1,2-环己二胺柠檬酸铂(Ⅱ)及异柠檬酸铂(Ⅱ)的合成和抗癌活性

报道了1,2-环己二胺异柠檬酸铂(Ⅱ)及1,2-环己二胺柠檬酸铂(Ⅱ)的合成及鉴定方法。抗癌试验表明前者在40及80mg/kg 剂量下对小鼠 L1210、P388及S180均有明显的抑瘤作用,且有部分动物可治愈;后者对 L1210也有明显的抑瘤作用,但较前者为弱。     

汉黄芩素在FVB小鼠体内的磺酸化代谢特征研究

目的探讨汉黄芩素Ⅱ相代谢中主要的磺酸化代谢反应特征。方法采用FVB小鼠肠灌流模型及FVB小鼠肝脏S9体外反应体系,通过采用高效液相色谱-质谱法(HPLC-MS/MS)和高效液相色谱-二极管阵列检测器(HPLC-DAD)测定汉黄芩素及其代谢产物,研究汉黄芩素主要的Ⅱ相代谢反应之一磺酸化代谢反应的特征。结果汉黄芩素在FVB小鼠小肠均发生葡萄糖醛酸化与磺酸化代谢反应,其中磺酸化代谢产物的排出速率为[(3.46±0.16)nmol/30 min/10 cm]。而汉黄芩素在结肠中只检测出磺酸化代谢产物,其排出速率为[(1.40±0.24)nmol/30 min/10 cm]。体外试验显示,汉黄芩素的磺酸化代谢符合双相酶代动力学特征,由两种磺酸化转移酶(Sult)亚型介导。结论汉黄芩素的磺酸化代谢反应是汉黄芩素肠道代谢的重要组成部分,其在肝脏的磺酸化代谢由两种Sult酶催化完成。     

5-孕甾烯-3β,17α-双醇-20-酮-3-醋酸酯-17α-脂肪酸酯类的合成及其构效关系研究

本文报告薯蓣皂甙元的降解物孕甾双烯醇酮醋酸酯通过环氧化、开环反应所得开环物Ⅰ经20%钯-碳催化氢解脱溴反应合成Ⅱ,进而合成Ⅲ,Ⅳ(未知物)和Ⅴ,并对这些化合物做了抗炎作用的试验,探寻其结构与抗炎活性的关系。本文还对Ⅱ与酸性活性氧化铝或碱作用后的产物结构进行了初步确证。     

5-孕甾烯-3β,17α-双醇-20-酮-3-醋酸酯-17α-脂肪酸酯类的合成及其构效关系研究

本文报告薯蓣皂甙元的降解物孕甾双烯醇酮醋酸酯通过环氧化、开环反应所得开环物Ⅰ经20％钯-碳催化氢解脱溴反应合成Ⅱ,进而合成Ⅲ,Ⅳ(未知物)和Ⅴ,并对这些化合物做了抗炎作用的试验,探寻其结构与抗炎活性的关系。本文还对Ⅱ与酸性活性氧化铝或碱作用后的产物结构进行了初步确证。     

鳕鱼肉酶解产物对小鼠抗疲劳和体内抗氧化作用

目的：研究鳕鱼肉酶解产物的抗疲劳和体内抗氧化作用。方法：以阿拉斯加狭鳕鱼肉为原料,经菠萝蛋白酶和风味蛋白酶分步酶解,通过离心、喷雾干燥等工艺制得鳕鱼肉酶解产物。测定酶解产物的氨基酸组成;给小鼠灌胃不同剂量的酶解产物,测定小鼠力竭游泳时间,肝糖原含量,血清中乳酸、尿素氮、丙二醛含量以及超氧化物歧化酶、谷胱甘肽过氧化物酶和过氧化氢酶活力。结果：酶解产物能显著延长小鼠的游泳时间,与空白对照组相比,低、中、高剂量组能够降低小鼠体内乳酸、血尿素氮和丙二醛含量,提高小鼠体内肝糖原含量,且能够提高小鼠体内超氧化物歧化酶、谷胱甘肽过氧化物酶和过氧化氢酶的活力。结论：酶解产物具有较好的抗疲劳和体内抗氧化作用。     

盐酸三环哌酯在大鼠体内外的代谢

用大鼠原位灌流肝脏、整体实验和大鼠肝脏微粒体酶制备对盐酸三环哌酯(TCPN)的代谢转化进行了研究。结果经大鼠原位肝脏灌流后,灌流液经提取和HPLC分离制备,得到两个代谢产物。经MS,NMR,IR和UV鉴定,证明产物I是TCPN氮上脱甲基的产物,产物I是TCPN苯环羟化的产物。从大鼠igTCPN后的尿中及在TCPN和肝脏微粒体的温孵液中均得到产物I和产物II,提示TCPN的代谢转化主要由大鼠肝脏微粒体酶催化。以[³H]QNB为配体对TCPN及其代谢产物的受体结合活性进行了研究,结果表明产物I和产物I与M受体的亲和力分别是TCPN的1/20和1/50。     

侧柏总黄酮的抗炎作用及机制

目的　研究侧柏总黄酮的抗炎作用及其作用机制。方法　以二甲苯致炎小鼠耳片肿胀及角叉菜胶诱发大鼠足爪肿胀模型分别探讨侧柏总黄酮对小鼠耳片肿胀及大鼠足爪肿胀的抑制作用。高效液相色谱法测定角叉菜胶致炎的大鼠中性粒细胞花生四烯酸代谢产物白三烯B4(LTB4)及 5 羟廿碳四烯酸 (5 HETE) ,荧光法测定 β 葡糖苷酸酶释放。结果　黄酮为 12 5,2 5 0 ,50 0mg·kg- 1,氢化可的松为3 5 0mg·kg- 1的剂量对二甲苯诱导的小鼠耳肿胀抑制率分别为 2 5 2 % ,3 5 1% ,47 7%和 66 5%。 2 5～ 50mg·kg- 1剂量能抑制大鼠足爪肿胀 ,2 5mg·kg- 1的总黄酮作用强于 2mg·kg- 1的地塞米松。浓度为 5 0～ 12 5 0mg·L- 1总黄酮对大白鼠中性粒细胞花生四烯酸代谢产物 5 HETE及LTB4生物合成的抑制率分别为 3 0 5%～ 87 3 %和 2 7 8%～84 3 %。 5 0 ,2 5 0 ,45 0mg·L- 1的总黄酮对A2 3 187诱导的 β 葡糖苷酸酶释放抑制率分别为 13 4% ,2 6 2 %和3 2 2 %。结论　侧柏总黄酮具有较强的抗炎作用 ,其对中性粒细胞花生四烯酸代谢产物LTB4 、5 HETE生物合成及 β 葡糖苷酸酶释放的抑制作用可能与其抗炎作用有关。     

去氢厄弗酚在小鼠肝微粒体中代谢产物及CYP450酶亚型的鉴定

目的建立去氢厄弗酚(DHE)小鼠体外肝微粒体孵育方法,鉴定DHE在小鼠肝微粒体中的代谢产物及参与DHE代谢的CYP450酶亚型。方法采用UPLC-Q-TOF-MS/MS分析鉴定DHE在体外肝微粒体共温孵后的代谢产物,筛选7种CYP450酶亚型,并通过特异性化学抑制剂法,鉴别参与DHE代谢的主要CYP450酶亚型。结果在体外肝微粒体共温孵后,检测到4个代谢产物;所筛选的7种CYP450酶亚型中,CYP1A2、CYP2C8和CYP2D2对DHE体外肝微粒体代谢的参与度较高。结论在肝脏中,有多种代谢酶亚型参与DHE的代谢,表明DHE在临床上不易与其他药物产生相互作用。     

护肝胶囊对人和小鼠体内乙醇脱氢酶活性的影响

目的 研究护肝胶囊对人和小鼠体内乙醇脱氢酶活性的影响，阐述护肝胶囊对乙醇所致肝脏损害的保护作用。方法 通过测定服用护肝胶囊前后及饮酒后人血和小鼠肝细胞匀浆中乙醇脱氢酶的活力变化，以反映护肝胶囊提高酶活力，加速乙醇代谢的作用。结果 护肝胶囊可以显著提高体内乙醇脱氢酶的活力。结论 护肝胶囊可以通过提高酶活力，加速乙醇代谢，降低乙醇对肝脏的损害，从而起到保护肝脏的作用。     

脑缺血再灌注小鼠脑内不同神经核团单胺递质及其代谢产物的变化

目的　测定脑缺血再灌注后小鼠脑内不同神经核团单胺递质及其代谢产物的动态变化。方法　阻断小鼠双侧颈总动脉 (CCAO)进行缺血再灌 ,于术后当天 (d 0 )及d 1、3、5、2 0用HPLC ECD动态检测小鼠海马 ,纹状体 ,皮层的神经递质及其代谢产物的变化。结果　与假手术对照组相比 ,脑缺血再灌注小鼠术后上述神经核团去甲肾上腺素 (NE) ,多巴胺 (DA) ,5 羟色胺 (5 HT)等神经递质及其代谢产物含量降低 ,其中海马表现尤为明显。结论　脑内多个神经系统参与了脑缺血再灌注小鼠的病理过程 ,小鼠海马对缺血损伤最为敏感。提示脑缺血再灌注后海马神经递质异常是其后期行为表现的物质基础 ,是临床治疗中应予以重视的靶点     

Toxicity of diazinon and its metabolites increases in diabetic rats

The effect of diazinon (DZN) on the activities of cholinesterase (ChE) in plasma and acetylcholinesterase (AChE) in erythrocyte and brain was investigated in normal and streptozotocin-induced diabetic rats. Hepatic drug-metabolizing enzyme activity was also estimated by measuring the systemic clearance of antipyrine, and the expression of hepatic cytochrome P450 (CYP) 3A2 and CYP1A2, which is closely related to the metabolism from DZN to DZN-oxon, a strong inhibitor of both ChE and AChE. No significant differences in the activities of ChE in plasma and AChE in erythrocyte were observed between normal and diabetic rats. Treatment with DZN significantly decreased these activities in diabetic rats more than in normal rats 6 h after injection (6.5 mg/kg). Treatment with DZN significantly decreased the activity of AChE in brain of diabetic rats than normal rats 3 h after injection (65 mg/kg), although no significant difference in the activity was found between normal and diabetic rats. The urinary recovery of diethylphosphate (DEP), a metabolite of DZN-oxon, was significantly increased in diabetic rats, but that of diethylthiophosphate (DETP), a metabolite of DZN, was unchanged. Significant increases in the systemic clearance of antipyrine and protein levels of hepatic CYP1A2, not CYP3A2, were observed in diabetic rats. These results suggest the possibility that a metabolite of DZN, DZN-oxon, causes higher toxicity in diabetic rats due to the enhancement of hepatic CYP1A2-mediated metabolism of DZN.     

Metabolism of the anticonvulsant agent zonisamide in the rat

The metabolism of zonisamide [3-(sulfamoylmethyl)-1,2-benzisoxazole], a new anticonvulsant, has been studied. In rats dosed with [14C]zonisamide (100 mg/kg, ip) 86.5% of the radioactive dose was excreted in the urine over 72 hr. The remainder of the radioactive dose (13.5%) was excreted in the feces over the same time period. Unchanged drug and eight metabolites were isolated from the urine, and the structures of five metabolites were assigned by physicochemical methods. metabolism of zonisamide primarily involves reductive and conjugative mechanisms, with oxidation of this compound being of minor metabolic significance. The percentage of urinary radioactivity accounted for by unmetabolized zonisamide and metabolites is as follows: unmetabolized zonisamide (metabolite 9), 32.8%; metabolite 8 [N-acetyl-3-(sulfamoylmethyl)-1,2-benzisoxazole], 7.7%; unidentified metabolite 7, 2.4%; metabolite 6 (zonisamide glucuronide), 7.6%; metabolite 5 [3-(carboxy)-1,2-benzisoxazole], 5.4%; unidentified metabolite 4, 13.1%; metabolite 3 [2-(sulfamoylacetyl)-phenol glucuronide], 12.6%; unidentified metabolite 2, 3.8%; and metabolite 1 (2-[1-(amino)sulfamoylethyl]phenol sulfate), 2.3%. A total of 87.7% of the 0-24 hr urinary radioactivity was accounted for by unchanged zonisamide and metabolites.     

Metabolism of the calcium antagonist gallopamil in man

The metabolism of gallopamil (5-[(3,4-dimethoxyphenyl)methylamino]-2-(3,4,5-trimethoxyphenyl) -2- isopropylvaleronitrile hydrochloride, Procorum, G) was studied after single administration (2 mg i.v., 50 mg p.o.) of unlabelled and labelled G (14G, 2H). TLC, HPLC, GLC, MS and RIA were used for assessment of G and its metabolites in plasma, urine and faeces. G clearance is almost completely metabolic, with only minimal excretion of unchanged drug. Metabolites represent most of the plasma radioactivity after p.o. administration. They are formed by N-dealkylation and O-demethylation with subsequent N-formylation, or glucuronidation, respectively. Compound A, derived by loss of the 3,4-dimethoxyphenethyl moiety of G is the main metabolite in plasma and urine (about 20% of the dose). This metabolite is accompanied by its N-formyl derivative (C), by the N-demethylated compound (H) and the acid (F), formed by oxidative deamination of A. Only 3 unconjugated monphenoles from several O-demthylated products showed distinct plasma levels which were nevertheless lower than metabolite A. These metabolites had no relevance to the pharmacodynamic action. Conjugated monophenolic and diphenolic products represented the major part in plasma and were excreted predominantly via the bile: they represented almost the whole faecal metabolite fraction. Less than 1% of the dose was recovered unchanged in the urine. About 50% of the dose is excreted by urine and 40% by faeces.     

Mechanism of differential inhibition of hepatic and pancreatic fatty acid ethyl ester synthase by inhibitors of serine-esterases: in vitro and cell culture studies

Earlier, we have shown that rat hepatic and pancreatic fatty acid ethyl ester (FAEE) synthases are structurally and functionally similar to rat liver carboxylesterase (CE) and pancreatic cholesterol esterase (ChE), respectively. We have also reported that only hepatic FAEE synthase is inhibited by tri-o-tolylphosphate (TOTP) in vivo and in human hepatocellular carcinoma (HepG2) cells. The metabolism of TOTP is a prerequisite for the inhibition of hepatic FAEE synthase as well as esterase activity. To further elucidate the mechanism of such differential inhibition by inhibitors of serine esterases, we synthesized two metabolites of TOTP, 2-(o-cresyl)-4H-1:3:2-benzodioxaphosphoran-2-one (CBDP; cyclic saligenin phosphate) and di-o-tolyl-o-(∝-hydroxy)tolylphosphate (HO-TOTP), and one ChE inhibitor, 3-benzyl-6-chloro-2-pyrone (3-BCP). The inhibitory effect of CBDP, HO-TOTP, and 3-BCP on FAEE synthase and esterase activity was studied using rat hepatic and pancreatic postnuclear (PN) fractions, commercial porcine hepatic CE and pancreatic ChE, and in HepG2 and rat pancreatic tumor (AR42J) cell lines. Only HO-TOTP and CBDP inhibited FAEE synthase as well as esterase activity of hepatic PN fraction and commercial CE and ChE in a concentration-dependent manner, and the inhibition was found to be irreversible. However, no inhibition was found in pancreatic PN fraction by both TOTP metabolites and 3-BCP. Although 3-BCP inhibited only the esterase activity of commercial ChE in a concentration-dependent manner, the activity was reversible within 30 min of incubation. Studies with HepG2 cells also showed a significant inhibition of FAEE synthase-esterase activity by CBDP and HO-TOTP within 15 min of incubation, while no inhibition was observed in AR42J cells. 3-BCP did not inhibit FAEE synthase-esterase activity either in HepG2 or AR42J cells. Such differential inhibitory effect of the TOTP metabolites on hepatic and pancreatic FAEE synthase-esterase is supported by our earlier in vivo and in vitro studies. Further investigations are needed to understand the biochemical mechanism(s) of inactivation of TOTP metabolites and 3-BCP in the pancreas and AR42J cells towards FAEE synthase-esterase activities.     

The metabolism of 1-phenyl-2-(N-methyl-N-furfurylamino)propane (furfenorex) in the rat in vivo and in vitro

The metabolism of 1-phenyl-2-(N-methyl-N-furfurylamino)propane (furfenorex) was studied in the rat in vivo and in vitro. Nine metabolites with only traces of the unchanged drug were obtained from urine after oral administration of furfenorex to rats. The major metabolite was an acidic compound, isolated and identified as 1-phenyl-2-(N-methyl-N-gamma-valerolactonylamino)propane. Amphetamine, methamphetamine and their hydroxylated metabolites were excreted as minor metabolites. Metabolites excreted in two days after administration of the drug amounted to about 20% of dose. The acidic metabolite, a major metabolite in vivo, was not detected after incubation of furfenorex with rat-liver microsomes. The major metabolic routes of furfenorex in vitro were N-demethylation and N-defurfurylation which produced 1-phenyl-2-(N-furfurylamino)propane (furfurylamphetamine) and methamphetamine, respectively. The formation of furfurylamphetamine and methamphetamine were catalysed by rat-liver microsomes supplemented with NADPH and O2, and were inhibited by either SKF 525-A or CO. The formation of both metabolites were inhibited by 2-methyl-1,2-bis-(3-pyridyl)-1-propanone (metyrapone), but not by 7,8-benzoflavone. They were enhanced by pretreatment of rats with phenobarbitone, but not with 3-methylcholanthrene. These data suggested that N-demethylation and N-defurfurylation of furfenorex were mainly mediated by cytochrome P-450 but not cytochrome P-448.     

Neuronal Differentiation in PC12 Cells Is Inhibited by Chlorpyrifos and Its Metabolites: Is Acetylcholinesterase Inhibition the Site of Action?

Developmental expression of AChE has been associated with neuronal differentiation (P. G. Layer and E. Willbold, Prog. Histochem. Cytochem. 29, 1-94, 1995). In this study we used pheochromocytoma (PC12) cells, a noncholinergic cell line, rich in acetylcholinesterase (AChE) activity, to examine the effects of cholinesterase-inhibiting pesticides on neural differentiation. The experimental paradigm was focused on whether alterations in cholinesterase (ChE) activity by a pesticide or its metabolites would affect neurite outgrowth, a morphological marker of neuronal differentiation. Results indicated that (1) in controls, both total ChE and AChE activities were significantly increased in NGF-primed PC12 cells compared to NGF-unprimed cells, while the basal expression of butyrylcholinesterase (BuChE) activity was much lower (1.3-7% of total ChE activity) in either the presence or the absence of NGF; (2) an increase in AChE activity was highly correlated (r(2) = 0.99) with the extension of neurite outgrowth, suggesting a link between the expression of AChE activity and the elaboration of neurite outgrowth; (3) NGF increased neurite outgrowth in a time- and concentration-dependent manner; and (4) either chlorpyrifos (CPF) or its metabolites (CPF oxon and TCP) inhibited NGF-induced neurite outgrowth (branches per cell, fragments per cell, total neurite outgrowth per cell) in PC12 cells. These data suggest that the expression of AChE activity is associated with the extension of neurite outgrowth. Both enzyme activity and neurite branching were disrupted by CPF oxon; however, CPF and its other metabolite TCP (1 microgram/ml) caused inhibition of neurite outgrowth in the absence of ChE inhibition, suggesting an alternative mechanism(s) may be involved in pesticide-induced inhibition of differentiation.     

Metabolism of the neuroleptic agent zetidoline in the rat and the dog

The metabolism of zetidoline, a new neuroleptic, in the rat and the dog has been studied. From the urine of rats and dogs given 5 mg/kg of [2-14C] zetidoline orally, unchanged drug and five metabolites were isolated and the structures of four of them assigned by physicochemical analysis. They are: metabolite B, 4'-hydroxy-3'-chlorophenyl zetidoline; metabolite D, zetidoline without the aryl group; metabolite E, the 6'-hydroxy-4'-beta-D-glucuronide of metabolite B, and metabolite F, the 4'-beta-D-glucuronide of metabolite B. The plasma levels of zetidoline and its metabolites after iv administration show that the drug is rapidly excreted and/or metabolized in both animal species. The plasma radioactivity in the dog consists mainly of the pharmacologically active (neuroleptic) metabolite B, whereas in the rat it consists of the more polar metabolites. After oral administration, elimination in both species occurs mostly via the kidneys. In the dog, within a 24-hr period, 6.2 +/- 0.4% of the dose is accounted for as unchanged zetidoline, 7.6 +/- 0.5% as metabolite B, 10.1 +/- 0.7% as the unidentified metabolite C, and 21.4 +/- 1.1% as metabolite F. In the rat, over the same period, zetidoline is present in traces, metabolite B accounts for 6.9 +/- 0.3% of the dose, metabolite D for 6.6 +/- 0.9%, metabolite E for 15.2 +/- 1.4%, and metabolite F for 31.7 +/- 2.2%.     

Disposition and metabolism of [14C]-amezinium metilsulfate in rats

Disposition and metabolism of [14C]-amezinium metilsulfate (4-amino-6-methoxy-1-phenylpyridazinium methylsulfate, Risumic) were systematically studied in rats after intravenous (5 mg/kg) or oral (20, 100 mg/kg) administration. After oral administration at 20 mg/kg, blood level reached the maximum (Cmax) of 0.65 microgram eq/ml at 3 h (tmax) and decreased with t1/2 of 8.1 h. Levels in plasma and most tissues elevated to the Cmax at 3 h. The liver level was the highest (61 times as high as plasma level) of all examined tissues. Most tissue levels decreased thereafter essentially in parallel with plasma levels. The findings by whole-body autoradiography essentially agreed with those by radiometry. In lactating rats, milk levels were virtually similar to plasma levels. [14C]-Amezinium metilsulfate radioactivity in fetus and fetal blood was around 0.3 microgram eq/g, being about 1/10 level of maternal plasma level. About 24, 72 and 42% were excreted in urine, feces and bile, respectively. Re-absorption of biliary metabolites accounted for about 31%, being about 13% of orally given [14C]-amezinium metilsulfate. Plasma and aorta contained unchanged amezinium and glucuronide of hydroxyl amezinium MIII. In the brain, the major metabolite was O-demethyl amezinium MV and unchanged drug was not detected. Urinary metabolites were largely MIII glucuronide and the unchanged drug. Biliary metabolite was found composed mostly from MIII glucuronide. In feces, MIII and the unchanged amezinium were found. MIII and its glucuronide were novel metabolites which were identified by thin-layer chromatography and mass spectrometry.     

N,N-二甲氨基甲酸5-(1,3,3-三甲基吲哚满)酯及其代谢产物在大鼠离体肝脏中的代谢动力学

利用大鼠肝脏灌流技术研究了N,N-二甲氨基甲酸5-(1,3,3-三甲基吲哚满)酯(TMDMC)及其代谢产物在大鼠离体肝脏中的代谢动力学,TMDMC在改良的灌流液中作循环式灌流,于不同时间留取少量灌流液,用高效液相色谱(HPLC)作药物的定量分析,结果显示其在离体灌流肝脏中的清除模型符合两相消除模型,动力学参数表明,TMDMC在肝内的分布较快,其分布半衰期仅为4min,肝脏分布容积为102.4 ml,清除率是0.67ml·min~(-1),清除比率为0.027.灌流2h时,其浓度已下降了73％.与此同时,TMDMC的代谢产物逐渐生成,其中以产物Ⅲ的生成量最大,其最高生成浓度(C_(max))为447.1 μg·ml~(-1),2 h产物Ⅲ的生成总量已达TMDMC灌流量的25.6％.而代谢产物Ⅱ,Ⅵ的生成较少,其C_(max)分别是20.4μg·ml~(-1)和20.7μg·ml~(-1).     

EFFECT OF INCREASED BILE FLOW AND BILE ACID SECRETION ON THE HEPATIC ELIMINATION OF SODIUM VALPROATE IN THE CAT

The effect of increased bile flow and hepatic bile acid flux on the systemic clearance and hepatic elimination of intravenously administered sodium valproate was studied in the bile fistula cat. Taurochenodeoxycholic acid (TCDC), tauro-3 alpha, 7 beta-dihydroxy-12-keto-5 beta-cholanoic acid (T12K), SC-2644, and secretin were infused intravenously to vary bile flow and biliary bile acid secretion. Control animals were infused with 0.15 mol/l NaCl. Less than 1% of the drug administered to controls appeared as unchanged valproate in the bile over 6 h. Although SC-2644, T12K, and secretin significantly increased biliary excretion of valproate, it did not exceed 2% of the intravenous dose. Biliary clearance was directly related to the rate of bile flow, but not to the bile acid flux. By contrast, 18-19% of the dose appeared in bile as metabolite in controls, and none of the choleretic agents significantly increased this percentage. As a result, systemic clearance of valproate was unaltered. We conclude that the movement of unchanged valproate into bile is consistent with a process of simple diffusion. The fact that choleretic agents do not increase metabolite excretion into bile suggests that metabolite formation may be the rate-limiting step in the hepatic elimination of valproate, rather than transport and excretion of metabolites into bile.