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The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1, on the catalytic activities and total content of hepatic P450 was determined in vivo and in vitro. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 h postdosing, and total P450 content and the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, P450 2E1, and P450 3A were determined. The lowest dose of DCE that yielded maximal inactivation of P450 2E1 was found to be 100 mg/kg. Significant decreases in total content of P450 or the activities of P450 1A2, P450 2A1, P450 2B, P450 2C6, P450 2C11, P450 2D1, and P450 3A were not observed during the 24 h following administration of DCE (100 mg/kg ip), but P450 2E1 activity was diminished about 65% at 2 and 5 h after DCE treatment and returned to control levels at 24 h. Additionally, there was little or no significant effect on the activities of hepatic cytosolic alcohol dehydrogenase or mitochondrial or microsomal aldehyde dehydrogenases 5 h postdosing. DCE showed the same selectivity for P450 inactivation in vitro, and P450 2E1 activity was inhibited by >80% without affecting the other isozymes. However, DCE (5 mM) also proved to be a good competitive inhibitor of the probe activities of P450 1A2 and P450 2C6. The in vivo inhibition of P450 2E1 was accompanied by decreases in the levels of the immunoreactive protein, and an additional immunoreactive band appeared at ca. 30 kDa in the Western blot of microsomes from DCE-treated rats, possibly arising from proteolytic degradation of P450 2E1 protein after covalent modification by the inhibitor. DCE is an effective, relatively nontoxic inhibitor of P450 2E1 in vivo and in vitro that has greater selectivity than other agents currently used.

The disposition of oral doses of [14C]benzene was investigated using a range of doses that included lower levels (0.02 and 0.1 mg/kg) than have been studied previously in rat, mouse, and in hamster, a species which has not been previously examined for its capacity to metabolize benzene. Saturation of metabolism of benzene was apparent as the dose increased, and a considerable percentage of the highest doses (100 mg/kg) was exhaled unchanged. Most of the remainder of the radioactivity was excreted as metabolites in urine, and significant metabolite-specific changes occurred as a function of dose and species. Phenyl sulfate was the predominant metabolite in rat urine at all dose levels (64-73% of urinary radioactivity), followed by prephenlmercapturic acid (10-11%). Phenyl sulfate (24-32%) and hydroquinone glucuronide (27-29%) were the predominant metabolites formed by mice. Mice produced considerably more muconic acid (15%), which is derived from the toxic metabolite muconaldehyde, than did rats (7%) at a dose of 0.1 mg/kg. Unlike both rats and mice, hydroquinone glucuronide (24-29%) and muconic acid (19-31%) were the primary urinary metabolites formed by hamsters. Two metabolites not previously detected in the urine of rats or mice after single doses, 1,2,4-trihydroxybenzene and catechol sulfate, were found in hamster urine. These data indicate the hamsters metabolize benzene to more highly oxidized, toxic products than do rats or mice.

The effect of trans-1,2-dichloroethylene (DCE), an inhibitor of cytochrome P450 (P450) 2E1 (CYP2E1), on the composition and quantity of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with hepatic P450 activity and content. Hepatic microsomes were prepared from groups of rats prior to dosing and at 2, 5, 12, and 24 hr postdosing with DCE (100 mg/kg ip), and total P450 content and the activity of CYP2E1 was determined. Breath was collected from parallel groups of rats predose and at several intervals that encompassed the time points for rats euthanized for microsome preparation. Over 100 breath components were identified by GC/MS and quantitated by GC/FID. The overall change in the profile of breath VOCs resulting from administration of DCE was striking. An increase of approximately 1000% was measured in the mass of non-DCE-derived VOCs exhaled 4-6 hr after dosing, but there was no increase in hepatic lipid peroxidation. In addition to hexane, short-chain methyl ketones were particularly affected, and percentage increases in response to inhibition were inversely related to chain length, with acetone and 2-butanone > 2-pentanone >> 2-hexanone > 2-heptanone. There were no statistically significant decreases in total content of P450, but the activity of CYP2E1 was diminished about 65% at 2 and 5 hr after DCE treatment. However, 24 hr after inhibitor administration the total mass of VOCs expired was only marginally elevated above baseline and CYP2E1 activity was not significantly different from that of untreated rats. The compounds most markedly increased upon inhibition of CYP2E1 are also excellent inducers of that isozyme, and this finding is consistent with the hypothesis that these chemicals are important to the normal homeostasis of CYP2E1. The increase in breath components observed following inhibition of CYP2E1 suggests that VOCs in breath can reflect the activity of that isozyme in vivo., (Copyright 1997 Academic Press.)

1. The disposition of [14C]diethanolamine (DEA) (1) was determined in rat after oral, i.v. and dermal administration, and in mouse after dermal administration. 2. Oral administration of DEA to rat was by gavage of 7 mg/kg doses once and after daily repeat dosing for up to 8 weeks. Oral doses were well absorbed but excreted very slowly. DEA accumulated to high concentrations in certain tissues, particularly liver and kidney. The steady-state of bioaccumulation was approached only after several weeks of repeat oral dosing, and the half-life of elimination was approximately 1 week. 3. DEA was slowly absorbed through the skin of rat (3-16% in 48 h) after application of 2-28 mg/kg doses. Dermal doses ranging from 8 to 80 mg/kg were more readily absorbed through mouse skin (25-60%) in 48 h of exposure, with the percent of the applied dose absorbed increasing with dose. 4. Single doses (oral or i.v.) of DEA were excreted slowly in urine (c. 22-25% in 48 h) predominantly as the parent compound. There was minimal conversion to CO2 or volatile metabolites in breath. The profile of metabolites appearing in urine changed after several weeks of repeat oral administration, with significant amounts of N-methylDEA and more cationic metabolites appearing along with unchanged DEA.

The disposition of carbon-14-labeled lauramide diethanolamine (LDEA) was determined in rats after iv, dermal, and oral administration, and in mice after iv and dermal administration. Intravenous doses of LDEA to rats and mice (25 and 50 mg/kg, respectively) were mostly excreted in the urine (ca. 80-90%), with only about 10% excreted in the feces 72 hr after dosing. No unchanged LDEA, diethanolamine, or diethanolamine-derived metabolites were detected in urine. LDEA concentrated to the highest levels in the adipose tissue, and was only very slowly cleared from that tissue. Residues were also observed in liver and kidney, but clearance from those tissues paralleled the decreases in blood concentrations. Incubations of LDEA with liver slices from rats and humans showed that the compound is well absorbed by hepatic tissue from both species. LDEA was readily converted to metabolites found in vivo in rats, as well as other metabolites that are potentially intermediate products formed after omega- and/or omega-1 to 4 hydroxylation. Treatment with diethylhexylphthalate, an inducer of cytochrome P4504A1, which catalyzes the omega-hydroxylation of lauric and other fatty acids, demonstrated the involvement of that isozyme in the hydroxylation of LDEA. Dermally applied LDEA, at doses of 25 and 400 mg/kg to rats, was moderately (25-30%) well absorbed. Repeat administration (25 mg/kg/day for 3 weeks) did not change the rate of LDEA absorption. The absorption of 100 mg/kg doses was studied in jugular vein-cannulated rats. Steady state levels of LDEA equivalents were reached 24 hr after dermal administration. LDEA comprised about 15% of the radioactivity in plasma, with the remainder present as polar metabolites. A range of 50-70% of the dermal doses to mice, applied at 50, 100, 200, and 800 mg/kg, was absorbed in 72 hr. Absorbed LDEA distributed into the tissues with the same relative profile as that for the iv dose, except that distribution into adipose tissue was considerably lower. High oral doses of LDEA (100 mg/kg) in rats were well absorbed and mostly excreted in the urine as two very polar metabolites. The metabolites were isolated and characterized as the half-acid amides of succinic and of adipic acid, presumably arising from omega-hydroxylation and eventual beta-oxidation to give the chain-shortened products.

p, p'-Dichlorodiphenyl sulfone (DDS) is a lipophilic monomer used extensively in the synthesis of high temperature plastics. Studies of the fate of uniformly labeled [14C]DDS in the rat have established that it is readily absorbed from the gastrointestinal tract, distributed to all tissues examined, and concentrated in adipose tissue. After intravenous administration of 10 mg/kg and determination of the time course of DDS distribution, increasing accumulation of DDS in adipose was observed up to 24 hr, followed by slow elimination with a half-life of approximately 12 days. DDS equivalents in tissues were primarily (> 90%) parent compound, whereas excreted DDS equivalents were primarily (> 80%) present as metabolites. On repeat oral dosing at 10 mg/kg, levels of DDS in tissues seemed to reach steady state after approximately 2 weeks, at which time the concentrations in adipose reached 265 micrograms/g tissue. Hepatic cytochrome P450 (CYP) content, ethoxyresorufin O-deethylase activities, and levels of metabolites arising from phase I metabolism were doubled after repeat oral administration of DDS, but benzphetamine N-demethylase activity was unchanged. Thus, it seems that DDS induces CYP1A forms, but not CYP2B isozymes. DDS-derived radioactivity was excreted primarily in feces and to a lesser extent in urine as a phenolic metabolite and its glucuronide. The aglycone of this glucuronide was isolated and characterized by NMR and MS as 3-hydroxy-4,4'-dichlorodiphenyl sulfone.

Lauramide diethanolamine (LDEA)--a compound used in cosmetics and soap products as an emollient, thickener, and foam stabilizer--was observed to be metabolized by rat liver microsomes to two major products that were identified by GC/MS to be the 11-hydroxy and 12-hydroxy derivatives of LDEA. The specific activities for LDEA 11- and 12-hydroxylation in microsomes prepared from control rats were 2.23 +/- 0.40 and 0.71 +/- 0.17 nmol/min/mg protein, respectively. Treatment of rats with the cytochrome P4504A inducer and peroxisome proliferator, diethylhexyl phthalate, increased the LDEA 12-hydroxylation rate to 3.50 +/- 0.48 nmol/min/mg protein, a 5-fold increase in specific activity, whereas the LDEA 11-hydroxylase activity remained unchanged. Because LDEA contains a 12-carbon side chain, LDEA hydroxylation rates were compared with the hydroxylation rates for lauric acid. The specific activities of lauric acid 11- and 12-hydroxylation reactions in diethylhexyl phthalate-treated rats were 1.7-fold and 3.2-fold greater than the LDEA 11- and 12-hydroxylation rates, respectively. When LDEA hydroxylation reactions were performed in the presence of a polyclonal antibody to the rat P4504A forms, formation of 12-hydroxy-LDEA was inhibited by 80%. Rat kidney microsomes also supported the hydroxylation of LDEA at its 11- and 12-carbon atoms, with specific activities of 0.05 +/- 0.01 and 0.28 +/- 0.02 nmol/min/mg protein, respectively. LDEA was also metabolized to 11- and 12-hydroxy derivatives by human liver microsomes at specific activities of 0.22 +/- 0.06 and 0.84 +/- 0.26 nmol/min/mg protein, respectively.

Abstract We have previously described a method to capture, identify and quantify volatile components in expired breath. The purpose of this research is to provide a non-invasive means to measure biomarkers of metabolism in vivo. In the present studies, the effect of 1-aminobenzotriazole (ABT), an inhibitor of diverse cytochrome P450 (P450) enzymes, on the composition of volatile organic chemicals (VOCs) expired in the breath of male F-344 rats was determined in parallel with the catalytic activities and total content of hepatic P450. lntraperitoneal administration of ABT (100 mg kg-(1)) to rats resulted in markedly diminished hepatic microsomal P450 content and activities. The extent of inhibition was near maximal at 4 h, at which time approximately 50% of the total P450 content, about 65% of the CYPlA2 activity, 55% of the CYP2E1 activity, and about 80% of CYP2B activity were lost. Inhibition was maintained to 48 h post-dosing, but P450 content and activities had largely been restored by day 7. Concomitant with the inhibition of P450 were corresponding increases (up to several hundred-fold) in the molar amount of volatiles appearing in the breath of ABT-treated animals, and the rebound of P450 levels was attended by corresponding decreases in the appearance of breath volatiles. These studies indicate that P450 plays a major role in the metabolism of VOCs appearing in breath, and that these chemicals can serve as markers on P450 activity in vivo.

Diethanolamine (DEA) is a major industrial chemical which has low acute toxicity, but, on repeat exposure, has significant cumulative toxicity. The present work suggests that the cumulative toxicity can be attributed to the fact that, unlike most small polar molecules, DEA accumulates to high concentrations in certain tissues following repeat exposure. The highest concentrations of DEA were seen in liver, kidney, spleen, and brain. Investigations described here have determined that DEA is metabolized by biosynthetic routes common to ethanolamine and is conserved, O-phosphorylated, N-methylated, and incorporated into phosphoglyceride and sphingomyelin analogues as the parent compound and as its N-methyl and N,N-dimethyl derivatives. This is the first report of the conjugation of a xenobiotic headgroup with a natural ceramide to form aberrant sphingomyelins. DEA-derived phosphoglycerides constituted the majority of aberrant phospholipid following acute administration. On repeat administration, DEA bioaccumulated to plateau levels at approximately 8 weeks. This bioaccumulation was accompanied by an increasing degree of methylation and accumulation of aberrant sphingomylenoid lipids in tissues. Uptake and incorporation of DEA into ceramide derivatives in human liver slices were also demonstrated in the present studies. It is speculated that the cumulative toxicity observed on repeat administration of DEA to rats is caused in part by increasing levels of aberrant phospholipids derived from this unnatural alkanolamine.

A method is described for the simultaneous determination of l-alpha-acetylmethadol (LAAM) and its N-demethylated metabolites, l-alpha-noracetylmethadol (norLAAM) and l-alpha-dinoracetylmethadol (dinorLAAM), in plasma by gas chromatography-chemical ionization mass spectrometry. Deuterated internal standards for each analyte serve as carriers and control for recovery during sample purification on a solid-phase extraction column (C18), and subsequent separation and analysis on a DB-17 capillary column. With this method, we have determined levels of LAAM, norLAAM, and dinorLAAM in small volumes of plasma (100 microliters). The limit of quantitation for all analytes was approximately 1.0 ng/g plasma and the limit of detection was approximately 0.5 ng/g plasma. An experimental application is also described where these analytes are quantitated in plasma obtained from rats before, during, and after chronic administration of LAAM-HCl. Since this technique affords a selective and sensitive means of detection of LAAM and its active, N-demethylated metabolites in small samples of blood, it may enable patient compliance to be more easily assessed by allowing samples to be collected by a simple finger-prick technique.

Two N-aralkylated (N-benzyl-and N-alpha-methylbenzyl-) derivatives of 1-aminobenzotriazole, a mechanism-based inhibitor of cytochrome P450 with low isozyme selectivity, were previously shown to be potent and isozyme-selective suicide substrates for rabbit and guinea pig pulmonary P450 in vitro (Mathews and Bend, 1986; Woodcroft et al., 1990). These three compounds were compared as inhibitors in vivo after i.v. administration to rabbits treated with the cytochrome P450 inducers beta-naphthoflavone or phenobarbital. By 1 hr after administration of N-alpha-methylbenzyl-1-aminobenzotriazole (1 mumol/kg), 80% of P450 2Bs-catalyzed benzphetamine N-demethylation in lung of beta-naphthoflavone-treated rabbits was inactivated and about 35% of P450 was lost without inhibition of P450 1A1-catalyzed activity; at a dose of 10 or 100 mumol/kg, this compound totally inactivated pulmonary P450 2Bs activity while exerting minimal effects on benzphetamine N-demethylation activity (< 20% inhibition) in liver of beta-naphthoflavone-treated rabbits. N-benzyl-1-aminobenzotriazole was also an isozyme- and tissue-selective inhibitor of pulmonary P450 2Bs in vivo. Relatively high doses (100 mumol/kg) of these compounds were compared in phenobarbital-induced rabbits. Virtually all (> or = 95%) of pulmonary P450 2Bs-dependent activity was inhibited by the two N-aralkylated compounds (vs. 50% for 1-aminobenzotriazole). At this dose, about 25% of hepatic P450 was destroyed by all three compounds, whereas 1-aminobenzotriazole and its N-benzyl and N-alpha-methylbenzyl derivatives inactivated 20, 50 and 85% of hepatic P450 2Bs-selective benzphetamine N-demethylation activity, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The disposition of carbon-14-labeled diethylene glycol (DEG) was determined in rats after oral, iv, and dermal administration, and in dogs after oral administration. Oral administration of DEG to rats was by gavage of 50 or 5000 mg/kg doses, or by provision of 0.3 1.0, and 3.0% in drinking water. Oral doses were well absorbed and excreted primarily (approximately 80%) in urine within 24 hr of administration. Greater than half of the dose was excreted unchanged, with 10-30% of the dose appearing as a single metabolite. The metabolite was isolated and characterized by 13C-NMR to be 2-(hydroxy) ethoxyacetic acid (HEAA). Confirmation of identity was provided by synthesis of HEAA and comparison of its NMR spectra and chromatographic behavior with those of the metabolite. Intravenous doses (50 mg/kg) were eliminated by the same routes and at the same rates as those administered orally and exhibited the same metabolic profile. The fate of oral doses of DEG administered to dogs (500 mg/kg) was similar to that of DEG in rats, with about 30% of the administered dose being excreted in urine as HEAA. DEG slowly penetrated the skin of rats after application of 50 mg to a 12-cm2 area. Only about 10% of the dose was absorbed in 72 hr of exposure, and the absorbed dose appeared to have the same fate as doses administered iv or orally. In all studies with rats, excretion of radiolabel in feces and persistence in tissues were low. The highest percentage of conversion to 14CO2 was 7%, found for doses of 0.3% DEG in drinking water.

The disposition of [14C]bromodichloromethane (BDCM) was studied in male Fischer rats after single oral doses of 1, 10, 32, or 100 mg/kg and 10-d repeat oral dosing of 10 or 100 mg/kg/d. Methods were developed to quantitate exhaled 14CO and 14CO2. Bromodichloromethane was extensively (approximately 80-90%) metabolized within 24 h postdosing with approximately 70-80% of the administered dose appearing as 14CO2 and approximately 3-5% as 14CO. Urinary and fecal elimination were low, accounting for 4-5% and 1-3% of the dose, respectively. Oral administration of BDCM at a level of 10 mg/kg/d for 10 d did not result in the bioaccumulation or altered disposition of the test chemical, but during the course of the repeat 100 mg/kg/d dosing the rate of production of 14CO2 increased, suggesting that this dose of BDCM induced its own metabolism. Persistence of radiolabeled residues in tissues collected 24 h after single-dose administration was low (3-4% of dose), with the most marked accumulation (1-3% of dose) in liver. Kidney tissue, particularly the cortical region, also contained significant concentrations of residues.

The autocatalytic destruction of pulmonary cytochrome P-450 (P-450) by 1-aminobenzotriazole (ABT) was investigated in microsomes and in isolated perfused lungs from untreated and beta-naphthoflavone-induced rabbits. Microsomal benzphetamine N-demethylase (BND) and 7-ethoxyresorufin O-deethylation (ERF) activities, catalyzed by P-450 isozymes 2 and 6, respectively, and specific P-450 content were determined after incubation with ABT. In vitro destruction of P-450 was dependent on ABT concentration and required NADPH. Significant losses of BND and ERF activities were observed only at ABT concentrations above 10 microM. Percent losses of BND and ERF activities equaled those of total P-450 at 1 mM and surpassed them at 10 mM. The time and concentration dependence of the destruction of P-450 by ABT was investigated in isolated perfused rabbit lungs. The percent loss of total P-450 increased with increasing ABT concentration (18 +/- 8% loss at 1 microM to 85 +/- 4% at 10 mM). Although extensive losses of P-450 occurred after perfusion with 10 mM ABT for 60 min, no ABT-dependent losses of flavin-containing monooxygenase activity were observed under these conditions. Percent losses of BND activity in these experiments were similar to those of total P-450 at 1 and 10 mM ABT but were less than P-450 losses at 0.01 and 0.1 mM ABT. Losses of ERF activity in lungs from beta-naphthoflavone-pretreated animals were also substantial and dependent upon perfusion time. Perfusion with 1 mM ABT for 2 to 60 min resulted in time-dependent losses of P-450 (42.8 +/- 7.2% at 2 min to 70.5 +/- 2.5% at 60 min) with equal or somewhat lesser diminishment of BND and ERF activities.(ABSTRACT TRUNCATED AT 250 WORDS)

The mouthparts of female Corethrella brakeleyi and C. wirthi were studied using light and electron microscopy. Mandibles, hypopharynx and labium are highly sclerotized and are modified for obtaining blood meals. All structures were larger in C. brakeleyi than in C. wirthi except mandibular and hypopharyngeal teeth; these were smaller and more numerous in C. brakeleyi. The labium of both species terminates in peg-like structures which are similar to those reported from several genera of mosquitoes. Sensillae on the second segment of the maxillary palps appear to be identical to those described in both biting and nonbiting male and female blackflies., (Copyright © 1979 Wiley-Liss, Inc.)

Single esophageal and paired cheliceral, palpal, pedal (I-IV), and opisthosomal nerves enter the synganglion and form specific neuropilar ganglia. The ganglia are integrated by a complex series of commissures and connectives. Eighteen paraldehyde-fuchsin-positive neurosecretory regions, which vary greatly in size and amount of granular neurosecretory material, are each associated (one or more) with neuropilar ganglia. Presumably transport of neurosecretory materials to target tissues occurs through axonal pathways, perineurial-neural lamella associations, and the neurohemal retrocerebral organ complex., (Copyright © 1982 Wiley-Liss, Inc.)

Destruction of hepatic cytochrome P-450 during catalytic processing of 1-amino-benzotriazole is accompanied by an equal loss of microsomal haem but not by loss of cytochrome b5, or stimulation of lipid peroxidation. An abnormal porphyrin, tentatively identified as an NN-bridged benzyne-protoporphyrin IX adduct, appears to be formed by the addition of catalytically generated benzyne to prosthetic haem.

Sperm induction pores, tubuli annulati, rami sacculi, sacculus foemineus, cornu sacculus and acantho-membranous hood in female Dermanyssus gallinae support the probability of coxal insemination as reported for some other mesostigmatid species. Development of the circular testis in males (from fusion of two anterolaterally projecting protonymphal testicular arms) and formation of haploid (n = 3) spermatids from haploid (n = 3) spermatogonial cells is entirely mitotic. Spermatogenesis begins within one hour after protonymphal feeding and continues through adult ecdysis in normally fed individuals. Nutritional deficit causes cessation of spermatogenic divisions in deutonymphs starved 23 days, but is rapidly rejuvenated upon feeding. No rejuvenation of division was observed in adult males given the opportunity to feed, thus adult males might not feed., (Copyright © 1976 Wiley-Liss, Inc.)

To produce potent, isozyme-selective suicide inhibitors of cytochrome P-450 (P-450), a series of N-alkylated 1-aminobenzotriazole (ABT) derivatives was synthesized; these included the N-methyl, N-butyl (BuBT), N-benzyl (BBT), and N-alpha-methylbenzyl (alpha MB) analogues of ABT. The suicide inhibitors showing the greatest potency and isozyme selectivity were BBT and alpha MB, compounds which included molecular features for P-450 inactivation (the ABT moiety) and similarity to benzphetamine. ABT and its N-alkylated derivatives were tested as suicide inhibitors in rabbit lung microsomes, whose P-450 monooxygenase system has been well characterized in both untreated and beta-naphthoflavone- or 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated animals. ABT (10 mM) destroyed up to 99% of the total P-450 content of lung microsomes of untreated rabbits. At equimolar concentrations (10 microM), ABT was less effective than the N-alkylated compounds for the inhibition of P-450 isozyme 2-catalyzed benzphetamine N-demethylation (BND); in fact, BuBT, BBT, and alpha MB completely inhibited BND activity at this concentration and destroyed less than 40% of total pulmonary P-450. However, these compounds also inactivated 69-85% of isozyme 6-catalyzed 7-ethoxyresorufin O-deethylation. The most potent and isozyme-selective suicide inhibitor prepared was alpha MB: at 1 microM this compound inhibited approximately 80% of isozyme 2-catalyzed and 20% of isozyme 6-catalyzed monooxygenase activity but spared P-450 isozyme 5; at 2.5 microM it caused a near-complete loss (96 +/- 2%) of BND activity. The partition ratio of alpha MB, i.e., the molar ratio of inhibitor present to that of the P-450 destroyed, was 11 +/- 2, further demonstrating the potency of this compound. Experiments with BBT- and sodium phenobarbital-treated rats showed that the mechanism for suicidal inactivation of P-450 by this N-alkylated compound was by benzyne release, the same mechanism demonstrated earlier for the parent compound ABT.

4-Ipomeanol is a naturally occurring toxin that induces lesions in the lung following its activation to an alkylating metabolite by the pulmonary cytochrome P-450 system. The aim of this study was to determine if an environmentally relevant concentration of carbon monoxide could inhibit the activation of 4-ipomeanol and prevent the associated toxic sequelae in the isolated perfused rabbit lung. The lungs of male New Zealand rabbits were removed and perfused with [14C]-4-ipomeanol for 2 h starting with an initial concentration of 0.1 mM. Lungs were ventilated with either air (control) or 7.5% CO/20% O2. 4-Ipomeanol-derived covalent binding was identical in the control and carbon monoxide treatment groups. Lungs perfused with 4-ipomeanol and ventilated with air or 7.5% CO/20% O2 both displayed alveolar type II cell hyperplasia and alveolar macrophage infiltration. Surprisingly, there was no histological evidence of Clara cell damage in any of the 4-ipomeanol-perfused lungs. These results suggest that the isozymes of pulmonary cytochrome P-450 that act in concert to metabolize 4-ipomeanol are relatively insensitive to inhibition by carbon monoxide.