thyrotoxic subjects against euthytoid healthy controls. In a second phase lmg vitamin D3 was injected intravenously (i.v.) in thyrotoxic subjects and in healthy euthyroid controls. 25OHD3 plasma levels were measured before and in post injection period in six hours intervals for 48 hours. In a third phase a couple of subjects one thyrotoxic and one euthyroid healthy control pretreated both with allopurinol injected lmg of vitamin D3 i.v. In all studied subjects 25OHD3 plasma levels were measured before and in post injection period in six hours intervals for 48 hours. The pre and post injection 25OHD3 plasma levels measured the size of activity of liver enzyme responsible for bioactivation of vitamin D3. In the first phase was indicated that 25OHD3 plasma levels were lower in thyrotoxic subjects comparing with that of euthyroid healthy controls (p 3 in thyrotoxic subjects was 2,5 to 8 times faster comparing with euthyroid healthy controls. In the third phase was shown that allopurinol decreases the activity of liver enzymes function as regard the bioactivation of vitamin D3. The bioactivation of vitamin D3 is accelerated in thyrotoxicosis compared with that in euthyroid state. This phenomenon produces low 25OHD3 plasma levels in thyrotoxic subjects which initially may be normal or slightly increased depended from the vitamin D3 status in the thyrotoxic subjects. By continuous stimulatory action of increased thyroid hormones on liver enzymes the 25OHD3 plasma levels earlier or later decline in levels of hypo-or avitaminosis D3. The previously described biological events may explain the decreased intestinal calcium absorption of vitamin D3 and the osteomalacic component found in a percentage of thyrotoxic bone histology. For the blocking effects of allopurinol on liver enzymes function and possibly of other pharmaceutical products in relation to vitamin D3 bioactivation, available data are still lacking.

A Dual Wavelength Differential First Derivative Spectrophotometric Method for Identification and Determination of Carbon Monoxide Generated During the Microsomal Metabolism of Xenobiotics in vitro

A dual wavelength differential first derivative spectrophotometric method has been developed to standardize the concentration of a saturated aqueous solution of carbon monoxide (CO) as the standard and to identify and to determine CO formed during the microsomal metabolism of xenobiotics in vitro. The method can significantly eliminate the background interference in the assay media and increase the quantitative accuracy and the sensitivity. There is a good linear relationship between CO concentration in the range of 2～10 μmol·L 1 CO and the distance D between the first derivative peak at 415 nm amd valley at 426 nm with r=0.9999(n=5),the regression equation being C (mmol·L 1 )=17.6D 0.4, the detection limit lower than 0.1 μmol·L 1 CO. The average recoveries of CO from the assay system and the sample were 102.1%, RSD=2.9% (n=7) and 79.7%, RSD=6.8% (n=12),respectively. The RSD of within day was 4.4%(n=18),and the RSD of day to day was 6.1%(n=16). By this method, four trihaloanilines and one trihalobenzene were tested, the results showed that only 2,4,5 trifluoroaniline could be converted to CO by the incubation with rat hepatic microsomes, NADPH and oxygen, the ability of phenobarbital or dexamethasone to induce rat hepatic microsomes to catalyze CO formation was 3 or 8 times higher than that of the control.

Identification of the metabolite and cytochrome P450 isoforms involved in rat liver microsomal metabolism of TM208

To identify the metabolite and CYP450 isoforms involved in rat liver microsomal metabolism of TM208. The present study investigated the metabolism of TM208 and the effects of selective CYP450 inhibitors on the metabolism of TM208 in rat liver microsomes. Various specific inhibitors of CYP were used to identify the isoforms of CYP involved in the metabolism of TM208. The inhibitor of CYP2D and that of CYP2B had strong inhibitory effects on TM208 metabolism in a concentration-de- pendant manner, the inhibitor of CYP1A had a modest inhibitory effect, and the inhibitor of CYP3A seemed not to have an obvious inhibitory effect on TM208 metabolism. TM208 might mainly be metabolized by CYP2D and CYP2B in rat liver microsomes.

Effect of In Vivo and in Vitro Treatment with Arsenite on Rat Hepatic Mitochondrial and Microsomal Enzymes

The effects of arsenite on activities of several enzymes including mitochondrial pyruvate dehydrogenase(PDH) and succinate dehydrogenase(SDH) ,microsomal cytochrome P450 and b5 , NAD(P)H cytochrome C reductase and glutathione S-transferase were studied. The effects of arsenite on the mitochondrial membrane lipid peroxidation(LPO), the content of hepatic cytosol reduced glutathione and the activity of glutathione peroxidase was also investigated in rats.The results indicated that the activities of mitochondrial PDH and SDH were inhibited to 59% and 57% of the control activities respectively after arsenite was administered by intraperitoneal injection(i. p.) for 7 consecutive days at a dose of 20 mg/kg. Administration of arsenite led to a potential decrease of GSH content.The increase in lipid peroxidation of liver mitochondrial membrane prepared from rats treated with arsenite was also observed(P<0. 05) . Arsenite did not appear to affect the liver cytosolic glutathione peroxidase and microsomal enzyme activities in vivo. In in vitro test, liver mitochondria and cytosol were treated with arsenite , which led to a decreased SDH activity and GSH content and increase of mitochondrial LPO in a dose-dependent pattern that was similar to the results obtained in in vitro experiments. Selenite played a significant antagonistic role in effects of arsenite either in vivo or in vitro on the activities of mitochondrial PDH and SDH, and the content of mitochondrial LPO and cytosolic GSH. This results suggested that the toxic effects of arsenite on rat were associated with increased levels of LPO and the injured SH group in body caused by arsenite.

Changes of Liver Microsomal Drug-metabolizing System and Lipoperoxidation Activity in Scalded Rats and the Effects of Silybin

The dynamic changes of liver microsomal drug-metabolizing system (MDMS) andlipoperoxidation were studied in scalded rats. The effects of treatment with vitamin E and silybinwere also evaluated. The results showeed that liver microsomal cytochrome P-450 content, and p-nitroanisole demethylase (P-NOD) and aniline hydroxylase (AH) activity decreased markedlypostburn. On the contrary, liver lipoperoxide and mierosomal lipoperoxidation increased significantlyafter scalding. Both the increase of liver lipoperoxide and mierosomal lipoperoxidation and the de-crease of MDMS activity were prevented by vitamin E and silybin treatments.

Effect of microsomal triglyceride transfer protein gene polymorphism in the promoter region on dyslipidemia in type 2 diabetic subjects

To explore the relationship between microsomal triglyceride transfer protein (MT P) gene variation and diabetic dyslipidemia among Chinese Methods Using PCR restriction fragment length polymorphism (PCR RFLP) analysis and gene sequencing, we studied the influence of a common MTP gene polymorphism in the p romoter region on the apoB containing lipoproteins in 44 Chinese type 2 diabeti c subjects and 32 non diabetic volunteers Results A common functional G/T polymorphism in 493 bp upstream from the transcriptional start point was detected among native Chinese There were 41 carriers (53 9%) of the MTP 493 G/G genotype, 28 (36 8%) of the MTP 493 G/T genotype and 7 (9 3%) of the MTP 493 T/T genotype The allele frequency of M TP 493 T in the diabetic group was 0 30 The MTP 493 T/T diabetic group had significantly higher TG ( P <0 05), VLDL CH ( P <0 05) and smaller LDL pa rticle size ( P <0 001) than the MTP 493 common genotype group Conclusion Genetic variation in the MTP promoter is likely to be highly involved in the pro duction of dyslipidemia in type 2 diabetic subjects

Relationship between polymorphisms of genes encoding microsomal epoxide hydrolase and glutathione S-transferase P1 and chronic obstructive pulmonary disease

Background Cigarette smoking is the major risk factor for chronic obstructive pulmonary disease (COPD) However, only 10%-20% of chronic heavy cigarette smokers develop symptomatic disease COPD is most likely the result of complex interactions between environmental and genetic factors Genetic susceptibility to COPD might depend on the variations in enzyme activities that detoxify cigarette smoke products, such as microsomal epoxide hydrolase (mEH) and glutathione S-transferase (GST) In this study, we investigated the relationship between polymorphisms in the genes encoding mEH and glutathione S-transferase P1 (GSTP1) and COPD in a Chinese population Methods Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was performed to find mEH polymorphism in exon 3 (Tyr113→His), exon 4 (His139→Arg) and GSTP1 polymorphism in exon 5 (Ile105→Val) in 100 COPD patients and 100 age- and sex-matched healthy controls Results The proportion of mEH exon 3 heterozygotes was significantly higher in patients with COPD than that in the control subjects (42% vs 32%) The odds ratio ( OR ) adjusted by age, sex, body mass index (BMI) and cigarette years was 2 96 (95% CI 1 24-7 09) There was no marked difference in very slow activity genotype versus other genotypes between COPD patients and the controls When COPD patients were non-smokers, the OR of very slow activity genotype versus other genotypes was more than 1 00; and when COPD patients were smokers (current smokers and ex-smokers), the OR was less than 1 00 There was no significant difference in GSTP1 polymorphism adjusted by age, sex, BMI and smoking between COPD patients and the controls Conclusions mEH exon 3 heterozygotes might be associated with susceptibility to COPD in China The interaction might exist between mEH genotype and smoke The gene polymorphism for GSTP1 might not be associated with susceptibility to COPD in the Chinese population

New insights into the role of cytochrome P450 reductase (POR) in microsomal redox biology

Cytochrome P450 reductase(POR)is an essential electron transfer protein located on the endoplasmic reticulum of most cell types,and has long been appreciated for its role in cytochrome P450-mediated drug metabolism.Additional roles and electron acceptors for POR have been described,but it is largely with the recent availability of POR-null tissues that these supplemental roles for POR have been able to be explored.These studies have confirmed POR as the principal redox partner for the microsomal P450s responsible for drug and xenobiotic metabolism as well as cholesterol and bile acid synthesis,and for heme oxygenase,which catalyzes the initial step in the breakdown of heme.Surprisingly,these studies have revealed that squalene monooxygenase,an enzyme essential to cholesterol synthesis,has a second unknown redox partner in addition to POR,and that 7-dehydrocholesterol reductase,previously proposed to require POR as an electron donor,functions fully independently of POR.These studies have also helped define the role of cytochrome b5 in P450 catalysis,and raise the question as to the extent to which POR contributes to b5-dependent redox pathways.

EPHX1 A415G基因多态性与胃肠道肿瘤易感性的Meta分析

目的：探讨微粒体环氧化物水解酶（ EPHX1） A415G基因多态性与胃肠道肿瘤易感性的关系。方法计算机检索PubMed、EMBASE、CBM、维普、万方及中国知网数据库，检索时间截至2013年5月，收集关于EPHX1 A415G基因多态性与胃肠道肿瘤易感性的研究。由2名评价者按照纳入和排除标准独立选择文献、提取资料、评价质量。采用STATA 11.0软件进行Meta分析，计算合并OR值及其95％CI并行敏感性分析和发表偏倚的评估。结果最终纳入18篇文献，包括5852例胃肠道肿瘤患者和8710例对照人群。纳入的结果在GG vs． AA、GA vs． AA、GG/GA vs． AA和GG vs． GA/AA基因型的比较模型中均无异质性。各遗传模型Meta分析结果显示，EPHX1 A415G基因多态性与胃肠道肿瘤遗传易感性的关联性无统计学意义[GG vs． AA：OR＝1.063，95％CI：0.888～1.273；GA vs． AA： OR＝0.935，95％CI：0.867～1.009；GG/GA vs． AA： OR＝0.948，95％CI：0.882～1.020；GG vs． GA/AA：OR＝1.091，95％CI：0.913～1.304]。结论 EPHX1 A415G基因多态性与胃肠道肿瘤易感性之间无明显相关性。

Effect of Quercetin on CYP1A2, CYP2E1, CYP3A2 Activities and its Inhibitory Mechanism Studies in Rat Liver Microsomes

Aim To assess the potential effect of quercetin （QU）, an natural plant estrogen, on CYP1A2, CYP2E1, and CYP3A2 activities in rat liver microsomes; and to identify the magnitude of inhibitory effect and the probable inhibitory mechanism of QU. Methods QU and specific substrate were concurrently incubated, with HPLC detection of the substrate metabolites for data analysis. The magnitude of inhibitory effect of QU on CYP3A2 was compared with those of ketoconazole （Ket） and erythromycin （Ery）. The mechanism of its inhibitory effect on CYP3A2 and CYP2E1 was derived from Lineweaver-Burk plots. Results HPLC methods were in good linear relationship with r〉0.999 1. Relative standard deviations for intra-day and inter-day were〈8.4%. Recovery of each analyte in the concentrations studied was between 91.1% and 107.6 %. QU （up to 8 μmol·L^-1） showed potent induction to CYP1A2 （338.1% of the negative control）while inhibited CYP2E1 （49.2% of the negative control） and CYP3A2 （60.3% of the negative control） activity. The magnitude of inhibitory effect for QU on CYP3A2 was between those for Ket and Ery （Ket〉QU〉Ery）. QU exhibited competitive inhibition of CYP3A2 dextromethorphan N-demethylation reaction and expressed noncompetitive inhibition of CYP2E1 chlorzoxazone-6-hydroxylation reaction. Conclusion HPLC assay has been validated with precision and accuracy. QU is an effective inhibitor of several CYP isoforms. It may cause relevant drug-drug interactions with CYP3A substrates. As a plant flavonoid, QU has potential not only in molecular advantage but also in CYP450 module capability for further application in cancer chemotherapy.

MK-0626,a selective DPP-4 inhibitor,attenuates hepatic steatosis in ob/ob mice

AIM: To investigate the mechanism and in vivo effects of MK-0626, a dipeptidyl peptidase-4 inhibitor, on hepatic steatosis using ob/ob mice.

Role of MGST1 in reactive intermediate-induced injury

Microsomal glutathione transferase (MGST1, EC 2.5.1.18) is a membrane bound glutathione transferase extensively studied for its ability to detoxify reactive intermediates, including metabolic electrophile intermediates and lipophilic hydroperoxides through its glutathione dependent transferase and peroxidase activities. It is expressed in high amounts in the liver, located both in the endoplasmic reticulum and the inner and outer mitochondrial membranes. This enzyme is activated by oxidative stress. Binding of GSH and modification of cysteine 49 (the oxidative stress sensor) has been shown to increase activation and induce conformational changes in the enzyme. These changes have either been shown to enhance the protective effect ascribed to this enzyme or have been shown to contribute to cell death through mitochondrial permeability transition pore formation. The purpose of this review is to elucidate how one enzyme found in two places in the cell subjected to the same conditions of oxidative stress could both help protect against and contribute to reactive oxygen species-induced liver injury.

mPGES-1 expression in non-cancerous liver tissue impacts on postoperative recurrence of HCC

AIM:To investigate whether microsomal prostaglandin E synthase-1 (mPGES-1) expression in hepatocellular carcinoma (HCC) and in non-cancerous liver affects HCC prognosis after hepatectomy. METHODS: The relationship between patient clinical prof iles, tumor factors, surgical determinants, and mPGES-1 expression and the recurrence-free survival rate were examined in 64 patients who underwent curative hepatectomy between March 2003 and December 2006. RESULTS: The scores for mPGES-1 expression were higher in well differentiated and moderately differentiated HCC tissues than in poorly differentiated HCC tissues (well differentiated, 5.1 ± 2.7; moderately differentiated, 5.1 ± 1.7; poorly differentiated, 3.0 ± 1.8). In noncancerous liver tissues, the mPGES-1 levels were higher in injured liver tissues than in normal tissues. Cirrhotic livers had higher mPGES-1 levels than livers with chronic hepatitis (normal livers, 3.3 ± 0.7; chronic hepatitic livers, 5.4 ± 1.9; cirrhotic livers, 6.4 ± 1.6). A univariate analysis revealed that the recurrence-free survival rate was signif icantly lower in patients with vascular invasion,a higher mPGES-1 level in non-cancerous liver tissue,a larger tumor diameter (≥5 cm), and a lower serum albumin level (≤3.7 g/dL). The mPGES-1 expression in HCC tissues did not correlate well with postoperative recurrence. A multivariate analysis demonstrated that the presence of vascular invasion and higher mPGES-1 levels were statistically significant independent predictors for early postoperative recurrence of HCC.CONCLUSION: Increased mPGES-1 expression in noncancerous liver tissues is closely associated with the early recurrence of HCC after curative resection.

Dyslipidaemia of diabetes and the intestine

Atherosclerosis is the major complication of diabetes and has become a major issue in the provision of medical care.In particular the economic burden is growing at an alarming rate in parallel with the increasing worldwide prevalence of diabetes.The major disturbance of lipid metabolism in diabetes relates to the effect of insulin on fat metabolism.Raised triglycerides being the hallmark of uncontrolled diabetes,i.e.,in the presence of hyperglycaemia.The explosion of type 2 diabetes has generated increasing interest on the aetiology ofatherosclerosis in diabetic patients.The importance of the atherogenic properties of triglyceride rich lipoproteins has only recently been recognised by the majority of diabetologists and cardiologists even though experimental evidence has been strong for many years.In the post-prandial phase 50% of triglyceride rich lipoproteins come from chylomicrons produced in the intestine.Recent evidence has secured the chylomicron as a major player in the atherogenic process.In diabetes chylomicron production is increased through disturbance in cholesterol absorption,in particular Neimann Pick C1-like1 activity is increased as is intestinal synthesis of cholesterol through 3-hydroxy-3-methyl glutaryl co enzyme A reductase.ATP binding cassette proteins G5 and G8 which regulate cholesterol in the intestine is reduced leading to chylomicronaemia.The chylomicron particle itself is atherogenic but the increase in the triglyceride-rich lipoproteins lead to an atherogenic low density lipoprotein and low high density lipoprotein.The various steps in the absorption process and the disturbance in chylomicron synthesis are discussed.

Electrochemical and in silico approaches for liver metabolic oxidation of antitumor-active triazoloacridinone C-1305

5-Dimethylaminopropylamino-8-hydroxytriazoloacridinone(C-1305)is a promising antitumor compound developed in our laboratory.A better understanding of its metabolic transformations is still needed to explain the multidirectional mechanism of pharmacological action of triazoloacridinone derivatives at all.Thus,the aim of the current work was to predict oxidative pathways of C-1305 that would reflect its phase I metabolism.The multi-tool analysis of C-1305 metabolism included electrochemical conversion and in silico sites of metabolism predictions in relation to liver microsomal model.In the framework of the first approach,an electrochemical cell was coupled on-line to an electrospray ionization mass spectrometer.The effluent of the electrochemical cell was also injected onto a liquid chromatography column for the separation of different products formed prior to mass spectrometry analysis.In silico studies were performed using MetaSite software.Standard microsomal incubation was employed as a reference procedure.We found that C-1305 underwent electrochemical oxidation primarily on the dialkylaminoalkylamino moiety.An unknown N-dealkylated and hydroxylated C-1305 products have been identified.The electrochemical system was also able to simulate oxygenation reactions.Similar pattern of C-1305 metabolism has been predicted using in silico approach.Both proposed strategies showed high agreement in relation to the generated metabolic products of C-1305.Thus,we conclude that they can be considered as simple alternatives to enzymatic assays,affording time and cost efficiency.

LC-MS检测肝微粒体孵育液中系列化合物

肝脏是最重要的药物代谢器官之一,肝微粒体孵育试验可在亚细胞水平确定药物代谢稳定性、药酶抑制、活性代谢物生成等重要特性[1].对孵育液中药物进行定性定量检测是一项关键性试验,本文利用液相色谱-离子阱质谱技术,成功地对肝微粒体孵育液中两个系列化合物进行了定性定量分析,探讨了样品前处理的重要影响因素.……

Effects of Diazepam,Phenobarbital,Propranolol,and Cimetidine on Diazepam Oxidizing Isoenzymes in Rat Liver Microsomes

Isolation and identification of the liver microsomal cytochrome P 450 isoen zymes responsible for the formation of diazepam main metabolites nordiazepam and temazepam in rats were studied. The effects of P 450 inducers and inhibitors on the protein contents in SDS poly acrylamide gel electrophoresis and thin layer chromatography to the corresponding diazepam me tabolizing activities of rat liver microsomes were observed. The P 450 contents were dramatically re duced by ip diazepam, cimetidine or propranolol. Diazepam and propranolol inhibited temazepam formation, high dose of propranolol also inhibited nordiazepam formation. Phenobarbital increased the P 450 contents and induced the production of both nordiazepam and temazepam. It also induced proteins with molecular weight (m) of 51 and 59 kDa in SDS PAGE and those with m ranging from 45 to 55 kDa and from 55 to 65 kDa in TLC. Propranolol inhibited both fractions, especially that of m 55～65 kDa, whereas diazepam tended to inhibit the fraction of 45～55 kDa. The protein of m 51 kDa could be mainly involved in diazepam C3 hydroxylation, whereas those of m 59 kDa could be responsible for the N demethylation of diazepam in rats.