Effect of steroid hormone treatment on aryl hydrocarbon hydroxylase activity in the Syrian hamster kidney

Aryl hydrocarbon hydroxylase (AHH) activity was determined in castrate and intact male Syrian hamster kidney and liver microsomes following in vivo treatment with either diethylstilbestrol (DES) or 17β-estradiol as well as other steroid hormones. After 1 month of estrogen treatment, there was a 5-fold decline in AHH activity in castrated hamster kidneys compared with untreated castrate levels. the amount of AHH activity in the kidney was depressed more than 75% of untreated castrate levels even after the estrogen had been withdrawn for 6 days. Consistent with a nearly 2.5-fold higher renal AHH activity observed in intact male hamsters compared to castrates was the finding of a 1.7-fold elevation in the activity of this enzyme after treatment of castrated animals with androgen[5α-dihydrotestrosterone (5α-DHT)] for 1 month. Moreover, following withdrawal of estrogen from intact hamsters, the increase in AHH activity in the kidney essentially paralleled the rise in serum testosterone levels. In castrated animals, the depression of AHH activity by estrogen was partially reversed by concomitant 5α-DHT treatment. However, no appreciable changes were seen in liver AHH activity with androgen treatment in the presence or absence of estrogen. Similarly, the level of AHH activity, which was nearly 7- and 14-fold higher than intact and castrate kidney levels, respectively, was not altered by estrogen treatment. Neither progesterone nor cortisone had any effect on the levels of AHH activity in either the kidney or liver. Therefore, AHH activity in the male hamster kidney, but not the liver, is responsive to both estrogens and androgenic hormone.     

Species differences in stimulation of intestinal and hepatic microsomal mixed-function oxidase enzymes

The effect of intraperitoneal (i.p.) administration of phenobarbital (PB) or 3-methylchol-anthrene (3-MC) on some mixed-function oxidase (MFO) enzymes was studied in small intestine and liver of male rats, mice, guinea pigs and rabbits. PB treatment enhanced intestinal and 7-ethoxycoumarin deethylase activities in the mouse and rat, whereas benzo[a]pyrene hydroxylase (AHH) activity was increased only in the mouse. Ethylmorphine demethylase and aniline hydroxylase activities in small intestine were not stimulated by PB in any species. Administration of 3-MC increased the activity of intestinal AHH in rat, mouse and guinea pig, but intestinal 7-ethoxycoumarin deethylase activity was elevated only in the rat. The guinea pig and mouse intestinal ethoxycoumarin deethylase activity was inhibited by 3-MC treatment. None of the enzymes tested in rabbit intestine was induced by PB or 3-MC. The hepatic activities of ethylmorphine demethylase, aniline hydroxylase, 7-ethoxycoumarin deethylase and AHH, and the cytochrome P-450 content were increased by PB in all species. In contrast, 3-MC enhanced hepatic aniline hydroxylase and AHH activities in rats, mice and guinea pigs, and hepatic 7-ethoxycoumarin deethylase activity in mice and rats. In rabbits, these hepatic enzymes were inhibited by 3-MC pretreatment. The hepatic cytochrome P-450 absorption spectra was shifted to 448 nm in all species. These results suggest that there are differences in induction of intestinal and hepatic MFO enzymes which are influenced by the type of inducing agent, substrate and animal species used.     

Some characteristics of hamster liver and lung microsomal aryl hydrocarbon (biphenyl and benzo(a)pyrene) hydroxylation reactions

Aryl hydrocarbon hydroxylation (AHH) reactions were compared using liver and lung microsomes of corn oil- and 3-methylcholanthrene (3-MC)-treated hamsters, employing benzo(a)pyrene (BAP) and biphenyl as substrates. The predominant AHH activity of liver and lung microsomes from corn oil- or 3-MC-treated hamsters was biphenyl 4-hydroxylase. Biphenyl 2-hydroxylase and BAP-hydroxylase activities were approximately 50 per cent as active as biphenyl 4-hydroxylase in liver and approximately 1–3 per cent as active as biphenyl 4-hydroxylase in lung microsomes. Biphenyl 4-hydroxylase activity was 70–80 per cent as active in lung as in liver microsomes. Treatment with 3-MC in vivo induced the biphenyl 4-hydroxylation reaction in liver but not in lung microsomes, the biphenyl 2-hydroxylation reaction both in lung and liver microsomes, and the BAP hydroxylation reaction in lung but not in liver microsomes. Biphenyl 2- and 4-hydroxylase activities of liver microsomes displayed similar sensitivities to inhibition by a number of chemical inhibitors in vitro. Inhibition of biphenyl hydroxylation reactions by metyrapone or carbon monoxide did not distinguish between lung or liver microsomal mono-oxygenases of corn oil- or 3-MC-treated hamsters. While small differences were expressed by inhibition with ethylmorphine, large differences became apparent through inhibition studies with BAP or α-naphthoflavone. It is concluded that the major aromatic hydroxylase activity of lung microsomes from corn oil- or 3-MC-treated hamsters resembles the constitutive (uninduced) AHH of the liver microsomes and that the minor aromatic hydroxylase activity of lung microsomes from corn oil- or 3-MC-treated hamsters resembles the induced AHH of the liver microsomes.     

Variation in inducibility of cytochrome P-450c and aryl hydrocarbon hydroxylase in rat liver, lung, kidney, pancreas and nasopharynx

The effect of 3-methylcholanthrene (MC) treatment on the cytochrome P-450c content of various rat tissues was examined by measuring the level of immunodetectable P-450c in conjunction with its aryl hydrocarbon hydroxylase (AHH) activity. Immunoblots revealed that P-450d was induced in the nasopharynx and pancreas in addition to its previously reported induction in the liver, lung and kidney. In contrast to P-450c, induction of the immunorelated P-450d was observed only in the liver. The specific content of immunodetected P-450c in the tissue homogenates decreased in the order: liver, nasopharynx, pancreas, lung, kidney. The corresponding AHH activities decreased in the order: liver, kidney, lung, nasopharynx, pancreas. The ratio of AHH activity to P-450c content varied widely among tissues: ratios of 37.2:1.7:0.47:0.04:0.02 were obtained for the kidney, liver, lung, nasopharynx and pancreas, respectively. The absence of a direct relationship between the levels of AHH and P-450c indicates that the extrahepatic activity may partially derive from P-450 forms other than P-450c and/or the specific activity of P-450c varies among different tissues.     

Induction of aryl hydrocarbon hydroxylase in rat tissue following intratracheal instillation of diesel particulate extract and benzo[a]pyrene

The potential for aryl hydrocarbon hydroxylate (AHH) induction by inhaled diesel particles was assessed by intratracheal administration. Benzo[a]pyrene, (B[a]P) a reference compound, or an extract of particles, dissolved in gelatin-saline solution was administered to Fischer 344 rats at several dose levels. Twenty-four hours after administration of B[a]P or diesel particulate extract, the AHH activity increased in a dose-response manner in the lung, but not in liver. The maximum increase in the AHH activity in the lung was observed 12 h after intratracheal instillation of B[a]P (5 mg/kg), and the levels remained elevated for seven days. The AHH activity in the liver reached the maximum 24 h after the administration, and returned rapidly to control values. In contrast, intratracheal instillation of diesel particulate extract resulted in a significant increase of AHH activity in the lungs only after doses greater than 6 mg kg-1. The activity, however, declined rapidly and returned to control values within 75 h. The liver AHH activity in this instance, remained unchanged throughout the experimental period. These data indicate that in the lung, hydrocarbons extracted from diesel particles are weak enzyme inducers and exposure to these compounds by intratracheal administration did not result in AHH induction in the liver. The results suggest that doses higher than those normally expected from occupational exposures will be required to induce AHH activity in organs examined.     

Induction of aryl hydrocarbon hydroxylase and epoxide hydrolase in rat liver,kidney, testis,prostate glands,and stomach by a potent nematocide, 1,2-dibromo-3-chloropropane

Because of environmental contamination with 1,2-dibromo-3-chloropropane (DBCP), a potent nematocide, it has become necessary to assess its adverse biological effects. The present data describe the ability of DBCP to induce aryl hydrocarbon hydroxylase (AHH) and epoxide hydrolase (EH) activities in the liver, kidney, testis, prostate glands, and stomach of the male rat. DBCP induced AHH in all organs studied except the liver and prostate glands. Maximum induction of AHH appeared 8, 8, and 16 hr following treatment for stomach, kidney, and testis, respectively. At the maximum induction, AHH activity in testis, kidney, and stomach was 2.1, 3.8, and 4.7 times that of controls, respectively. EH activity was also induced at varying times following DBCP treatment in the liver, kidney, testis, and prostate glands. The maximum induction occurred at 48 hr in kidney and testis, and at 74 hr in liver and prostate glands. At the maximally induced state, EH activity in prostate, testis, kidney, and liver was 2.3, 1.4, 1.9, and 2.6 times that of controls, respectively. Thus, EH induction was slightly less than that of AHH in respective organs. Furthermore, DBCP induction of AHH and EH activity was inhibited by either actinomycin D or cycloheximide, suggesting that this enzyme induction is due to de novo synthesis of new hemoproteins.     

Organ specificity of induction of activating and inactivating enzymes by cigarette smoke and cigarette smoke condensate.

Inhalation of cigarette smoke specifically induces the rat lung and kidney aryl hydrocarbon hydroxylase (AHH) in less than 4 h. The epoxide hydratase (EH) and the glutathione S-transferase are not significantly modified by a similar treatment in any of the rat tissues. Compared to the kidney AHH, the lung hydroxylase is 3--4 times more sensitive to small concentrations of cigarette smoke and seems to have a longer biological half-life. In both tissues, the induced AHH presents the same in vitro sensitivity to various inhibitors as a polycyclic hydrocarbon induced AHH. In primary fetal rat liver cell culture, the cigarette smoke condensate fractions (CSCF) induce both the AHH and EH activity. Nevertheless, the AHH activity responds faster and to lower concentrations of CSCF than the EH activity. The liver cell culture constitutes a unique tool for a comparative study of the AHH and EH induction mechanism. Low concentration (10 muM) of benz(a)anthracene induces only the AHH activity while trans-stilbene oxide enhances selectively the EH activity. Appropriate concentrations of CSCF or of phenobarbital (PB) determine a parallel induction of both enzymes. The results are discussed on the basis of (a) the existence of specific mechanisms of AHH regulation in the lung and in the kidney and (b) the existence of coordinated or independent biochemical control of the AHH and EH activity.     

Transplacental induction of mixed-function oxygenases in extra-hepatic tissues by 2,3,7,8-tetrachlorodibenzo-p-dioxin

Treatment of pregnant rats with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a dose-dependent induction of a mixed-function oxidase system in fetal and maternal extra-hepatic tissues. At doses of 6 μmg/kg, aryl hydrocarbon hydroxylase (AHH) activity was increased 24-, 22- and 4-fold in fetal lung, kidney and skin, respectively, while maternal lung, kidney and adrenal AHH activity was increased 4-, 2- and 2-fold respectively. High-pressure liquid chromatographic (H.P.L.C.) analysis of benzo(a)pyrene (BP) metabolism after TCDD induction indicated that fetal lung, kidney and skin produced significant quantities of benzo(a)pyrene-7,8-dihydrodiol (BP-7,8-diol), benzo(a)pyrene-4,5-dihydrodiol (BP-4,5-diol) and 9- and 3-phenols of BP. The fetal liver produced benzo(a)pyrene-9,10-dihydrodiol (BP-9,10-diol), BP-4,5-diol, BP-7,8-diol and 9- and 3-phenols of BP. Maternal lung also produced BP-9,10-diol, while maternal adrenal gland yielded primarily the 9-phenol of BP. Epoxide hydratase activity was increased 2- to 3-fold in maternal lung, fetal lung and skin after TCDD pretreatment, but was not affected significantly in liver, kidney or placenta. Treatment of pregnant rats with TCDD increased the covalent binding of BP to DNA in preparations containing maternal liver, lung and placenta as well as fetal liver, lung and skin. Pretreatment with TCDD resulted in increased epoxide hydratase and AHH activities in extra-hepatic tissues but only AHH was increased in hepatic tissues, indicating that the inducing capabilities of TCDD differ from, but share some similarities with, both phenobarbital (PB) and 3-methylcholanthrene (MC). Thus, TCDD appears to provide an exceptionally potent and broad-spectrum transplacental induction of carcinogen-transforming enzymes in extra-hepatic tissues.     

The formation of 3-methylcholanthrene-initiated lung tumors correlates with induction of cytochrome P450IA1 by the carcinogen in fetal but not adult mice

The administration of 3-methylcholanthrene (MC) to pregnant mice results in the formation of lung tumors in the offspring. Previous work has shown that fetuses demonstrating inducibility of aryl hydrocarbon metabolism develop two to five times more lung tumors than induction-nonresponsive littermates. In this study, the effects of fetal versus adult MC exposure were compared with regard to both induction of aryl hydrocarbon hydroxylase activity (AHH) in lung and dependence of lung tumorigenesis on the Ah genotype. In inducible (C57BL/6 X DBA/2)F1 fetal lung supernatants, a single ip injection of 100 mg/kg of MC to the mothers resulted in a maximal 50-fold induction of AHH activity by 8 hr, which persisted for 48 hr. The enzyme data agreed well with RNA blot analysis, as MC caused maximal induction of P450IA1 RNA by 4 hr. For comparison, adult (F1 X DBA/2) mice were given three weekly injections of 100 mg/kg MC and tumor incidences were determined after 16 weeks. No differences were observed between responsive and nonresponsive mice of either sex in the number of mice bearing lung tumors, nor did the tumor multiplicity differ between responsive and nonresponsive males. However, noninducible female mice had a significantly higher tumor multiplicity than their inducible counterparts (p less than 0.025). Single ip injections of MC to adult F1 mice revealed that lung AHH activity was increased only 4- to 7-fold in the adult animal compared to the large fetal induction ratio. The difference in the magnitude of induction was due to the higher constitutive levels of AHH activity seen in adult tissue (4- to 14-fold greater than maximal basal fetal levels), as fetal and adult supernatants showed similar levels of induced activity following MC treatment. These results suggest that the correlation between susceptibility to MC-initiated lung tumors and induction of cytochrome P450IA1 is a unique property of the fetus and may be due, in part, to the low basal levels of fetal activating enzymes and their high induction ratio during the fetal period.     

Responses of rodent hepatic,renal and pulmonary aryl hydrocarbon hydroxylase following exposure to cigarette smoke

Using the British-American Tobacco Co. (B.-A.T.)-Mason inhalation system which releases a precisely-calibrated dilution of tobacco smoke into a chamber, male and female rats, guinea pigs, hamsters and gerbils were exposed to the optimum smoke concentration found to induce rat renal aryl hydrocarbon hydroxylase (AHH) (40 puffs of a 1 : 5 dilution of smoke from cigarettes prepared from a blend of Canadian flue-cured tobaccos). The tissue activity was measured in 9000 g supernatants of homogenates of lung, liver and kidney 6 h following exposure.Cigarette smoke was found to be a potent inducer of AHH, dilutions as high as 1 : 40 inducing this enzyme in rat kidney. Marked tissue, sex and species differences in basal AHH were observed. Induction up to 6-fold, was observed only in lung and kidney of male and female rats. In hamsters and gerbils, lung AHH was induced in both sexes but only renal AHH in female hamsters. In male and female guinea pigs, only the renal AHH was induced some 5-fold. Hepatic AHH was not inducible in any of the species studied. The analysis of changes in AHH activity in a responsive species and tissue(s) could be a valuable technique for the quantitative evaluation of biological effects of low concentrations of cigarette smoke.     

Components of the heme biosynthetic pathway and mixed function oxidase activity in human fetal tissues

Components of the enzyme systems involved in heme biosynthesis and mixed function oxidase activity were examined in tissues from human fetuses between the ages of 10.8 and 17.5 weeks, aborted by hysterotomy. The activity of δ-aminolevulinic acid synthetase (ALAS) was highest in liver, and successively lower in adrenal, placenta, kidney and lung. The mean level of ALAS activity in fetal liver [61.9 ± 13.4(S.E.)nmoles ALA/g/hr] was three times higher than the level reported in human adult liver. ALAS activity was directly correlated with the concentrations of porphyrins in liver, lung and placenta (r = 0.96). Protoporphyrin predominated in liver, while coproporphyrin predominated in lung and kidney. Ferrochelatase measured in livers from two fetuses (47.5 and 60.2 nmoles heme/g/hr) was sufficient to account for complete conversion to heme of the ALA produced by ALAS. As with other species, ALAS and ferrochelatase were found mainly in the mitochondrial subfraction of cells. Aryl hydrocarbon hydroxylation (AHH) could be measured in liver, adrenal, lung, kidney, intestine and placenta, but aminopyrine demethylation could not. In the adrenal, the concentration of cytochrome P-450 (1.92 nmoles/mg of microsomal protein) and mean AHH activity [258.2 ± 36.6 (S.E.) pmoles 3-OH benzo(a)pyrene/mg of protein/hr] were both four times higher than in the liver. In the fetal liver, the mean concentration of P-450 was within the range reported for human adult liver, but the activity of AHH [55.1 ± 17.3 (S.E.) pmoles/mg of protein/hr] was only 2 per cent of the activity reported for the adult. Cytochrome P-450 could not be detected in kidney or lung, though low levels of AHH were found (7.1 and 7.2 pmoles/mg of protein/hr). The presence of higher levels of ALAS and lower levels of cytochrome P-450 and AHH in the fetal liver than in the adrenal indicates that the activity of the heme biosynthetic pathway is not the main determinant of hemoprotein concentration and the extent of mixed function oxidase activity in human fetal tissues. The data also suggest that limitations in heme and hemoprotein synthesis may contribute to the very low mixed function oxidase activity in human fetal lung and kidney, but that other factors must account for the disparity in hepatic mixed function oxidase activity between the human fetus and adult.     

Effect of asbestos fibers on aryl hydrocarbon hydroxylase and aminopyrine N-demethylase activities of rat liver microsomes

Chrysotile asbestos fibers impair the activities of rat liver microsomal aryl hydrocarbon hydroxylase (AHH), aminopyrine (AP) N-demethylase and dimethylnitrosamine (DMN) demethylase in vitro. This inhibition is concentration-dependent. Preincubation of 3-methylcholanthrene (3-MC)-pretreated rat liver microsomes with chrysotile depresses the overall metabolism of [G-3H]benzo[a]pyrene (BaP). Various forms of asbestos employed inhibit AHH activity to the same extent. However, other types of asbestos are not as effective as chrysotile in diminishing AP demethylase activity. Chrysotile and crocidolite fibers are not found to significantly change the apparent Km of AHH activity, from 3-MC-pretreated rat liver microsomes, for BaP. Increasing the microsomal protein concentration partially abolishes the inhibition of AHH activity caused by chrysotile fibers. Inhibition of AP demethylase and AHH activities is attenuated by bovine serum albumin (BSA) or ferritin. Depression of AHH activity by crocidolite is significantly reversed by ferritin. Since polymers such as ferritin override enzyme inhibition by chrysotile as well as crocidolite, surface chemical groups of the fibers may be involved in enzyme modification.     

Aryl hydrocarbon hydroxylase induction in rat lung, liver, and male reproductive organs following inhalation exposure to diesel emission

Due to increasing use of diesel-powered vehicles, it has become necessary to assess adverse biological effects of diesel emissions in our environment. The present data describe the effects of inhalation exposure of diesel emission on the specific activities of aryl hydrocarbon hydroxylase (AHH) and epoxide hydrase (EH) in rat lung, liver, testis, and prostate gland. Adult CD strain, Sprague-Dawley male rats (8–10 weeks old) were exposed to diesel emission (1:13 dilution) containing 14.2 ppm ($\text{v}\text{v}$) total hydrocarbon, 20 hr/day for 42 days. Although liver exhibited the greatest overall AHH activity among the organs tested, the percentage increase over control values was highest in the prostate gland. On Day 15 of exposure, AHH activity had increased to 4.5-fold that of the control and remained elevated throughout the entire exposure period. In contrast, AHH induction in liver and lung occurred on Day 33 of exposure, and the maximum AHH induction was observed on Day 42 (1.4- and 1.3-fold increase in lung and liver, respectively). In all the organs tested, EH activity was not changed significantly during the experimental period.     

Induction of aryl hydrocarbon hydroxylase in rodent lung by cigarette smoke: a potential short-term bioassay.

Aryl hydrocarbon hydroxylase (AHH) activity was increased several fold in the lungs of hamsters, mice and rats after inhalation of cigarette smoke. Hamsters had low basal activity of lung AHH but showed the greatest inducibility (the ratio of induced to noninduced enzyme). Inducibility was lower but the actual levels of enzyme activity, both basal and induced, were higher in mice and highest in rats. Several criteria were met which could qualify the lung AHH assay as a short-term bioassay to aid in the measurement of cigarette toxicity. (1) Within a relatively narrow range, AHH activity increased with the number of cigarettes smoked. (2) In tests with standard reference cigarettes and three commercial brands, cigarettes which delivered high levels of total particulate matter (TPM) in the smoke induced AHH in lung to the highest degree; measures which reduced the TPM, primarily filtering methods, reduced the enzyme-inducing effect. (3) Also, with regard to filtering methods, the type of cigarettes which have been reported to cause the most extensive damage to the respiratory tract of animals in chronic inhalation studies caused the greatest enzyme induction in acute experiments. (4) Assay results can be obtained rapidly; maximum induction occurs within 24 hr after smoke exposure.     

Effect of polybrominated biphenyls, beta-naphthoflavone and phenobarbital on arylhydrocarbon hydroxylase activities and chloroform-induced nephrotoxicity and hepatotoxicity in male C57BL/6J and DBA/2J mice

Administration of chloroform (CHCl3) to male C57/6J (C57) and DBA/2J (DBA) mice produced dose-dependent hepatic and renal damage. Hepatic arylhydrocarbon hydroxylase (AHH) activity was higher in C57 than DBA mice; in kidney, AHH activity was higher in DBA than in C57 mice. CHCl3 caused the same degree of liver damage in both strains of mice; however, nephrotoxicity of CHCl3 was greater in DBA than in C57 mice. Pretreatment of C57 and DBA mice with phenobarbital (PB) markedly increased hepatic AHH activity and hepatotoxicity of CHCl3 in both strains but did not affect renal AHH or nephrotoxicity of CHCl3. Similarly, beta-naphthoflavone (BNF) enhanced AHH activity and CHCl3 hepatotoxicity in C57 mice, but had little effect on nephrotoxicity. BNF did not affect hepatic AHH nor CHCl3-induced hepatic injury in male DBA mice. Pretreatment with polybrominated biphenyl (PBB) enhanced AHH activity in liver and CHCl3 hepatotoxicity in both strains. After PBB, nephrotoxicity of CHCl3 and renal AHH activity were increased in C57 mice whereas PBB did not alter nephrotoxicity or renal AHH in DBA mice. These results suggest that CHCl3-nephrotoxicity is independent of hepatotoxicity.     

Effect of topical application of defined constituents of coal tar on skin and liver aryl hydrocarbon hydroxylase and 7-ethoxycoumarin deethylase activities

A single topical application of coal tar solution (USP) to neonatal rats resulted in the induction of aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase activities in skin, liver, lung, kidney, and intestine. The induction response of AHH in these tissues was in the order of skin > liver > intestine > lung > kidney. The induction response of 7-ethoxycoumarin O-deethylase was highest in the lung and followed the order of lung > kidney > skin > liver > intestine. Twenty-eight defined chemical constituents present in coal tar solution were individually analyzed for their induction effect on skin and liver AHH and 7-ethoxycoumarin O-deethylase activities. A single topical application of anthracene, 1,2-benzanthracene, 2,3-benzanthracene, benzo(a)pyrene, 2,3-benzofluorene, carbazole, chrysene, coronene, 1,2,3,4-dibenzanthracene, 1,2,5,6-dibenzanthracene, 7,12-dimethylbenzanthracene, fluorene, isoquinoline, 3-methylcholanthrene, or phenanthrene at a dose of 1 mg/10 g body weight to neonatal rats resulted in statistically significant induction of skin and liver AHH and 7-ethoxycoumarin O-deethylase activities. The induction response varied from chemical to chemical. Acridine was found to be an inducer of the skin enzymes only. Topical application of triphenylene, benzo(ghi)perylene, fluoranthene, 1-methylphenanthrene, and perylene caused induction of liver enzymes without producing effects on skin enzymes. These studies indicate that several hydrocarbons present in coal tar solution have induction effects on drug and carcinogen metabolism in skin and liver and that there are tissue-specific responses to some of these hydrocarbons.     

Inhibitor panel studies of human hepatic and placental cytochrome P-450-associated monooxygenase activities

1. A panel of nine inhibitors displaying some P-450 isozyme specificity was used to characterize aryl hydrocarbon hydroxylase (AHH) and 7-ethoxyresorufin 0-deethylase (ERDE) activities in human liver and placenta in vitro in comparison with liver enzymes from control, phenobarbital (PB) and 3-methylcholanthrene (MC) treated rats. 2. SKF 525A and cimetidine inhibited more potently hepatic AHH than the placental enzyme. 7,8-Benzoflavone inhibited more efficiently placental AHH than the hepatic enzyme, whereas ERDE was inhibited at the same level in both tissues. Quinine, quinidine, SKF 525A and metyrapone inhibited ERDE almost to the same extent in both tissues, but the variability was larger with the liver enzyme. Aminoglutethimide, debrisoquine or tetrahydrofuran did not inhibit AHH or ERDE significantly in either tissue. 3. When compared with inhibition profiles obtained with rat liver microsomes, the human hepatic and placental ERDE resembled most that of MC-treated rat liver enzyme. Inhibition profile of placental AHH activity was also similar, but the inhibition characteristics of hepatic AHH activity resembled more closely control or PB-induced rat liver. It also seems that isozymes for alcohol induction or debrisoquine hydroxylation do not contribute significantly to hepatic or placental AHH or ERDE. 4. The inhibitor panel selected on the basis of known pretreatment and isozyme specificity might be useful in the characterization of enzymes and metabolic biotransformations participating in the metabolism of new substrates.     

Pulmonary microsomal alterations following short-term low level inhalation of p-xylene in rats

Rats exposed to 300 ppm para-xylene vapor for 1, 3 or 5 days, 6 h/day, exhibited alterations in pulmonary microsomal membrane structural and metabolic parameters. Following 1 day of exposure, conjugated diene levels were elevated while total phospholipid levels, P-450 content, benzyloxyresorufin O-dealkylase activity and 2-aminofluorene N-hydroxylase activity were decreased. Core and leaflet membrane fluidity, ethoxyresorufin O-deethylase activity and aryl hydrocarbon hydroxylase (AHH) activity were unchanged at this time. Altered parameters began to return to control values by day 3 of exposure except for 2-aminofluorene N-hydroxylase activity, which remained decreased throughout the time course, and core membrane fluidity which was increased following 3 days of exposure. After 5 days of exposure, all parameters returned to control levels with the exception of AHH activity which was increased 41% at this time. Extracellular surfactant levels were also decreased by 1 and 3 days of exposure but returned to control values after 5 days. Initial pulmonary alterations produced by low level p-xylene exposure may be mediated by a peroxidative process. The initial damage triggers an adaptive response in lung tissue which possibly involves enzyme induction and/or cell proliferation. The increase in AHH activity after 5 days of exposure could have important consequences on the metabolism of co-administered xenobiotics.     

Comparative induction of xenobiotic metabolism in rodent kidney, testis and liver by commercial mixtures of polybrominated biphenyls and polychlorinated biphenyls, phenobarbital and 3-methylcholanthrene: absolute and temporal effects

Male Fischer 344 rats were killed at various times after single or multiple treatments with polybrominated biphenyls (PBB), polychlorinated biphenyls (PCB), sodium phenobarbital (NaPB) or 3-methylcholanthrene (3MC). p-Chloro-N-methyl-aniline N-demethylase (PCNMA) and aryl hydrocarbon hydroxylase (AHH) activities were determined in the 14 000 g supernatant fraction (postmitochondrial supernate, PMS) of renal, testicular and hepatic homogenates. Cytochrome P-450 (p-450) concentrations were determined in the 100 000 g pellet fractions of the same homogenates and the effects of enzyme induction on the sensitivities of AHH in PMS to inhibition by alpha-napthoflavone (ANF) and metyrapone (MET) in vitro were determined. Single treatments with PBB or PCB induced hepatic P-450 only, while multiple treatments with PBB, PCB or 3MC induced both renal and hepatic P-450; NaPB induced only hepatic P-450, while testicular P-450 concentration was unaffected by the inducers. Treatments with PBB, PCB or 3MC shifted the Soret maxima of renal and hepatic dithionite-reduced P-450 difference spectra to shorter wavelengths. Multiple treatments with PBB, PCB or 3MC increased renal and hepatic AHH activities, but NaPB induced hepatic AHH only. Renal AHH activity was increased more rapidly than hepatic AHH after a single treatment with PBB, PCB or 3MC and returned more rapidly to control. The renal AHH induced by PBB and PCB, like that induced by 3MC, was more sensitive to inhibition by ANF in vitro than was renal AHH from naive rats. Hepatic AHH induced by PBB and PCB, unlike that induced by NaPB or 3MC, exhibited no net alterations in sensitivities to the inhibitory effects of ANF or MET. Testicular AHH activity was not induced by PBB, PCB , NaPB or 3MC. Multiple treatments with PBB, PCB or NaPB increased hepatic, but not renal or testicular PCNMA activities. The organ-specificity and time-dependency of the effects of PBB, PCB, NaPB and 3MC on P-450 concentrations and AHH activities suggest that drug metabolism in kidney, testis and liver are regulated by separate control mechanisms. It may be possible to exploit such differences in organ response to enzyme inducers as tools with which to discern the roles of local metabolism in renal and testicular chemical injury.