Effect of stress by repeated immobilization on hepatic alcohol dehydrogenase activity and ethanol metabolism.

The hepatic activity of alcohol dehydrogenase was increased after 7, 14 and 42 days of stress induced by immobilization of rats for 2.5 $\text{hr}\text{day}$. A single immobilization had no effect on the activity of alcohol dehydrogenase. Immobilization for 14 days resulted in increases in the rates of ethanol metabolism. This was not associated with changes in the activity of the microsomal ethanol-oxidizing system, microsomal catalase, cytochrome P-450, or NADPH cytochrome c reductase. A decrease in the hepatic phosphorylation potential ([ATP]/[ADP][P_i]) was found to be due to a decrease in [ATP] and an increase in [P_i]; however, there were no changes in O₂ consumption by liver slices or in hepatic (Na⁺ + K⁺)-stimulated adenosine triphosphatase activity. The increased rate of ethanol metabolism after stress remains unexplained since alcohol dehydrogenase activity is not rate-limiting in ethanol oxidation and there were no increases in ethanol oxidation by microsomes or in mitochondrial oxidative rate.     

Effect of ethylene glycol toxicity on hepatic carbohydrate metabolism in rats

The effects of ethylene glycol (EG) ingestion on glucose tolerance, hepatic glycogen metabolism, anerobic glycolysis, pentose phosphate pathway, and Embden-Meyerhof-tricarboxylic acid (EM-TCA) cycle pathway were investigated in male albino rats. EG was administered po at a daily dose of 2 ml/kg for 6 days. The analyses were done on Day 7. An impaired glucose metabolism was seen from diminished glucose tolerance. Hepatic glycogen concentrations were low associated with decreased glycogen synthetase and increased phosphorylase activities. [U-¹⁴C]Glucose incorporation into liver glycogen both in vivo and in vitro was decreased. Studies on the incorporation of ¹⁴C of [1-¹⁴C]- and [6-¹⁴C]glucose into respiratory CO₂ showed augmentation of the pentose phosphate pathway, while no significant alteration was observed in glucose oxidation through the EM-TCA cycle pathway. Anerobic glycolysis by liver slices was decreased. The increased NADPH made available by the enhanced pentose phosphate pathway activity following EG treatment may suggest possible oxidation of EG through the microsomal ethanol oxidizing system (MEOS) which is NADPH dependent, as well as through the alcohol dehydrogenase system.     

Effects of pyrazole and 3-amino-1,2,4-triazole on methanol and ethanol metabolism by the rat

The metabolism of methanol-¹⁴C and ethanol-1-¹⁴C in rats was evaluated from the rates of ¹⁴CO₂ production. 3-Amino,1,2,4-triazole, a known catalase inhibitor, decreased by 10 and 35 per cent the rates of oxidation of ethanol and methanol, whereas pyrazole, an alcohol dehydrogenase inhibitor, decreased the rates 85 and 50 per cent respectively. However, the simultaneous use of both inhibitors gave the same effects produced by pyrazole alone. Thus the relative contributions in vivo to alcohol metabolism of rat liver alcohol dehydrogenase and catalase-mediated peroxidation, cannot be estimated only in this way. Rat liver alcohol dehydrogenase was purified 14·7 times. At pH 7·0 and 30°, the K_m for methanol was 340 mM and for ethanol 0·26 mM. The V_max/e was 2·36 nM for methanol and 22·3 nM for ethanol (NADH × U^?1 × 1^?1 × sec^?1). 3-Amino-1,2,4-triazole inhibited the purified enzyme with a K_i of 55 mM for methanol and 33 mM for ethanol. The K_i of pyrazole was 2·3 mM for methanol and 2·2 mM for ethanol. The amount of alcohol dehydrogenase present in rat liver, with the found kinetic constants, can account for the ethanol oxidation in vivo, but fails to account, as methanol dehydrogenase, for the observed pyrazole-sensitive methanol oxidation. A mechanism for the complete oxidation of methanol to CO₂ and water through the concerted action of catalase and alcohol dehydrogenase is suggested. 3-Amino-1,2,4-triazole in a dose of 1 g/kg decreases more than 90 per cent of the catalatic activity of catalase, but under certain conditions in vitro, only about 50 per cent of the peroxidative activity of catalase towards methanol and ethanol. Consequently, the degree of catalase-mediated peroxidation should not be controlled or estimated from the residual catalatic activity when using catalase inhibitors. Pyrazole, at a dose of 0·3 g/kg, does not affect catalase activity 1 hr after administration, but decreases it more than 90 per cent after 24 hr. This effect is completely prevented in the presence of alcohol.     

Effect of hexachlorobenzene on the activities of hepatic alcohol metabolizing enzymes

To study the effect of experimental hepatic porphyria on the activities of hepatic alcohol metabolizing enzymes, female rats received a chow diet containing 0.05% hexachlorobenzene (HCB). After long-term HCB treatment for 60 days hepatic porphyria developed as evidenced by increased hepatic delta-aminolevulinic acid synthase activity and enhanced urinary excretion of delta-aminolevulinic acid, porphobilinogen and total porphyrins. Concomitantly, the activities of the hepatic microsomal ethanol oxidizing system (MEOS) were strikingly augmented by 213% (P less than 0.05) and 177% (P less than 0.01) when expressed per g of liver wet weight or per 100 g of body weight, respectively, whereas hepatic alcohol dehydrogenase activities remained virtually unchanged. Moreover, hepatic catalase showed only a trend for a slightly lower enzymic activity under these experimental conditions. The present data therefore show that experimental hepatic porphyria is associated with alterations of hepatic MEOS activities, which in turn may be a factor for the manifestation of human hepatic porphyrias in the course of alcohol consumption.     

EFFECTS OF DISULFIRAM AND THREE RELATED COMPOUNDS ON THE ACTIVITY OF ALCOHOL DEHYDROGENASE AND ALDEHYDE DEHYDROGENASE IN RAT LIVER AND GASTRIC MUCOSA

SUMMARY 1. Disulfiram or related compounds were administered to rats by stomach tube and the activities of alcohol dehydrogenase and aldehyde dehydrogenase in the liver and the gastric mucosa were determined 43 h later.
2. In liver, disulfiram did not affect alcohol dehydrogenase activity but reduced aldehyde dehydrogenase activity. The disulfiram metabolite diethyldithiocarbamate was without action.
3. In gastric mucosa, disulfiram had no effect on aldehyde dehydrogenase activity but enhanced alcohol dehydrogenase activity. Diethyldithiocarbamate had a similar effect.
4. The increase in alcohol dehydrogenase activity in the gastric mucosa might explain the hyperacetaldehydaemia produced by ethanol in disulfiram-treated patients.     

Enhancement of alcohol dehydrogenase activity in vitro by acetylsalicylic acid

The interaction of acetylsalicylic acid with alcohol dehydrogenase was investigated. Horse liver alcohol dehydrogenase bound to a p-hydroxyacetophenone affinity column was eluted by acetylsalicylic acid. In vitro enzymatic activity of alcohol dehydrogenase in the presence of ethanol as a substrate was significantly increased by incubation with acetylsalicylic acid. These results suggest that acetylsalicylic acid has an affinity with alcohol dehydrogenase and enhances its activity.     

5-Hydroxytryptamine metabolism in rat brain and liver homogenates

1. The metabolism of 5-hydroxyindoleacetaldehyde derived from 5-hydroxytryptamine incubated with tissue homogenates was studied as an indicator of aldehyde dehydrogenase and alcohol dehydrogenase activities.2. In liver and brain from rats, there were indications of the presence of one or more aldehyde dehydrogenases which were stimulated by NAD(+) to a greater extent than by NADP(+).3. In liver from rats, there were indications of the presence of one or more alcohol dehydrogenases, which were stimulated by NADH to a greater extent than by NADPH.4. In brain from rats, there were indications of the presence of one or more alcohol dehydrogenases which were stimulated by NADPH to a greater extent than by NADH.     

Effects of castration and testosterone administration on rat liver alcohol dehydrogenase activity

The effects of castration and testosterone administration on the activity of liver alcohol dehydrogenase and on the rate of ethanol elimination were determined in male Sprague-Dawley rats. Castration increased liver alcohol dehydrogenase activity. The total liver activity in castrated animals was 2.37 ± 0.229 (S.E.) $\text{mmoles}\text{hr}$ as compared with a value of 1.39 ± 0.125 $\text{mmoles}\text{hr}$ in sham-operated controls (P < 0.01). Testosterone administration partially suppressed the enhanced activity of liver alcohol dehydrogenase produced by castration. By contrast, in control animals testosterone administration resulted in a small paradoxical increase in liver alcohol dehydrogenase. The increase in the enzyme activity in castrated animals was associated with a parallel increase in the rate of ethanol elimination. Castrated and control animals showed decreases in free cytosolic and mitochondrial NAD⁺/NADH ratios after ethanol administration. These observations suggest that testosterone (and probably other as yet unknown factors modified by castration) affects liver alcohol dehydrogenase activity, and that the total enzyme activity can be a principal limiting factor in ethanol elimination.     

Disulfiram enhances ethanol pharmacological activity and impairs its elimination

Disulfiram or diethyldithiocarbamate (DDC) significantly prolonged ethanol-induced loss of righting reflex in mice. The disappearance of ethanol from blood, and brain was significantly delayed in disulfiram-treated animals, suggesting an impairment in the activity of alcohol dehydrogenase in these animals. DDC, an active metabolite of disulfiram, inhibited mouse liver alcohol dehydrogenase (LADH) in vitro. Pyrazole, a known inhibitor of alcohol dehydrogenase, affected ethanol elimination and ethanol-induced loss of righting reflex in mice in a manner similar to that seen with disulfiram.     

解酒保肝口服液对小鼠酒精中毒的影响

目的：观察解酒保肝口服液对小鼠醉酒实验,血清乙醇浓度和肝、胃组织乙醇脱氢酶活性的影响。方法：将生理盐水和将葛根,甘草等中药用水煎煮制成解酒保肝口服液灌服于小鼠后30min,灌服白酒,记录小鼠翻正反射消失（醉酒）至恢复（醒酒）所需时间（min),及24h内小鼠的死亡只数,另以相同操作连续6d后眼眶取血并处死动物,立即取出肝脏和胃,分别用生化比色法测定血肖乙醇浓度和肝、胃组织乙醇脱氢酶活性。结果：在醉酒实验中,。与对照组相比服用解酒保肝口服液组小鼠从饮酒到翻正反射消失（醉酒）的时间明显延长（P＜0．01）,醒酒时间明显缩短,且小鼠的死亡率明显降低（P＜0．05）,血清乙醇含量明显降低,肝脏ADH高于对照组, 结论：解酒保肝口服液具有解酒作用。     

Effect of pyrazole on rat liver catalase

Pyrazole alone does not affect catalase activity in vitro; however, its administration in vivo produces irreversible inhibition of catalase in rat liver and kidney but not in blood. The inhibition in the liver, after a 70 mg/kg single dose of pyrazole, follows first-order kinetics with a half-life of 8 hr. The activity reaches a minimum at 28 hr followed by gradual recovery at a rate corresponding to a half-life of 1.19 days. This value agrees with previous half-life determinations for rat liver catalase; therefore it is taken as evidence that the irreversibility of the inhibition demonstrated in vitro is also maintained in vivo. The inhibition of catalase is mediated by a product from the metabolism of pyrazole by the microsomal mixed-function oxidase system. This active pyrazole derivative presumably reacts with catalase hydrogen peroxide complex I, and not with the native catalase, in a process that can be prevented by alcohol. It is shown that pyrazole, a drug also used as an alcohol dehydrogenase inhibitor, is eliminated from the liver in a simple exponential process with a half-life of 3.45 hr, which agrees with its reported effects on ethanol metabolism in vivo.     

Alteration of the enzymology of chloral hydrate reduction in the presence of ethanol.

The enzymology of chloral hydrate reduction to trichloroethanol was studied in rat liver slices and homogenates. Two enzymes capable of reducing chloral hydrate are present in rat liver and by their properties were found to be aldehyde reductase and alcohol dehydrogenase. The alcohol dehydrogenase catalyzed reaction was very sensitive to the NAD/NADH ratio of the incubation medium and was found to be virtually incapable of performing the reduction with a simulated in vivo coenzyme ratio. The aldehyde reductase catalyzed reaction was relatively insensitive to the NADP/NADPH ratio. Hence, only one of the two possible enzyme systems appears to catalyze the reduction in vivo. Incubations performed with liver slices in the presence or absence of inhibitors and alternative substrates for the two enzyme systems indicated that in the absence of ethanol only aldehyde reductase catalyzed the reduction of chloral hydrate. About a 1.5-fold increase in the rate of reduction of chloral hydrate was observed when 40 mM ethanol was added to the liver slice incubation. Further, deuterium was incorporated into trichloroethanol when the incubations were performed with deuteroethanol. The increased rate of reduction and the deuterium incorporation were both prevented by the inclusion of alcohol dehydrogenase inhibitors (pyrazole and isobutyramide). Thus, in the presence of ethanol, both alcohol dehydrogenase and aldehyde reductase contribute to the reduction of chloral hydrate. Alcohol dehydrogenase is capable of reducing chloral hydrate in the presence of an oxidizable alcohol because it is converted into an enzyme—NADH complex which can then reduce the compound.     

The discovery of the microsomal ethanol oxidizing system and its physiologic and pathologic role

Oxidation of ethanol via alcohol dehydrogenase (ADH) explains various metabolic effects of ethanol but does not account for the tolerance. This fact, as well as the discovery of the proliferation of the smooth endoplasmic reticulum (SER) after chronic alcohol consumption, suggested the existence of an additional pathway which was then described by Lieber and DeCarli, namely the microsomal ethanol oxidizing system (MEOS), involving cytochrome P450. The existence of this system was initially challenged but the effect of ethanol on liver microsomes was confirmed by Remmer and his group. After chronic ethanol consumption, the activity of the MEOS increases, with an associated rise in cytochrome P450, especially CYP2E1, most conclusively shown in alcohol dehydrogenase negative deer mice. There is also cross-induction of the metabolism of other drugs, resulting in drug tolerance. Furthermore, the conversion of hepatotoxic agents to toxic metabolites increases, which explains the enhanced susceptibility of alcoholics to the adverse effects of various xenobiotics, including industrial solvents. CYP2E1 also activates some commonly used drugs (such as acetaminophen) to their toxic metabolites, and promotes carcinogenesis. In addition, catabolism of retinol is accelerated resulting in its depletion. Contrasting with the stimulating effects of chronic consumption, acute ethanol intake inhibits the metabolism of other drugs. Moreover, metabolism by CYP2E1 results in a significant release of free radicals which, in turn, diminishes reduced glutathione (GSH) and other defense systems against oxidative stress which plays a major pathogenic role in alcoholic liver disease. CYP1A2 and CYP3A4, two other perivenular P450s, also sustain the metabolism of ethanol, thereby contributing to MEOS activity and possibly liver injury. CYP2E1 has also a physiologic role which comprises gluconeogenesis from ketones, oxidation of fatty acids, and detoxification of xenobiotics other than ethanol. Excess of these physiological substrates (such as seen in obesity and diabetes) also leads to CYP2E1 induction and nonalcoholic fatty liver disease (NAFLD), which includes nonalcoholic fatty liver and nonalcoholic steatohepatitis (NASH), with pathological lesions similar to those observed in alcoholic steatohepatitis. Increases of CYP2E1 and its mRNA prevail in the perivenular zone, the area of maximal liver damage. CYP2E1 up-regulation was also demonstrated in obese patients as well as in rat models of obesity and NASH. Furthermore, NASH is increasingly recognized as a precursor to more severe liver disease, sometimes evolving into "cryptogenic" cirrhosis. The prevalence of NAFLD averages 20% and that of NASH 2% to 3% in the general population, making these conditions the most common liver diseases in the United States. Considering the pathogenic role that up-regulation of CYP2E1 also plays in alcoholic liver disease (vide supra), it is apparent that a major therapeutic challenge is now to find a way to control this toxic process. CYP2E1 inhibitors oppose alcohol-induced liver damage, but heretofore available compounds are too toxic for clinical use. Recently, however, polyenylphosphatidylcholine (PPC), an innocuous mixture of polyunsaturated phosphatidylcholines extracted from soybeans (and its active component dilinoleoylphosphatidylcholine), were discovered to decrease CYP2E1 activity. PPC also opposes hepatic oxidative stress and fibrosis. It is now being tested clinically.     

Biochemical and ultrastructural alterations in the rat ventral prostate due to repetitive alcohol drinking

Previous studies showed that cytosolic and microsomal fractions from rat ventral prostate are able to biotransform ethanol to acetaldehyde and 1-hydroxyethyl radicals via xanthine oxidase and a non P450 dependent pathway respectively. Sprague Dawley male rats were fed with a Lieber and De Carli diet containing ethanol for 28 days and compared against adequately pair-fed controls. Prostate microsomal fractions were found to exhibit CYP2E1-mediated hydroxylase activity significantly lower than in the liver and it was induced by repetitive ethanol drinking. Ethanol drinking led to an increased susceptibility of prostatic lipids to oxidation, as detected by t-butylhydroperoxide-promoted chemiluminiscence emission and increased levels of lipid hydroperoxides (xylenol orange method). Ultrastructural alterations in the epithelial cells were observed. They consisted of marked condensation of chromatin around the perinuclear membrane, moderate dilatation of the endoplasmic reticulum and an increased number of epithelial cells undergoing apoptosis. The prostatic alcohol dehydrogenase activity of the stock rats was 4.84 times lower than that in the liver and aldehyde dehydrogenase activity in their microsomal, cytosolic and mitochondrial fractions was either not detectable or significantly less intense than in the liver. A single dose of ethanol led to significant acetaldehyde accumulation in the prostate. The results suggest that acetaldehyde accumulation in prostate tissue might result from both acetaldehyde produced in situ but also because of its low aldehyde dehydrogenase activity and its poor ability to metabolize acetaldehyde arriving via the blood. Acetaldehyde, 1-hydroxyethyl radical and the oxidative stress produced may lead to epithelial cell injury.     

ETHANOL METABOLISM IN THE LIVER

Summary: Ethanol elimination by the liver, a relatively constant process, may be increased at high concentrations of ethanol, when certain substances like fructose or pyruvate are metabolized together with ethanol or after prolonged exposure for ethanol. The metabolic effects on the liver are different at high and at low concentrations of ethanol. A number of enzymes or enzyme systems, – liver alcohol dehydrogenase, catalase and mixed-function oxidase – can in vitro catalyze the oxidation of ethanol, but little is known about the actual role of each enzyme at different metabolic conditions. The existence of more than one pathway for ethanol metabolism in the liver is now becomming increasingly evident, but whether the non-ADH mediated ethanol oxidation occurs via catalase, or mixed-function oxidase system, or both, cannot at present be decided. The activity of liver alcohol dehydrogenase cannot be induced by continuous use of ethanol. The ADH-mediated ethanol oxidation may be increased when the steady state concentration of free NADH in the cytoplasm is lowered. The rate of ethanol oxidation under in vivo conditions seems not to be determined by the rate of acetaldehyde elimination, although acetaldehyde is a product of ethanol metabolism. The reoxidation of NADH may proceed by NADH-linked substrate system, by transhydrogenation to NADP⁺ or by transporting reducing equivalents into mitochondria where they are oxidized. In this review an attempt is made to examine the effects of a number of substrates or metabolic conditions which may enhance ethanol oxidation (concentration of ethanol, fructose, pyruvate, D-glyceraldehyde, oxygen, CO₂ and 2,4-dinitrophenol) and to discuss the mechanisms involved in this action. It is concluded that the effect of pyruvate and fructose (maybe also CO₂ and D-glyceraldehyde) proceeds via ADH-mediated pathway (possibly involving the so-called “malic enzyme shuttle”) whereas the acceleration in ethanol metabolism, observed in rat liver preparations when high concentrations of ethanol are metabolized, is associated with the participation of non-ADH pathway (s) in ethanol metabolism.     

Antioxidant effect of 2-hydroxy-4-methoxy benzoic acid on ethanol-induced hepatotoxicity in rats

Alcoholic liver disease (ALD) is one of the most common diseases in society. A large number of studies are in progress to identify natural substances that are effective in reducing the severity of ALD. 2-Hydroxy-4-methoxy benzoic acid (HMBA), the active principle of Hemidesmus indicus, an indigenous Ayurvedic medicinal plant in India, is expected to significantly inhibit the development of liver injury in ethanol administration. It is expected to reduce the severity of liver damage in terms of body weight, hepatic marker enzymes, oxidative stress, antioxidant status and histological changes in ethanol-induced hepatotoxic rats. Hepatotoxicity was induced by administering 20% ethanol (5 g kg(-1) daily) for 60 days to male Wistar rats, which resulted in significantly decreased body weight and an increase in liver-body weight ratio. The liver marker enzymes aspartate transaminase, alanine transaminase, alkaline phosphatase, gamma-glutamyl transpeptidase and lactate dehydrogenase were elevated. In addition, the levels of plasma, erythrocyte and hepatic thiobarbituric acid reactive substances, hydroperoxides and conjugated dienes were also elevated in ethanol-fed rats as compared with those of the experimental control rats. Decreased activity of superoxide dismutase, catalase, glutathione peroxidase, reduced glutathione, vitamin C and alpha-tocopherol was also observed on alcohol administration as compared with experimental control rats. HMBA was co-administered at a dose of 200 mug kg(-1) daily for the last 30 days of the experiment to rats with alcohol-induced liver injury, which significantly increased body weight, significantly decreased the liver-body weight ratio, transaminases, alkaline phosphatase, gamma-glutamyl transpeptidase and lactate dehydrogenase, significantly decreased the levels of lipid peroxidative markers, significantly elevated the activity of enzymic and non-enzymic antioxidants in plasma, erythrocytes and liver and also increased levels of plasma and liver vitamin C and alpha-tocopherol at the end of the experimental period as compared with untreated ethanol-administered rats. The histological changes were also in correlation with the biochemical findings. The results suggest that HMBA administration may afford protection against ethanol-induced liver injury in rats.     

Taraxerone enhances alcohol oxidation via increases of alcohol dehyderogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities and gene expressions

The present study, taraxerone (d-friedoolean-14-en-3-one) was isolated from Sedum sarmentosum with purity 96.383%, and its enhancing effects on alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities were determined: EC₅₀ values were 512.42 ± 3.12 and 500.16 ± 3.23 μM for ADH and ALDH, respectively. In order to obtain more information on taraxerone related with the alcohol metabolism, 40% ethanol (5 mL/kg body weight) with 0.5–1 mM of taraxerone were administered to mice. The plasma alcohol and acetaldehyde concentrations of taraxerone-treated groups were significantly lowered than those of the control group (p < 0.01): approximately 20–67% and 7–57% lowered for plasma alcohol and acetaldehyde, respectively. Compare to the control group, the ADH and ALDH expressions in the liver tissues were abruptly increased in the taraxerone-treated groups after ethanol exposure. In addition, taraxerone prevented catalase, superoxide dismutase, and reduced glutathione concentrations from the decrease induced by ethanol administration with the concentration dependent manner.     

扁桃酸在大鼠、小鼠和兔组织中的立体选择性代谢(英文)

目的研究扁桃酸(MA)在大鼠、小鼠和兔组织中的立体选择性代谢,探讨MA代谢酶存在的部位、辅酶依赖性等性质以及可能的种属差异。方法MA对映体与大鼠、小鼠和兔的肝脏、肺、肾脏S9和微粒体共孵育,HPLC检测代谢并用柱前衍生化方法进行手性分析。同时考察辅酶NADH和NADPH及醇脱氢酶竞争性底物乙醇和抑制剂4-甲基吡唑对S-MA代谢的影响。结果S-MA在大鼠肝和肾S9中被代谢为PGA,而R-MA无代谢。两对映体在小鼠和兔组织中均不被代谢。乙醇和4-甲基吡唑不影响酶的活性,该代谢顺利进行的重要辅酶是NADPH而非NADH。结论大鼠中参与MA立体选择性代谢的酶是存在于胞浆或线粒体中的具有NADPH依赖性的非微粒体酶,而不是醇脱氢酶。MA的立体选择性代谢存在种属差异性。     

Ethyl carbamate metabolism: in vivo inhibitors and in vitro enzymatic systems

The metabolism of ethyl carbamate and the localization of its metabolites have been shown to be almost completely inhibited by ethanol in the mouse [Waddell, Marlowe, Pierce: Food Chem. Toxicol.25, 527 (1987); Yamamoto, Pierce, Hurst, Chen, Waddell: Drug Metab. Dispos. 16, 355 (1988)]. The enzyme system catalyzing this metabolism which is inhibited by ethanol now has been further investigated in both in vivo and in vitro studies. There is a direct, highly significant relationship between the extent of metabolism of ethyl carbamate and covalent binding of metabolites to liver protein. Paraoxon, carbaryl, CCl4 ethanol, methimazole, 4-methylpyrazole, diethyl maleate, ethyl N-hydroxycarbamate, and t-butyl carbamate inhibit, to different extents, the metabolism of ethyl carbamate in vivo; SKF-525A, CoCl2, Cacyanamide, chloral hydrate, 2-oxo-4-thiazolidine carboxylic acid, allopurinol, and methyl carbamate do not. Porcine liver esterase, yeast aldehyde dehydrogenase and mouse liver catalase catalyzed the metabolism in vitro; dog or bovine catalase, acid phosphatase, alcohol dehydrogenase, or carbonic anhydrase did not under the conditions tested. Paraoxon, 4-methylpyrazole, carbaryl, and NaF significantly inhibited the hydrolytic activity of mouse liver homogenates toward p-nitrophenyl acetate; ethanol or ethyl carbamate did not. However, each of these, except 4-methylpyrazole, inhibited the metabolism of ethyl carbamate by mouse liver homogenate or porcine liver esterase to about the same extent. Ion exchange chromatography of mouse liver cytosol revealed that the fraction with ability to metabolize ethyl carbamate co-chromatographed almost exactly with the ability to hydrolyze p-nitrophenyl acetate. It is proposed that ethyl carbamate is metabolized in the mouse, at least partially, by esterases; however, metabolism by other enzyme systems cannot be excluded.     

Cyclobenzaprine and ethanol interaction

The effects of cyclobenzaprine, a tricyclic compound, on the central depressant action of ethanol and on hepatic ethanol metabolizing enzymes were studied in rodents. Administration of cyclobenzaprine, 5 mg/kg, IP, 30 min prior to a narcotic dose of ethanol solution, 5 g/kg, IP, enhanced ethanol-produced narcosis in mice. This effect was greater in male than in female mice. Cyclobenzaprine inhibited endogenous rat liver alcohol dehydrogenase in vitro in the concentration range between 10⁻⁵M and 10⁻⁶M. Cyclobenzaprine exerted little effect on hepatic aldehyde dehydrogenase in vitro. The results suggest that cyclobenzaprine possesses depressant properties and inhibition of liver alcohol dehydrogenase may underlie the observed behavioral response studied. It is concluded that alteration of endogenous liver alcohol dehydrogenase by certain tricyclic antidepressant drugs may be involved in the mechanism(s) of their toxic interaction with ethanol.