Rat Liver Alcohol Dehydrogenase Research Articles

Effect of water-soluble propolis administration on the ethanol-induced hangover in rats.

Water soluble propolis was prepared using β-cyclodextrin, and its effect on an ethanol-induced hangover was examined in Sprague-Dawley (SD) rats fed with ethanol. When SD rats were administrated with propolis 30min after ethanol feeding, ethanol content in the rat serum decreased 2.1 times 1h after ethanol feeding. Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) activity in rat liver increased 3.0 and 4.4 times, respectively, 1h after ethanol feeding and administration of propolis 30min after ethanol feeding. There were no differences in the expression of ADH and ALDH genes regardless of propolis administration. These results indicated that a decrease in ethanol content in the serum was not due to an increase in the expression of ADH or ALDH genes but rather, an increase in activities of ADH and ALDH.

Contribution of liver alcohol dehydrogenase to metabolism of alcohols in rats

The kinetics of oxidation of various alcohols by purified rat liver alcohol dehydrogenase (ADH) were compared with the kinetics of elimination of the alcohols in rats in order to investigate the roles of ADH and other factors that contribute to the rates of metabolism of alcohols. Primary alcohols (ethanol, 1-propanol, 1-butanol, 2-methyl-1-propanol, 3-methyl-1-butanol) and diols (1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol) were eliminated in rats with zero-order kinetics at doses of 5–20mmol/kg. Ethanol was eliminated most rapidly, at 7.9mmol/kgh. Secondary alcohols (2-propanol-d7, 2-propanol, 2-butanol, 3-pentanol, cyclopentanol, cyclohexanol) were eliminated with first order kinetics at doses of 5–10mmol/kg, and the corresponding ketones were formed and slowly eliminated with zero or first order kinetics. The rates of elimination of various alcohols were inhibited on average 73% (55% for 2-propanol to 90% for ethanol) by 1mmol/kg of 4-methylpyrazole, a good inhibitor of ADH, indicating a major role for ADH in the metabolism of the alcohols. The Michaelis kinetic constants from in vitro studies (pH 7.3, 37°C) with isolated rat liver enzyme were used to calculate the expected relative rates of metabolism in rats. The rates of elimination generally increased with increased activity of ADH, but a maximum rate of 6±1mmol/kgh was observed for the best substrates, suggesting that ADH activity is not solely rate-limiting. Because secondary alcohols only require one NAD+ for the conversion to ketones whereas primary alcohols require two equivalents of NAD+ for oxidation to the carboxylic acids, it appears that the rate of oxidation of NADH to NAD+ is not a major limiting factor for metabolism of these alcohols, but the rate-limiting factors are yet to be identified.

Ethanol as a Prodrug: Brain Metabolism of Ethanol Mediates Its Reinforcing Effects - A Commentary

This commentary discusses a study by Karahanian and colleagues (2011) on the role of central nervous system acetaldehyde in the reinforcing effects of ethanol. The goal is to emphasize the importance of the study and to discuss future directions. This important paper solidifies the idea that the levels of acetaldehyde in the central nervous system have profound effects in mediating the reinforcing actions of ethanol. This is accomplished by manipulating the brain levels of acetaldehyde produced from ethanol by the injection of lentivirus containing either an anti-catalase shRNA construct or a rat liver alcohol dehydrogenase into the central nervous system and observing the effects on alcohol preference by high ethanol-consuming rats. A factor not directly considered is that acetaldehyde is further metabolized to acetate, which also has some behavioral actions. The efficacy of lentivirus injections of enzyme inhibitors or enzymes themselves to alter a behavioral response to ethanol is clearly demonstrated here. The many other actions of ethanol that are postulated to be a result of the production of acetaldehyde in the brain remain to be investigated by similar techniques. Possible "therapeutic avenues to reduce chronic alcohol use" are envisioned.

Establishment of steady-state metabolism of ethanol in perfused rat liver: the quantitative analysis using kinetic mechanism-based rate equations of alcohol dehydrogenase

Alcohol dehydrogenase (ADH) catalyzes oxidation of ingested ethanol to acetaldehyde, the first step in hepatic metabolism. The purpose of this study was to establish an ex vivo rat liver perfusion system under defined and verified steady states with respect to the metabolites and the metabolic rates, and to quantitatively correlate the observed rates with simulations based on the kinetic mechanism-based rate equations of rat liver ADH. Class I ADH1 was isolated from male Sprague–Dawley rats and characterized by steady-state kinetics in the Krebs–Ringer perfusion buffer with supplements. Nonrecirculating liver perfusion with constant input of ethanol at near physiological hepatic blood flow rate was performed in situ. Ethanol and the related metabolites acetaldehyde, acetate, lactate, and pyruvate in perfusates were determined. Results of the initial velocity, product, and dead-end inhibition studies showed that rat ADH1 conformed to the Theorell–Chance Ordered Bi Bi mechanism. Steady-state metabolism of ethanol in the perfused liver maintained up to 3 h as evidenced by the steady-state levels of ethanol and metabolites in the effluent, and the steady-state ethanol disappearance rates and acetate production rates. The changes of the metabolic rates were qualitatively and in general quantitatively correlated to the results from simulations with the kinetic rate equations of ADH1 under a wide range of ethanol, in the presence of competitive inhibitor 4-methylpyrazole and of uncompetitive inhibitor isobutyramide. Preliminary flux control analysis estimated that apparent C ADH J in the perfused liver may approximate 0.7 at constant infusion with 1–2 mM ethanol, suggesting that ADH plays a major but not the exclusive role in governing hepatic ethanol metabolism. The reported steady-state rat liver perfusion system may potentially be applicable to other drug or drug–ethanol interaction studies.

알코올 대사 효소 alcohol dehydrogenase (ADH) 및 acetaldehyde dehydrogenase (ALDH) 활성에 미치는 아미노산의 영향

본 연구에서는 숙취해소에 좋은 것으로 알려진 식품 소재의 주요 아미노산을 포함하여 효소 활성에 영향을 미치는 것으로 알려진 아미노산을 선택하였고, 효소 활성도가 상대적으로 높은 yeast와 rat liver 유래의 ADH 및 ALDH 효소를 대상으로 알코올 대사에 관련된 효소 활성의 촉진 효과에 대하여 검토하였다. Rat liver 유래의 ADH 활성은 처리한 아미노산 중에서 arginine에서 가장 높았다. Arginine의 첨가 농도를 달리하여 효소 활성을 측정한 결과 <TEX>$10{\sim}50\;mg$</TEX>/ml 농도에서 <TEX>$118{\sim}120.6%$</TEX>로 양성대조구의 90.6% 보다 약간 높은 것으로 나타났다. 또한, yeast 유래의 ADH 활성은 methionine에서 가장 높은 활성을 보였고, methionine의 처리 농도를 달리한 경우에서는 첨가 농도 의존적으로 높은 활성을 보였다. Rat liver 유래의 ALDH 활성은 methionine이 가장 높은 활성을 보였다. Methionine의 첨가 농도별 측정에서는 10 mg/ml에서 30 및 50 mg/ml 첨가 농도에서 보다 높은 활성을 보였으며, 이들 모든 처리 농도에서 양성대조구 보다 상당히 높은 활성을 보였다. 한편 yeast 유래의 ALDH 활성은 각 아미노산별 큰 차이는 없었으나, arginine에서 높은 활성을 보였다. Arginine의 첨가 농도별 측정에서는 처리 농도 의존적으로 활성이 약간씩 증가하는 경향을 보였으며, 양성대조구 보다 높은 활성을 나타내었다. 효모 유래 ALDH 및 rat liver 유래 ADH 효소 활성을 촉진시키는 작용을 가진 arginine을 효모 배양에 첨가시킬 경우 세포 내 ALDH 및 ADH 활성 염색 정도가 증가함으로써 arginine은 ALDH 및 ADH 활성을 촉진시키는 효능이 in vivo 실험계에서도 확인되었다. 이상의 실험 결과에서 아미노산 중에서는 arginie과 methionine이 ADH 및 ALDH 활성을 촉진시키는 작용에 의해 알코올 분해뿐만 아니라 acetaldehyde의 분해도 촉진시킬 가능성이 높아 숙취해소 효과는 물론 간 보호 효과도 동시에 있을 것으로 시사 되어 진다. 따라서 arginine과 methionine과 같은 아미노산을 주류 제품에 첨가하게 될 경우 숙취해소 경감과 간 보호 효능을 어느 정도 나타낼 수 있을 가능성이 제기되었다. The present study examined the comparative effects of various amino acids on the alcohol dehydrogenase (ADH) and acetaldehyde dehydrogenase (ALDH) activities of yeast Saccharomyces cereviciae and rat liver homogenate in vitro. Methionine showed the highest activity in yeast ADH among the amino acids used in this study, but this was not higher than that of the hangover product, Condition-Power (CP) used as positive control. Methionine was also found to be the best amino acid in terms of the ALDH activity in rat liver homogenate among the treatment amino acids, which was comparatively higher than that of positive control CP. It was chosen for further experiments and yeast ADH activity increased in parallel with increased methionine concentration, but not rat liver ALDH activity, and it was comparatively higher than those of the positive control. Arginine showed the highest values in yeast ALDH and rat liver ADH activities among amino acids, and it was chosen for further experiments. Yeast ALDH activity increased in parallel with increased arginine concentration, which was higher than that of positive control CP, and rat liver ADH activity was also comparatively higher in all treatment concentrations of arginine than that of positive control CP. The native electrophoresis of ADH and ALDH from cell-free extracts of yeast Saccharomyces cerevisiae cultured in the growth medium containing various arginine concentrations by <TEX>$0{\sim}0.1%$</TEX> showed two active bands upon zymogram staining analysis, and the straining intensity of ADH and ALDH active bands in arginine treatment yeast was stronger than that of non-yeast or low treatment yeast. These results indicate that alcohol metabolizing enzyme activities can be enhanced by arginine and methionine, suggesting that arginine and methionine have potent ethanol-metabolizing activities.

Severity of alcohol withdrawal symptoms depends on developmental stage of Long–Evans rats

To investigate alcohol dependency and the potential role of age of initial alcohol consumption, Long–Evans (LE) rats were fed an ethanol-containing liquid diet starting at postnatal (P) ages (days): P23–27 (juvenile), P35–45 (adolescent) or P65–97 (young adult). Severity of subsequent withdrawal symptoms was dependent on age when consumption began and on duration of alcohol consumption. Frequency of withdrawal seizures was highest for rats starting consumption as juveniles, intermediate for adolescents and lowest for adults. Normalized to body weight, alcohol consumption was significantly higher for adolescent and juvenile rats than for adults. Sprague–Dawley rats that began alcohol consumption as adolescents (P35) had a level of alcohol consumption identical to that of the adolescent LE rats but showed much lower frequency of withdrawal seizures when tested after 2, 3 and 5 weeks of alcohol consumption. Based on several indicators, the capacity of the juveniles to metabolize ethanol is equal to or exceeds that of adults. Recoveries from a single dose of ethanol (2.5 g ethanol/kg body weight) were faster for juvenile LE rats than adults. The rate of decline in blood ethanol concentration was identical for juvenile and adult rats while the corrected ethanol elimination rate was higher for juveniles. The primary isozyme of alcohol dehydrogenase (ADH) in rat liver, ADH-3, had a similar Km and higher activity in liver preparations from juveniles. In conclusion, LE rats beginning alcohol consumption as juveniles or adolescents develop a severe alcohol withdrawal syndrome that may not be attributed entirely to higher levels of consumption and was not explained by any obvious deficiencies in metabolism.

Effect of dihydrotestosterone on rat liver alcohol dehydrogenase activity.

Castration was previously demonstrated to result in an increase in liver alcohol dehydrogenase and in rates of ethanol elimination in male rats. In this study, the effect of dihydrotestosterone, which is a more potent androgen than testosterone in the rat, was determined on liver alcohol dehydrogenase and ethanol elimination in the castrated rat. Dihydrotestosterone was found to be a substrate of liver alcohol dehydrogenase in the reductive direction and a competitive inhibitor of ethanol oxidation by the enzyme. Also, the administration of a single dose of dihydrotestosterone inhibited liver alcohol dehydrogenase 4 hr after the injection, but this effect was not persistent at later intervals following injection. This transient in vivo inhibition of liver alcohol dehydrogenase was associated with a delay in ethanol elimination. The microsomal ethanol-oxidizing enzyme system was found to play no role in the changes in ethanol elimination observed after castration and dihydrotestosterone administration since its activity remained unchanged. These studies provide further evidence of an effect of androgenic steroids on liver alcohol dehydrogenase activity and ethanol metabolism.

Post-transcriptional Regulation of Sterol Regulatory Element-binding Protein-1 by Ethanol Induces Class I Alcohol Dehydrogenase in Rat Liver

Members of the sterol regulatory element-binding protein (SREBP) family of transcription factors control the synthesis and uptake of cholesterol, fatty acids, triglycerides, and phospholipids. Continuous intragastric infusion of ethanol-containing diets as part of total enteral nutrition generates well defined 6-day cycles (pulses) of urine ethanol concentrations (UECs) in rats. Pulsatile UECs are the result of cyclical expression and activity of the principal alcohol-metabolizing enzyme, hepatic Class I alcohol dehydrogenase (ADH), and this mechanism involves regulated CCAAT/enhancer-binding protein-beta expression and binding to the ADH promoter. In this study, we further explore the molecular mechanism for ethanol-induced ADH expression during the UEC pulse in adult male rats fed ethanol by total enteral nutrition for 21-30 days. In hypophysectomized rats, in which the ADH protein increased by approximately 6-fold, the nuclear form of SREBP-1 decreased by approximately 7-fold. Because the ADH promoter contains two canonical sterol response element (SRE) sites (-63 to -53 and -52 to -40 relative to the transcription start site), electrophoretic mobility shift assays were conducted using an ADH-specific SRE site. Hepatic nuclear protein binding decreased by 2.4-fold on the ascending limbs and by 3.6-fold on the descending limbs of UEC pulses (p < 0.05). The specificity of nuclear protein binding to the ADH-SRE site was confirmed using antibody and UV cross-link assays. The in vivo binding status of SREBP-1 to ADH-SRE sites, as measured by the chromatin immunoprecipitation assay, had a pattern very similar to the electrophoretic mobility shift assay results. Functional analysis of the ADH-SREs demonstrated these sites to be essential for ADH transcription. In vitro transcription assays demonstrated that depletion of the SREBP-1 protein from nuclear extracts increased transcription activity by approximately 5-fold and that the liver X receptor agonist T0901317 (a known activator of SREBP-1c transcription) reduced in vitro expression of ADH mRNA by 2-fold. We conclude that SREBP-1 is a negative regulator of the ADH gene and may work in concert with the CCAAT/enhancer-binding proteins to mediate ethanol induction of ADH in vivo.

Sexual dimorphic expression of ADH in rat liver: importance of the hypothalamic-pituitary-liver axis.

Hepatic alcohol dehydrogenase (ADH) activity is higher in female than in male rats. Although sex steroids, thyroid, and growth hormone (GH) have been shown to regulate hepatic ADH, the mechanism(s) for sexual dimorphic expression is unclear. We tested the possibility that the GH secretory pattern determined differential expression of ADH. Gonadectomized and hypophysectomized male and female rats were examined. Hepatic ADH activity was 2.1-fold greater in females. Because protein and mRNA content were also 1.7- and 2.4-fold greater, results indicated that activity differences were due to pretranslational mechanisms. Estradiol increased ADH selectively in males, and testosterone selectively decreased activity and mRNA levels in females. Effect of sex steroids on ADH was lost after hypophysectomy; infusion of GH in males increased ADH to basal female levels, supporting a role of the pituitary-liver axis. However, GH and L-thyroxine (T4) replacements alone in hypophysectomized rats did not restore dimorphic differences for either ADH activity or mRNA levels. On the other hand, T4 in combination with intermittent administration of GH reduced ADH activity and mRNA to basal male values, whereas T4 plus GH infusion replicated female levels. These results indicate that the intermittent male pattern of GH secretion combined with T4 is the principal determinant of low ADH activity in male liver.

Liver Alcohol Dehydrogenase Is Degraded by the Ubiquitin–Proteasome Pathway

Dihydrotestosterone (DHT) decreases rat liver alcohol dehydrogenase (ADH) due principally to an increased rate of degradation of the enzyme. The pathway of degradation of ADH was investigated. Exposure of hepatocytes in culture to lactacystin or to MG132, which are inhibitors of the ubiquitin–proteasome pathway of protein degradation, resulted in higher ADH. Furthermore, both lactacystin and MG132 prevented the decrease in ADH caused by DHT. By contrast, the lysosomal proteolytic inhibitors 3-methyladenine and leupeptin as well as inhibitors of the calcium-activated neutral protease calpain system had no effect on ADH in the absence or presence of DHT. ADH isolated by immunoprecipitation from hepatocytes exposed to DHT reacted specifically with anti-ubiquitin antibody. Ubiquitinated ADH was also demonstrated in hepatocytes exposed to MG132. The combination of DHT and MG132 resulted in more ubiquitinated ADH than exposure to either compound alone. These results suggest that the ubiquitin–proteasome pathway plays a role in the degradation of ADH and in the enhanced degradation of this enzyme by DHT.

Effect of STAT5b on Rat Liver Alcohol Dehydrogenase

Growth hormone (GH) enhances rat liver alcohol dehydrogenase (ADH) due to an increase in enzyme synthesis, which is mediated at the level of transcription. Previous studies have shown that the effect of GH in enhancing activation of the ADH promoter is mediated by C/EBPβ binding to region −22 to −11 relative to the start of transcription. In this study, STAT5b and C/EBPβ were found to bind to adjacent nucleotide sequences on a region between −226 and −194. Expression vectors for both STAT5b and C/EBPβ independently activated the promoter. Furthermore, the expression vector for the GH receptor also activated the ADH promoter, and this effect was abrogated by mutations of the adjacent STAT5b and C/EBPβ binding sites. These observations indicate that the enhancing effect of GH is mediated by both STAT5b and C/EBPβ.

Effects of Vitamin A Deficiency on Rat Liver Alcohol Dehydrogenase Expression and Alcohol Elimination Rate in Rats

Background: Vitamin A has been suggested to regulate the expression of liver alcohol dehydrogenase (ADH) in humans. There are few studies on the ability of retinoic acid to affect ADH expression in vivo and none on its effects on alcohol metabolic rate. Methods: Male Sprague Dawley® rats were used for isolation of hepatocytes or were rendered vitamin A deficient by feeding a deficient diet for 7 weeks. ADH, retinoic acid receptor β, and retinoid X receptor α protein levels were analyzed by Western blotting. Alcohol elimination rate was determined by following blood alcohol levels after administering a 1.5 g/kg dose of ethanol intraperitoneally. Results: Retinoic acid had no effect on ADH protein in cultured hepatocytes. In the vitamin A deficient rats, retinol was not detectable in serum or liver at the time animals were killed. ADH and retinoid X receptor α protein levels were unchanged in the deficient group compared with a vitamin A sufficient control group, whereas retinoic acid receptor β levels increased 40%. The deficient rats had a reduced volume of distribution of alcohol, but this largely was accounted for by their smaller body size. The alcohol elimination rates were lower in the deficient animals, but this was accounted for by reduced body and liver weights. Conclusions: Severe vitamin A deficiency did not alter liver ADH protein expression or rates of alcohol elimination when expressed per gram of body or liver weight.

Effects of Vitamin A Deficiency on Rat Liver Alcohol Dehydrogenase Expression and Alcohol Elimination Rate in Rats

Vitamin A has been suggested to regulate the expression of liver alcohol dehydrogenase (ADH) in humans. There are few studies on the ability of retinoic acid to affect ADH expression in vivo and none on its effects on alcohol metabolic rate. Male Sprague Dawley rats were used for isolation of hepatocytes or were rendered vitamin A deficient by feeding a deficient diet for 7 weeks. ADH, retinoic acid receptor beta, and retinoid X receptor alpha protein levels were analyzed by Western blotting. Alcohol elimination rate was determined by following blood alcohol levels after administering a 1.5 g/kg dose of ethanol intraperitoneally. Retinoic acid had no effect on ADH protein in cultured hepatocytes. In the vitamin A deficient rats, retinol was not detectable in serum or liver at the time animals were killed. ADH and retinoid X receptor alpha protein levels were unchanged in the deficient group compared with a vitamin A sufficient control group, whereas retinoic acid receptor beta levels increased 40%. The deficient rats had a reduced volume of distribution of alcohol, but this largely was accounted for by their smaller body size. The alcohol elimination rates were lower in the deficient animals, but this was accounted for by reduced body and liver weights. Severe vitamin A deficiency did not alter liver ADH protein expression or rates of alcohol elimination when expressed per gram of body or liver weight.

The Metabolism and Toxicity of .ALPHA.,.BETA.-Unsaturated Aldehydes. The Role of Glutathione S-Transferase.

This article describes sources and mechanisms of formation of α, β-unsaturated aldehydes, their reactivity with respect to glutathione and amino-groups, their toxicity based on interaction with sulfhydryl and amino targets in cells, and modulation of gene expression by the aldehydes. Among the many different aldehydes generated durimg lipid peroxidation, 4-hydroxy-2 (E)-nonenal (4-HNE) is one of the major products and has been shown to have a number of adverse biological effects. All previous studies on biological and toxicological effects of 4-HNE have been carried out using its racemate. Therefore, nothing has been known of which enantiomer of the racemate is more toxic, more reactive with biomacromolecules, or more readily detoxified by glutathione S-transferase (GST) and alcohol dehydrogenase (ADH) than the other. This article also describes the first evidence for the marked enantioselectivity by 4-HNE enantiomers in the irreversible inactivation of the glycolytic enzyme, rabbit muscle glyceraldehyde-3-phosphate dehydrogenase, and in their detoxification by rat liver cytosolic GST A4-4 and ADH.

Sex-dependent developmental change of rat liver cytosolic alcohol dehydrogenase activity.

Rat liver cytosolic alcohol dehydrogenase (ADH) is the principal enzyme which catalyzes the oxidation of ethanol. ADH activity is known to be significantly higher in females than in males. However, the precise mechanism of the sex-difference in ADH activity is uncertain. Recently, we have shown that the inhibitory action of androgen and the slight facilitatory actions of progestin and estrogen are involved in the mechanism of sex-difference in adult rat liver ADH activity. In the present study, we studied the difference of the postnatal developmental changes of ADH activity between males and females. ADH activity increased rapidly after birth up to about 12 d of age, and was not different in the two sexes. In female rats, ADH activity peaked at about 30 d of age and then increased gradually to plateau levels. However, the ADH activity of male rats fell markedly between 30 and 45 d old, and the reduced enzyme activity was observed until 104 d old. In conclusion, the ADH activity of male rats fell between 30 and 45 d after birth. At the ages over the turning point, the ADH activity was significantly lower in male than in female rats.

ChemInform Abstract: Amides of Benzoic and Heterocyclic Carboxylic Acids as Rat Liver Alcohol Dehydrogenase Inhibitors.

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Acetylcarnitine Inhibits Alcohol Dehydrogenase

Carnitine and acetylcarnitine are used as dietary supplements and as therapeutic agents. Carnitine attenuates ethanol metabolism in intact animals but the in vitro activities of alcohol dehydrogenase (ADH), microsomal ethanol oxidizing system (MEOS) or catalase are not significantly altered by carnitine. Since acetylcarnitine was a far more potent inhibitor of ethanol oxidation than carnitine in hepatocytes, the activities of rat liver ADH and MEOS were determined with or without acetylcarnitine. The activity of ADH, not MEOS, was significantly inhibited by acetylcarnitine at NAD : acetylcarnitine ≤ 1. The inhibition is of a competitive nature where acetylcarnitine competes with NAD+ (Ki = 135 μmol.L−1). This finding is unique in that this is the first report of this function of acetylcarnitine and it is a novel interaction between two important nutrients, niacin and carnitine.

Amides of benzoic and heterocyclic carboxylic acids are inhibitors of rat liver alcohol dehydrogenase

Amides of benzoic and heterocyclic carboxylic acids are inhibitors of rat liver alcohol dehydrogenase

Effects of thyroxine on the expression of alcohol dehydrogenase in rat liver and kidney

We studied the effect of thyroxine on alcohol dehydrogenase activity, immunoreactive protein levels and messenger RNA levels in the livers of thyroidectomized and sham-operated male rats. Effects on kidney alcohol dehydrogenase activity were also examined. Sham-operated rats injected with 100 micrograms thyroxine/kg/day, which induced hyperthyroidism, showed a 30% decrease in liver and a 40% decrease in kidney alcohol dehydrogenase activity compared with sham-operated rats injected with vehicle. Hypothyroid rats exhibited a 1.5-fold increase in alcohol dehydrogenase activity in liver and kidney compared with thyroidectomized rats injected with a replacement dose of 20 micrograms thyroxine/kg/day. We saw a twofold and a 2.5-fold higher level of alcohol dehydrogenase activity in liver and kidney, respectively, of hypothyroid rats compared with hyperthyroid rats. These effects were not accounted for by nutritional differences; daily food intake did not differ between groups. Immunoreactive protein levels as seen on Western blots varied in the same direction as enzyme activity. Northern-blot analysis showed higher levels of liver alcohol dehydrogenase messenger RNA in hypothyroid rats compared with euthyroid rats. These studies show that liver alcohol dehydrogenase activity and protein levels are modulated by thyroxine at pathophysiologically relevant levels and that this effect is not due to changes in food intake; kidney alcohol dehydrogenase activity is regulated in parallel. The change in alcohol dehydrogenase activity appears to be controlled in part by pretranslational mechanisms in hypothyroid animals and by posttranslational mechanisms in hyperthyroid animals.

Differences in kinetic characteristics and in sensitivity to inhibitors between human and rat liver alcohol dehydrogenase and aldehyde dehydrogenase

1. On the basis of kinetic properties and sensitivity to pyrazole inhibition, it is shown that liver alcohol dehydrogenase present in human mainly corresponded to class I and in rat to class ADH-3 which differed in a number of parameters. 2. Two different aldehyde dehydrogenase (ALDH) isoenzymes were detected in both human and rat liver. The human isoenzymes corresponded to the ALDH-I and ALDH-II type. 3. In the rat, one isoenzyme had low K m and showed similar activity than in human liver but differed in their sensitivity to both disulfiran and nitrofazole inhibition whereas the other presented high K m and showed greater activity than the human one. 4. Caution must be therefore paid when extrapolating to human subjects the data on ethanol metabolism obtained with rats.