K-region epoxides of polycyclic hydrocarbons: formation and further metabolism by rat-lung preparations

Epoxides of 7-methylbenz[a]anthracene and of benzo[a]pyrene that have been identified as the K-region epoxides, 7-methylbenz[a]anthracene 5,6-oxide and benzo[a]pyrene 4,5-oxide, have been detected as microsomal metabolites using preparations from the lungs of rats that had been pretreated with the microsomal mixed function oxidase inducer, 3-methylcholanthrene. It was also possible, using lung microsomal preparations from uninduced animals, to demonstrate the formation of an epoxide identified as the K-region derivative, benz[a]anthracene 5,6-oxide, as a microsomal metabolite of benz[a]anthracene. The K-region epoxides of 7-methylbenz[a]anthracene and of benzo[a]pyrene could not always be detected as metabolites when lung microsomal preparations from uninduced rats were used. The activities of two other enzymes present in pulmonary tissue fractions that are involved in the further metabolism of polycyclic hydrocarbon epoxides have also been measured and the values compared with those obtained with rat-liver. When benz[a]anthracene 5,6-oxide was used as substrate, much lower levels of microsomal epoxide hydrase activity were found in lung than in liver, but soluble-supernatant fractions of rat-lung appeared to possess higher levels of glutathione S-epoxide transferase activity than were present in rat-liver.The significance of these results in relation to the metabolic activation of polycyclic hydrocarbons by epoxide formation and to the induction of tumours of the respiratory tract by members of this class of chemical carcinogens is discussed.     

The biochemical and genetic characteristics of murine ovarian aryl hydrocarbon (Benzo[a]pyrene) hydroxylase activity and its relationship to primordial oocyte destruction by polycyclic aromatic hydrocarbons

Primordial oocyte destruction by polycyclic aromatic hydrocarbons requires metabolic activation of the polycyclic hydrocarbon to an ovotoxic metabolite. The first and perhaps subsequent step(s) in the metabolism of polycyclic aromatic hydrocarbons to the proximate ovotoxin occurs via a microsomal cytochrome P-450-dependent monooxygenase. The role of aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH, EC 1.14.14.2) in activation of polycyclic hydrocarbons to ovotoxic products was studied in 11 inbred and two F₁ heterozygote murine strains. The polycyclic aromatic hydrocarbon responsive C57BL/6N and C57BL/6J mice had two- to threefold increases in ovarian AHH activity after polycyclic hydrocarbon treatment. The polycyclic aromatic hydrocarbon nonresponsive DBA/2N and DBA/2J mice had no change in ovarian AHH activity after similar polycyclic hydrocarbon treatment. The polycyclic aromatic hydrocarbon responsive C57BL/6N and C57BL/6J mice had more rapid primordial oocyte destruction after polycyclic hydrocarbon treatment than the nonresponsive DBA/2N and DBA/2J mice. The (DBA/2N)(C57BL/6N)F₁ and (DBA/2J)(C57BL/6J)F₁ mice were responsive to polycyclic hydrocarbons with two- to threefold increases in ovarian AHH activity after treatment, however, the rate of oocyte destruction was similar to that observed in the nonresponsive DBA/2N and DBA/2J mice. Survey of seven additional inbred strains of mice failed to demonstrate a strong correlation between either absolute ovarian AHH activity or fold induction of ovarian AHH activity and oocyte destruction. Similarly, treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin, a potent inducer of ovarian AHH activity in both polycyclic hydrocarbon responsive and nonresponsive strains, did not alter the rate of oocyte destruction after treatment with benzo[a]pyrene or 3-methylcholanthrene. Although metabolic activation of polycyclic aromatic hydrocarbons to an ovotoxin is necessary for primordial oocyte destruction, strain differences in sensitivity to oocyte destruction reflect the biological sum of activation, detoxification, and repair. Therefore, differences in ovarian AHH activity or inducibility may not reflect differences in oocyte destruction after polycyclic hydrocarbon treatment.     

Acute tobacco smoke exposure alters the profile of metabolites produced from benzo[a]pyrene by the isolated perfused rabbit lung

The influence of whole tobacco smoke or the gas phase from smoke on the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$ was e xamined using the isolated perfused rabbit lung model. Fresh whole tobacco smoke mixed with the air ventilating the perfused lung produces an immediate and dose related decrease in the metabolism of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$. The metabolites of $\text{[}{}^{14}\text{C]benzo}\text{[a]}\text{pyrene}$, diols, quinones, phenols and polar compounds are generally decreased in quantity. At the lowest level of smoke administered the percentage of BP-7,8-diol produced is increased dramatically. The results indicate that one of the factors contributing to the carcinogenicity of tobacco smoke may be its ability to produce an immediate alteration in the pulmonary metabolism of polycyclic aromatic hydrocarbons.     

Differential effects of 12-O-tetradecanoylphorbol 13-acetate on cytochrome P-450-dependent monooxygenase activities in rat hepatoma cells: induction of P-450I and suppression of P-450II

We have studied the effects of the tumor promoter 12-O-tetradecanoylphorbol 13-acetate (TPA) on cytochrome P-450-dependent monooxygenase activities in several differentiated and dedifferentiated Reuber rat hepatoma cell lines using aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH), ethoxyresorufin O-deethylase (EROD), and aldrin epoxidase (AE) as test systems. The following results were obtained: (1) Exposure of cultures to 400 nM TPA for 18-24 h increased AHH activities in the differentiated lines 2sFou, H41IEC3/G- and Fao as well as in the dedifferentiated line 5L, 1.5-2.5-fold. The phorbol ester did not affect AHH activity in the dedifferentiated line H5. (2) EROD, a marker for P-450I, was induced by the phorbol ester to a similar degree as AHH. (3) A monoclonal antibody directed against P-450I strongly inhibited the AHH activity induced by TPA. (4) The onset of AHH or EROD induction by TPA was much later than that elicited by benz[a]anthracene. (6) In contrast to the induction of AHH and EROD, TPA decreased AE activity, a marker for P-450II, by about 50% in all the cell lines containing this monooxygenase activity. (7) The half-maximum-effect concentration of TPA for inducing or suppressing AHH and AE, respectively, was approximately 20 nM. (8) TPA did not interfere with AHH induction by benz[a]anthracene. However, the phorbol ester moderately decreased AHH induction and markedly suppressed AE induction by dexamethasone. The results indicate that TPA simultaneously induces P-450I and suppresses P-450II forms in rat hepatoma cells. P-450I induction by TPA in these cells did not appear to depend on their status of differentiation. Furthermore, the results suggest that the mechanism of P-450I induction by TPA differs from that elicited by polycyclic aromatic hydrocarbons or glucocorticoids.     

Uptake of 7,12-Dimethylbenz(a)anthracene and Benzo(a)pyrene in Melanin-Containing Tissues

Abstract: It is widely accepted that UV exposure is the main etiological factor for malignant melanoma. Epidemiologic studies, however, have indicated that also chemical carcinogens may be a risk factor for the disease. Polycyclic aromatic hydrocarbons such as 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene represent an important class of carcinogenic chemicals. It is known that 7,12-dimethylbenz(a)anthracene can induce melanotic tumours in various animal species, and human melanocytes in culture have been found to be capable of metabolizing benzo(a)pyrene to its proximate carcinogen benzo(a)pyrene-7,8-diol. In the present study the disposition of ¹⁴C- and ³H-7,12-dimethylbenz(a)anthracene and ¹⁴C-benzo(a)pyrene was studied in pigmented and albino mice and Syrian golden hamsters by whole-body autoradiography. The results showed pronounced retention of label in the melanin-containing structures of the eyes and the hair follicles in the pigmented animals. The labelling of the corresponding structures in the albino animals was low. Additional experiments showed that 7,12-dimethylbenz(a)anthracene and benzo(a)pyrene as well as some of their metabolites are bound to melanin in vitro. The specific localization of the polycyclic aromatic hydrocarbons in pigmented tissues due to melanin affinity, combined with bioactivating capacity of melanocytes, suggest that these substances may play a role in the induction of malignant melanoma.     

The effectiveness of chemical carcinogens to induce atherosclerosis in the white Carneau pigeon

The frequency of atherosclerotic lesions of the abdominal aorta has been reported to increase significantly in chickens exposed to benzo[a]pyrene and 7,12-dimethylbenz[a,h]anthracene. The present studies were performed to determine in another experimental model frequently used in atherosclerotic studies (i.e. White Carneau Pigeons) whether these and other chemical carcinogens enhance atherosclerosis. The induction and enhancement of atherosclerotic lesions were observed in pigeons treated with 7,12-dimethylbenz[a,h]anthracene, benzo[a]pyrene and 3-methylcholanthrene. The number and size of plaques in the aorta were frequently greater in pigeons treated with the higher concentration (i.e. 100 mg/kg) of these 3 polycyclic aromatic hydrocarbons. Benzo[e]pyrene and 2,4,6-trichlorophenol were ineffective in the induction or enhancement of atherosclerosis in the pigeons. The results of the present and previous studies suggest that the polycyclic aromatic hydrocarbons (excluding benzo[e]pyrene) may be the only potential atherogens in avian atherosclerosis. This relationship may be associated with how these hydrocarbons are transported in the plasma (i.e. by lipoproteins) as demonstrated by the present distribution studies.     

Metabolism of polycyclic hydrocarbons by rat-lung preparations

The metabolism of benz[a]anthracene, 7-methylbenz[a]anthracene and benzo[a]pyrene has been studied in homogenates and microsomal fractions prepared from rat-lung. The results have been compared with those obtained in parallel experiments where rat-liver preparations were used and they show that, qualitatively, the hydrocarbons are metabolized to similar ethylacetate soluble products by both tissues. Quantitative estimations of the metabolism of the hydrocarbons indicated that rat-liver was more active than rat-lung when compared on the basis of the weight of tissue involved. Comparisons made on the basis of the protein content of the tissue preparations showed, however, that rat-lung was at least as active as rat-liver in the metabolism of polycyclic hydrocarbons. The metabolites found are mainly ring-hydroxylated products; this implies, therefore, that epoxides are formed from polycyclic hydrocarbons by the enzymes present in rat-lung.     

Morphology of oocyte and follicle destruction by polycyclic aromatic hydrocarbons in mice

The carcinogenic polycyclic aromatic hydrocarbons, benzo(a)pyrene, 3-methylcholanthrene, and 7,12-dimethylbenz(a)anthracene, destroy primordial oocytes in the mouse ovary. The rate of oocyte destruction was proportional to the activity of the ovarian microsomal cytochrome P-450-dependent monooxygenase, aryl hydrocarbon (benzo(a)pyrene) hydroxylase (EC 1.14.14.2) as well as to the carcinogenicity of the polycyclic hydrocarbon. After treatment with benzo(a)pyrene or 3-methylcholanthrene only primordial oocyte destruction occurred, and no evidence of toxicity was observed in surrounding granulosa or ovarian stromal cells. 7,12-Dimethylbenz(a)anthracene was much more toxic and destroyed large follicles and oocytes in addition to primordial oocytes and primary follicles. Seven weeks after treatment with 3-methylcholanthrene the ovary had the bland afollicular appearance characteristic of ovarian failure. These three polycyclic aromatic hydrocarbons are capable of producing premature ovarian failure in rodents.     

Excretion of THC and its metabolites in ewes' milk

After single iv injections of either 0.02 mg/kg or 1 mg/kg of $\text{[}{}^{14}\text{C}\text{]Δ}{}^9\text{-}\text{tetrahydrocannabinol}$, [¹⁴C]THC, to lactating ewes, radioactivity was detected in the milk at all subsequent time intervals tested (4–96 hr). Radioactivity was found in unchanged THC as well as in various unidentified metabolites. Only about 15% of the administered radioactivity was excreted by the ewes in the first 48 hr; most of this was in the urine and feces. Radioactivity appeared in the feces and urine of a lamb suckling milk from a ewe injected with [¹⁴C]THC, indicating transfer of THC and its metabolites via the milk. These results confirm previous literature reports indicating slow elimination of THC, and show that milk is an additional route of excretion.     

Sensitivity of Syrian golden hamster fetal lung cells to benzo[a]pyrene and other polycyclic hydrocarbons in vitro

Dose responses were compared of cultured fetal Syrian golden hamster lung cells (FSHL) to the toxic and transforming effects of benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), benz[a]anthracene (B[a]a) indeno[1,2,3-c,d]pyrene (I[c,d]P), benzo[k]fluoranthene (B[k]F) and benzo[e]pyrene (B[e]P). Effort was first given to standardising the techniques for evaluating B[e]P dose-responses. These polycyclic aromatic hydrocarbons (PAH) were then tested at concentrations of up to 1 μg/ml, and only B[a]P showed clear cytotoxicity. The transforming effects of B[b]F, B[a]A and I[c,d]P at 1 μg/ml appeared comparable to those of B[a]P at 0.05 μg/ml.     

The interrelationship of polycyclic hydrocarbon metabolism and steroidogenesis in primary cultures of bovine adrenal cortical cells

The interrelationship between adrenal steroidogenesis and polycyclic aromatic hydrocarbon metabolism has been examined in cultured bovine adrenal cortical (BAC) cells. Adrenocorticotropin (ACTH) selectively induced steroidogenic cytochrome P-450-dependent enzyme activities from BAC cell cultures. In the presence of 10(-7) M ACTH, steroid production requiring 17 alpha-hydroxylation (cortisol + androgens) was increased 5-fold over the formation of 17- deoxysteroids (corticosterone). The effect of 10 microns benz[a]anthracene on steroidogenesis was characterized by suppression of both steroid 17 alpha-hydroxylation (90%) and total steroidogenesis (50%), with a concomitant rise in 17- deoxysteroid formation. The order of stimulation of steroidogenic enzyme activities by ACTH (17 alpha-hydroxylase greater than side chain cleavage greater than 21-hydroxylase) paralleled the order of suppression by benz[a]anthracene. BAC cell cultures incubated with Su-10603, a specific 17 alpha-hydroxylase inhibitor, exhibited similar changes in the pattern of steroidogenesis, as did benz[a]anthracene-treated cells, suggesting that benz[a] anthracene also inhibits steroidogenesis as an inhibitor of 17 alpha-hydroxylase. In addition, benz[a]anthracene induced benzo[a]pyrene metabolism 4- to 6-fold over control levels in these cells. The profile of benzo[a]pyrene metabolites revealed predominantly water-soluble products (nonhydrolyzable greater than sulfates greater than glucuronides), 9,10- monooxygenation products, and 3-phenol. ACTH (10(-7) M) and 0.5 mM cyclic AMP each decreased benzo[a]pyrene metabolism by more than 50%. Both benz[a]anthracene-induced and uninduced benzo[a]- pyrene metabolism were equally reduced in response to ACTH and cyclic AMP. In the presence of 0.2 mM aminoglutethimide, which completely inhibited steroidogenesis, ACTH decreased benz[a]anthracene induction of benzo[a]pyrene metabolism to the same extent as ACTH treatment alone. It is concluded that the suppression of benzo[a]pyrene metabolism by ACTH is mediated by cyclic AMP and does not involve steroids generated in response to ACTH. These studies demonstrate that cytochrome P-450 isozymes involved in steroidogenesis and polycyclic aromatic hydrocarbon metabolism are regulated, in opposing directions, by ACTH.     

Effect of carcinogenic polycyclic aromatic hydrocarbons on mouse embryonic cells in culture: Induction of spindle-shaped cells

In cultured mouse embroyonic cells (MECs) treated with benzo[a]pyrene(B[a]P), there appeared unusual type of fibroblasts, spindle-shaped cells (SP cells), which were characterized by their narrow bipolar shape, long cellular processes and optically distinct cell borders. Appearance of SP cells was massive and irreversible. The amount of SP cells increased with increased with increasing concentrations of B[a]P, while early cytotoxicity did not. In various polycyclic aromatic hydrocarbons (PAHs) tested, only potent carcinogens {7,12-dimethylabenz[a]anthracene (DMBA), 3-methylcholanthrene (MCA), B[a]P and dibenz[a, e]pyrene (DB[a, e]P)} induced SP cells. Among them, PAH having higher Iball's index induced SP cells at lower concentration and at an earlier time. Weak or non-carcinogenic PAHs including 3-hydroxybenzo-[a]-pyrene(3-H-B[a]P) did not induce SP cells. α-Napthoflavon (αNF) suppressed the induction of SP cell by carcinogenic PAH. SP cells did not appear spontaneously under various abnormal culture conditions. These results indicate that carcinogenic PAHs induce the appearance of a specific type of fibroblast, SP cells in MEC cultures in accordance with their carcinogenicity.     

Polycyclic aromatic hydrocarbons stimulate human CYP3A4 promoter activity via PXR

Metabolic activation of polycyclic aromatic hydrocarbons (PAH) is mediated mainly by cytochrome P₄₅₀ monooxygenases (CYP) CYP1A1, 1A2 and 1B1. Several PAH are known to induce these CYP via aryl hydrocarbon receptor (AhR) signaling. Recently, it was shown that the PAH benzo[a]pyrene (BaP) can induce CYP3A4 as well. The induction was suggested to be mediated by the pregnane X receptor (PXR) rather than AhR. Metabolism by CYP3A4 is only known for dihydrodiol metabolites of PAH but not for their parent compounds.     

Hydrocarbons and metabolites in english sole (Parophrys vetulus) exposed simultaneously to [3H]benzo[a]pyrene and [14C]naphthalene in oil-contaminated sediment

English sole (Parophrys vetulus) were exposed to $\text{[}{}^3\text{H]benzo}\text{[a]}\text{pyrene (B}\text{[a]}\text{P}\text{)}$ and [¹⁴C]naphthalene (NPH) in sediment containing 1% Prudhoe Bay crude oil (PBCO). Bioeoncentration values (pmoles of hydrocarbon equivalents in g of dry tissue/pmoles of hydrocarbon equivalents in g of sedimentassociated water (SAW)) for NPH were greater than corresponding values for B[a]P in tissues of fish exposed for 24 h. However, from 24 to 168 h of the exposure, a substamial decline (P < 0.05) in NPH-derived radioactivity and a significant (P < 0.05) increase in B[a]P-derived radioactivity occurred in most of the tissues examined. When fish were transferred for 24 h to sediment free of radioactivity and PBCO, the retention of B[a]P-derived radioactivity in the tissues of fish was considerably greater than that for NPH.Metabolites of B[a]P and NPH in sediment, SAW, liver and bile of fish were characterized by thinlayer chromatography (TLC). For liver, a two-dimensional TLC was devised to separate B[a]P and its metabolites from liver lipids. An important finding was that liver of English sole metabolized B[a]P to a far greater extent than NPH; at 24 h after the exposure, the ratio of concentrations of B[a]P to its metabolites was 1 to 49 whereas that for NPH was 6 to 1. Larger proportions of glucuronide conjugates than sulfate conjugates of both NPH and B[a]P were present in bile of English sole. Naphthalene was largely converted into a glucuronide conjugate of l,2-dihydro-l,2-dihydroxynaphthalene. A number of metabolites of B[a]P known to be toxic to mammals were detected in both liver and bile including 7,8-dihydro-7,8-dihydroxy B[a]P and its conjugates.These findings of extensive metabolism of B[a]P by fish liver very probably explain why B[a]P is usually not detected in liver of fish even when considerable concentrations of B[a]P are detected in the environment of the fish.     

Polycyclic aromatic hydrocarbons of coal fly ash: analysis by gas-liquid chromatography using nematic liquid crystals

The seasonal variations over a period of 12 m in the amounts of polycyclic aromatic hydrocarbons (PAH) in fly-ash samples collected from the electrostatic precipitator of a thermal power plant have been studied. PAH generally did not show much seasonal variation. The gas-liquid chromatographic (GLC) analysis of benzene extract of fly ash showed the presence of 28 polyaromatic hydrocarbons, of which only phenanthrene, anthracene, pyrene, benz[a]anthracene, chrysene, and benzo[a]pyrene could be identified.     

Effect of diphenylhydantoin on the uptake and catabolism of l-[3H]norepinephrine in vitro in rat cerebral cortex tissue

The effect of diphenylhydantoin on the accumulation of [³H]norepinephrine in vitro was examined in brain slices prepared from rat cerebral cortex. High concentrations of diphenylhydantoin (10^?3 M) caused a significant reduction in the 5-min accumulation of [³H]norepinephrine. On the other hand, 10^?5–10^?4 M diphenylhydantoin facilitated the 20-min accumulation of [³H]norepinephrine. This facilitative action of diphenylhydantoin was (1) associated with a reduction in oxidative catabolism of [³H]norepinephrine and (2) abolished by the 2-hr pretreatment of rats with 100 mg/kg of nialamide (i.p.). The inhibitory action of diphenylhydantoin on the oxidative catabolism of [³H]norepinephrine was observed in both whole and lyzed crude synaptosomal preparations. When diphenylhydantoin and pargyline were compared, it was found that pargyline $\text{(}\text{id}{}_{50}\text{= 1.5 × 10}{}^{\mathrm{?6}}\text{M}\text{)}$ was 37 times more effective than diphenylhydantoin $\text{(}\text{id}{}_{50}\text{= 5.5 × 10}{}^{\mathrm{?5}}\text{M}\text{)}$ in inhibiting the oxidative deamination of [³H]norepinephrine. These results suggest that diphenylhydantoin alters norepinephrine metabolism in cerebral cortex slices by an inhibitory action on (1) monoamine oxidase activity and (2) the neuronal uptake system.     

Similar activities of nerve growth factor and its homologue proinsulin in intracellular hydrogen peroxide production and metabolism in adipocytes: Transmembrane signalling relative to insulin-mimicking cellular effects

Generation of hydrogen peroxide in adipocyte plasma membrane and its intracellular metabolism and regulatory role have been shown by Mukherjee and co-workers to be a major effector system for insulin [Fedn Proc.35, 1694 (1976); Archs Biochem. Biophys.184, 69 (1977); Biochem. Pharmac.27, 2589 (1978); Fedn Proc.37, 1689 (1978); and Biochem. Pharmac.29, 1239 (1980)]. The possible involvement of this mechanism in the action of structurally similar polypeptides having some insulin-like metabolic effects was investigated. The β-subunit of nerve growth factor (2.5 S NGF, mol. wt 13,500) which has a striking structural homology with proinsulin and has been reported to exert certain insulin-like metabolic effects in its own target tissues (e.g. growing neurites and sympathetic ganglia), and the insulin-derived polypeptides, desalanine-insulin and desoctapeptide-insulin, as well as proinsulin, were examined for their effects on rat adipocytes, employing the technique of formate oxidation. Both NGF and proinsulin caused increased [¹⁴C]formate oxidation, showing similar intrinsic activities, up to a maximum of 140–160% of the basal rate; insulin increased the rate to 190–210% of the basal rate. The relative potencies of the hormones toward H₂O₂ formation and stimulation of the pentose phosphate pathway activity were: insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?11}}\text{M}\text{)}$, desalanine-insulin $\text{(}\text{EC}{}_{50}\text{: 2.5 × 10}{}^{\mathrm{?10}}\text{M}\text{)}$ , proinsulin $\text{(}\text{EC}{}_{50}\text{: 8 × 10}{}^{\mathrm{?9}}\text{M}\text{)}$, and NGF $\text{(}\text{EC}{}_{50}\text{: 10}{}^{\mathrm{?9}}\text{M}\text{)}$. The biologically inactive derivative, desoctapeptide-insulin, did not stimulate glucose oxidation, although it caused a small increase in formate oxidation, with an $\text{EC}{}_{50}\text{of}\text{5 × 10}{}^{\mathrm{?7}}\text{M}$, indicating a suboptimal level of H₂O₂ formation in the elevation of the hexose monophosphate shunt activity. 3-Amino-1,2,4,-triazole (50 mM), which irreversibly decomposes the peroxidatic compound II of the catalase: H₂O₂ complex, inhibited formate oxidation to a greater extent in the hormone-treated cells than in the control cells, whereas sodium azide, an inhibitor of the hemoprotein, catalase, completely inhibited it. The abilities of the polypeptides to stimulate H₂O₂ formation correlated with their abilities to promote lipogenesis from [U-¹⁴C]-D-glucose, as expected of insulin. The cellular GSH/GSSG ratio increased concomitantly with the stimulation of glucose oxidation via the shunt, indicating a tight coupling between these processes. The results confirm that the hydrogen peroxide production is a common basis of the metabolic actions of growth-promoting polypeptide hormones or mitogens beyond their respective receptors.     

The inhibitory action of ketamine HC1 on [3H]5-hydroxytryptamine accumulation by rat brain synaptosomal-rich fractions: comparison with [3H]catecholamine and [3H]gamma-aminobutyric acid uptake.

Ketamine HO was incubated with synaptosomal-rich fractions prepared from rat cerebral cortex to evaluate the effect of this agent upon the synaptosomal accumulation of [³H]5-HT. Accumulation of [³H]5-HT was shown to be reduced by ketamine in a concentration-related fashion. This action of ketamine was also found in synaptosomal rich fractions prepared from hypothalamus, corpus striatum, medulla oblongata and midbrain. Accumulation studies carried-out in the presence of reserpine and pargyline indicated that ketamine reduced the accumulation of [³H]5-HT through a competitive action on the synaptosomal membrane high affinity transport system (neuronal reuptake system). The effect of ketamine on the high affinity transport of [³H]NE, [³H]DA and [³H]GABA was also examined. The order of inhibition of transport by ketamine was [³H]5-HT >$\text{[}{}^3\text{H}\text{]}\text{DA}\text{= [}{}^3\text{H}\text{]}\text{NE}\text{> [}{}^3\text{H}\text{]}\text{GABA}$. These results show that ketamine is a potent and preferential inhibitor of the 5-HT neuronal reuptake system. The possible role of this action of ketamine, in the post anaesthetic excitatory response seen following the administration of ketamine, is discussed.     

Synergistic and antagonistic interactions of binary mixtures of polycyclic aromatic hydrocarbons in the upregulation of CYP1 activity and mRNA levels in precision‐cut rat liver slices

The current studies investigate whether synergistic or antagonistic interactions in the upregulation of CYP1 activity occur in binary mixtures of polycyclic aromatic hydrocarbons (PAHs) involving benzo[a]pyrene and five other structurally diverse PAHs of varying carcinogenic activity. Precision‐cut rat liver slices were incubated with benzo[a]pyrene alone or in combination with a range of concentrations of a second PAH, and ethoxyresorufin O‐deethylase, CYP1A1 and CYP1B1 mRNA levels determined. Concurrent incubation of benzo[a]pyrene with either dibenzo[a,h]anthracene or fluoranthene in liver slices led to a synergistic interaction, at least at low concentrations, in that ethoxyresorufin O‐deethylase activity was statistically higher than the added effects when the slices were incubated with the individual compounds. In contrast, benzo[b]fluoranthene and, at high doses only, dibenzo[a,l]pyrene gave rise to antagonism, whereas 1‐methylphenanthrene had no effect at all concentrations studied. When CYP1A1 mRNA levels were monitored, benzo[b]fluoranthene gave rise to an antagonistic response when incubated with benzo[a]pyrene, whereas all other compounds displayed synergism, with 1‐methylphenathrene being the least effective. A similar picture emerged when CYP1B1 mRNA levels were determined, though the effects were less pronounced. In conclusion, it has been demonstrated that the benzo[a]pyrene‐mediated upregulation of CYP1, at the mRNA and activity levels, is synergistically and antagonistically modulated by other PAHs. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 764–775, 2017.