Differential inhibition of rat hepatic glutathione S-transferase isoenzymes in the course of fascioliasis.

The effects of a subclinical fascioliasis at various stages of its development (at week 3, 6 and 9 after infection by oral administration of 20 metacercariae of Fasciola hepatica) in rats were determined on the activity of enzymes involved in liver metabolism of glutathione and on the subunit pattern of cytosolic glutathione S-transferase. The parasitic pathology was ascertained by clinical observation of the rats and at autopsy. Hepatic microsomal cytochrome P-450 content was significantly decreased in infected rats by week 3 and 6 post-infection. Not correlatively, the catalytic activities of glutathione S-transferase towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene were significantly lowered in last stages of the experimental fascioliasis (by week 6 and 9 post-infection). These decreases were correlated to that of subunit 1 as determined by means of high-performance liquid chromatography of cytosolic proteins whereas subunit 6 could also be decreased. Fascioliasis did not alter cytosolic glutathione, glutathione reductase and glutathione peroxidase activities or plasma glutathione S-transferase activity accepting 1-chloro-2,4-dinitrobenzene as the substrate.

Inducing effect of oxfendazole on cytochrome P450IA2 in rabbit liver. Consequences on cytochrome P450 dependent monooxygenases.

Male New Zealand rabbits were dosed with either 0.9, 4.5 or 22.5 mg/kg/day of oxfendazole by gastric intubation for 10 days. Oxfendazole administered at the therapeutic dose (4.5 mg/kg) and at the highest dose (22.5 mg/kg) increased 1.54- and 2.36-fold the total liver microsomal cytochrome P450 and more particularly the isoenzyme P450IA2 (95 and 184% increases) as demonstrated by western blotting. Increases in ethoxyresorufin O-deethylation and hydroxylations of benzopyrene and acetanilide occurred in livers of the same animals without any change in N-demethylation of aminopyrine, benzphetamine or erythromycin. Because of the unchanged level of mRNA specific to cytochrome P450IA2, as shown by northern blot analysis of poly mRNA, an enzyme stabilization rather than a transcriptional activation of IA2 genes should be involved in the P450IA2 regulation mechanisms. Oxfendazole bound strongly to cytochrome P450, giving rise to a type II spectrum, and inhibited noncompetitively the ethoxyresorufin O-deethylase and acetanilide hydroxylase activities, this confirmed that oxfendazole interacts only with the P450IA2 family. On the basis of a comparison of the enzymatic activities induced by various imidazole drugs, it was concluded that oxfendazole, like omeprazole and albendazole, behaved as a 3-methylcholanthrene-type inducer. These three benzimidazoles did not all belong to the same category of cytochrome P450 inducers as the antifungal drugs miconazole, clotrimazole and ketoconazole.

Comparative effects of cytokines on constitutive and inducible expression of the gene encoding for the cytochrome P450 3A6 isoenzyme in cultured rabbit hepatocytes: consequences on progesterone 6beta-hydroxylation.

Cultured rabbit hepatocytes were used to compare the relative activities of cytokines to inhibit the constitutive or rifampicin (RIF)-induced expression of the cytochrome P450 3A6 gene (CYP3A6). Human recombinant cytokines tested were interleukin-1beta (IL-1beta) (2 U/mL), interleukin-2 (IL-2) (5,000 U/mL) and interferon-gamma (IFN-gamma) (50 U/mL). Hepatocytes were cultured in the presence or absence of 25 microM RIF for 24 hr, with or without cytokines alone or in combination. All these cytokines inhibited RIF-induced P4503A6 expression without apparent cellular toxicity. By contrast, only IFN-gamma treatment provided a significant decrease (41%) in the constitutive P4503A6 protein level. Moreover, cytokines differed in their ability to repress RIF-dependent transcriptional induction of CYP3A6: IL-1beta and IL-2 were approximately equipotent, causing an almost 40-50% suppression of CYP3A6 mRNA and protein levels, whereas IFN-gamma exerted repressive effects only on P4503A6-related erythromycin N-demethylase activity and inducible protein expression. In fact, although strongly reducing P4503A6 protein content (an approximate 70% decrease), IFN-gamma did not exhibit any influence on CYP3A6 mRNAs with the exception of its association with interleukins. All these results suggest that IL-1beta and IL-2 mainly promote a transcriptional repression mechanism, given the absence of effect of these cytokines on the basal P4503A6 level, whereas IFN-gamma exerts a post-transcriptional suppressive action on both induced and constitutive P4503A6 expression. Consequently, P4503A6-dependent progesterone 6beta-hydroxylase activity also presented a cytokine-specific pattern of inhibition, with a much greater sensitivity than P4503A6 immunoreactive protein to IL-1beta and IL-2 + IFN-gamma treatments. Thus, this study underlines the significant impact of inflammation on steroid metabolism.

Comparison of hepatic and extrahepatic drug-metabolizing enzyme activities in rats given single or multiple challenge infections with Fasciola hepatica.

The activity of drug-metabolizing enzymes was compared in liver, kidneys and lungs of rats given single or repetitive fluke infections. Fascioliasis was induced by oral administration of 20 metacercariae of F. hepatica to rats, either 6, or 12 and 6, or 12, 9 and 6 weeks before sacrifice. In the liver of mono-infected rats, significant reductions (24-67%) were observed in microsomal content of cytochrome P450 and all P450-dependent monooxygenases investigated. Conjugations to glutathione or acetate were lowered by 34-50% in these animals. In multiply infected animals, a majority of specific enzymatic activities were unchanged, while some monooxygenase activities such as aminopyrine demethylation or benzo(a)pyrene hydroxylation were increased by 26-76% in the liver of tri-infected rats. A renal compensatory process occurred in all infected groups, since cytochrome P450, benzphetamine demethylation and glutathione conjugation were significantly increased. By contrast, dealkylation of benzphetamine and pentoxyresorufin were decreased in the lungs of monoinfected rats. The development of parasite resistance would account for the recovery of liver drug metabolizing capabilities in multi-infected animals.

Comparison of hepatic and renal drug-metabolising enzyme activities in sheep given single or two-fold challenge infections with Fasciola hepatica.

The activity of drug-metabolising enzymes was compared in liver and kidneys of adult sheep given single or two-fold fluke infection. Fascioliasis was induced by oral administration of 200 metacercariae of Fasciola hepatica to female sheep either 10 or 20 weeks (mono-infections) or 10 and 20 weeks (bi-infection) before killing. The parasitic pathology was ascertained at autopsy and by clinical observation of animals. In the liver of both mono- and bi-infected animals, significant decreases (P<0.05) (17-44%) were observed in the microsomal content of cytochrome P450 and in the two measured P450-dependent monooxygenase activities, benzphetamine and ethylmorphine N-demethylations. Moreover, Western blot analysis of microsomes demonstrated a decrease in the expression of cytochrome P4503A subfamily correlative with that of its presumed corresponding activity ethylmorphine N-demethylase. By contrast, the conjugation of chloro-dinitrobenzene to glutathione remained unchanged in liver cytosolic fractions prepared from all these animals. In kidneys, a significant decrease (P<0.05) (30%) in microsomal cytochrome P450 level of 10-week mono-infected sheep was observed whereas there was no change in the other groups of animals. The inflammatory origin and the consequences in terms of pathology and animal productivity of the fascioliasis-induced decreases in tissue-oxidative drug metabolism are discussed, particularly in the case of adult sheep suffering repetitive infections.

Consequences of challenge infections with Fasciola hepatica on rat liver P450-dependent metabolism of sex hormones.

The effect of single or repetitive fluke-infections on rat liver steroid hormone metabolism was studied. Fascioliasis was induced by oral administration of 20 metacercariae of Fasciola hepatica to rats, by week-6 (mono-infected) or 12 and 6 (bi-infected), or 12, 9 and 6 (tri-infected) before killing. Total microsomal cytochrome P450 and P450 isoenzymes were measured spectrophotometrically and by Western-blot analysis, respectively. Progesterone and testosterone metabolism were quantified by normal phase high performance liquid chromatography. In control rats, progesterone and testosterone were mainly converted to 2 alpha- and 16 alpha-hydroxymetabolites. In the liver of mono-infected rats, hepatic cytochrome P450 was significantly decreased by 36-64% whereas the expression of all investigated isoenzymes was decreased by 36-82% with the exception of the unchanged P4502E1. 16 alpha- and 2 alpha-hydroxylations of progesterone and testosterone were significantly decreased by 50-90%, these decreases were correlated with those of P4502B1/2 and P4502C11 isoenzymes, respectively. In bi- and tri-infected rats, steroid hormones were metabolized similarly to control rats. The return of steroid drug metabolizing enzyme activities to control level could be related to the immune response associated to the development of the animal resistance to the parasitic infection.

Ontogenic development of liver progesterone metabolism in female sheep. Contribution of cytochrome P4502B and P4503A subfamilies.

Age-related changes in progesterone hepatic metabolism were measured in Lacaune ewes in the foetal, neonatal (1 and 4 weeks), growing (7 months), pregnant (11 months) and adult (6 years) stages. 6 beta-Hydroxylation and 20 alpha-reduction were found to be the most efficient metabolic process in ovine microsomes. These activities were detected in 3-month-old foetuses and they increased rapidly during the first month of life, in a similar manner to the developmental expression of the cytochrome P4503A subfamily. 16 alpha- and 21-hydroxylation of progesterone were characterized by low, constant turn over in sheep liver microsomes during development. The hepatic ovine P4502B isozyme was purified to electrophoretic homogeneity by means of successive DEAE cellulose, hydroxylapatite and CM cellulose chromatographic separations. This hemoprotein had an apparent molecular weight of 51 kDa and was characterized by spectral data, NH2-terminal amino-acid sequence, immunological and catalytic properties. The relative contribution of this form and of the previously purified ovine P4503A subfamily was investigated in liver progesterone metabolism by immunoinhibition studies using polyclonal antibodies raised in rabbits and from the existence of induction and of significant correlations between microsomal activity and specific P450 content. In sheep liver microsomes, it would appear that cytochrome P4502B is involved in progesterone 21-hydroxylation whereas P4503A participates in the 6 beta- and 16 alpha-hydroxylation and possibly in the reductive conversion of progesterone in its 20 alpha-hydroxy derivative.

Dose-related effect of aflatoxin B1 on liver drug metabolizing enzymes in rabbit.

The effects of chronic administration of aflatoxin B1 (AFB1) on liver drug metabolism enzymes were measured in New Zealand rabbits divided into three groups of 5 animals, each receiving over 5 days either arabic gum or AFB1 in arabic gum at a daily oral dose of 0.05 or 0.10 mg/kg. These treatments did not lead to any lethality in any of the treated groups, but the body weight gain was altered. Biochemical exploration of plasma components revealed a dose-dependent hepatotoxicity characterized by cytolysis and cholestasis. At 0.10 mg/kd/day of AFB1, significant decreases were observed in total liver microsomal cytochrome P450, several P450-dependent monooxygenase activities, all individual P450 isoenzymes levels analysed by Western-blotting and glutathione S-transferase activities. By contrast, at 0.05 mg/kg/day of AFB1, even though total cytochrome P450 was decreased by 30%, only P450 1A1 and 3A6 isoenzymes, and aniline hydroxylation, pentoxyresorufin O-depentylation, aminopyrine, erythromycin, ethylmorphine and dimethylnitrosamine N-demethylations were affected. In the same animal group, the only glutathione S-transferase accepting CDNB (1-chloro-2,4-dinitrobenzene) as substrate was decreased by 22%. UDP-glucuronyltransferase accepting p-nitrophenol as substrate was increased in both groups of animals (33-62%). The mechanisms that could contribute to the observed changes in drug metabolizing enzymes are discussed.

Identification of human and rabbit cytochromes P450 1A2 as major isoforms involved in thiabendazole 5-hydroxylation.

This report characterized one of the major cytochrome P450 isozyme involved in thiabendazole metabolism. This study was undertaken by using both cultured rabbit hepatocytes treated or not with drugs known to specifically induced various cytochromes P450 isoenzymes (i.e., P450 1A1/2 by beta-naphthoflavone, P450 2B4 by phenobarbital, P450 3A6 by rifampicine and P450 4A by clofibrate) and human liver (THLE-5) and bronchial (BEAS-2B) epithelial cells expressing or not the major constitutive human cytochromes P450 (i.e., CYP1A2, 2A6, 2B6, 2C9, 2D6, 2E1 or 3A4). Only hepatocytes exposed to beta-naphthoflavone and clofibrate significantly metabolized thiabendazole to 5-hydroxythiabendazole. Extensive biotransformation of this anthelmintic only occurred in human cells expressing CYP1A2. Moreover, experiments performed on rabbit preparations showed good correlations between thiabendazole 5-hydroxylase activity and both ethoxyresorufin and methoxyresorufin O-dealkylase activities. Thus, CYP1A2 is a major isoenzyme involved in thiabendazole 5-hydroxylation.

Evidence for cytochrome P4501A2-mediated protein covalent binding of thiabendazole and for its passive intestinal transport: use of human and rabbit derived cells.

Thiabendazole (TBZ), an anthelmintic and fungicide benzimidazole, was recently demonstrated to be extensively metabolized by cytochrome P450 (CYP) 1A2 in man and rabbit, yielding 5-hydroxythiabendazole (5OH-TBZ), the major metabolite furtherly conjugated, and two minor unidentified metabolites (M1 and M2). In this study, exposure of rabbit and human cells to 14C-TBZ was also shown to be associated with the appearance of radioactivity irreversibly bound to proteins. The nature of CYP isoforms involved in this covalent binding was investigated by using cultured rabbit hepatocytes treated or not with various CYP inducers (CYP1A1/2 by beta-naphthoflavone, CYP2B4 by phenobarbital, CYP3A6 by rifampicine, CYP4A by clofibrate) and human liver and bronchial CYP-expressing cells. The covalent binding to proteins was particularly increased in beta-naphthoflavone-treated rabbit cells (2- to 4-fold over control) and human cells expressing CYP1A2 (22- to 42-fold over control). Thus, CYP1A2 is a major isoenzyme involved in the formation of TBZ-derived residues bound to protein. Furthermore, according to the good correlation between covalent binding and M1 or 5OH-TBZ production, TBZ would be firstly metabolized to 5OH-TBZ and subsequently converted to a chemically reactive metabolic intermediate binding to proteins. This metabolic activation could take place preferentially in liver and lung, the main biotransformation organs, rather than in intestines where TBZ was shown to be not metabolized. Moreover, TBZ was rapidly transported by passive diffusion through the human intestinal cells by comparison with the protein-bound residues which were not able to cross the intestinal barrier. Consequently, the absence of toxicity measured in intestines could be related to the low degree of TBZ metabolism and the lack of absorption of protein adducts. Nevertheless, caution is necessary in the use of TBZ concurrently with other drugs able to regulate CYP1A2, particularly in respect to liver and lung tissues, recognised as sites of covalent-binding.

Effect of low doses of a trichothecene mycotoxin (diacetoxyscirpenol) on rat gastric glycoproteins: a histochemical study.

A histochemical study was carried out to evaluate the changes occurring in the glycoproteins of the stomach of the rat following short-term treatment with the trichothecene mycotoxin, diacetoxyscirpenol (DAS). Staining with alcian blue methods for detecting complex carbohydrates and with lectin conjugates (Con A, LTA, PNA, SBA and WGA) showed an increased alcianophilia at pH 2.6 and pH 1.0 for various parts of the fundic glands. With respect to lectin staining, DAS intoxication was characterized by enhanced labelling with LTA and SBA in the surface epithelium and in the foveolae, while WGA binding appeared in the lower mucous neck cells. These data suggest that the contents of the mucus-producing cells of the fundic glands of the rat stomach could be affected by low doses of diacetoxyscirpenol even following only 2 days of treatment.

Time-dependent variations of drug-metabolising enzyme activities (DMEs) in primary cultures of rabbit hepatocytes.

In the present study, time-dependent variations of drug-metabolising enzyme activities (DMEs) in primary cultures of rabbit hepatocytes, a species of economic importance in Mediterranean countries, were investigated. Cross-bred rabbits were anesthetised and their livers perfused in situ by a two-step collagenase technique; cells suspensions were filtered, seeded in collagen-coated dishes and cultivated at 37 degrees C in a controlled atmosphere for 24 and 72 h. Cytochrome P450 and b(5) contents as well as the catalytic activity of some P450-dependent monooxygenases were measured in subcellular fractions obtained by differential ultracentrifugation; microsomal proteins were also subjected to immunoblotting, using antibodies to rat P4501A, 2B, 2E1 and 3A isoforms. The activity of some microsomal hydrolytic enzymes was also determined. As regards conjugative enzymes, glutathione content and activities of glutathione S-transferase, uridindiphosphoglucuronosyl-transferase, acetyl-transferase and 1,2-epoxibuthane glutathione transferase were assayed. An overall reduction of the catalytic activity was observed 72 h after plating, reaching in certain instances the level of statistical significance. On the whole, our data confirm those previously reported with hepatocytes obtained from other species; however, the evidence that DMEs were still measurable after 72 h supports the usefulness of this in vitro method for drug metabolism studies in the rabbit as well.

Comparative effects of T-2 toxin and diacetoxyscirpenol on drug metabolizing enzymes in rat tissues.

The effects of T-2 toxin and diacetoxyscirpenol on tissue drug-metabolizing enzymes in young male rats were compared. Mycotoxicoses were produced by daily oral administration of toxins at 1.0 mg/kg body weight for 1, 4 or 8 days. Many hepatic, renal and pulmonary oxidative and conjugative enzymes were measured in animals killed 24 hr following the last administration. The effects of the two trichothecene mycotoxins were generally similar. In liver the decrease in microsomal and cytosolic proteins paralleled the decline in total plasma proteins or the increase in plasma GOT activity. Hepatic microsomal cytochrome P-450 decreased in rats receiving trichothecenes for 8 days. This effect was more marked when aminopyrine, benzphetamine, ethylmorphine and ethoxycoumarin dealkylations or aniline and benzopyrene hydroxylations were measured. p-nitrophenol glucuronyltransferase activity was enhanced in animals receiving at least one administration of trichothecenes, whereas there was no change in conjugation to glutathione or acetate. In other tissues, there was no change in any renal enzymes whereas a significant rise in pulmonary monooxygenase was observed in T-2 toxin administered to rats for 4 or 8 days.

In vitro metabolism of 14C-moxidectin by hepatic microsomes from various species.

Moxidectin is an antiparasitic drug widely used in cattle, sheep and companion animals. No data were available on its metabolism in wild species or in monogastrics. The in vitro metabolism of 14C-moxidectin was studied using hepatic microsomes from several different species: cow (Bos taurus). sheep (Ovis ovis), goat (Capra hircus), deer (Cervus dama), rat (Rattus norvegicus), pig (Sus scrofa and rabbit (Oryctolagus cuniculus). After separation and quantification by HPLC, the extent of metabolism of 14C-moxidectin was greatest with microsomes from sheep (32.7%) as compared to those from cows (20.6%), deer (15.4%), goats (12.7%). rabbits (7.0%) or rats (3.0%). The least metabolism occurred with microsomes from pigs. with 0.8% of total detected metabolites. A C29 monohydroxymethyl metabolite was detected in the greatest amounts. providing 0.4% out of the total detected radioactivity in pigs and 19.3% in sheep. In addition, the importance of P450 3A in the metabolism of 14C-moxidectin was confirmed by using in vivo induced P450 in combination with various P450 inhibitors.

Fasciola hepatica: liver enzymes in rats and interaction with chemical inducers.

Adult male rats were sorted into control and infected groups, the latter receiving an oral dose of 20 metacercariae of Fasciola hepatica. In Weeks 3 and 6 after infection, some rats received phenobarbital or 3-methylcholanthrene which induced drug metabolizing enzymes. The parasitic pathology was ascertained by clinical observation of the rats and at autopsy. Hepatic microsomal cytochrome P-450 content was significantly decreased in infected rats compared to untreated phenobarbital treated groups. In all infected rats, the simultaneous increase in cytosolic calcium and decrease in cytosolic glutathione corresponded to oxidative cell injury occurring in the course of fascioliasis. Both arylamine acetyltransferase (EC 2.3.1.5.) and glutathione transferase (EC 2.5.1.18) activities were decreased in all newly infected and 6 week infected groups. Fascioliasis did not alter the substrate related uridine diphosphate glucuronosyltransferase activities (EC 2.4.1.17) of any rat group.

Ontogenic development of drug-metabolizing enzymes in male chicken liver.

The ontogenic study of the hepatic biotransformation enzymes revealed the early development of both oxidative and conjugative enzymes in male chickens ranging in age from 3 to 12 weeks. Although the rate of microsomal cytochrome P450 reactions progressively increased during the first 9 weeks, it decreased thereafter. Furthermore, the proteins revealed by the antibodies to anti-cytochrome P450 1A2, 2B4, 2C7, and 3A4 appeared to be constitutively expressed. Hepatic monooxygenases were characterized by different developmental patterns. The demethylase activities increased progressively up to 9 weeks, then they declined, in 12 weeks reaching the activity level observed in 3-week-old chickens. In contrast, alkoxyresorufin O-dealkylases and benzopyrene hydroxylase activities continued to increase with age. Significant variability was noted for aniline hydroxylase. Among conjugation enzymes, UDP-glucuronyltransferase towards p-nitrophenol and isoniazid N-acetyltransferase activities increased with the age of the fowl, but with different profiles. Concerning glutathione S-transferase accepting 1-chloro-2,4-dinitrobenzene or 1,2-dichloro-4-nitrobenzene, the chickens aged from 3 to 9 weeks were less well developed in this enzyme than 12-week-old ones.

The development of drug-metabolizing enzymes in female sheep livers.

The purpose of this investigation was to determine age-related changes of some hepatic drug-metabolizing activities in Lacaune ewes in the foetal, neonatal (1 and 4 weeks), growing (7 months), pregnant (11 months) and adult (6 years) stages. Although microsomal cytochrome P-450 was not detected in 3-month-old foetuses, it increased regularly from 1-week- to 11-month-old animals. Among mixed-function oxidases, the development of aminopyrine and ethylmorphine N-demethylases, benzo(alpha)pyrene hydroxylase and ethoxycoumarin O-deethylase were correlated to that of total cytochrome P-450. Due to their presence in foetal liver or their more rapid evolution, cytochrome b5, NADPH cytochrome c reductase, aniline hydroxylase, benzphetamine N-demethylase and erythromycin N-demethylase did not parallel the ontogenesis of cytochrome P-450. Hepatic transferases showed different developmental patterns from mono-oxygenases, so UDP glucuronyltransferase was detected in the foetus, reached maximum activity in all young ages up to the pregnant stage and subsequently fell in adult ewes. Concerning glutathione S-transferase accepting 1-chloro-2,4-dinitrobenzene as substrate, similar values were obtained in the foetus and all young animals, whereas five- to tenfold higher values were obtained in both pregnant and adult female sheep. N-acetyltransferase using sulphamethazine did not significantly change from foetuses to adults but there were large differences in the capacity of hepatic acetylation between animals belonging to the same group.

The effects of T-2 toxin exposure on liver drug metabolizing enzymes in rabbit.

High doses of T-2 toxin are known to decrease protein synthesis and mono-oxygenase activities in rat liver. The purpose of this study was to investigate whether exposure at a low dose could alter the normal metabolism of the xenobiotic by the liver. Three doses of T-2 toxin, dissolved in olive oil, were orally and daily administered to New Zealand white rabbits for five days. At 0.5 mg/kg, three of the five animals died, whereas only a weak decrease in body weight gain and moderate signs of toxicity occurred in rabbits receiving 0.25 mg/kg/day, and the body weight increased without signs of toxicity at 0.1 mg/kg/day. At 0.25 mg/kg/day, total liver microsomal P450 content, and the activities of aminopyrine and benzphetamine N-demethylases, pentoxyresorufin O-depentylase, glutathione S-transferases accepting 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene as substrates, were decreased. By contrast, ethylmorphine and erythromycin N-demethylases, ethoxyresorufin and methoxyresorufin O-dealkylases, aniline hydroxylase, and UDP-glucuronyltransferase accepting p-nitrophenol as substrate, were unaffected. The expression of P450 1A1, 1A2, 2A1, and 2B4, but not P450 2C3 and 3A6, were also decreased, whereas microsomal conjugated dienes, fluorescent substances, and malondialdehyde contents were increased. At 0.1 mg/kg/day, neither significant effects on drug metabolizing enzymes nor microsomal oxidative damages were obtained. Taken together, these results suggest that a short exposure time to the mycotoxin would not be associated with significant changes in the normal metabolism of xenobiotics by the liver.

Comparison of hepatic drug metabolizing enzymes in three-month-old lambs and kids.

1. The comparative activity of hepatic cytochrome P-450 monooxygenase system, glucuronyl-transferase, glutathione S-transferase and N-acetyltransferase was studied in three-month-old male and female Lacaune lambs and male Saanen kids. 2. The study of mixed-function oxidase components showed that total cytochrome P-450 ranged from 0.54 in kids to 0.85-0.88 nmol/mg-1 in lambs. Male lambs had higher levels than kids (122-165%) for aminopyrine, benzphetamine, ethylmorphine and erythromycin demethylases or benzo(a)pyrene hydroxylase whereas NADPH-cytochrome c reductase was 1.19-fold lower in lambs. 3. Sex-related changes were observed in lambs in case of microsomal benzo(a)pyrene hydroxylase activity which appeared 1.31-fold more potent in male liver. Cytosolic N-acetyltransferase accepting sulfamethazine as substrate was about 8-fold higher in female than in male lambs. 4. The analysis of samples from various liver lobes, indicated the heterogenous distribution of microsomal proteins which is related to higher concentrations of both cytochrome b5, NADPH-cytochrome c reductase and p-nitrophenol glucuronyltransferase in left lobes.