Plasma High-Density Lipoproteins and Liver Lipids and Proteins in Man

ABSTRACT. The association of high-density lipoproteins (HDL) in plasma with liver lipids and proteins was investigated in 28 subjects with diagnostic liver biopsy. Lipids and proteins were evaluated in relation to hepatic histology and microsomal enzyme induction, assessed by liver cytochrome P-450. Moderate-severe hepatic parenchymal changes were associated with low liver phospholipids, protein and cytochrome P-450, low plasma HDL cholesterol (HDL-C), and high hepatic triglycerides. Liver microsomal induction accompanying anti-convulsant therapy was associated with high liver phospholipids and protein, high plasma HDL-C, apoproteins A-I and A-II, and high HDL-C/total cholesterol (T-C) ratio. HDL-C, A-I and the HDL-C/T-C ratio were directly proportional to liver phospholipids, protein and cytochrome P-450, inversely related to hepatic triglycerides. Increases in hepatic phospholipids and protein, characteristic of microsomal induction, may lead to the elevation of plasma HDL apoprotein and HDL-C levels and HDL-C/T-C ratios, and thus reduce the risk of coronary heart disease.     

Lipoproteins and plasma cholesterol esterification in normal and diabetic subjects

Serum lipoproteins, separated by preparative ultracentrifugation and the activity of the plasma enzyme lecithin: cholesterol acyltransferase (LCAT) have been measured in insulin-dependent diabetics, non-insulin-dependent diabetics and in age-matched non-diabetic controls. In the insulin-dependent diabetics, mean total serum cholesterol and high density lipoprotein cholesterol (HDL-C) concentrations were significantly higher than in controls. Non-insulin-dependent diabetics had significantly raised total triglycerides and cholesterol, but HDL-C levels were essentially normal. The increased low density lipoprotein cholesterol (LDL-C) in both diabetic groups was statistically significant in men. A methodological study of HDL separation techniques was carried out to facilitate interpretation of these findings. Mean LCAT activity, by a method reflecting combined enzyme and substrate effects was significantly increased in these diabetic groups. The results confirm recent reports of a raised HDL-C in those insulin-dependent diabetics who are prone to coronary heart disease.     

Hypoglycemic activity of Hemidesmus indicus R. Br. on streptozotocin-induced diabetic rats

OBJECTIVE:

To evaluate the antidiabetic activity of an aqueous extract of the roots of Hemidesmus indicus on blood glucose, serum electrolytes, serum marker enzymes, liver microsomal P-450 enzymes, and lipid peroxidation in the liver and kidney of streptozotocin-induced diabetic rats.

MATERIALS AND METHODS:

Effect of H. indicus extract on blood glucose was studied with fed, fasted and glucose-loaded diabetic and nondiabetic rat models. The effect of the extract on serum electrolytes, serum levels of key glucose metabolizing enzymes, hepatic microsomal protein and hepatic cytochrome P-450-dependent mono-oxygenase enzyme systems and lipid peroxidation in the liver and kidney of diabetic rats. One way analysis of variance and Duncan''s multiple range test was used for statistical analysis.

RESULTS:

Oral administration of H. indicus aqueous extract to fed, fasted and glucose-loaded diabetic rats decreased blood glucose level significantly at 5 h and restored serum electrolytes, glycolytic enzymes and hepatic cytochrome P-450-dependent enzyme systems by preventing the formation of liver and kidney lipid peroxides at the end of 12 weeks of the study period.

CONCLUSION:

From the studies, it can be concluded that the aqueous extract of the roots of H. indicus at a dosage of 500 mg/kg/day exhibits significant antidiabetic activity. It restores the concentrations of electrolytes, glucose metabolizing enzymes, hepatic microsomal protein and hepatic cytochrome P-450-dependent mono-oxygenase enzyme systems to near normal level and also corrects the related metabolic alterations in experimentally induced diabetic rats. H. indicus administration also decreased liver and kidney lipid peroxidation products. On the basis of our findings, H. indicus could be used as an antidiabetic and antioxidant agent for the prevention and treatment of diabetes mellitus.     

Cobalt Induction of Hepatic Heme Oxygenase; with Evidence That Cytochrome P-450 Is Not Essential for This Enzyme Activity

Treatment of rats in vivo with cobalt chloride stimulated heme oxidation by hepatic microsomes to levels up to 800% above controls. This treatment also caused increases in liver weight and in total microsomal protein; in contrast, marked decreases were produced in microsomal oxidation of ethylmorphine (80%), and in cytochrome P-450 (60-70%) and heme (30-50%) contents. Cobalt chloride treatment did not affect heme oxidation by the spleen heme oxygenase system.The rate of heme oxidation by hepatic microsomal enzymes and the microsomal content of cytochrome P-450 were found to be unrelated. This conclusion was reached from studies in which microsomal heme oxygenase activity from cobalt-treated animals could be increased by 900% above control levels in the same microsomal preparation in which cytochrome P-450 content was decreased to spectrally unmeasurable amounts after incubation with 4 M urea. The same treatment eliminated ehtylmorphine demethylation and decreased microsomal NADPH-cytochrome c reductase (EC 1.6.2.4) activity by 75%.It is concluded that (i) the hepatic microsomal enzyme system that oxidizes heme compounds is not the same as that which metabolizes drugs, (ii) cytochrome P-450 is not essential for the oxidation of heme by liver cells, (iii) there is no direct relationship between the rate of heme oxidation and the level of NADPH-cytochrome c reductase activity, and (iv) the oxidation of heme is protein-dependent and the active proteins are inducible, but are different from those involved in drug metabolism.     

Effect of portal arterialization on hepatic cytochrome P-450 in rats with portacaval shunt.

Fractional clearance of colloidal gold particles (k), liver weight and hepatic cytochrome P-450 were measured in rats with portacaval shunt and in rats with portacaval shunt plus arterialization of the hepatic stump of the portal vein. The effects of enzyme induction by phenobarbital was studied in both groups. Total arterialization of the liver provides a probably normal hepatic blood flow and seems to protect the liver from post-shunt atrophy. Nevertheless, in both arterialized and shunted rats, the cytochrome P-450 concentration was significantly lower than in controls. The same results were obtained after treatment by phenobarbital. These findings suggest that normal hepatic blood flow and oxygen supply are not the main determinant of a normal activity of the hepatic microsomal biotransformation system. Substances present in portal blood would probably be necessary in maintaining hepatic cytochrome P-450 level.     

17 beta-estradiol 2- and 4-hydroxylation catalyzed by rat hepatic cytochrome P-450: roles of individual forms, inductive effects, developmental patterns, and alterations by gonadectomy and hormone replacement

The participation of rat hepatic P-450 in the conversion of 17 beta-estradiol to catechol estrogens was examined by means of enzyme reconstitution and immunoinhibition studies. It was thus demonstrated that three rat liver microsomal cytochrome P-450 forms, designated P-450UT-A, P-450PCN-E, and P-450ISF-G, each contribute to the 2- and 4-hydroxylation of 17 beta-estradiol catalyzed by hepatic microsomal preparations. Two of these enzymes, P-450UT-A and P-450PCN-E, are expressed constitutively, are male-specific, and are regulated by testosterone as well as influenced by the administration of various chemicals. Consistent with these observations, 17 beta-estradiol 2- and 4-hydroxylation activities both increased rapidly during puberty in male rats and were induced by treatment of rats with phenobarbital or pregnenolone 16 alpha-carbonitrile. Castration of male rats at birth or at 5 weeks of age suppressed the levels of 17 beta-estradiol 2- and 4-hydroxylase activities measured at 10 weeks of age. This suppression of activity was reversed upon administration of testosterone during the neonatal period (days 1 and 3 of life) or by capsule implantation at 5 weeks of age. These patterns of 17 beta-estradiol 2- and 4-hydroxylation are discussed in terms of the previously characterized response of the multiple rat hepatic P-450 forms to ontogenic, hormonal, and xenobiotic factors.     

Identification of heme oxygenase and cytochrome P-450 in the rabbit heart

The regulation of cardiac heme oxygenase and cytochrome P-450 mixed function oxidase was studied in the rabbit heart. Heme oxygenase activity is found in ventricular and atrial microsomal fractions. This activity is NADPH dependent, and is inhibited by tin and zinc protoporphyrin, but not by either SKF 525A or 7,8-benzoflavone. Immunologic studies of cardiac heme oxygenase demonstrate that antibodies prepared against human purified hepatic heme oxygenase recognize rabbit atrial heme oxygenase and inhibit the enzyme activity by 92%. In contrast, control immunoglobulin does not inhibit heme oxygenase activity. Further, the western blotting technique demonstrates that a similar band of protein with a molecular weight of 32,000 exists in cardiac microsomes and that no protein cross-reacts with purified hepatocyte heme oxygenase. Marked induction of atrial heme oxygenase is observed in microsomal fractions prepared from rabbits treated with cobalt chloride. Atrial microsomes possess 0.24 nmol of cytochrome P-450 as compared to 0.68 nmol/mg protein in microsomes from the liver. The levels of aryl hydrocarbon hydroxylase (AHH) activity, a cytochrome P-450-dependent enzyme, in ventricle and atrium are stimulated by a NADPH-generating system and are sensitive to 7,8-benzoflavone, and SKF 525A, known inhibitors of cytochrome P-450 mixed function oxidase. AHH activity in ventricular and atrial microsomes is 2-3% of that seen in liver microsomes whereas the P-450 content/mg protein is about 20% of that observed in the liver. AHH activity is mediated by a form of cytochrome P-450 that is inducible by 3-methylcholanthrene/beta-naphthoflavone. A possible new role of the heart cytochrome P-450 system in cardiac function is proposed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Different effects of short- and long-term dietary choline-deficiency on hepatic microsomal phospholipids and drug oxidation

Prolonged administration of a choline-deficient diet to male rats results in the development of hepatic cirrhosis and alterations in oxidative drug metabolism. The present study was designed to assess whether the changes in drug metabolism were related to the development of cirrhosis or merely to the effects of choline-deficiency on hepatic microsomal lipid composition. Male rats were given a synthetic choline-deficient diet for either 1 week (short-term) or 30 weeks (long-term), and results at each time were compared with age-matched control rats given the same diet but with supplementary choline.
After both 1 week and 30 weeks of the choline-deficient dietary regimen, the proportion of microsomal phospholipid present as phosphatidylcholine was significantly decreased, and that present as phosphatidylethanolamine was significantly increased, compared with appropriate controls. However, microsomal cholesterol content (per mg of microsomal protein) was not significantly changed at either time. Cytochrome P-450 levels and the turnover of ethylmorphine N -demethylase (enzyme activity/nmol cytochrome P-450) were significantly reduced in the cirrhotic (30 week) model whereas short-term intake of the diet did not alter the levels of cither enzyme. These findings suggest that the effects of changes in phosphatidylcholine and phosphatidylethanolamine levels in choline-deficiency cirrhosis have minimal importance with respect to changes in drug oxidation. Instead, altered regulation of specific cytochrome P-450 isozymes appears to be the principal cause of impaired oxidation.     

Hepatic Glucose-6-Phosphatase Activity in Non-Insulin Dependent Diabetics

ABSTRACT The role of glucose-6-phosphatase (G6Pase) in postreceptional glucose handling in non-insulin dependent diabetics (NIDDs) was investigated by comparing the enzyme values in diagnostic liver biopsy samples with fasting blood glucose (BG), immunoreactive insulin (IRI) and plasma antipyrine half-life (T/2). The NIDDs, treated with sulphonylureas, had elevated serum aminotransferase and alkaline phosphatase values associated with fatty liver with or without fibrosis. G6Pase activity was reduced in the NIDDs compared with subjects who had undergone gallstone surgery (p<0.001), insulin dependent diabetics (p<0.001), and age- and sex-matched non-diabetics (p<0.001). G6Pase was inversely related to BG and antipyrine T/2, but not to IRI or conventional liver function tests. Therapy with phenobarbital and medroxyprogesterone acetate, known inducers, increased G6Pase activity, shortened antipyrine T/2, reduced BG and did not alter IRI, in four NIDDs. Low liver G6Pase activity in NIDDs may hence be one factor underlying the impaired glycemic control.     

Immunofluorescent determination of the lobular distribution of a constitutive form of hepatic microsomal cytochrome P-450

We have used an immunohistochemical approach to study the lobular distribution of constitutive liver microsomal cytochrome P-450. Cytochrome P-450 isolated (10.3 nmoles per mg protein) from hepatic microsomes from untreated, mature male Sprague-Dawley rats was used to produce antisera in rabbits. The IgG fraction produced single precipitin lines of identity with liver microsomes after double immunodiffusion, precipitated 80% of the total microsomal cytochrome P-450 and inhibited three cytochrome P-450-dependent enzyme activities. By these criteria, the IgG appeared to be specific for a constitutive form (or immunochemically related family) of liver microsomal cytochrome P-450. The pattern of fluorescence after indirect immunofluorescent labeling of liver sections depended on the route of tissue preparation and the concentration of primary antibody. In frozen sections, the labeling was uniform throughout the lobule, whereas in "antigen-depleted" paraffin-embedded sections it was heaviest in the centrilobular and midzonal regions. Increasing the concentration of primary antibody to 500 micrograms per ml inhibited the centrilobular labeling in frozen sections in a concentration-dependent manner. When specific isozymes of cytochrome P-450 were induced with phenobarbital or 3-methylcholanthrene, the constitutive cytochrome P-450 was localized predominantly in the periportal region. Decreases in cytochrome P-450 in rats treated with carbon tetrachloride or 1,2-dibromo-3-chloropropane were associated with antigen loss only in necrotic cells. Regional differences in the loss of antigen in paraffin sections and the inhibition of fluorescence in frozen sections establish that the lobular distribution of constitutive hepatic microsomal cytochrome P-450 is qualitatively heterogeneous and may be altered during hepatocellular responses to chemical treatment.     

Effect of amphotericin B on hepatic cytochrome P-450 and glucose-6-phosphatase in the rat.

The effect of amphotericin B on hepatic microsomal cytochrome P-450 (P-450) concentration was measured in vitro, in vivo and ex vivo in the rat. In vitro, both amphotericin B (0-500 micrograms/ml) and its vehicle, sodium deoxycholate (0-410 micrograms/ml), caused similar dose-dependent decreases of P-450 concentrations and glucose-6-phosphatase activity. Intravenous amphotericin B (3 mg/kg) given daily for 3 days decreased antipyrine clearance from control values of 1.24 +/- 0.24 ml/min to 0.67 +/- 0.12 ml/min (p less than 0.001); whereas antipyrine clearance was unchanged by sodium deoxycholate. The P-450 concentration on the third day was reduced from 0.74 +/- 0.14 nmol/mg protein in control rats to 0.33 +/- 0.09 nmol/mg protein in rats treated with amphotericin B (p less than 0.001). Sodium deoxycholate had no effect on P-450 concentration. In contrast, amphotericin B had no effect on either antipyrine clearance or P-450 concentration following enzyme induction by phenobarbital. Amphotericin B had no effect on microsomal glucose-6-phosphatase activity in vivo. Neither amphotericin B nor sodium deoxycholate induced lipid peroxidation, measured as malondialdehyde production. These results show that amphotericin B decreases hepatic cytochrome P-450 content and function in the rat. These effects can not be observed in the enzyme induced state. Amphotericin B has no effect on glucose-6-phosphatase in vivo, the key enzyme of the gluconeogenesis, indicating selective effects on hepatic microsomal function.     

Differential inhibition of individual human liver cytochromes P-450 by cimetidine

Cimetidine binds to cytochrome P-450 and inhibits hepatic metabolism of various drugs in humans. However, cytochrome P-450 is a family of enzymes rather than a single protein, and effects of cimetidine on individual human liver cytochromes P-450 have not been previously characterized. Metabolism of selected substrates and cimetidine-binding assays have been performed using human liver microsomes, purified human liver cytochromes P-450, and cytochrome P-450 complementary DNA-expressed yeast proteins to probe interaction of cimetidine with these individual enzymes. Cimetidine (3.0 mmol/L) in incubations reduced bufuralol hydroxylase activity by 80% and strongly inhibited microsomal nifedipine oxidation (23% +/- 13% of control activity). The same concentration of cimetidine produced intermediate inhibition of cytochrome enzymes responsible for ethoxyresorufin deethylation and aniline hydroxylation (77% +/- 6% and 68% +/- 17% of activity in control microsomal incubations, respectively), but little effect on tolbutamide hydroxylation was observed. Concordantly, the calculated binding constant for the binding of cimetidine to a purified cytochrome P-450 with high tolbutamide hydroxylase activity was 4.4 mmol/L, whereas the calculated binding concentration constant for a purified cytochrome P-450-metabolizing nifedipine was 0.7 mmol/L. These studies show a high variability in the effect of cimetidine on drug metabolism by individual human liver cytochromes P-450. In vitro studies using human liver microsomes and genetically engineered human cytochromes P-450 can be very useful in exploring important clinical questions of hepatic drug metabolism.     

Treatment of liver cirrhosis with microsomal enzyme-inducing compound in the rat

The effect of therapy with a microsomal enzyme-inducing drug on the cirrhotic liver in male Wistar rats was investigated by morphological and biochemical means. The cirrhotic animals were treated with medroxyprogesterone acetate (MPA) 100 mg/kg body wt, i.p. daily for a week. In the cirrhotic rats liver weight was enhanced, liver protein content was increased while total liver DNA content remained unchanged upon MPA treatment. The hepatic regenerative nodule size increased, as determined by morphological means. Hepatic microsomal metabolic activity was improved, as seen by increases in NADPH-cytochrome P-450 reductase and aminopyrine N-demethylase activities and cytochrome P-450 content. Since the increases in liver protein content and metabolic activity were relatively greater in the cirrhotic than intact animals upon MPA treatment, it was suggested that the spontaneous regeneration associated with liver cirrhosis may affect the induction phenomenon. The results demonstrate that an enzyme inducer may have beneficial effects on the cirrhotic liver by elevating metabolic activity and parenchymal mass.     

Hepatic microsomal protein and cytochrome P-450 in BALB/c mice infected with Leishmania

The effects of infection of mice with Leishmania major on liver microsomal protein and cytochrome P-450 were examined. The levels of hepatic microsomal protein and cytochrome P-450 were monitored at 6, 7, 9 and 12 weeks post-infection. The results indicated that the amount of hepatic microsomal protein and cytochrome P-450 were unchanged throughout the course of infection with L. major, despite the high degree of parasite proliferation in Kupffer cells and marked reduction in phagocytosis. The current results clearly indicate that Leishmania-induced macrophage suppression has no inhibitory effect on hepatic microsomal protein and cytochrome P-450.     

Effects of aging and long-term caloric restriction on hepatic microsomal monooxygenases in female fischer 344 rats: Alterations in basal cytochrome P-450 catalytic activities

The effects of aging and caloric restriction on uninduced levels of hepatic microsomal cytochrome P-450s and specific P-450-related catalytic activities were evaluated in female Fischer 344 rats. Microsomes were isolated from livers of ad libitum (AL) fed rats 1, 3, 6, 16 and 26 months of age, and from calorie-restricted (CR) rats 6, 16 and 26 months of age. The recovery of microsomal protein was higher in CR than AL rats at 6, 16 and 26 months of age. Between ages 3 and 26 months there was a gradual decline in recovered microsomal P-450, but the differences between successive age categories were not significant. A different trend was observed for total cytochrome P-450 per liver. AL rats showed a 2-fold decline in P-450/liver between 6 and 26 months of age, while P-450/liver of corresponding CR rats increased 1.7-fold. Neither cytochrome b₅ nor NADPH cytochrome C reductase varied consistently as a function of increased age, with all age groups showing greater reductase activity for CR rats than for AL rats. Phenobarbital (PB) and methylcholenthrene (MC) inducible cytochrome P-450 catalytic activities (pentoxy [PROD] and ethoxy [EROD] resorufin O-deethylases) exhibited similar age-related alterations that were distinctly different from the two other enzymes examined. Both PROD and EROD showed dramatic declines in activity between 1 and 3 months of age, with a slight increase in activity at 6 months and maintenance of the activity levels through 26 months. Benzphetamine N-demethylase (BND) and aniline p-hydroxylase (APH) activities were also altered as a function of increased age, with CR rats exhibiting increased isozyme activity above that seen for aging AL rats. Calorie restriction appears to have a modulating effect, compensating for an age-related decline of hepatic microsomal monooxygenase activity in female Fischer 344 rats.     

Inhibition of rat methylbenzylnitrosamine metabolism by dietary zinc and zinc in vitro.

Methylbenzylnitrosamine is an esophageal-specific carcinogen in the rat, and the incidence of methylbenzylnitrosamine-induced esophageal carcinoma is increased by dietary zinc deficiency. Methylbenzylnitrosamine requires activation by cytochrome P-450 to be mutagenic; the present study examined the role of dietary zinc deficiency and the in vitro addition of zinc on the cytochrome P-450-dependent microsomal metabolism of methylbenzylnitrosamine. Dietary zinc deficiency significantly increased the cytochrome P-450-dependent esophageal and hepatic microsomal metabolism of methylbenzylnitrosamine. These changes occurred without alteration in the specific content of total microsomal cytochrome P-450 of the esophagus or liver. The addition of zinc in vitro, at concentrations found in normal tissues, irreversibly inhibited the esophageal and hepatic cytochrome P-450-dependent microsomal metabolism of methylbenzylnitrosamine. These results suggest that physiological levels of zinc may be an endogenous inhibitor of methylbenzylnitrosamine metabolism. Dietary zinc deficiency appears to reduce this inhibition of cytochrome P-450 activity, resulting in an increase in carcinogen activation.     

Effect of age on rat liver heme and drug metabolism

Old (24-months) rats have lower activities of hepatic delta-aminolevulinic synthase and the microsomal cytochrome P-450 monooxygenase activities--aminopyrine N-demethylase and aniline hydroxylase--as compared to young (2-months) animals. In contrast, the activity of the heme degradative enzyme, heme oxygenase, is higher in the old rats. Cytochrome P-450 and microsomal heme contents were maintained in the old. When inducibility and inhibition of these enzymes were studied, the old rats responded to the same degree as the young. These results indicate that the ability of the heme synthetic and degradative enzymes to respond to decreasing cellular heme levels is not significantly altered with age. The observations that there is a lower baseline activity of ALA-synthase and good maintenance of microsomal heme and cytochrome P-450 content, in spite of elevated heme oxygenase activity in the old, suggest that, at least in the senescent rat, hepatic heme utilization and degradation are only loosely coupled to heme production. It appears, therefore, that alternate sources of heme for cytochrome P-450 are available in the old animals. Furthermore, it is suggested that the old rat has a baseline change in ALA-synthase, heme oxygenase, and cytochrome P-450 that may be overcome under the appropriate conditions.     

Caloric restriction affects liver microsomal monooxygenases differentially in aging male rats

Caloric restriction (CR) extends life span and retards the onset of physiological changes and pathologies associated with aging, but the underlying mechanisms remain unresolved. This study demonstrates that CR postpones the documented age-related declines in and/or enhances the activity and microsomal concentration of several liver monooxygenases in male rats, i.e., NADPH cytochrome P-450 reductase, total cytochromes P-450. However, the relative concentration of cytochrome P-450b+C did not exhibit statistically significant changes, whereas another isozyme, the male specific P-450h, declined significantly in both ad libitum-fed and CR rats as a function of increasing age. While CR appears to retard age-associated changes in certain liver enzymes, this effect is by no means universal. The hepatic monooxygenases constitute a well-characterized enzyme system in which to examine the perturbation of the aging process by CR.     

Role of RNA in Induction of Hepatic Microsomal Mixed Function Oxidases

Induction of hepatic microsomal cytochrome P-450 and ethylmorphine N-demethylase activity by phenobarbital requires de novo synthesis of mRNA. Inhibition of RNA synthesis by alpha-amanitin given up to 8 hr after phenobarbital administration substantially inhibits this induction. However, beyond 8 hr after phenobarbital administration, RNA synthesis is not required for induction of these hepatic microsomal systems. Thus, mRNAs for cytochrome P-450 and ethylmorphine N-demethylase appear to be stable. Furthermore, these experiments reveal that the lag period for RNA synthesis approximates the length of the lag period for induction of the hepatic microsomal enzyme systems.     

Studies of the hepatic mitochondrial and microsomal mixed-function oxidase system during Plasmodium yoelii infection and inducer treatment in Swiss albino mice

Plasmodium yoelii infection resulted in depression of hepatic mitochondrial and microsomal mixed-function oxidase system indices, e.g. cytochrome P-450, cytochrome b5 and phase II detoxification enzyme glutathione-S-transferase, while heam and haemozoin registered a marked increase in Swiss albino mice. Phenobarbitone (inducer) treatment showed induced levels of hepatic mitochondrial and microsomal cytochrome P-450 and glutathione-S-transferase in normal as well as in infected mice. The induced cytochrome P-450 and glutathione-S-transferase activities were similar in normal and infected mice. The findings were further supported by the isoenzymic profile and drug-binding properties of the terminal monoxygenase, cytochrome P-450.