Lung Aryl Hydrocarbon Hydroxylase Research Articles

Monoclonal Antibody-Directed Analysis of Benzo[

Monoclonal antibody (MAb) 1-7-1 against 3-methylcholanthrene (MC)-induced forms of cytochrome P-450 (CYP) was used to characterize benzo[a]pyrene (B[a]P) metabolism in rat liver and extrahepatic tissues and its modulation by phenolic antioxidants, propyl and octyl gallates. Male Wistar rats were treated with these food additives (50 mg/kg body wt ip) twice weekly for 14 days alone or in combination with MC. Immunochemical inhibition of aryl hydrocarbon hydroxylase (AHH) and [<O*>14C]B[a]P metabolism (analyzed by high-performance liquid chromatography) were measured in liver, kidney, and lung microsomes. Organ-specific changes in levels of MAb-mediated inhibition of microsomal metabolism of B[a]P were observed. In liver microsomes from untreated rats, AHH was not affected by MAb, but in kidney and lung, there was 70% and 50% inhibition, respectively. In MC-treated rats, MAb reduced AHH activity by 43% in liver. Kidney and lung AHH was inhibited up to 80% by this MAb. Formation of B[a]P metabolites in MC-induced microsomes from liver and kidney was affected by MAb in a similar way. In lung, the total metabolism was inhibited by 50% by MAb treatment, but significant differences in inhibition of individual metabolites were observed. Treatment with propyl or octyl gallate alone had no effect on MAb inhibition of AHH activity in liver and lung but decreased the level of inhibition in kidney. Combined treatment with MC and propyl or octyl gallate slightly reduced the effect of MAb on AHH activity in liver and significantly reduced the level of inhibition in kidney but did not affect AHH activity in lung. The same treatment regimen dramatically reduced MAb inhibition of B[a]P metabolism in kidney but had no effect on B[a]P metabolite formation in liver. Inhibition by MAb of renal 3-hydroxy-B[a]P, 7,8-B[a]P-dihydrodiol, and 1,6-quinone-B[a]P was the most affected. In lung, treatment with gallates affected only formation of 7,8-B[a]P-dihydrodiol. These results suggest that treatment with gallates affects the CYP 1A and may change the CYP isozyme composition and, thus, alter the tissues' susceptibility to tumor induction by B[a]P.

INHIBITION OF RAT LUNG MIXED-FUNCTION OXIDASE ACTIVITY FOLLOWING REPEATED LOW-LEVEL TOLUENE INHALATION: POSSIBLE ROLE OF TOLUENE METABOLITES

Toluene is a commonly used solvent that has been shown to alter mixed-function oxidase (MFO) activity, in an organ- and isozyme-specific pattern, following intraperitoneal administration. The purpose of this study was to determine whether similar changes occurred following repeated, low-level inhalation exposure, and to investigate the role of toluene metabolites in these alterations. Exposure to 375 ppm toluene, 6 h/d for up to 5 d, resulted in significant inhibition of the activity of pulmonary arylhydrocarbon hydroxylase (AHH), cytochrome P-4502B1 (CYP2B1), and CYP4B1, but not CYP1A1. After exposure to lower toluene levels (125 ppm, 6 h/ d, 3 d), the activities of lung AHH, CYP2B1, and CYP4B1 were also significantly decreased, but in a dose-related manner. MFO activity was not consistently altered in liver. Control pulmonary or liver microsomes were incubated with various concentrations (0.01-10 m M) of toluene or its metabolites and CYP2B1, CYP1A1, and/or CYP4B1 activities were subsequently determined. Benzaldehyde produced a significant dose-related inhibition in the activity of all three lung P-450s examined (IC50 10-3 M). Toluene was found to be a more potent inhibitor of lung CYP2B1 and CYP1A1 (IC50, 10-4 M) than benzaldehyde, but neither toluene nor benzyl alcohol was an effective inhibitor of lung CYP4B1. Toluene and its metabolites were weaker inhibitors of CYP1A1 than of CYP2B1. For CYP2B1 and CYP1A1, the order of inhibitory potency was toluene > benzaldehyde > benzyl alcohol and suggests that both the parent molecule and its metabolites may act in concert to inhibit catalytic activity of these cytochromes. The MFO inhibition seen after repeated low-level toluene inhalation exposure could result in altered metabolic profiles of other xenobiotics in an organ-specific fashion.

Aryl Hydrocarbon Hydroxylase Activity in Human Lung Tissue: In Relation to Cigarette Smoking and Lung Cancer

In order to investigate the relationship between aryl hydrocarbon hydroxylase (AHH) activity and smoking or lung cancer, AHH activities in fresh lungs (normal tissue, tumorous tissue, and surrounding tissue of tumor) obtained from lung cancer patients and non-lung cancer patients were measured. There were no differences in lung AHH activity in the lung lobes. In the non-lung cancer patients, AHH activities ranged from 0.13 to 2.37 (pmol 3 hydroxybenzo[ a]pyrene/20 min/mg protein), and whereas in the normal tissues of the lung cancer patients they ranged from 0.19 to 5.05. Lung AHH activities showed normal distribution, and a large variation (26 times) was observed in normal tissues in the lung cancer patients. In most cases, AHH activities in the tumorous tissues and the surrounding tissue of the tumor were lower than those in the normal tissues of the lung cancer patients. In the non-lung cancer group, the means of AHH activity of the nonsmoker subgroup (NN) and the smoker subgroup (SN) were 0.62 and 0.96, respectively. On the other hand, in the lung cancer group the means of AHH activity of the nonsmoker subgroup (NC) and smoker subgroup (SC) were 0.85 and 1.05, respectively. Statistically significant differences were observed between NN and SN, NN and NC, and NN and SC. These results suggest that human lung AHH activity was increased by cigarette smoke as in rodent lungs, and the distribution of basal AHH activity in lung tissue of the nonsmokers group in the lung cancer patients shifted toward high levels compared to the nonsmokers group in the non-lung cancer group. The effect of the histological cell types of the lung cancer on the AHH activity was not observed in this study.

Differential activation and inactivation of benzo[ a]pyrene in various hepatoma cell lines

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.

Differential induction of cytochrome P-450 catalyzed activities by polychlorinated biphenyls and benzo[ a]pyrene in B6C3F 1 mouse liver and lung

The properties of some constitutive and inducible enzyme activities of liver and lung microsom̀es were determined in B6C3F 1 mice pretreated by either intratracheal (i.t.) administration of benzo[ a]pyrene (BaP) or polychlorinated biphenyl (PCBs) mixture (Aroclor 1254), or intraperitoneal (i.p.) administration with Aroclor 1254. After i.p. administration of Aroclor 1254, liver cytochrome P-450 content, aryl hydrocarbon hydroxylase (AHH), benzphetamine N-demethylase and nitroreductase activities were increased 2.8-, 2.0-, 2.2-, and 2.0-fold, respectively. Lung cytochrome P-450 content was also increased (1.9-fold) after i.p. administration of Aroclor 1254; AHH and nitroreductase activities, however, were not affected and benzphetamine N-demethylase activity was decreased. Aroclor 1254 administered i.t. did not affect liver cytochrome P-450 content. However, AHH and benzphetamine N-demethylase activities were decreased 1.4- and 1.2-fold, respectively, and nitroreductase activity was increased 1.6-fold. After i.t. administration of Aroclor 1254, lung cytochrome P-450 content and AHH activity were increased 1.4- and 2.2-fold, respectively. Benzphetamine N-demethylase activity was decreased 2.1-fold and nitroreductase activity was not affected. After i.t. administration of BaP, liver 7-ethoxyresorufin O-deethylase and nitroreductase activities were increased 2.2- and 1.5-fold, respectively, and benzphetamine N-demethylase activity was decreased 1.3-fold. Lung AHH and 7-ethoxyresorufin O-deethylase activities were increased 4.3- and 3.1-fold, respectively, and cytochrome P-450 content, benzphetamine N-demethylase and nitroreductase activities were decreased 1.4-, 1.2- and 1.3-fold, respectively, after BaP administration. These data indicate that different cytochrome P-450 isozymes induced in B6C3F 1 mice are responsible for monooxygenase and nitroreductase activities, and that the route of administration of chemicals is important in the expression of cytochrome P-450 catalyzed activities.

Inhibition of coal fly ash polycyclic aromatic hydrocarbons and metals induced mixed-function oxidase activity in rat lung and liver by vitamin A and citrate.

Administration of benzene-soluble fraction (FAE) and benzene-insoluble fraction (FAR) of fly ash for 3 consecutive days to rats significantly raised cytochrome P-450 levels, aryl hydrocarbon hydroxylase (AHH) activity, and glutathione S-transferase activity in liver. This treatment also significantly increased pulmonary AHH and glutathione S-transferase activity. Intratracheal administration of FAR (5 mg/100 g body weight) alone for 6 consecutive days also significantly increased hepatic cytochrome P-450 levels and the activity of glutathione S-transferase. Intragastric administration of retinyl palmitate (5000 IU/100 g body weight), along with intratracheal FAE and FAR administration, significantly reduced P-450 levels, activity of glutathione S-transferase in liver, and activity of AHH and glutathione S-transferase in lung of rats. Intraperitoneal administration of citrate (40 mg/100 g body weight) along with FAR significantly reduced FAR-induced increase in hepatic cytochrome P-450 levels and glutathione S-transferase activity. The activity of AHH was not affected by these treatments.

Interaction of Certain Metal Ions with Aryl Hydrocarbon Hydroxylase of Rat Lung Microsomes

The effect of varying concentrations of cadmium, copper, zinc, and selenite on the activity of aryl hydrocarbon hydroxylase (AHH) of rat lungs was studied in vitro. All the metals resulted in a strong inhibition of enzyme activity. Copper and zinc were more inhibitory to rat lung AHH than cadmium and selenite. There was an additive inhibition of AHH activity when copper or zinc was added in the presence of cadmium. EDTA or glutathione exerted a protective effect on cadmium-induced inhibition of AHH activity. Prior incubation of the microsomes with N-ethylmaleimide, a thiol-blocking agent, had no effect on the inhibition of AHH activity caused by cadmium. Addition of cadmium along with zinc-thionein resulted in increased inhibition of rat lung AHH.

Chronic phenytoin administration and the hepatic mixed function oxidase system in female rats

1. 1. The long term effects of phenytoin administration on mixed function oxidase activities and serum estradiol in female rats were examined. 2. 2. No induction of hepatic mixed function oxidases was seen until 8 days after the administration of 100 mg phenytoin/kg/day either orally or intraperitoneally. 3. 3. Maximum increase in aniline hydroxylase, aryl hydrocarbon hydroxylase (AHH) and ethylmorphine- N-deethylase activities occurred between days 8 and 16 of treatment and decreased thereafter. No induction of lung or intestinal AHH activity was observed. 4. 4. Serum levels of estradiol were significantly decreased after 16 days of phenytoin treatment. 5. 5. Maximal increases in hepatic cytochrome P-450 and cytochrome c reductase occurred after 8–16 days of treatment. Furthermore, pentobarbital sleeping times were shortest after 16 days of phenytoin administration. The activities of all enzymes after 32 days of phenytoin treatment were less than at the peak activities at 8–16 days.

Lung aryl hydrocarbon hydroxylase: Inhibition following cadmium chloride inhalation

Polycyclic hydrocarbon metabolism in male Spraque-Dawley rats following inhalation of aerosolized cadmium chloride (CdCl 2) was examined. Constitutive activity of microsomal aryl hydrocarbon hydroxylase (AHH) (benzo( a)pyrene substrate) was monitored in lung and liver homogenates up to 10 days after exposure. Lung AHH activity was reduced by 85% during the first 2 days following cadmium inhalation, and did not return to normal levels until 7 days after exposure. Enzyme activity in the livers of cadmium-treated animals was similarly depressed (by 65%) within 24 hr. Cadmium inhalation also inhibited (by 50%) 3-methylcholanthrene (MC) induction of lung AHH when compared with MC-treated controls. No significant effect on AHH inducibility by MC was noted in liver homogenates from cadmium-exposed animals. Nonspecific microsomal damage appeared not to occur since glucose-6-phosphatase activity in lung was unaffected by cadmium treatment. Although the mechanism of cadmium's action remains unclear, it appears not to involve a direct interaction of the metal with enzyme. The alteration of AHH activity by cadmium may result from injury to a specific cell type within the lung, which may be a major site of pulmonary AHH activity, or may result from modulation of synthesis and/or degradation of heme proteins in the lung. These results suggest that cadmium, under these conditions, markedly reduces the constitutive and inducible activity of AHH in the lung.

Chronic cigarette smoke exposure adversely alters 14C-arachidonic acid metabolism in rat lungs, aortas and platelets

Male rats were exposed to freshly generated cigarette smoke once daily, 5 times a week for 10 weeks. Inhalation of smoke was verified by elevated carboxyhemoglobin in blood sampled immediately after smoke exposure and by increased lung aryl hydrocarbon hydroxylase activity 24 hours after the last smoke exposure. Aortic rings isolated from smoke-exposed rats synthesized less prostacyclin (PGI 2) from 14C-arachidonic acid than rings from sham rats. Platelets from smoke-exposed rats synthesized more thromboxane (TXA 2) from 14C-arachidonic acid than platelets from room controls but not those from sham rats. Lung microsomes from smoke-exposed rats synthesized more TXA 2 and had a lower PGI 2/TXA 2 ratio than lung microsomes from room controls and shams. It is concluded that chronic cigarette smoke exposure alters arachidonic acid metabolism in aortas, platelets and lungs in a manner resulting in decreased PGI 2 and increased TXA 2, thereby creating a condition favoring platelet aggregation and a variety of cardiovascular diseases.

Altered activities of hepatic and extrahepatic microsomal mixed function oxidase enzymes in diabetic and adrenalectomized diabetic rats.

Microsomal aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin-O-deethylase (ECD) activities were determined in liver, lung and intestine of control, streptozotocin(STZ)-diabetic, and diabetic-adrenalectomized male and female rats. Hepatic cytochrome P-450 content was also determined. The diabetic state reduced hepatic AHH activity and increased ECD activity in control male rats, and failed to do so in the adrenalectomized male rats. The diabetic state increased hepatic AHH and ECD activities in the control female rats, while in the adrenalectomized female rats the activities of both enzymes were decreased compared to the control diabetic rats. STZ-induced diabetes produced a decrease in pulmonary AHH and ECD activities and increased intestinal AHH and ECD activities in both sexes. The diabetic state in the adrenalectomized rats resulted in further reduction in pulmonary AHH and ECD activities in both sexes, but failed to increase the intestinal AHH activity only in the female rat. Hepatic cytochrome P-450 contents were increased in the female but not male adrenalectomized rats when treated with STZ. The effects of STZ-induced diabetes in adrenalectomized rats on AHH, ECD and hepatic cytochrome P-450 content in liver, lung and intestine depended upon sex of animal, substrate and tissue.

The induction of rat lung aryl hydrocarbon hydroxylase by diluted smoke from commercial cigarettes

Induction of pulmonary aryl hydrocarbon hydroxylase (AHH) by cigarette smoke in small rodents is well established. However, studies on dose-response relationships particularly at the lower ends of such relationships are few indeed. Availability of the British-American Tobacco Co. (B.-A.T.)-Mason inhalation system, in which precisely-calibrated dilutions of cigarette smoke can be released into an inhalation chamber, enables excellent dose-response relationships to be established. Using this inhalation system and cigarettes delivering tar (total particulate matter, water and nicotine free) equal to 1, 4 and 20 mg/cigarette, it has been shown that induction of AHH in male Sprague-Dawley rat lung is an extremely sensitive system to inhaled cigarette smoke. AHH induction was observed at a 200-s exposure to 40 puffs of a 1 : 5 dilution of smoke from an ultra mild cigarette delivering 1 mg tar. At this low concentration, it is not even possible to accurately weigh the TPM from diluted smoke in the exposure chamber. This extremely sensitive rat pulmonary enzyme system may prove valuable in the biological testing of modern low tar cigarettes.

Factors affecting induction of lung aryl hydrocarbon hydroxylase in rats exposed to cigarette smoke

Induction of lung aryl hydrocarbon hydroxylase (AHH) activity has been studied in rats following their exposure to different regimes of cigarette smoke produced from tobacco and the tobacco substitute NSM ∗ ∗ Trade mark of New Smoking Materials, Limited. . The rate of induction of AHH was maximal during the first 3 days of exposure to tobacco smoke. The frequency of exposure to tobacco smoke was apparently more important in influencing induction of AHH than was the duration of the exposure. After cessation of exposure to smoke, AHH activity declined to control levels within about 3 days. Tobacco smoke was a more potent inducer of AHH than was smoke from NSM®. Measurement of AHH may provide a useful means of assessing whether animals involved in toxicity studies of smoking materials inhale sufficient total particulate matter to provoke a biological response, such as induction of AHH.

Effect of gonadectomy on hepatic, lung and intestinal mixed function monooxygenase enzymes in the rat.

Aryl hydrocarbon hydroxylase (AHH) and 7-ethoxycoumarin O-deethylase (ECD) activities of microsomes from liver, lungs, and intestine of control and gonadectomized male and female rats were examined. Estradiol-treated ovariectomized female rats and testosterone-treated castrated male rats were also employed. Castration decreased hepatic AHH and ECD activities by 50% and 27%, respectively, whereas ovariectomy had no effect on these enzymes. Testosterone treatment of castrated male animals returned AHH and ECD activities to control values. Estradiol treatment of the ovariectomized female rats had no effect on the activities of these two enzymes. Gonadectomy of either sex did not alter AHH or ECD activities in microsomes from lungs and intestinal mucosa. No sex differences in lung AHH activities or lung and intestinal ECD activities were noted. AHH activities of liver and intestinal mucosa were greater by 86% and 42%, respectively, in male rats as compared to the female rats. Castration decreased the hepatic cytochrome P-450 content by 15%, while ovariectomy had no effect. The hepatic cytochrome P-450 content of control male rats was 27% higher than in the females. Organ specific alterations of mixed function monooxygenase enzymes occur with castration of male animals but not following ovariectomy of female rats.

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.

Mutagenicity and metabolism of dimethylnitrosamine and benzo[α]pyrene in tissue homogenates from inbred syrian hamsters treated with phenobarbital, 3-methylcholanthrene or polychlorinated biphenyls

There are significant differences between mice and hamsters in polycyclic hydrocarbon and nitrosamine metabolism. Homogenates of liver, lung and intestinal mucosa from 6 strains of Syrian golden hamster were compared for their ability to metabolize benzo[α]pyrene (BP) and dimethylnitrosamine (DMN) to mutagens. Females of strains MHA/SsLak, LSH/SsLak, CB/SsLak, PD4/Lak LHC/Lak and Lak:LVG (SYR) were either untreated or received phenobarbital (PB), 3-methylcholanthrene (MC) or polychlorinated biphenyls (AR) to induce drug-metabolizing enzymes. Salmonella typhimurium TA92 and TA98 were used as indicators of the formation of mutagens. Dimethyl-nitrosamine demethylase (DMND) was assayed using 1 mM DMN as substrate. Aryl hydrocarbon hydroxylase (AHH) was measured using benzo[α]pyrene as substrate. MC does not induce AHH activity in hamster liver, but is an excellent inducer of enzymes converting BP to mutagens. This lack of correlation between increased AHH activity and increased metabolism of BP to mutagen in liver is in marked contrast to correlations seen in mice. MC induces AHH in hamster lung and intestinal mucosa. AR induces AHH in liver, lung and intestinal mucosa. Activity of DMND in liver is not affected by treatment of hamsters with BP or AR, but is repressed approx. 30% by treatment with MC.

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.

Induction by cigarette smoke of aryl hydrocarbon hydroxylase activity in the rat kidney and lung.

In both the rat kidney and lung, inhalation of cigarette smoke diluted with air (1/15) for a limited period of time (15 min) specifically induces aryl hydrocarbon hydroxylase (AHH)2 in less than 4 h. Up to four successive inhalations administered at 2-h intervals activities. The maximal effect corresponds to about 10 times the control value. Compared to the kidney enzyme, the lung AHH activity is about three or four time more sensitive to small concentrations of cigarette smoke. The biological half-life of the lung AHH activity is longer than 24 h, while it is only 3-4 h in the kidney. In both tissues, the induced enzyme presents the same in vitro thermolability and sensitivity to various inhibitors. For the establishment of the AHH induction, protein synthesis is continuously required, while RNA synthesis is only necessary during the first 2 h following the smoke treatment.

Organ specificity of the sex dependent regulation of aryl hydrocarbon hydroxylase (AHH) in rat

Aryl hydrocarbon hydroxylase (AHH) activity was measured in liver, kidneys and lungs of control and gonadectomized Sprague-Dawley rats. There was a six-fold difference in hepatic AHH activity between male and female rat. Activity in male was highest, castration reduced this activity by about 50%, whereas ovariectomy had little effect on activity in female. No sex difference in lung AHH activity was discernable; on the other hand kidney AHH activity was higher in females than in males. These data suggest that, at least in the rat, sex dependent regulation of microsomal mixed function oxygenases is organ specific.

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.