Genetic variation of drug-metabolizing enzymes in the wistar rat

The Basis for Strain-Dependent Rat Aldehyde Dehydrogenase 1A7 (ALDH1A7) Gene Expression

Aldehyde hydrogenases (ALDHs) belong to a large gene family involved in oxidation of both endogenous and exogenous compounds in mammalian tissues. Among ALDHs, the rat ALDH1A7 gene displays a curious strain dependence in phenobarbital (PB)-induced hepatic expression: the responsive RR strains exhibit induction of both ALDH1A7 and CYP2B mRNAs and activities, whereas the nonresponsive rr strains show induction of CYP2B only. Here, we investigated the responsiveness of ALDH1A1, ALDH1A7, CYP2B1, and CYP3A23 genes to prototypical P450 inducers, expression of nuclear receptors CAR and pregnane X receptor, and structure of the ALDH1A7 promoter in both rat strains. ALDH1A7 mRNA, associated protein and activity were strongly induced by PB and modestly induced by pregnenolone 16α-carbonitrile in the RR strain but negligibly in the rr strain, whereas induction of ALDH1A1 and P450 mRNAs was similar between the strains. Reporter gene and chromatin immunoprecipitation assays indicated that the loss of ALDH1A7 inducibility in the rr strain is profoundly linked with a 16-base pair deletion in the proximal promoter and inability of the upstream DNA sequences to recruit constitutive androstane receptor-retinoid X receptor heterodimers. SIGNIFICANCE STATEMENT: Genetic variation in rat ALDH1A7 promoter sequences underlie the large strain-dependent differences in expression and inducibility by phenobarbital of the aldehyde dehydrogenase activity. This finding has implications for the design and interpretation of pharmacological and toxicological studies on the effects and disposition of aldehydes.

Phenobarbital inducibility and differences in protein expression of an animal model

Aldehyde dehydrogenases (ALDHs) are a group of enzymes which catalyze the conversion of aldehydes to the corresponding carboxylic acids in a NAD(P)(+)-dependent reaction. In mammals, different ALDHs are constitutively expressed in liver, stomach, eye and skin. In addition, inducible ALDH-isoenzymes are detectable in many tissues; apart from other physico- and immuno-chemical differences, two cytosolic ALDHs (ALDH1A3 and ALDH3A1) are known to be activated in rat liver, by different types of inducers of drug metabolism. Phenobarbital-type inducers increase the ALDH1A3, while polycyclic hydrocarbons (such as BaP and TCDD) increase the expression of the two members of ALDH3A subfamily (3A1 and 3A2). In this study, we used two Wistar rat substrains which have been well-characterized for different inducibility of ALDH1A3 enzyme activity after treatment with phenobarbital. Animals that respond (RR) or do not respond (rr) to treatment have been inbred for almost 25 years, offering a useful experimental model. Apart from the level of ALDH1A3 induced enzyme expression after phenobarbital treatment, no other differences between the two substrains have been noticed, as far as drug metabolizing enzyme activities (like the pentoxy- and ethoxy-O-dealkylation rate) are concerned. According to the present results, the ALDH1A3 expression is still the only difference between the two substrains. Immunoblotting experiments with polyclonal antibodies raised against CYP2B1 or/and CYP1A1/1A2 showed no differences between the two substrains. Additionally, data concerning time- and dose-response induction of ALDH1A3 after phenobarbital and griseofulvin treatment are presented. It is concluded that these two Wistar rat substrains represent a unique animal model for studying what seems to be the only difference between these substrains - the genetic basis of the phenobarbital induction.

Alterations in central monoaminergic neurotransmission induced by polycyclic aromatic hydrocarbons in rats

Benzo[alpha]pyrene (B[a]P) is a product derived from incomplete combustion of organic material and is considered responsible for chemically-induced cancer in humans. In the present study, the levels of noradrenaline (NA), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the brains of female Wistar rats 6, 12, 24 and 96 h after a single dose of B[alpha]P (50 mg kg(-1) b.w., i.p.), and also after repeated administration of B[alpha]P (50 mg kg(-1) b.w., i.p., 2 x wk, 1 mo). The brain regions studied were the striatum, hypothalamus, midbrain and cortex. Catecholamines were measured using high performance liquid chromatography (HPLC) and electrochemical detection. Significant changes were observed in the striatum where NA, DA, DOPAC were decreased after 24 h and HVA was decreased after 6 h. In contrast, no major alterations occurred in 5-HT and 5- HIAA. In the hypothalamus, a significant decrease in NA was observed after 96 h. In the midbrain, the most important change observed was the decrease in NA after 24 h. A trend toward an increase in 5-HIAA was observed in the cortex after 6 h. The results demonstrate that B[alpha]P induces alterations in the dopaminergic and serotoninergic systems throughout the brain. These alterations may lead to behavioural and hormonal disturbances.

Zoxazolamine-induced paralysis in two rat substrains: differences in hepatic drug metabolism

Aldehyde dehydrogenase (ALDH) is involved in the metabolism of endogenous and exogenous aldehydes originating from biogenic amines, lipids, food and drugs. Rat liver contains at least two cytosolic ALDHs that can be stimulated by inducers of drug metabolism. Phenobarbital- type inducers increase ALDH1 activity while polycyclic aromatic hydrocarbons (such as benzo[alpha]pyrene) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) increase ALDH3c isoenzyme activity. Two rat substrains were isolated according to a different induction of hepatic ALDH after treatment with phenobarbital (PB). Animals that responded to treatment (RR) and those that did not respond (rr) were inbred and divided into two homogenous groups. These animals constituted an ideal experimental model due to their common origin. Apart from the dramatic induction of cytosolic ALDH1 and ALDH3c, the effects of PB on pentoxy-, ethoxy- and methoxy-resorufin-O-dealkylase (P-, E-, and MROD) between the two substrains were also studied. 3-Methylcholanthrene (3MC) greatly increased ALDH3c levels in both substrains, although it was slightly more pronounced in the rr rats, in which it was assessed either as ALDH3c or as total cytosolic ALDH. A similar trend was also noted in EROD, PROD and MROD activities. Dealkylation of the methoxy group was found to be statistically different between the two substrains (rr > RR). The relevance of the biochemical findings with the in vivo hepatic capacity for drug metabolism was investigated by measuring the duration of zoxazolamine paralysis. Both animal substrains were tested with zoxazolamine either without pretreatment or after administration of PB or 3MC: the paralysis produced by zoxazolamine lasted for a longer period in rr than in RR rats. After pretreatment with PB, the duration of paralysis was greatly reduced, but the differences between the two substrains remained. Pretreatment with various doses of 3MC produced differences in the duration of paralysis in RR and rr rats, although the time period was much shorter than that observed in control animals.

Ligands of four receptors in the nuclear steroid/thyroid hormone superfamily inhibit induction of rat cytosolic aldehyde dehydrogenase-3 (ALDH3c) by 3-methylcholanthrene

Using six ligands that bind to four different receptors in the nuclear steroid/thyroid hormone superfamily, we have examined the effects of these chemicals on induction of the cytosolic aldehyde dehydrogenase (ALDH3c) activity by 3-methylcholanthrene (3MC) in rat liver and uterus. In contrast to negligible activities in the untreated rat, ALDH3c enzyme activities are induced after a single dose of 3MC. Hepatic ALDH3c induction is decreased 60% to 90% when 3MC is administered together with any of the following ligands: estradiol, testosterone, progesterone, hydrocortisol, diethylstilbestrol, or tamoxifen. None of these same doses of chemicals, administered alone, affects ALDH3c enzyme activity. In addition, when these ligands are injected 2 days after 3MC, no changes are observed in liver or uterus ALDH3c induction. These results suggest that ligands that bind to different receptors in the nuclear steroid/thyroid hormone superfamily might inhibit the ALD3H3c induction process by polycyclic aromatic hydrocarbons; the molecular mechanism(s) of this inhibitory effect is not yet understood.

Induction of class 3 aldehyde dehydrogenase in the mouse hepatoma cell line Hepa-1 by various chemicals

The mouse hepatoma cell line Hepa-1 was shown to express an aldehyde dehydrogenase (ALDH) isozyme which was inducible by TCDD and carcinogenic polycyclic aromatic hydrocarbons. The induced activity could be detected with benzaldehyde as substrate and NADP as cofactor (B/NADP ALDH). As compared with rat liver and hepatoma cell lines, the response was moderate (maximally 5-fold). There was an apparent correlation between this specific form of ALDH and aryl hydrocarbon hydroxylase (AHH) in the Hepa-1 wild-type cell line--in terms of inducibility by several chemicals. However, the magnitude of the response was clearly smaller for ALDH than for AHH. Southern blot analysis showed that a homologous gene (class 3 ALDH) was present in the rat and mouse genome. The gene was also expressed in Hepa-1 and there was a good correlation between the increase of class 3 ALDH-specific mRNA and B/NADP ALDH enzyme activity after exposure of the Hepa-1 cells to TCDD. It is concluded that class 3 ALDH is inducible by certain chemicals in the mouse hepatoma cell line, although the respective enzyme is not inducible in mouse liver in vivo.

Effect of various chemicals on the aldehyde dehydrogenase activity of the rat liver cytosol

The cytosolic activity of aldehyde dehydrogenase (ALDH) was studied in the rat liver, after acute administration of various carcinogenic and chemically related compounds. Male Wistar rats were treated with 27 different chemicals, including polycyclic aromatic hydrocarbons, aromatic amines, nitrosamines, azo dyes, as well as with some known direct-acting carcinogens. The cytosolic ALDH activity of the liver was determined either with propionaldehyde and NAD (P/NAD), or with benzaldehyde and NADP (B/NADP). The activity of ALDH remained unaffected after treatment with 1-naphthylamine, nitrosamines and also with the direct-acting chemical carcinogens tested. On the contrary, polycyclic aromatic hydrocarbons, polychlorinated biphenyls (Arochlor 1254) and 2-naphthylamine produced a remarkable increase of ALDH. In general, the response to the effectors was disproportionate between the two types of enzyme activity, being much in favour for the B/NADP activity. This fact resulted to an inversion of the ratio B/NADP vs. P/NAD, which under constitutive conditions is lower than 1. In this respect, the most potent compounds were found to be polychlorinated biphenyls, 3-methylcholanthrene, benzo(a)pyrene and 1,2,5,6-dibenzoanthracene. Our results suggest that the B/NADP activity of the soluble ALDH is greatly induced after treatment with compounds possessing aromatic ring(s) in their molecule. It is not known, if this response of the hepatocytes is related with the process of chemical carcinogenesis.

Further studies on the high-affinity binding of 3H-alaproclate to membranes from rat liver and some other tissues

The high affinity binding of 3H-alaproclate to membranes in liver homogenates from naive rats and those treated with phenobarbital sodium, 75 mg/kg intraperitoneally, alaproclate hydrochloride, 40 mg/kg intraperitoneally proadifen hydrochloride, 40 mg/kg intraperitoneally once daily for 7 days and killed 24 hr after the last injection was examined. The treatment increased the normal number of alaproclate binding sites (Bmax: 1.1 nmol/g tissue, KD: 0.6 nM) by factors of about 10, 4 and 6, respectively. About 80% of the binding was localized to the microsomal fraction in both normal and phenobarbital treated rats. Ninety % of the alaproclate displaceable binding in a microsomal preparation of the normal liver was inhibited by low (nM) concentrations of proadifen whereas only about 20% in the liver preparations from phenobarbital treated rats was inhibited by low concentrations of proadifen. Thus, the main part of the induced binding sites was insensitive to proadifen. The same was found for the alaproclate and proadifen-induced alaproclate binding sites. The stereoselectivity of alaproclate enantiomers for binding to the normal and the induced binding sites was different: the S-(-) form was 100 times more potent than the R-(+)- enantiomer in inhibiting binding of racemic alaproclate to the normal sites, whereas the latter form was 3 times more potent than the former in inhibiting the binding to the phenobarbital-induced proadifen insensitive binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in the inducibility of a hepatic aldehyde dehydrogenase by various effectors

A hepatic soluble aldehyde dehydrogenase (ALDH), inducible by polycyclic aromatic hydrocarbons, was studied in Wistar rats in connection with substances known to affect drug metabolism or aldehyde dehydrogenase activity, such as phenobarbital (PB), disulfiram (DS), beta-diethylaminoethyl diphenylpropylacetate (SKF 525A) and calcium cyanamide (CC). 3-Methylcholanthrene (MC) was given as a model inducer of ALDH (100 mg/kg, i.p., as a single dose) and the animals were killed after 3 days. Pretreatment with PB (1 g/l drinking water, for 2 weeks) enhanced the inducing effect of MC. On the contrary, pretreatment with DS (100 mg/kg, i.p., daily x 4) reduced by 70% the expected increase in ALDH activity. Neither SKF 525A (25 mg/kg, i.p., daily x 4), nor CC (5 mg/kg, i.p., daily x 4) could affect the action of the inducer. At the above doses, basal ALDH activity was inhibited by DS (30%) and CC (70%), but was not affected at all by PB or SKF 525A. The results were somewhat different when the various effectors tested were administered to animals already treated with MC (20 mg/kg, i.p., daily x 6). In this case, DS did not affect the already induced ALDH activity. On the contrary, CC was still an effective inhibitor. Unexpectedly, post-treatment with SKF 525A further enhanced the initial induction brought about by MC. Our findings show that substances affecting microsomal drug metabolism can interfere with the process of ALDH induction by MC. The additive result of PB pretreatment is probably due to the enhanced accumulation of an active metabolite of MC.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of inducible aldehyde dehydrogenase activity in the rat after treatment with phenobarbital or methylcholanthrene

Two genetically distinct substrains of the Wistar rat (RR and rr) were used to study the tissue distribution of the inducibility of aldehyde dehydrogenase (ALDH). The RR substrain is responsive to phenobarbital (PB), as far as the induction of the hepatic ALDH activity is concerned, whereas the rr substrain is deprived of this biochemical property. Both substrains, however, respond to treatment with methylcholanthrene (MC), exhibiting a uniform increase of the ALDH activity in the liver. It is known that PB and MC induce two different isozymes of the hepatic cytosol. The effect of PB (1 g/l in drinking water, for 12 days) on the inducibility of ALDH in extrahepatic tissues was examined in the RR substrain. On the contrary, MC was given (50 mg/kg x 4, intraperitoneally) to rr animals. The activity of ALDH was found to be induced by PB in the liver and the intestinal mucosa, when measured with NAD and propionaldehyde (P/NAD) or phenylacetaldehyde (Ph/NAD). An increase of the activity was also noticed when ALDH was measured with NADP and benzaldehyde (B/NADP). In rr animals, MC induced the B/NADP activity in the liver, the intestinal mucosa, the kidneys, the lungs, the spleen, the brain, the urinary bladder and the heart. The effect of MC on various tissues was less distinct, when ALDH was measured as P/NAD or Ph/NAD activity. It is concluded, that PB and MC not only induce different types of ALDH activity, but they also reveal differences in the tissue distribution of the inducibility of ALDH.

Inducibility of liver cytosolic aldehyde dehydrogenase activity in various animal species

1. The inducibility of hepatic cytosolic aldehyde dehydrogenase activity was studied in rat, mouse, guinea pig, chicken, frog, salamander and rainbow trout, by using two different types of inducers of drug metabolism. 2. Phenobarbital (a type I inducer of drug metabolizing enzymes) increased total liver cytosolic aldehyde dehydrogenase activity (up to 20-fold) in a genetically defined substrain of responsive rats (RR) and only slightly, if at all, in a non-responsive substrain (rr). On the contrary, both types of rats showed a highly induced aldehyde dehydrogenase activity after treatment with methylcholanthrene (a type II inducer). Phenobarbital is affecting mainly an isozyme of aldehyde dehydrogenase which is best measured with propionaldehyde as the substrate and NAD as the coenzyme (P/NAD). 3. Administration of phenobarbital to mice produced only a slight increase (2-fold) in the P/NAD aldehyde dehydrogenase activity. 4. Methylcholanthrene treatment caused a 2-fold increase of the hepatic P/NAD aldehyde dehydrogenase activity in the chicken. 5. In the guinea pig, phenobarbital produced an approximate 3-fold increase of the P/NAD activity. Methylcholanthrene had a similar effect, although to a lesser extent. 6. In the salamander, a 4-fold increase was detected in the enzyme activity measured with benzaldehyde as the substrate and NADP as the coenzyme (B/NADP), after treatment with either phenobarbital or methylcholanthrene. 7. The hepatic aldehyde dehydrogenase activities were found unchanged in the rainbow trout, after treatment with phenobarbital or 2,3,7,8-tetrachlorodibenzo-p-dioxin. 8. The rat model remains the only one examined that shares with human hepatocytes strong inducibility of the B/NADP aldehyde dehydrogenase isozyme upon treatment with polycyclic aromatic hydrocarbons.

Phenobarbital enhances the aldehyde dehydrogenase activity of rat hepatocytes in vitro and in vivo

Aldehyde dehydrogenase (ALDH) was measured in primary cultures of hepatocytes obtained with collagenase perfusion from livers of Long-Evans rats. After seven days in culture, basal ALDH activity, protein content and DNA content are significantly decreased. Exposure of the cultures to phenobarbital (PB, 3 mM in the media) does not prevent the decrease of DNA content, although it keeps protein at relatively higher levels. The activity of ALDH is not only preserved, but also significantly enhanced, when propionaldehyde, phenylacetaldehyde, benzaldehyde and D-glucuronolactone are used as substrates and NAD as the coenzyme. A relative increase of activity is also noted when ALDH is measured with benzaldehyde and NADP. Treatment of Long-Evans animals with PB (1 mg/ml, in drinking water for 2 weeks) leads to similar relative increases of the ALDH activity. In absolute values, however, enzyme activities found after in vivo treatment with PB are higher, compared to those obtained after in vitro exposure. These results show that ALDH activity can be greatly enhanced by PB in primary hepatocyte cultures, free from any indirect endogenous influences.

Comparative study of the effects of some inducers with or without protein binding properties on bioavailability of isoxazolylpenicillins in rats

The effect of various inducers with or without protein binding properties on serum levels and half life of Oxacillin, Cloxacillin and Dicloxacillin was studied. A total of 102 male rats classified in 3 "categories" according to the administered penicillin with 6 groups of rats in each of them were used. Each group was pretreated for 15 days with the following inducers: phenobarbital, diphenylhydantoin, diazepam, chlorpromazine and phenylbutazone. The control groups received saline. The d-glucaric acid concentration in the urine prior to and after the administration of inducers and the liver weight were taken as enzyme induction indices. The results showed a decrease of serum levels and half life of three penicillins with a negative correlation between urine d-glucaric acid and serum penicillin levels. Phenobarbital, diphenylhydantoin and chlorpromazine affected the 3 penicillins in the following statistically significant order: oxacillin, dicloxacillin, cloxacillin. Diazepam affected: cloxacillin, dicloxacillin, oxacillin, and phenylbutazone: dicloxacillin, cloxacillin and oxacillin. However all drugs finally produced a uniform effect on all 3 penicillins in the following decreasing order: phenobarbital (r = -0.910), diphenylhydantoin (r = -0.864), phenylbutazone (r = -0.851), chlorpromazine (r = -0.842) and diazepam (r = -0.821). For all inducers, the effect was most significant for oxacillin (r = -0.869), second most significant for dicloxacillin (r = -0.811) and finally for cloxacillin (r = -0.778). The results suggested an interaction of isoxazolylpenicillins and the above drugs.

Enhancement of aldehyde dehydrogenase activity in human and rat hepatocyte cultures by 3-methylcholanthrene

Aldehyde dehydrogenase was measured in primary cultures of hepatocytes obtained with a two-step collagenase perfusion either from human hepatic tissue or from livers of Fisher rats. Basal enzyme activity declines gradually as a function of time in culture, but remains at all times higher when measured with propionaldehyde and NAD (P/NAD) than with benzaldehyde and NADP (B/NADP). Treatment of the cultures with 2 microM of 3-methylcholanthrene for four days significantly increased the B-NADP activity of human and rat hepatocytes (tenfold and eightfold respectively). In human hepatocytes 3-methylcholanthrene increases also the P/NAD activity, but to a lesser extent (twofold), compared to the B/NADP activity. Due to the significant enhancement of B/NADP activity in cultures of human and rat hepatocytes after application of 3-methylcholanthrene, the initial difference in the basal activity levels between the P/NAD and B/NADP forms diminishes or, in the case of human hepatocytes, is even inverted. These results show for the first time that aldehyde dehydrogenase activity is increased in cultured human hepatocytes. This biochemical property is preserved in human and rat hepatocyte cultures, despite the rather quick loss of the basal aldehyde dehydrogenase activity.

Liver cytosolic aldehyde dehydrogenases in rats with different predisposition to induction by phenobarbital. Partial purification and characterization of the enzymes at basal state

Liver cytosolic aldehyde dehydrogenases were partially purified from rats with different genetic predisposition to induction of aldehyde dehydrogenase activity by phenobarbital. The enzymes were studied at basal state without any pretreatment with an inducer. The main aldehyde dehydrogenases from the non-, high- and intermediate reactor animals could not be differentiated by substrate specificity or thermostability. The enzyme from the non-reactor rats was more resistant to changes of pH and to the inhibitory effects of disulfiram than the enzymes from the high- or intermediate reactors. Immunochemical studies suggested a dissimilarity of these enzymes.

Serum lipids and hepatic microsomal enzymes with special reference to serum cholinesterase in Wistar rats

Serum pseudocholinesterase in accordance with indicators revealing the lipid metabolism and liver function was studied in rats exposed to phenobarbital, bis-p-nitrophenylphosphate and disulfiram in vivo. Phenobarbital markedly induced the hepatic microsomal drug-metabolizing enzymes and tended to decrease the triglyceride content in serum. Serum lipids remained almost unaffected after the treatment of bis-p-nitrophenylphosphate. However, serum gamma-glutamyltransferase activity showed a marked decrease to this organophosphorus compound. Disulfiram activated the microsomal UDP-glucuronosyltransferase (p-nitrophenol) activity, and caused an enhancement of serum total cholesterol, which suggests that this drug might be atherogenic.

Enhancement of cytosolic carboxylesterase by phenobarbital in the rat

Previously suggested identity of soluble hepatic carboxylesterase and cytosolic aldehyde dehydrogenase was studied in the liver of the rr and RR rat substrains after phenobarbital administration. Results showed over 30% increase of carboxylesterase activity in all animals treated with phenobarbital. The total aldehyde dehydrogenase activity was increased only in RR substrain. These animals had no similar enhancement in the activity of carboxylesterase. The results indicate that the two enzymes are not identical.

Increase of hepatic and serum aldehyde dehydrogenase activity after TCDD treatment

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a contaminant of some herbicides, is an extremely potent enzyme inducer. Male albino rats of two genetically different substrains developed for the inducibility (RR) and noninducibility (rr) of aldehyde dehydrogenase by phenobarbital were given TCDD 80 microgram/kg as a single dose 6 days before analysis. rr-Animals having no induction of the hepatic soluble high-Km aldehyde dehydrogenase by phenobarbital showed an approximate 25-fold increase in activity after TCDD treatment. The increase in aldehyde dehydrogenase activity could be detected only when measured with a millimolar substrate concentration. The aldehyde dehydrogenase activity in serum was increased 3-fold after TCDD administration in both substrains.

Inducible aldehyde dehydrogenases in the hepatic cytosol of the rat

Rats of the Wistar/Af/Han/Mol/(Han 67) strain have previously been shown to respond in a variable way to phenobarbital treatment, as far as the induction of aldehyde dehydrogenase activity is concerned (Marselos 1976). This biochemical property is genetically determined and concerns the high-Km aldehyde dehydrogenase of the hepatic cytosol. In this study, administration of phenobarbital (1 mg/mo of drinking water, for 1 week) produces a uniform induction of aldehyde dehydrogenase in all rats, when measured with micromolar substrate concentration. The inducible low-Km enzyme of the cytosol is not genetically determined like the high-Km enzyme, and shows a wide specificity for aliphatic as well as for aromatic aldehydes. Despite the inducibility of the cytosolic enzymes, no alterations are found in the mitochondrial aldehyde dehydrogenase activities after phenobarbital treatment. The oxidation of D-glucuronolactone takes place only in the cytosol, and seems to be dependent on the low-Km aldehyde dehydrogenase. This is consistent with NMR studies, which showed that a very minimal amount of D-glucuronolactone is in aldehyde form under the measurement conditions usually applied. Further, the oxidation of D-glucuronolactone is also enhanced by phenobarbital in all rats without a genetic predisposition, and its dose-response curve is very similar to that of the low-Km aldehyde dehydrogenase.