Effects of picloram on xenobiotic biotransformation in rat liver

1. The effect of picloram on model xenobiotic substrate biotransformation in vivo was studied in female and male rat liver.

2. Treatment with picloram had little effect on epoxide hydratase and glutathione S-transferase activity, but caused a dose-dependent increase in ethoxyresorufin-O-deethylase activity and a concomitant decrease in aldrin epoxidase activity in male rats.

3. Treatment of male rats with equivalent doses of 2-acetylaminofluorene, 2-amino-anthracene and picloram induced ethoxyresorufin-O-deethylase activity to the same degree.

4. Treatment of female rats with picloram resulted in dose-dependent increases in ethoxyresorufin and ethoxycoumarin-O-deethylation without decreasing aldrin epoxidase activity.

5. Picloram binds to liver microsomal preparations from rats pretreated with phenobarbitone and/or 3-methylcholanthrene, giving a type I spectrum.

6. The results indicate that picloram is a 3-methylcholanthrene-type inducer, and the implications are discussed.     

Effects of mutagenic and non-mutagenic aniline derivatives on rat liver drug-metabolizing enzymes

1. The effect of 4,4'-methylene bis(2-chloroaniline) (MOCA), 4,4'-methylene dianiline (MDA) and 4,4'-sulphonyldianiline (Dapsone) in vivo on xenobiotic biotransformation in male rat liver was studied. 2. Treatment with MOCA or MDA but not Dapsone caused a dose-dependent increase in ethoxyresorufin O-deethylase activity and a concomitant decrease in aldrin epoxidase activity in male rats. 3. Treatment with MOCA or MDA resulted in dose-dependent increases in ethoxycoumarin O-deethylation and epoxide hydrolation, while only MOCA induced cytosolic glutathione S-transferase activity. 4. Treatment with Dapsone resulted in no changes in xenobiotic biotransformation except for the induction of aniline hydroxylation. 5. The results are consistent with the contention that there is a relationship between carcinogenic chemicals and particular alterations in the activities of biotransformation enzymes.     

Effects of mutagenic and non-mutagenic aniline derivatives on rat liver drug-metabolizing enzymes

1. The effect of 4,4′-methylene bis(2-chloroaniline)(MOCA), 4,4′-methylene dianiline (MDA) and 4,4′-sulphonyldianiline (Dapsone) in vivo on xenobiotic biotransformation in male rat liver was studied.

2. Treatment with MOCA or MDA but not Dapsone caused a dose-dependent increase in ethoxyresorufin O-deethylase activity and a concomitant decrease in aldrin epoxidase activity in male rats.

3. Treatment with MOCA or MDA resulted in dose-dependent increases in ethoxy-coumarin O-deethylation and epoxide hydrolation, while only MOCA induced cytosolic glutathione S-transferase activity.

4. Treatment with Dapsone resulted in no changes in xenobiotic biotransformation except for the induction of aniline hydroxylation.

5. The results are consistent with the contention that there is a relationship between carcinogenic chemicals and particular alterations in the activities of biotransformation enzymes.     

Differences in the biochemical properties of aldrin epoxidase, a cytochrome P-450-dependent monooxygenase, in various tissues

Aldrin epoxidase, a cytochrome P-450-dependent monooxygenase, was studied in the lung and kidney of male rats. The sensitivity of the liver enzyme activity to different chemicals in vitro was influenced by the treatment of the animals with phenobarbital or methylcholanthrene. These results confirm that more than one form of cytochrome P-450 supports aldrin epoxidase in the liver. The lung and kidney aldrin epoxidase activity was not modified by the administration of chemical inducers to the rats. In vitro, the lung and kidney aldrin epoxidase activities were activated by tetrahydrofurane and progesterone, respectively. The results obtained from the lung and kidney indicate that one single species of cytochrome P-450, associated with aldrin epoxidase, exists in these organs, but it may be a different type, or regulated in a different manner in these tissues.     

Rat liver cytochrome P-450 isozymes as catalysts of aldrin epoxidation in reconstituted monooxygenase systems and microsomes

To explore which rat liver cytochrome P-450 species are involved in aldrin epoxidation, we have studied the catalytic activities of a series of cytochrome P-450 isozymes purified from untreated and inducer-treated Sprague-Dawley rats. Of ten cytochrome P-450 forms analyzed, seven isozymes, listed in order of decreasing activity, catalyzed aldrin epoxidation: P-450UT-A, P-450PB-C, P-450UT-H, P-450PB-B, P-450PCN-E, P-450UT-F, and P-450PB-D. P-450UT-I, P-450BNF-B, and P-450ISF-G were not very active at all. A novel aldrin metabolite, endo-dieldrin, was formed by cytochrome P-450UT-F in a 6-fold excess over dieldrin, which is the exo-isomer. The activity of aldrin epoxidase furthermore was assayed in liver microsomes from Sprague-Dawley rats of diverse physiological status and after pretreatment with various inducers resulting in a peculiar pattern of cytochrome P-450 isozymes. Untreated animals, at an age of 3 weeks, showed similar enzyme activities in both genders. During maturation, the activity of males increased by 3-fold, while the activity in females did not significantly change during this period. Pretreatment with pregnenolone-16-alpha-carbonitrile or dexamethasone strongly increased the activity in females. Pretreatment with dexamethasone did not increase the activity of males. A 50% depression of epoxidase activity was noted for males pretreated with 5,6-benzoflavone. Phenobarbital pretreatment increased the activity of females by 12-fold and of males by 2-fold. Males responded to pretreatment with polychlorinated biphenyls in a strain dependent fashion: enzyme activity was increased 2-fold in Sprague-Dawley rats but was not altered in Wistar rats. "Theoretical" values of microsomal epoxidase activity were calculated for weanling and adult Sprague-Dawley rats from turnover numbers and published data on the relative abundance of aldrin epoxidizing P-450 isozymes (Waxmann et al., Biochemistry 24, 4409, 1985). These values agreed with the activities determined. A similar statement can be made for male rats of both strains pretreated with inducers, when the ratio of enzyme activity of pretreated to control animals was used as a basis of comparison. The activity ratio of females pretreated with pregnenolone-16-alpha-carbonitrile, dexamethasone and phenobarbital, however, was much higher than the ratio calculated. Our results reveal that aldrin epoxidation is a reaction indicative of male specific and of phenobarbital-inducible cytochrome P-450 isozymes in rat liver.(ABSTRACT TRUNCATED AT 400 WORDS)     

The profile of rat liver enzyme induction produced by prochloraz and its major metabolites.

1. The profile of the hepatic mixed-function oxidase system of male rats has been examined following treatment with prochloraz (I) and three of its major metabolites (II, III and IV). 2. The overall induction profile of prochloraz reflected the contribution of the individual metabolites. There was a slight increase of lauric acid hydroxylase, but by far the major induction was seen in the activity of aldrin epoxidase and 7-pentoxyresorufin-O-dealkylase (7- and 14-fold respectively). 3. N-Propyl-N-[2-(2,4,6-trichlorophenoxy)ethyl]urea (II), a primary intermediate in the metabolism of prochloraz, was a phenobarbitone-type inducer, increasing the activity of aldrin epoxidase and 7-pentoxyresorufin-O-dealkylase by 120% and 8-fold respectively. 4. The prochloraz metabolites, trichlorophenoxyethanol (III) and trichlorophenoxyacetic acid (IV) were both inducers of the clofibrate type, increasing the activity of lauric acid 12-hydroxylase. 5. The induction profile of prochloraz was of a mixed type, but the predominant characteristics were those of phenobarbitone induction.     

Role of the pituitary and neonatal androgenic imprinting in the hormonal regulation of liver alcohol dehydrogenase activity

Liver alcohol dehydrogenase activity is increased by thyroidectomy, orchidectomy, or hypophysectomy. We investigated the mechanisms of these hormonal effects by examining the effects of testosterone, dexamethasone and thyroid hormone on liver alcohol dehydrogenase activity in hypophysectomized rats and in cultured hepatocytes, and the effect of administration of androgens to neonatal female rats. Testosterone did not lower alcohol dehydrogenase activity in hypophysectomized rats, whereas dexamethasone and thyroxine produced moderate decreases in activity. Triiodothyronine reduced alcohol dehydrogenase activity of cultured hepatocytes from male and hypothyroid female rats in a dose-dependent fashion, confirming that thyroid hormone had pituitary-independent effects on the enzyme activity. Dexamethasone was required for the expression of alcohol dehydrogenase activity in cultured cells, and it increased the enzyme activity when present at supraphysiologic concentrations. Treatment of neonatal female rats with testosterone reduced the activity of the enzyme in adulthood. The difference in alcohol dehydrogenase activity in adult male and female rats appears to be determined in part by neonatal imprinting by androgens and in part by an effect of testosterone that is either mediated by or dependent upon the pituitary. Thyroid hormone reduces alcohol dehydrogenase activity by a direct effect on the liver.     

Phase I and phase II xenobiotic biotransformation in cultures and co-cultures of adult rat hepatocytes

The aim of this study was to measure the activity of phase I and II key enzymes in the biotransformation of xenobiotics and their inducibility by phenobarbital (2 mM) in two currently used in vitro models, namely adult rat hepatocytes, conventionally cultured or co-cultured with rat epithelial cells derived from primitive biliary duct cells. For phase I, the cytochrome P450 content and the enzymic activities of 7-ethoxycoumarin O-deethylase and aldrin epoxidase have been determined, for phase II glutathione S-transferase activity was measured. In conventional cultures, all phase I parameters investigated declined continuously as a function of culture time. Two mM phenobarbital had inducing effects on 7-ethoxycoumarin O-deethylase and glutathione S-transferases but not on aldrin epoxidase. In co-cultures, after an initial decrease, a steady state situation developed for all the parameters measured, lasting for at least 10 days. The cytochrome P450 content, the 7-ethoxycoumarin O-deethylase, aldrin epoxidase and glutathione S-transferase activities were maintained from 3 to 4 days on at 25, 100, 15 and 50%, respectively, of their corresponding value obtained for freshly isolated hepatocytes. After phenobarbital treatment, the parameters mentioned were significantly increased with the exception of the aldrin epoxidase activity of which the inducibility was nearly completely lost.     

Evidence for a PCN-P450 enzyme in chickens and comparison of its development with that of other phenobarbital-inducible forms

Of four monoclonal antibodies to purified rat liver cytochrome P450s, including those from 3-methylcholanthrene-, phenobarbital-, ethanol-, and pregnenolone-16-alpha-carbonitrile-treated rats, only the monoclonal antibody against pregnenolone-16-alpha-carbonitrile-inducible P450 immunodetected proteins in chicken liver microsomes after blotting from sodium dodecyl sulfate-polyacrylamide gels. This protein migrated identically with the pregnenolone-16-alpha-carbonitrile-inducible P450 detected in microsomes from dexamethasone-treated rats. It was most predominant in liver microsomes from chickens at 1 day posthatching, whereas much lower levels were observed in the embryo and at 36 days posthatch. Phenobarbital and dexamethasone were both effective inducers of this protein. The developmental profile and induction by phenobarbital and dexamethasone of several cytochrome P450-associated catalytic activities were compared with those of the immunodetected protein. Chicken liver microsomal erythromycin demethylase, a characteristic activity of rat pregnenolone-16-alpha-carbonitrile-inducible P450, was similar in developmental profile and induction to the immunodetected protein, with a high degree of augmentation at 1 day posthatch compared with that in the embryo and at 36 days posthatch; aldrin epoxidase, benzphetamine demethylase, ethylmorphine demethylase, and aminopyrine demethylase were more similar to each other in development and induction and were less well correlated with the immunodetected protein. This evidence suggests the presence in chicken liver of at least two types of P450, one a form related to the pregnenolone-16-alpha-carbonitrile-inducible P450 family. All of the catalytic activities were induced after pretreatment of chickens with phenobarbital but aldrin epoxidase was most effectively induced. Aldrin epoxidase was also detected in microsomes from untreated embryos as early as 7 days of incubation. Erythromycin demethylase was the only catalytic activity induced by dexamethasone. There was a trend of increased specific activity toward all the substances after hatching, indicating a more efficient P450 system, possibly due to a sharp increase in some isozymes, including the form from the pregnenolone-16-alpha-carbonitrile-inducible P450 family. This evidence for a pregnenolone-16-alpha-carbonitrile-inducible P450 in chickens agrees with sequence information that suggests the early evolution of this form and demonstrates the suitability of the chicken for studies of P450 evolution.     

Rat hepatic microsomal enzyme induction by pretreatment with toxaphene and toxaphene fractions

The levels of hepatic microsomal induction caused by toxaphene were determined. Young Sprague-Dawley rats (70 g) were administered toxaphene (ip injection, daily for 5 d) at 0, 5, 25, and 100 mg/kg. All doses caused increases in liver/body weight ratio, cytochrome P-450 level, aminopyrine demethylation, and aldrin epoxidation. The aldrin epoxidase activity increased almost 700% at the 100-mg/kg dose. Toxaphene was separated into nonpolar (S-A) and polar (S-B) fractions and administered as before at 25 mg/kg. All treatments caused significant increases in cytochrome P-450, aminopyrine demethylation, and aldrin epoxidation. A comparison of the treatments, however, did not reveal any significant differences between the treatments.     

Organic solvents as modifiers of aldrin epoxidase in reconstituted monooxygenase systems and in microsomes

To examine the response of individual cytochrome P-450 species catalysing the epoxidation of aldrin (Wolff T and Guengerich FP, Biochem Pharmacol 36: 2581-2588, 1987), monooxygenase systems reconstituted from these species were assayed in the presence of 5% (v/v) = 0.87 M ethanol. The activity of cytochromes P-450PB-B and P-450PB-D, two enzymes inducible by phenobarbital was increased seven-fold. The activity of two other P-450 enzymes purified from these animals was either inhibited by 50%, as observed for cytochrome P-450PB-C or remained unchanged, as noted with cytochrome P-450PCN-E. Two P-450 enzymes purified from untreated rats, cytochromes P-450UT-F and P-450UT-H, showed an inhibition by 50 and 20%, respectively, while the activity of cytochrome P-450UT-A was slightly increased by 50%. Indirect evidence that solvents enhance aldrin epoxidation by interacting with the hemoprotein was obtained by the finding that ethanol stimulated the activity of cytochrome P-450PB-B already, before addition of the lipid component, L-alpha-1,2-dilauroyl-sn-glycero-3-phosphocholine. The Km of cytochrome P-450PB-B for NADPH cytochrome P-450 reductase was not altered by ethanol indicating that the interaction between the two enzymes was not affected by the solvent. Other results indicate that the stimulatory solvent binds to a site, apart from the type I or type II binding site. The potency of various hydrophylic solvents to modify aldrin epoxidase activity was assayed in microsomes of rats pretreated with phenobarbital and of untreated male rats. Ethanol, n-propranol, n-butanol, acetone and tetrahydrofuran enhanced enzyme activity of phenobarbital pretreated rats to a maximal extent of two-fold and, at similar concentrations, inhibited the enzyme activity of untreated rats by 50%. The potency of these solvents correlated with their lipophilicity. Methanol and dimethylsulfoxide only slightly modified the activity of induced and noninduced animals. In the presence of 0.5 M n-propranol as the modifying agent, microsomal epoxidase activity of rats pretreated with pregnenolone-16 alpha-carbonitrile, dexamethasone, 3-methylcholanthrene and of control rats was inhibited by 60-80%, whereas the activity of animals pretreated with phenobarbital, DDT, or the polychlorinated biphenyl mixture, Clophen A 50, was stimulated between two- and three-fold. The results reveal that organic solvents frequently used to dissolve monooxygenase substrates may considerably modify the activity of cytochrome P-450 dependent reactions, in particular when purified enzymes are assayed.     

Aldrin-induced stimulation of locomotor activity and brain regional glutamate.

Single administration of aldrin (2-10 mg/kg) to adult male albino rats (120-130 g) enhanced locomotor activity (LA), with the maximum effect reached 2 h after treatment. The measurement of steady state levels of glutamate, glutamine and the activities of their metabolizing enzymes in different regions of the brains of rats treated with aldrin under its nontolerant condition showed that aldrin enhanced the activity of the neuronal glutamate system in the cerebral cortex, cerebellum and hypothalamus. Moreover, treatment with the glutamatergic NMDA receptor antagonist D,L-2-amino-7-phosphonoheptanoic acid, in the absence and presence of aldrin, reduced the LA of control rats and attenuated the aldrin-induced increase in LA of treated rats. These results suggest that aldrin-induced activation of the central glutamate system may be a cause of stimulation of LA with aldrin under its nontolerant condition.     

The effects of twenty-two organochlorine pesticides as inducers of the hepatic drug-metabolizing enzymes

The effects of 22 organohalogen pesticides as inducers of hepatic drug-metabolizing enzymes in the immature male Wistar rat have been determined, this group includes four isomeric hexachlorocyclohexanes, technical chlordane, alpha-chlordane, gamma-chlordane, oxychlordane, trans-nonachlor, heptachlor, heptachlor epoxide, aldrin, dieldrin, kepone, toxaphene, mirex, hexachlorobenzene (HCB) and several DDT analogs. With the exception of HCB, all of the pesticides induced microsomal dimethylaminoantipyrine, N-demethylase and aldrin epoxidase activities and the cytochrome P-450 content of microsomes from animals pretreated with most of the compounds was also increased compared to control rats. These pesticides all resembled phenobarbitone in their mode of induction. The effects of HCB as a microsomal enzyme inducer resembled those observed after coadministration of phenobarbitone plus 3-methylcholanthrene.     

Dietary toxicity of picloram herbicide in rats

The toxicity of orally administered technical-grade picloram was evaluated in male and female Fischer 344 rats. Dietary dose levels were up to 2000 mg/kg body weight (bw) X d for 2 wk, 500 mg/kg bw X d for 13 wk, or 200 mg/kg bw X d for 12 mo. Routine indices of toxicity were evaluated at all of the respective time periods. Body weight, food consumption, clinical chemistries, urinalyses, and hematological determinations were considered unaffected by treatment. The only treatment-related effect, regardless of the duration of exposure, was in the liver of both male and female rats. This was generally manifested as an increase in the liver-to-body weight ratio and slight hypertrophy and pallor of the centrilobular hepatocytes. These effects were consistently present in rats receiving 1000 mg/kg bw X d for 2 wk, 300 mg/kg bw X d for 13 wk, or 200 mg/kg bw X d for 6 or 12 mo. Similar effects were marginally evident for rats receiving 500 mg/kg bw X d for 2 wk, 150 mg/kg bw X d for 13 wk, or 60 mg/kg bw X d for 6 or 12 mo. At 60 mg/kg bw X d, the effects were not progressive from 6 to 12 mo. The no-observable-effect level (NOEL) was 20 mg/kg bw X d for male and female rats fed picloram for 12 mo.     

Sex-related effect of hemin on cytochrome P450 and drug-metabolizing enzymes in rat liver

We examined the effect of hemin on rat hepatic microsomal cytochrome P450 (P450) and its molecular species (P450 2E1, 3A2, 2C11 and 2C12) under the induction of heme oxygenase activity in male and female rats. Hemin produced an inverse relationship between the induction of heme oxygenase activity and the decrease of P450 content in a dose-dependent manner. A time course study revealed that hemin produced a significant decrease in total P450 content in male rats to about 37% that of the controls at 24 hr after its administration. Western and Northern blot analyses revealed that the increase in both heme oxygenase-1 (HO-1) protein and HO-1 mRNA reached a maximum at 24 hr and returned to control levels within 120 hr in both sexes. With respect to P450-dependent monooxygenase activities, we found that there was a significant decrease of aniline p-hydroxylase activity to about 30% of the control animals, but not in erythromycin N-demethylase activity at various time intervals. Immunoblot analysis revealed that P450 2E1 in male rat liver was dramatically decreased at 24 hr to about 20% of the controls, but not P450 3A2. Parallel to the decrease of androstenedione 16 alpha-hydroxylase activity, there was a marked decrease of P450 2C11 or 2C12 in male or female rats, respectively, at 72 hr after the treatment; however, hemin did not decrease androstenedione 16 alpha-hydroxylase activity in phenobarbital-pretreated rat liver. These findings suggest that hemin predominantly affects constitutively expressed isozymes rather than inducible P450 species in rat liver.     

A mode of action for induction of liver tumors by Pyrethrins in the rat

High doses of Pyrethrins produce liver tumors in female rats. To elucidate the mode of action for tumor formation, the hepatic effects of Pyrethrins have been investigated. Male Sprague-Dawley CD rats were fed diets containing 0 (control) and 8000 ppm Pyrethrins and female rats' diets containing 0, 100, 3000 and 8000 ppm Pyrethrins for periods of 7, 14 and 42 days and 42 days followed by 42 days of reversal. As a positive control, rats were also fed diets containing 1200-1558 ppm sodium Phenobarbital (NaPB) for 7 and 14 days. The treatment of male rats with 8000 ppm Pyrethrins, female rats with 3000 and 8000 ppm Pyrethrins and both sexes with NaPB resulted in increased liver weights, which were associated with hepatocyte hypertrophy. Hepatocyte replicative DNA synthesis was also increased by treatment with Pyrethrins and NaPB. The treatment of male and female rats with Pyrethrins and NaPB produced significant increases in hepatic microsomal cytochrome P450 (CYP) content and a marked induction of CYP2B-dependent 7-pentoxyresorufin O-depentylase and testosterone 16beta-hydroxylase activities. Significant increases were also observed in CYP3A-dependent testosterone 6beta-hydroxylase activity. The hepatic effects of Pyrethrins were dose-dependent in female rats with 100 ppm being a no effect level and on cessation of treatment were reversible in both sexes. This study demonstrates that Pyrethrins are mitogenic CYP2B form inducers in rat liver. The mode of action for Pyrethrins-induced rat liver tumor formation appears to be similar to that of NaPB and some other non-genotoxic CYP2B inducers of hepatic xenobiotic metabolism.     

Identification of the hepatic cytochrome P-450 isozymes induced and decreased by picloram

Microsomes from male rats treated with picloram (100 mg/kg/day) for 7 days showed a 48% decrease in 16 alpha-hydroxylase activity when incubated with (4-14C) androstenedione. These data are consistent with the assertion that picloram decreases the titer of hepatic male specific cytochrome P-450h. Several lines of evidence suggested that picloram is an inducer of hepatic cytochrome P-450 in male rats. First, SDS polyacrylamide gel electrophoresis revealed an intensified hepatic microsomal polypeptide (MW 54,000) following picloram pretreatment. This polypeptide co-migrated with protein bands which were correspondingly intensified after pretreatment with known inducers of cytochrome P-450d (3-methylcholanthrene and isosafrole). Second, no increase in the binding of metyrapone to picloram treated microsomes was noted compared with controls, suggesting no increase in phenobarbital-inducible forms of cytochrome P-450. Third, hepatic microsomes from picloram treated rats activated 2-amino-3-methylimidazo [4,5-f] quinoline (a cytochrome P-450d mediated catalysis) causing a 5-fold increase in the number of induced Salmonella typhimurium TA98 revertant colonies formed compared with control microsomes. Fourth, the binding of n-octylamine to hepatic microsomes from picloram-treated rats showed, like microsomes from 3-methylcholanthrene-treated rats, an increase in the proportion of high-spin cytochrome P-450 present. Cytochrome P-450d is known to be a high spin haemoprotein.     

Acute, 14-Day Repeated Dosing, and 90-Day Subchronic Toxicity Studies of Potassium Picloram

Acute, 14-Day Repeated Dosing, and 90-Day Subchronic ToxicityStudies of Potassium Picloram. HAYES, J.R., CONDIE, L.W., ANDBORZELLECA, J.F. (1986). Fundam. Appl. Toxicol. 7,464-470. Potassiumpicloram was administered either by gavage (acute studies) orin drinking water to male and female Sprague-Dawley-derivedrats (14-day and 90-day studies). The acute oral LD50 was 950mg/kg (812-1120) for males and 686 mg/kg (599-786) for females.Depression, prostration, ataxia, tremors, and convulsions precededdeath. There were no consistent biologically significant compound-relatedeffects in rats that received 60, 190, or 600 mg potassium picloram/kg/dayfor 14 days. In the subchronic study, rats received 60, 190,600, or 1070 mg potassium picloram/kg/day in drinking waterfor 90 consecutive days. There were only 4 male and 2 femalesurvivors out of 20 rats of each sex at the 1070 mg/kg doseand 16 male and 18 female survivors at the 600 mg/kg dose. Mortalitywas dose dependent. Administration of picloram appeared to exacerbaterenal and hepatic lesions commonly noted in rats of this age.For example, at levels up to 1070 mg/kg mild lesions in thekidney of treated rats, especially in males at 600 mg/kg, werenoted. Also noted were an increased incidence of mononuclearliver foci in male rats that received 190 and 600 mg/kg andan increased severity of mononuclear liver foci in females thatreceived 600 mg/kg. There were no other consistent biologicallysignificant compound-related effects. No specific organ sitetoxicity could be identified in these studies. Toxicity fromexposure to picloram in drinking water is apparently low.     

The inducing and inhibiting effects of sodium valproate in vivo on the biotransformation systems of xenobiotics in isolated rat hepatocytes

1. The induction and inhibition of some biotransformation enzymes by valproate have been studied in hepatocytes isolated from rats treated with sodium valproate either i.p. or by subcutaneous implantation of osmotic pumps. 2. When valproate was given i.p., the cytochromes P-450 and b5, and aldrin epoxidase and glutathione S-transferase activities were significantly induced. 3. In contrast, valproate administered by osmotic pumps induced 7-ethoxycoumarin-O-deethylase activity, whereas aldrin expoxidase and glutathione S-transferase activities were significantly inhibited. At a valproate serum concentration of about 100 micrograms/ml for 2 weeks a significant induction of the cytochromes P-450 and b5 was observed. 4. Since there is a large difference between the half-lives of valproate in man and rodent, constant-rate delivery of valproate represents a better model for induction studies than i.p. injection.     

Modulation of hepatic CYP2A1, CYP2C11, and CYP3A9 expression in adult rats by neonatal administration of tamoxifen.

To examine the effect of neonatal administration of tamoxifen on adult expression of hepatic cytochrome P-450 (CYP) enzymes and steroid 5alpha-reductase, male and female Sprague-Dawley rats were injected s.c. with tamoxifen (20 microg) or peanut oil (control) once daily at days 1 to 5 of age and sacrificed at 3 months of age. Neonatal tamoxifen treatment did not affect b.wt. or liver weight of adult male and female rats, but decreased testicular weight by approximately 40% in adult male rats. Neonatal administration of tamoxifen decreased hepatic microsomal testosterone 6beta- and 7alpha-hydroxylase activities in adult female rats whereas it did not alter steroid 5alpha-reductase activity. The same treatment increased testosterone 7alpha-hydroxylase activity, but did not affect testosterone 6beta-hydroxylase or steroid 5alpha-reductase activity in adult male rats. Immunoblot analysis indicated that neonatal tamoxifen treatment decreased CYP2C11 protein level by 26% and increased CYP2A1 protein content by 2.6-fold in adult male rats, whereas it had no effect on CYP3A or CYP2B protein expression. The reduction in the CYP3A-mediated testosterone 6beta-hydroxylase activity in adult female rats was accompanied by a decrease in CYP3A9 mRNA expression. Analysis of serum hormone levels indicated that neonatal exposure to tamoxifen resulted in a decrease in serum 17beta-estradiol concentration in adult female rats, whereas it did not alter serum testosterone concentration in adult male rats. In summary, treatment of neonatal rats with tamoxifen produced a long-lasting effect on hepatic CYP2A1, CYP2C11, and CYP3A9 expression in addition to testicular weight and serum 17beta-estradiol concentration.