The effects of streptozotocin-induced diabetes and fasting on hepatic cytochrome P-450 enzymes in sexually mature male rats were studied by immunochemical techniques and enzyme assays. The level of cytochrome P-450ac (an acetone/ethanol inducible form), 65 pmol/mg microsomal protein in control rats, increased 4- to 5-fold in diabetic rats and 3- and 5-fold in fasting rats. In contrast, P-450 UT-A (a male specific form) decreased drastically from 295 pmol/mg in the control group to about 10% of this value in diabetic rats and to 50% in fasting rats. P-450 PCN-E (a 16 alpha-cyanopregnenolone/dexamethasone inducible form), on the other hand, decreased from 151 pmol/mg to 38% in diabetic rats and increased 2-fold in fasting rats. These changes were also reflected in catalytic activities using N-nitrosodimethylamine, benzphetamine, and erythromycin as substrates. Slight changes in cytochromes P-450 UT-F, P-450 UT-I and P-450 PB-C were also observed under these conditions, but the biological significance is not known. These results suggest that different mechanisms exist for the regulation of the expression of cytochrome P-450 enzymes in diabetic and fasting rats.

Rats display a marked sex difference in the oxidation of the pyrrolizidine alkaloid senecionine, especially with respect to N-oxidation. This sex difference was largely eliminated following treatment with dexamethasone. These observations suggested the potential involvement of the male-specific cytochrome P-450 UT-A and the P-450 PCN-E in the metabolism of this pyrrolizidine alkaloid. Reconstituted rat P-450 UT-A exhibited a high rate of N-oxidation (15 nmol min-1 nmol P-450-1) which is almost 3-fold higher than the turnover number observed with male rat liver microsomes. In contrast, rat P-450 UT-A displayed a much lower activity toward necine pyrrole [+/-)-6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine, DHP) formation (1.0 nmol min-1 nmol P-450-1). The N-oxygenation and pyrrole formation activities displayed by rat cytochromes P-450 PB-B and P-450 BNF-B toward senecionine were low, with rates less than 1 nmol min-1 nmol P-450-1. Rabbit antibody to rat P-450 UT-A inhibited the senecionine-N-oxidation activity of untreated male rat liver microsomes by 60%, with lesser inhibition of DHP production. Rabbit antibody to human P-450NF (the human homologue to rat P-450 PCN-E) was a potent inhibitor of DHP production by untreated male rat liver microsomes. With microsomes from dexamethasone-pretreated rats, anti-P-450NF inhibited DHP and N-oxide production in parallel. We conclude that the large sex difference in senecionine N-oxidation probably is the result of the specificity of P-450 isozymes UT-A and PCN-E.(ABSTRACT TRUNCATED AT 250 WORDS)

Total microsomal cytochrome P-450 levels were decreased, to about 50% of control, in liver of male rats made cirrhotic by the prolonged intake of a choline-deficient diet. We have suggested previously that this decrease in cytochrome P-450 levels is not a generalized one, but is selective for certain forms of the enzyme. In the present study, levels of six cytochrome P-450 forms including the sex-specific cytochrome P-450 forms, P-450UT-A, P-450PCN-E, and P-450UT-l, were quantitated immunochemically in hepatic microsomes prepared from control and cirrhotic male rats and were related to changes in the regioselectivity of cytochrome P-450-mediated androst-4-ene-3,17-dione hydroxylation in these fractions. The principal finding of this study was that the male-specific androst-4-ene-3,17-dione 16 alpha-hydroxylase was decreased in cirrhotic microsomes to about 20% of control. The content of P-450UT-A decreased concurrently from about 0.40 to less than 0.01 nmol/mg of microsomal protein. Other pathways of androst-4-ene-3,17-dione hydroxylation were also affected, but to different extents than the 16 alpha-hydroxylase. 6 beta-Hydroxylation decreased in cirrhotic microsomes to about 45% of control, despite a marked decrease in P-450PCN-E from 0.27 to less than 0.002 nmol/mg of microsomal protein. The rate of androst-4-ene-3,17-dione 7 alpha-hydroxylation underwent a less pronounced reduction in cirrhosis to about two-thirds of control microsomal activity, and levels of the cytochrome P-450 associated with this activity, P-450UT-F, were decreased in proportion with the decrease in total microsomal cytochrome P-450. 16 beta-Hydroxylase activity was unaffected by the cirrhotogenic process. From spectral binding studies it was apparent that androst-4-ene-3,17-dione elicited a high affinity type I interaction in control microsomal fractions (Ks = 4.5 microM), whereas no interaction was apparent in cirrhotic liver microsomes. Levels of three other forms of cytochrome P-450--P-450PB-C (a constitutive form inducible by phenobarbital), P-450ISF-G (a major isosafrole-inducible form), and P-450UT-I (the major female sexually-differentiated isozyme)--were apparently unaltered in cirrhosis. These findings are consistent with the assertion that specific forms of cytochrome P-450 are subject to altered regulation in hepatic cirrhosis.

Conference Article| August 01 1987 Cytochrome P-450 enzymes involved in genetic polymorphism of drug oxidation in humans F. PETER GUENGERICH; F. PETER GUENGERICH 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar PHILIPPE H. BEAUNE; PHILIPPE H. BEAUNE 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar DIANE R. UMBENHAUER; DIANE R. UMBENHAUER 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar PERRY F. CHURCHILL; PERRY F. CHURCHILL 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar RICHARD W. BORK; RICHARD W. BORK 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar GHAZI A. DANNAN; GHAZI A. DANNAN 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar ROBERT G. KNODELL; ROBERT G. KNODELL 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar R. STEPHEN LLOYD; R. STEPHEN LLOYD 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar MARTHA V. MARTIN MARTHA V. MARTIN 1Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232, U.S.A. Search for other works by this author on: This Site PubMed Google Scholar Author and article information Publisher: Portland Press Ltd Received: February 05 1987 Online ISSN: 1470-8752 Print ISSN: 0300-5127 © 1987 Biochemical Society1987 Biochem Soc Trans (1987) 15 (4): 576–578. https://doi.org/10.1042/bst0150576 Article history Received: February 05 1987 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Facebook Twitter LinkedIn Email Cite Icon Cite Get Permissions Citation F. PETER GUENGERICH, PHILIPPE H. BEAUNE, DIANE R. UMBENHAUER, PERRY F. CHURCHILL, RICHARD W. BORK, GHAZI A. DANNAN, ROBERT G. KNODELL, R. STEPHEN LLOYD, MARTHA V. MARTIN; Cytochrome P-450 enzymes involved in genetic polymorphism of drug oxidation in humans. Biochem Soc Trans 1 August 1987; 15 (4): 576–578. doi: https://doi.org/10.1042/bst0150576 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll JournalsBiochemical Society Transactions Search Advanced Search This content is only available as a PDF. © 1987 Biochemical Society1987 Article PDF first page preview Close Modal You do not currently have access to this content.

Treatment of rats with the cytochrome P-450 suicide substrate, 3,5-diethoxycarbonyl-2,6-dimethyl-4-ethyl-1,4-dihydropyridine (DDEP), produced a 95% inhibition of the in vivo demethylation of either aminopyrine or morphine within 2 hr. One-carbon metabolism of formaldehyde or formate to carbon dioxide was not altered. DDEP also produced a time-dependent decrease in total hepatic microsomal cytochrome P-450 but had no effect on either NADPH-cytochrome c reductase or p-nitrophenol glucuronyl-transferase activities up to 24 hr after administration. A rapid decrease in rat liver microsomal aniline hydroxylation and ethoxyresorufin deethylation was observed in vitro following DDEP administration. Although in vitro testosterone metabolism to 16 alpha-, 16 beta-, and 2 alpha-hydroxy metabolites was depressed profoundly by DDEP in microsomes from untreated and 3-methylcholanthrene-treated animals, 7 alpha-hydroxylation of testosterone was much less affected. Immunochemical quantification of various microsomal cytochrome P-450 protein moieties showed that cytochromes P-450 beta NF-B, P-450UT-A, P-450PCN-E, and P-450PB-C were decreased in hepatic microsomes from DDEP-treated rats. However, the protein moiety of cytochrome P-450UT-H was not diminished and the immunoreactive protein for cytochromes P-450UT-F, P-450PB-B, and P-450ISF-G was only slightly decreased. These results show that DDEP treatment leads to marked decreases in holoprotein and apoproteins of many but not all hepatic microsomal cytochrome P-450 isozymes.

Neonatal gonadectomy studies and hormonal replacement regimens were employed to characterize the regulation of delta 4-steroid 5 alpha-reductase, microsomal flavin-containing monooxygenase, and several forms of rat hepatic microsomal cytochrome P-450, including three that are sexually differentiated. Rats of both sexes that had been gonadectomized at birth were either untreated or were administered testosterone propionate or estradiol benzoate neonatally (subcutaneous injection on days 1 and 3 of life), postpubertally (an implant of a hormone-packed capsule at 5 weeks of age), or both neonatally and postpubertally. At the age of 10 weeks, all rats were killed, and several liver microsomal enzymes were assayed using immunochemical and catalytic techniques. Expression in the 10-week-old male and female rats of two male-specific cytochrome P-450 forms, termed P-4502c/UT-A and P-4502a/PCN-E, and their associated respective 16 alpha- and 6 beta-steroid hydroxylase activities could either be imprinted (programmed) by androgen exposure during the early neonatal period or, alternatively, could be stimulated by continuous hormone treatment after the age of 5 weeks. By contrast, hepatic expression of two female-specific enzymes, P-4502d/UT-1 and delta 4-steroid 5 alpha-reductase, was only partially dependent on estradiol; birth-gonadectomized rats expressed as much as 30-50% of the enzyme levels present in untreated adult females. Expression of both female-specific enzymes was fully suppressed upon postpubertal exposure to testosterone. In another study, birth sham-operated female rats were administered testosterone using the same regimens described above for the birth-gonadectomized rats. Although neonatal testosterone treatment alone did not affect the expression in these females of the four sex-specific enzymes examined in this study, it did enhance significantly the masculinization effected by postpubertal androgen exposure. This resulted in expression of the male-specific enzymes P-4502c/UT-A and P-4502a/PCN-E in these females at levels comparable to those found in adult males, while simultaneously suppressing the two female-specific enzymes, P-4502d/UT-I and delta 4-steroid 5 alpha-reductase, by approximately 70-75% to levels characteristic of prepubertal rats of either sex. The levels of another microsomal enzyme, flavin-containing monooxygenase, were also measured and found to be regulated by testosterone, but the ontogenic profiles and the effects of gonadectomy and hormone replacement indicated clear differences in its regulation when compared to the other male-specific enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

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

We prepared primary monolayer cultures of adult rat hepatocytes and measured the losses of cytochromes P-450 with the use of specific antibodies directed against purified forms of hepatic cytochrome P-450 which predominate in untreated rats (P-450UT-A, P-450UT-F) or in rats treated with phenobarbital (P-450PB-B/D, P-450PB-C, P-450PB/PCN-E) or with 3-methylcholanthrene (P-450 beta NF-B, P-450 beta NF/ISF-G). In hepatocytes prepared from an untreated rat and incubated in control medium, total cytochrome P-450, measured spectrally as CO-binding hemoprotein, declined 68% during the first 72 hr in culture. However, the sum of the immunoreactive cytochromes P-450 declined only 24%, indicating that loss of heme rather than of protein accounts for much of the well-known loss of cytochromes P-450 in hepatocyte cultures. In cultures prepared from untreated rats or from rats treated with phenobarbital or with 3-methylcholanthrene, individual forms of cytochrome P-450 declined at markedly differing rates. Incubation of cultures in three different media previously reported to maintain levels of total cytochrome P-450 failed to prevent the decline in total cytochrome P-450 during the first 24 to 72 hr in culture. However, in cultures incubated in medium containing metyrapone, the level of holocytochrome P-450 was maintained at the initial value during the first 72 hr, apparently by preventing the net loss of cytochrome P-450 heme and by increasing the concentrations of immunoreactive P-450PB/PCN-E and P-450 beta NF-B. Medium containing nicotinamide increased the proportion of P-450 beta NF-B relative to the other forms of cytochrome P-450, whereas cysteine-free medium increased P-450UT-F. We conclude that loss of cytochrome P-450 in cultured hepatocytes involves loss of its heme moiety coupled with changes in the concentrations of the individual forms. Recognition of these changes as influenced by specific components of the culture medium is important when using primary hepatocyte cultures for study of xenobiotic metabolism and toxicity in the liver.

The in vitro metabolism of polybrominated biphenyl (PBB) congeners by cytochrome P-450-dependent monooxygenases was investigated using hepatic microsomes isolated from immature male rats pretreated with 3-methylcholanthrene (MC) or phenobarbital (PB). MC pretreatment increased the NADPH-dependent microsomal metabolism of pure PBB congeners which possessed adjacent nonhalogenated ortho and meta carbons on at least one ring. 4,4'-Dibromobiphenyl (-DBB) was metabolized at the fastest rate, followed by 3,4,4'-tribromobiphenyl, 3,4,3',4'-tetrabromobiphenyl (-TBB), 2,3,3',4'-TBB, 2,5,3',4'-TBB, and 2,4,2',5'-TBB in decreasing order. It appeared that further bromination prevented metabolism since 2,4,5,3',4'-pentabromobiphenyl (-PBB), 2,3,4,2',4',5'-hexabromobiphenyl (-HBB), and 2,3,4,5,3'.4'-HBB were not metabolized although they possess adjacent nonhalogenated ortho and meta carbons. PB pretreatment increased in vitro rat hepatic microsomal metabolism of PBB congeners which possessed adjacent nonhalogenated meta and para carbons on at least one ring. 2,2'-DBB was metabolized at the fastest rate, followed by 2,4,2',5'-TBB, 2,5,2',5'-TBB, 2,3,3',4'-TBB, 2,5,3',4'-TBB, and 2,4,5,2',5'-PBB in decreasing order. The results suggest that the rates of metabolism of PBB congeners are dependent upon the positions of bromine and the form of cytochrome P-450 induced. In vitro rates of metabolism of 3,4,3',4'-TBB using hepatic microsomes isolated from rats pretreated with either 3,4,5,3',4',5'-HBB or 3,4,3',4'-TBB were also investigated. There was good correlation between the rates of 3,4,3',4'-TBB metabolism, induction of microsomal ethoxyresorufin-O-deethylase activity, and specific content of MC-inducible cytochrome P-450 (P-450 beta NF-B). The results suggest that the isozyme P-450 beta NF-B is responsible for the metabolism of 3,4,3',4'-TBB.

The influence of age, sex, and hormonal status on the expression of eight rat hepatic cytochrome P-450 (P-450) isoenzymes was evaluated by both catalytic and immunochemical methods. The male specificity of P-450 2c(male)/UT-A, the major microsomal steroid 16 alpha-hydroxylase of uninduced rat liver [Waxman, D.J. (1984) J. Biol. Chem. 259, 15481-15490], was shown to reflect its greater than or equal to 30-fold induction at puberty in male but not in female rats. The female specificity of P-450 2d(female)/UT-I was shown to reflect its developmental induction in females. P-450 PB-2a/PCN-E was shown to mediate greater than or equal to 85% of microsomal steroid 6 beta-hydroxylase activity; the male specificity of this P-450 largely reflects its developmental suppression in female rats. Neonatal gonadectomy and hormonal replacement experiments established that neonatal androgen "imprints" or programs the male rat for developmental induction of P-450 2c(male)/UT-A, for maintenance of P-450 PB-2a/PCN-E, and for suppression of P-450 2d(female)/UT-I, all of which occur in male rats at puberty. By contrast, the expressed levels of P-450 isoenzymes PB-1/PB-C, 3/UT-F, PB-4/PB-B, ISF-G, and beta NF-B were mostly unaffected by the rats' age, sex, and hormonal status. Studies on the sex specificity of P-450 induction established that the response of these latter five isoenzymes to the P-450 inducers phenobarbital, beta-naphthoflavone, pregnenolone-16 alpha-carbonitrile, and isosafrole is qualitatively and quantitatively equivalent in females as in males.

Pretreatment of adult male rats with sulmazole (AR-L 115 BS) results in a 2-6-fold increase of the liver microsomal scoparone O-demethylation and 7-ethoxycoumarin O-deethylation activity. The change in the ratio of the demethylation products scopoletin to isoscopoletin from 1 : 1.8 +/- 0.1 in control microsomes to 1: 2.5 +/- 0.1 in microsomes from sulmazole pretreated rats is statistically significant. Sulmazole produces a modified type II difference spectrum when added to microsomes of control or sulmazole-pretreated rats. Immunoquantitation of seven cytochromes P-450 showed that two forms, namely P-450 beta NF/ISF-G and P-450 beta NF-B, are increased 3-4-fold in the microsomes of sulmazole-pretreated rats.

The composition of isozymes of hepatic microsomal cytochrome P-450 (P-450) from C57BL/6 (B6) and DBA/2 (D2) inbred strains of mice, uninduced and treated with phenobarbital (PB), pregnenolone-16 alpha-carbonitrile (PCN), and beta-naphthoflavone (BNF), were assessed. The assessment was based on comparisons of the regioselectivity and stereoselectivity of warfarin metabolism, inhibition of metabolism by antibodies raised against highly purified rat P-450 isozymes (the specificity of these antibodies in inhibiting rat microsomal metabolism of warfarin was also determined), and by immunoelectrophoresis using the anti-(rat P-450). Isozymes were considered to be the same or very similar if they exhibited the same substrate specificity, antigenicity, and molecular weight. Untreated D2 and B6 mice had similar compositions of P-450 isozymes which were independent of the Ah receptor. Both strains contained an isozyme very similar to rat P- 450UT -A. PB or PCN induction of the two mouse strains proceeded independently of the Ah receptor and yielded isozymes which are the same as or very similar to the rat P- 450UT -A, P- 450PB -B, P- 450PB -C, and P- 450PB /PCN-E isozymes. D2 and B6 mice had similar isozyme compositions when treated with PB or PCN, but isozyme compositions varied in differently induced mice. BNF treatment of the D2 mice was without effect, but the B6 mice produced an isozyme(s) which was different from rat P- 450BNF -B, the major BNF-induced isozyme in rat liver.

Seven isozymes of cytochrome P-450 were tested to establish whether they could N-oxidize azoprocarbazine to form the two isomeric azoxy metabolites after optimizing the reconstitution of various purified isozymes with regard to substrate concentration, exogenous lipid, and reduced nicotinamide adenine dinucleotide phosphate-cytochrome c (P-450) reductase concentration. Two isozymes, cytochromes P-450PB-C (an isozyme present in untreated rats or in rats treated with phenobarbital or beta-naphthoflavone) and P-450 beta NF-B (the major beta-naphthoflavone-induced isozyme), had appreciable turnover numbers for the N-oxidation reaction. The product ratio [N-isopropyl-alpha-(methyl-ONN-azoxy)-p-toluamide formation relative to N-isopropyl-alpha-(methyl-NNO-azoxy)-p-toluamide formation] obtained with cytochrome P-450PB-C was nearly identical to those values obtained with liver microsomes from untreated and phenobarbital-treated rats. In addition, cytochrome P-450 beta NF-B and liver microsomes from beta-naphthoflavone-treated rats had nearly identical product ratios. Specific inhibitory antibodies to four purified isozymes were used to titrate the N-oxidase activity of liver microsomes from untreated, phenobarbital-, pregnenolone-16 alpha-carbonitrile-, or beta-naphthoflavone-treated rats. Anti-cytochrome P-450PB-C globulin inhibited more than 70 to 90% of the formation of N-isopropyl-alpha-(methyl-ONN-azoxy)-p-toluamide in microsomes from untreated, phenobarbital-, and pregnenolone-16 alpha-carbonitrile-treated rats, respectively, but only 20 to 50% of N-isopropyl-alpha-(methyl-NNO-azoxy)-p-toluamide formation. A small amount (25 to 30%) of inhibition was observed with anti-cytochrome P-450PB/PCN-E globulin. Anti-cytochrome P-450 beta NF-B globulin inhibited more than 85% of the synthesis of either azoxy isomer catalyzed by liver microsomes from beta-naphthoflavone-treated rats. These results demonstrate that two isozymes are responsible for the oxidative metabolism of azoprocarbazine and can account for the major portion of this N-oxidase activity in liver microsomes from untreated and phenobarbital-, pregnenolone-16 alpha-carbonitrile-, or beta-naphthoflavone-treated rats.

Genetic polymorphism in oxidative drug metabolism is perhaps best exemplified in the case of debrisoquine 4-hydroxylase activity, where the incidence of deficient metabolism ranges from 1% to 30% in various populations and this defect is also linked to an impaired ability to metabolize a number of other drugs effectively. Sprague-Dawley (SD) rats possess this activity, but females of the DA strain do not, although total cytochrome P-450 (P-450) levels are similar. We have purified, by using debrisoquine 4-hydroxylase activity as an assay, a minor P-450 to electrophoretic homogeneity from male SD rats and designate this as P-450UT-H. P-450UT-H differs from eight other purified rat liver P-450s as judged by peptide mapping and immunochemical analysis and thus appears to be isozymic with these other P-450s. P-450UT-H exhibited considerably more debrisoquine 4-hydroxylase activity than any of the other purified P-450s and, on a total P-450 basis, more than total microsomal P-450. Antibodies raised against P-450UT-H specifically recognized P-450UT-H and inhibited more than 90% of the debrisoquine hydroxylase activity present in SD rat liver microsomes. The level of P-450UT-H in SD rat liver microsomes accounted for less than 10% of the total P-450, as judged by immunochemical quantitation. These assays also indicated that the level of P-450UT-H in female DA rat liver microsomes is only about 5% of that in male or female SD rat liver microsomes, consonant with the view that deficiency of this form of P-450 is responsible for the defective debrisoquine 4-hydroxylase activity in the former animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific immunochemical techniques were used to quantitate the levels of eight isozymes of cytochrome P-450 (P-450) and epoxide hydrolase in liver microsomes of untreated rats and rats treated with phenobarbital, 3-methylcholanthrene, a mixture of these two compounds, nine individual polybrominated biphenyl (PBB) congeners, and a commercial mixture of PBBs. Levels of two 3-methylcholanthrene-inducible P-450s (designated P-450 beta NF-B and P-450 beta NF/ISF-G) varied over two orders of magnitude and were highly correlated. The levels of four phenobarbital-inducible P-450s (designated P-450PB-B, P-450PB-C, P-450PB-D, and P-450PB/PCN-E) were all correlated to each other. The level of one form, P-450UT-A, which was present at substantial levels in untreated rats, was inversely correlated to the levels of P-450 beta NF-B and P-450 beta NF/ISF-G. Among the PBB congeners which were examined, the presence of bromine at carbons o to the biphenyl bridge favored the induction of P-450PB-B, P-450PB-C, P-450PG-D, and P-450PB/PCN-E but did not necessarily eliminate the ability to induce P-450 beta NF-B and P-450 beta NF-ISF-G. PBB congeners with 2,2'-dibromo substitution induced P-450 beta NF-B and P-450 beta NF/ISF-G if one of the biphenyl rings contained bromines at positions 2,3, and 4. The induction of P-450UT-F was found to occur to a small extent with three of the compounds and is not readily explained in terms of structure-activity relationships. Although correlations were found among levels of some of the forms of P-450, several important exceptions were noted in relative levels of the individual enzymes. While the correlative data are useful in predicting induction patterns, all eight forms of P-450 appear to be independently regulated to some extent.