Mixed function oxidase activities in lactating rats and their offspring following dietary exposure to polybrominated biphenyls.

Exposure of pregnant rats to diet containing 50 ppm polybrominated biphenyls (PBBs) from day 8 of gestation to day 15 postpartum caused significant increases in hepatic and extrahepatic microsomal mixed function oxidase activity. Hepatic arylhydrocarbon hydroxylase (AHH), epoxide hydratase (EH), hexobarbital hydroxylase (hex-OH), and the 2- and 4-hydroxylation of biphenyl (2-OHBP, 4-OHBP) were increased 10, 3, 3, 23, and 6-fold respectively in animals fed diet containing PBBs. The hex-OH, 2-OHBP, and 4-OHBP activities were not detectable in the S9 fraction from maternal mammary glands of control or PBB-fed rats; however, exposure to PBBs increased mammary AHH 2.5-fold and decreased EH activity 45%. Renal AHH activity was increased 7-fold but renal EH activity was unaltered by feeding PBBs. Pups from control and PBB-exposed mothers were crossfostered at birth to give offspring which received PBB exposure prenatally, postnatally (via mothers milk), or both pre- and postnatally. Each type of exposure produced increases in hepatic AHH and EH activities over those found in pups born to and raised by mothers which received no PBBs. The results demonstrate that PBBs induce hepatic and extrahepatic mixed function oxidase activity in nursing rats and that the extrahepatic effects of the mixture are different from the hepatic effects. Furthermore, PBBs were effective stimulators of hepatic enzymes in 15-day-old rats when the neonates were exposed transplacentally and/or via the mothers' milk. The results suggest potential toxic interaction between PBBs and other agents which are of importance to both mother and young.     

Induction of liver microsomal drug-metabolizing enzymes by 2,2',4,4',5,5'-hexabromobiphenyl.

The major component of Firemaster, a mixture of polybrominated biphenyls (PBBs), is 2,2′,4,4′,5,5′-hexabromobiphenyl (HBB). HBB was isolated to greater than 99.9% purity, and its effects on tissue structure and liver microsomal drug-metabolizing enzymes were examined. Male rats were injected ip with 90 mg of HBB/kg and sacrified 1 to 14 days later. Ten tissues were examined microscopically; only liver revealed HBB-dependent lesions. Hepatic cells were swollen and vacuolated, predominantly in the midzonal region. Liver to body weight ratios were increased by a third, and microsomal protein was nearly tripled. NADPH-cytochrome P-450 reductase was induced, and cytochrome P-450 was increased more than 2.5-fold, with the spectral maximum remaining at 450 nm. Aminopyrine demethylation was doubled by HBB, while PBBs and phenobarbital (Pb) both tripled this activity. Induction of benzo[a]pyrene hydroxylation was similar to that caused by Pb, but the level was fivefold smaller than that obtained by 3-methylcholanthrene (MC) induction. PBBs induced this activity to half of the MC level. HBB induced epoxide hydratase more than threefold. While PBBs tripled UDP-glucuronyltransferase activity, HBB was a poor inducer. SDS-polyacrylamide gel electrophoresis of HBB-induced microsomes revealed heme and protein profiles similar to those of microsomes induced by Pb, but markedly different from those of control microsomes. While PBBs are a mixed-type inducer of microsomal drug-metabolizing enzymes, these results show that HBB is strictly a Pb-type inducer.     

Kinetics of calcium influx into rat intestine in vitro, after oral cadmium administration.

Polybrominated biphenyls (PBBs) and polychlorinated biphenyls (PCBs) stimulate microsomal mixed function monooxygenases in liver and extrahepatic tissues. These compounds accumulate to high concentration in fatty tissues and are excreted into milk. Human populations that have been exposed to PBBs are also likely to have been exposed to PCBs. Therefore, to assess potential hazard of simultaneous exposure to PCBs and PBBs, it was of interest to determine the distribution of PCBs (Aroclor 1254) and PBBs (Firemaster BP6) in several tissues of lactating rats, to determine the concentrations of both agents in milk and to study the effects of these agents on hepatic and extrahepatic arylhydrocarbon hydroxylase (AHH) after concomitant dietary exposure. Sprague-Dawley rats were placed on diets containing PBBs and/or PCBs from the eighth day of pregnancy to 14 days postpartum. Treatment with the highest dose of PBBs (200 ppm) retarded both dam and pup body weight gain. Stimulation of AHH was greater after treatment with PBBs alone than PCBs alone. Extrahepatic tissue concentrations of PCBs and PBBs were similar regardless of whether these agents were administered together or alone. Liver and milk contained lower concentrations of PBBs after treatment with an equal mixture of PCBs and PBBs than when PBBs were administered alone. Milk contained higher concentrations of PCBs than PBBs indicating that this route of excretion may be more important for PCBs.     

Effects of commonly consumed vegetables on hepatic xenobiotic-metabolizing enzymes in the mouse

To investigate the effects of consuming a variety of common vegetables on the activities of xenobiotic-metabolizing enzymes in the mouse liver, male C57BL/6 mice were fed purified diets supplemented isocalorically with 20% freeze-dried powdered kidney bean, soya bean, alfalfa, cauliflower, mustard greens, carrot, kale, Brussels sprouts, beet, egg plant or onion or with 40% sweet potato. Hepatic ethoxycoumarin O-deethylase (ECD) activity was increased significantly (P less than or equal to 0.05) over the controls in the mice fed diets containing kidney bean (1.5-fold), alfalfa (1.6-fold), cauliflower (2.2-fold), mustard greens (1.2-fold), carrots (1.2-fold) and kale (1.3-fold). No significant increases in ECD activity were seen in the other groups. Aryl hydrocarbon hydroxylase (AHH) activity was assayed in the cauliflower and Brussels sprouts groups and was found to be unaffected by these diets. Glutathione S-transferase (GST) and epoxide hydratase (EH) activities were increased (P less than or equal to 0.05) by soya bean (1.2- and 1.6-fold respectively), Brussels sprouts (2.0- and 1.6-fold), cauliflower (1.2- and 1.6-fold), alfalfa (1.3- and 2.0-fold) and onion (1.8- and 2.3-fold). No significant increases in GST or EH activities were seen in the other groups. Of the twelve vegetables investigated, only three (sweet potato, beet and egg plant) had no statistically significant effects on any of the xenobiotic-metabolizing parameters tested. However, the beet diet caused an apparent inhibition of ECD activity (74% of control) and the sweet potato diet caused an apparent increase (1.3-fold) in GST activity, although statistical significance could not be established at P less than or equal to 0.05.     

The effects of dietary cabbage on xenobiotic-metabolizing enzymes and the binding of aflatoxin B1 to hepatic DNA in rats

The effect of dietary cabbage (Brassica oleracea) on the binding of aflatoxin B1 (AFB1) to hepatic DNA and on the activities of liver and intestinal microsomal and cytosolic enzymes was studied in weanling male Fischer 344 rats. Freeze-dried cabbage was fed to rats at a level of 25% in the diet for 21 days, while others received a basal diet. In the cabbage-fed group there was an 87% (P less than 0.01) reduction in the binding of AFB1 to hepatic DNA 2 hr after the ip injection of [3H]AFB1 (3 micrograms/kg). There was also a 41% (P less than 0.05) increase in liver weight expressed relative to body weight. Hepatic and intestinal glutathione S-transferase activities were significantly increased (2.1- and 2.3-fold, respectively) over those in rats fed the basal diet. Hepatic and intestinal microsomal epoxide hydrolase activities were significantly increased (2.6- and 1.4-fold, respectively) over the basal group. Intestinal aryl hydrocarbon hydroxylase (AHH) and ethoxycoumarin O-deethylase (ECD) activities were significantly increased (2.3- and 2.5-fold, respectively), over the basal group but dietary cabbage had no significant effect on hepatic AHH or ECD activities.     

A comparison of the effects of hexachlorobenzene, beta-naphthoflavone, and phenobarbital on cytochrome P-450 and mixed-function oxidases in Japanese quail

Hexachlorobenzene (HCB), beta-naphthoflavone (BNF), or phenobarbital (PB) was administered to Japanese quail to determine their effects on hepatic porphyrin levels and drug-metabolizing enzymes. While HCB increased porphyrin levels, PB slightly reduced them, and BNF had no effect. HCB was an excellent inducer in quail, increasing the specific content of cytochrome P-450 to levels similar to those produced by BNF. Additional similarities between HCB- and BNF-treated quail included a comparable hypsochromic absorption shift in the CO-reduced difference spectra of cytochrome P-450 and similar effects on the activities of cytosolic glutathione S-transferase (GSH-t), biphenyl hydroxylase (BPH), and ethoxyresorufin O-deethylase (EROD). However, a differential response to HCB and BNF treatment was seen in the activities of hepatic NADPH-cytochrome P-450 reductase, epoxide hydrolase, GSH-t (microsomal), aryl hydrocarbon hydroxylase (AHH), and ethoxycoumarin O-deethylase (ECOD). The activities of NADPH-cytochrome P-450 reductase, AHH, and ECOD following treatment with HCB were similar to those found after dosing with PB. HCB caused a pattern of induction that was distinct from either BNF or PB and appeared to be a "mixed-type" inducer. The rapidity of the HCB-induced porphyrogenic response of Japanese quail, as compared to mammals, may provide unique advantages for making correlations between the in vivo metabolism of haloaromatic hydrocarbons and their effects on porphyrin metabolism.     

The effect of structurally divergent herbicides on mouse liver xenobiotic-metabolizing enzymes (P-450-dependent mono-oxygenases, epoxide hydrolases and glutathione S-transferases) and carnitine acetyltransferase.

Male mice were treated with structurally diverse herbicides to study their effect on liver xenobiotic-metabolizing enzymes. Chlorfiurecol, trifluralin, alachlor, propham, MCPP and 2,4-DP caused increases in phase I (cytochrome P-450, ethoxycoumarin O-deethylase, and/or aminopyrine N-demethylase) and phase II (microsomal epoxide hydrolase and cytosolic glutathione S-transferase) activities. MCPP and 2,4-DP also increased cytosolic epoxide hydrolase and carnitine acetyltransferase activities suggestive of peroxisome proliferation. Benthiocarb and molinate increased only some phase II enzyme activities. Dicamba, at the dose employed, caused mortality and decreases in some of the enzymes monitored. Most of the herbicides tested induced xenobiotic-metabolizing enzyme activities, the pattern of induction being dependent on herbicide structure.     

Effect of hypolipidemic compounds on lauric acid hydroxylation and phase II enzymes

Treatment of male Fischer 344 rats with various hypolipidemic drugs of different peroxisome proliferating potency (1-benzylimidazole, acetylsalicylic acid, clofibrate, tiadenol) led to an induction of liver lauric acid hydroxylase, whereas probucol, which is not a peroxisome proliferator, did not induce this enzyme. Activity of bilirubin UDP-glucuronosyltransferase was increased by all the compounds tested. The highest increase was observed after treatment with acetylsalicylic acid (2.3-fold). High correlation (r = 0.953) was observed between the activities of lauric acid hydroxylase and the corresponding activities of cytosolic epoxide hydrolase reported previously. The amount of microsomal epoxide hydrolase was not changed by any of the compounds. Whereas clofibrate and tiadenol decreased glutathione S-transferase activity with 1-chloro-2,4-dinitrobenzene as substrate, 1-benzylimidazole and probucol increased this activity. With 4-hydroxynonenal as a substrate qualitatively the same results were obtained with the exception that probucol did not affect the enzyme activity. When glutathione S-transferase activity was measured with cis-stilbene oxide as substrate only the more than five-fold increase after treatment with 1-benzylimidazole was significantly different from control values. Activity of dihydrodiol dehydrogenase was increased after treatment of rats with 1-benzylimidazole (1.5-fold), whereas application of tiadenol led to a decrease of enzyme activity. Feeding of male guinea pigs with clofibrate did not change the activity of peroxisomal beta-oxidation, cytosolic epoxide hydrolase or lauric acid hydroxylase. However, treatment with tiadenol caused an increase of these activities.     

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.     

Effects of tetraethyl lead on the activities of drug metabolizing enzymes in different tissues of the rat.

The present study describes the effects of tetraethyl lead on various drug metabolizing enzymes in different tissues of the rat. Tetraethyl lead was administered intraperitoneally to rats (250 mumol/kg) on two consecutive days. The animals were killed on day 3. Tetraethyl lead-treatment decreased the concentration of hepatic cytochrome P-450 (to 45 per cent of the control), the hepatic activity of aryl hydrocarbon hydroxylase (to 41 per cent of the control) and ethoxycoumarin deethylase (to 45 per cent of the control). Epoxide hydratase activity was enhanced in the liver (1.3-fold), kidney (3.3-fold), and small intestinal mucosa (4.7-fold). The activity of glutathione S-transferase decreased in the liver (to 69 per cent of the control) but increased in the kidney (1.5-fold) and small intestinal mucosa (1.7-fold). The glucuronidation of o-aminophenol was enhanced (2.2-fold) in the kidney of tetraethyl lead treated rats. It is concluded that exposure to tetraethyl lead brings about widespread changes in the ability of mammals to detoxify foreign compounds.     

Effects of Tetraethyl Lead on the Activities of Drug Metabolizing Enzymes in Different Tissues of the Rat

Abstract The present study describes the effects of tetraethyl lead on various drug metabolizing enzymes in different tissues of the rat. Tetraethyl lead was administered intraperitoneally to rats (250 γmol/kg) on two consecutive days. The animals were killed on day 3. Tetraethyl lead-treatment decreased the concentration of hepatic cytochrome P-450 (to 45 per cent of the control), the hepatic activity of aryl hydrocarbon hydroxylase (to 41 per cent of the control) and ethoxycoumarin deethylase (to 45 per cent of the control). Epoxide hydratase activity was enhanced in the liver (1.3-fold), kidney (3.3-fold), and small intestinal rnucosa (4.7-fold). The activity of glutathione S-transferase decreased in the liver (to 69 per cent of the control) but increased in the kidney (1.5-fold) and small intestinal mucosa (1.7-fold). The glucuronidation of o-aminophenol was enhanced (2.2-fold) in the kidney of tetraethyl lead treated rats. It is concluded that exposure to tetraethyl lead brings about widespread changes in the ability of mammals to detoxify foreign compounds.     

Microsomal enzyme induction, egg production, and reproduction in three lines of Japanese quail fed polybrominated biphenyls

The sensitivity of three genetic lines of Japanese quail to polybrominated biphenyls (PBBs) was evaluated using criteria of egg production, reproduction, and induction of the hepatic microsomal mixed-function oxidase (MFO) system. Two genetic lines of quail, developed to diverge in their plasma cholesterol response to exogenous adrenocorticotropin (ACTH) (a "Low" line and a "High" line), were compared to a random-bred line ("Random"). ACTH administration caused increases in plasma cholesterol in the Low line that were 15 and 39% below the Random-line values in males and females, respectively, while High-line values were 31% higher in males and 36% higher in females when compared to the respective Random-line values. Hepatic activities of aryl hydrocarbon hydroxylase (AHH) and hexobarbital hydroxylase (HxH) were not significantly influenced by ACTH administration or by genetic line in either sex. PBBs fed at 40 or 80 mg/kg diet for 5 wk resulted in significant increases in hepatic AHH and aminopyrine N-demethylase (APND) activities and cytochrome P-450 concentrations. The induction of AHH, APND, and cytochrome P-450 was significantly less in Low-line males in comparison to Random- and High-line males, while the induction of AHH was less in Low-line females when compared to females from the other two lines, based on covariance analysis. In terms of reproductive parameters, there was a greater adverse effect on egg production at 80 ppm PBBs in Low-line females when compared to the Random and High lines. These data indicate an example in which the biological toxicity of a compound and the induction of a 3-methylcholanthrene-type hepatic enzyme are not directly correlated.     

Stimulation of hepatic microsomal metabolism in mice by a mixture of polybrominated biphenyls.

The pattern of stimulation of hepatic microsomal mixed function oxidases has been studied in female NMRI mice following a single ip injection of 150 mg/kg polybrominated biphenyls (PBBs) and compared to the patterns produced by phenobarbital (PB), 3 X 100 mg/kg; 3-methylcholanthrene (MC), 3 X 20 mg/kg; and these two agents administered together at these doses. Cytochrome P450, ethylmorphine N-demethylase, and epoxide hydratase reached maximums of 200, 200, and 350% of control values, respectively, at 48 hr after treatment with PBBs. Ethoxycoumarin O-deethylase and arylhydrocarbon hydroxylase were maximally increased to 400 and 180% of control values, respectively, 96 hr after PBBs. The reduced cytochrome P450 ethylisocyanide difference spectra and the inhibition of ethoxycoumarin O-deethylase and arylhydrocarbon hydroxylase activity by metyrapone and alpha-naphthoflavone indicated that the characteristics of the cytochrome P450 and the cytochrome P450-dependent enzymes changed with time after administration of PBBs. These results indicate that the enzyme-stimulating properties of PBBs alter, changing from PB-like to MC-like, with time after administration. These findings provide an explanation for the effects of PBBs on the toxicity of bromobenzene, indicating that PBBs represent a new and previously unrecognized calss of toxicity-modifying agents sharing properties of both PB and MC.     

Effects of Phenoxyherbicides and Glyphosate on the Hepatic and Intestinal Biotransformation Activities in the Rat

Abstract: The effects of phenoxyacid herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and MCPA (4-chloro-2-methylphenoxyacetic acid), clofibrate, and glyphosate on hepatic and intestinal drug metabolizing enzyme activities were studied in rats intragastrically exposed for 2 weeks. The hepatic ethoxycoumarin O-deethylase activity increased about 2-fold with MCPA. Both 2,4-D and MCPA increased the hepatic epoxide hydrolase activity and decreased the hepatic glutathione S-transferase activity. MCPA also increased the intestinal activities of ethoxycoumarin O-deethylase and epoxide hydrolase. Glyphosate decreased the hepatic level of cytochrome P-450 and monooxygenase activities and the intestinal activity of aryl hydrocarbon hydroxylase. Clofibrate decreased the hepatic activities of UDPglucuronosyltransferase with p-nitrophenol or methylumbelliferone as the substrate. Also 2,4-D decreased the hepatic activity of UDPglucuronosyltransferase with p-nitrophenol as the substrate. MCPA decreased the intestinal activities of UDPglucuronosyltransferase with either p-nitrophenol or methylumbelliferone as the substrate. The results indicate that phenoxyacetic acids, especially MCPA, may have potent effects on the metabolism of xenobiotics. Glyphosate, not chemically related to phenoxyacids, seems to inhibit monooxygenases. Whether these changes are related to the toxicity of these xenobiotics remains to be clarified in further experiments.     

Age-related changes in benzo(a)pyrene metabolism and epoxide-metabolizing enzyme activities in rat skin

The postnatal development of microsomal aryl hydrocarbon hydroxylase (AHH), 7-ethoxycoumarin O-deethylase (ECD), epoxide hydrolase (EH) [benzo(a)pyrene (BP)-4,5-oxide as substrate], and cytosolic glutathione S-transferase (GST) was studied in skin of Sprague-Dawley rats. Animals were treated with skin application of 3-methylcholanthrene (MCA) (40 mg/kg, 24 hr before sacrifice) or acetone. Enzyme activities were detected in animals of all ages. AHH and ECD in control rats showed slight age-dependent variation. Age-dependent differences in inducibility of skin AHH and ECD by topically applied MCA were observed. At 4, 6, 10, 18, 24, 32, and 55 days of age, the inducibility of AHH was 11, 18, 18, 19, 20, 23, and 21-fold, respectively. A similar pattern was observed for ECD. EH activity in 24-day-old skin was twice that in 4-day-old animals. GST activity remained constant throughout maturation. EH and GST activities were not altered by MCA. BP metabolism was studied in control and MCA-induced neonatal (4-day-old), young (18-day-old), and adult (55-day-old) animals. MCA treatment increased the rate of metabolism of BP at all ages studied. Higher rates of BP metabolism occurred in adult skin as compared to younger or neonatal rat skin. Inducibility of trans-7,8-diol formation by topically applied MCA was highest in the adult (19-fold) rat skin as compared to younger (12-fold) or neonatal rat skin (10-fold). These studies suggest that xenobiotic metabolism in skin of rats undergoes variable changes during aging which could exert some influence on pharmacologic responses to topically applied agents in cutaneous tissue.     

Aflatoxin B1 metabolism in the rat: polyhalogenated biphenyl enhanced conversion to aflatoxin M1

The effects of polychlorinated biphenyls (PCBs) and polybrominated biphenyls (PBBs) on the formation in vitro of aflatoxin Q1 and aflatoxin M1 from aflatoxin B1 by rat-liver microsomes were investigated. AFB1 metabolism by hepatic microsomes from PBB- and PCB-treated rats resulted in 16- and 30-fold increases, respectively, in levels of aflatoxin M1. The enhanced formation of aflatoxin M1 did not correlate with PBB and PCB stimulation of benzo[a]pyrene hydroxylase (AHH) activity. Studies in vivo clearly demonstrated enhanced secretion of aflatoxin M1 by female lactating rats with prior exposure to PCBs. PCB pretreatment enhanced the activity of mammary as well as hepatic tissue microsomal preparations in converting aflatoxin B1 to aflatoxin M1. Our findings indicate that PCB exposure increases the production of aflatoxin M1 in vitro and also increases the levels of aflatoxin M1 released into the milk.     

Effects of tebuconazole on cytochrome P450 enzymes,oxidative stress,and endocrine disruption in male rats

The major objective of the present study was to determine the ability of a triazole fungicide tebuconazole to induce cytochrome P450‐dependent monooxygenases, oxidative stress, and endocrine‐disrupting activity using male rats treated with tebuconazole at 10, 25, and 50 mg/kg p.o. once daily for 28 days. In liver, tebuconazole dose‐dependently increased microsomal contents of cytochrome P450 and cytochrome b₅ and the activities of NADPH‐cytochrome P450 reductase, 7‐ethoxyresorufin O‐deethylase, methoxyresorufin O‐demethylase, pentoxyresorufin O‐dealkylase, 7‐ethoxycoumarin O‐deethylase, aniline hydroxylase, and erythromycin N‐demethylase. In kidney, tebuconazole increased 7‐ethoxycoumarin O‐deethylase activity without affecting other monooxygenase activities. In marked contrast to liver and kidney, tebuconazole decreased testicular 7‐ethoxyresorufin O‐deethylase, methoxyresorufin O‐demethylase, 7‐ethoxycoumarin O‐deethylase, aniline hydroxylase, and erythromycin N‐demethylase activities. The results of immunoblot analysis of liver microsomes of controls and tebuconazole‐treated rats revealed that tebuconazole induced CYP1A1/2, CYP2B1/2, CYP2E1, and CYP3A proteins in liver. Additions of tebuconazole to liver microsomes inhibited microsomal 7‐ethoxycoumarin O‐deethylase activity in vitro (IC₅₀ = 1.50–1.69 µM). Treatment of rats with tebuconazole decreased glutathione content and increased glutathione S‐transferase, superoxide dismutase, catalase, and glutathione peroxidase activities in liver; increased superoxide dismutase activities in kidney and testis; but decreased glutathione S‐transferase activity in testis. Treatments with tebuconazole decreased serum testosterone concentration and cauda epididymal sperm count. The present study demonstrates that tebuconazole induces a multiplicity of CYPs and oxidative stress in liver; inhibits testicular P450 and glutathione S‐transferase activities; and produces anti‐androgenic effects in male rats.     

Biotransformation enzymes in nasal mucosa and liver of Sprague-Dawley rats

The metabolism of hexamethylphosphoramide (HMPA), aminopyrine, ethoxycoumarin, ethoxyresorufin and pentoxyresorufin, by the monooxygenase cytochrome P-450-dependent system, was studied in microsomes from nasal epithelial membranes and liver tissue of Sprague-Dawley rats. Nasal metabolism rates for the different substrates ranged from 9% of liver values for aminopyrine to 83% for ethoxycoumarin. HMPA-demethylase activity followed Michaelis-Menten kinetics in nasal mucosa microsomes but was biphasic in those from liver. SKF 525A, metyrapone, dioxolane and α-naphthoflavone (ANF), inhibitors of various P-450 monooxygenases, were examined with regard to inhibition of nasal and liver ethoxycoumarin deethylase. In addition, activity of epoxide hydrolase, glutathione S-transferase, DT-diaphorase and UDP-glucuronyltransferase (UDP-GT) in nasal tissue homogenates were investigated. These activities were generally lower than those present in the liver. Various attempts to increase the activity of oxidative enzymes in nasal tissue by PB, 3-MC and ethanol failed, 3-MC and PB doubled the microsomal UDP-GT and the epoxide hydrolase activities. The results together with data from the literature suggest that the balance between P-450 isozymes and detoxifying enzymes differs in the nose compared with the liver. The activities of these enzymes in nasal tissue of different strains of rats also varies substantially with implications regarding the metabolic fate and activitation of inhaled xenobiotics.     

Concomitant induction of microsomal epoxide hydrolase and UDP-glucuronosyltransferase activities by dipyridine compounds.

The coordinated response of the major rat hepatic phase II xenobiotic-metabolizing enzymes following 3-day exposure to diaryl compounds was investigated. Four diaryl compounds containing heterocyclic nitrogen atoms elevated microsomal epoxide hydrolase activity from 2- to 4-fold. Equivalent compounds lacking the heteroatom, when given in the same dosing regimen (75 mg/kg, ig, daily for 3 days), did not induce this or any other drug-metabolizing enzyme activity. Epoxide hydrolase activity closely paralleled UDP-glucuronosyltransferase activity toward three aglycones: 4-nitrophenol (r = 0.87), morphine (r = 0.84), and 1-naphthol (r = 0.78). There was less correlation (r = 0.60) between epoxide hydrolase activity and both UDP-glucuronosyltransferase activity toward testosterone and cytosolic glutathione S-transferase activity. There was no correlation between microsomal epoxide hydrolase activity and cytochrome P-450 or the monooxygenase reaction (4-nitrophenol hydroxylase) preferentially induced by pyridine-containing compounds. Induction of rat hepatic microsomal epoxide hydrolase activity by some pyridine-containing compounds appears coordinately regulated with glucuronidation rather than oxidation enzymes.     

The effects of dietary brussels sprouts and Schizandra chinensis on the xenobiotic-metabolizing enzymes of the rat small intestine

After an initial equilibration period of 7 days on a semi-synthetic basal diet, male Sprague-Dawley rats were fed for 2 wk on either the basal diet (controls), the basal diet containing 5% Schizandra chinensis or 25% Brussels sprouts, or on rat chow. One group of chow-fed rats was pretreated with 20 mg 3-methylcholanthrene (3-MC)/kg body weight, 24 hr before they were killed. Microsomal and cytosolic fractions were prepared from small intestine mucosa. Microsomes were assayed for cytochrome P-450, aryl hydrocarbon hydroxylase (AHH), ethoxycoumarin O-deethylase (ECD) and epoxide hydrolase (EH) activities, and for metabolism of benzo[a]pyrene (BaP), Cytosols were assayed for glutathione S-transferase (GST) activity. The largest increase in intestinal mixed-function oxidase activity over levels in the controls was seen in the 3-MC-treated group. However, EH and GST activities in these animals were not significantly increased. Increases in cytochrome P-450 levels and significant increases in AHH, ECD, EH and GST activities occurred in the rats fed Brussels sprouts. Rats in the S. chinensis group showed inhibition of AHH activity relative to controls, but increased activity of ECD, EH and GST. In the rats fed chow there were significant increases in the activities of all the enzymes assayed except GST. The percentage conversion of BaP to metabolites reflected the results of the AHH assay and the groups were ranked in the following order: 3-MC greater than Brussels sprouts greater than rat chow greater than basal diet greater than S. chinensis. The profile of BaP metabolites showed a larger proportion of the BaP diols and 3-hydroxybenzo[a]pyrene, and a smaller proportion of BaP-4,5-epoxide and the BaP quinones, for the Brussels sprouts- and S. chinensis-fed groups. The significance of these results is discussed in regard to the role of the small intestine as a mediator of toxicity induced by ingested chemicals.