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  • 1
    Electronic Resource
    Electronic Resource
    Methodological investigations on the determination of n-hexane metabolites in urine (1986)
    Springer
    International archives of occupational and environmental health 57 (1986), S. 149-158 
    Details
    ISSN: 1432-1246
    Keywords: n-Hexane ; Urine ; 2-Hexanone ; 2-Hexanol ; 2,5-Hexanedione
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Male Wistar rats were exposed to 1000 ppm n-hexane, and the excreted urinary metabolites were analyzed by capillary gas chromatography-mass spectrometry (GC-MS). 1-Hexanol, 2-hexanol, 3-hexanol, 2-hexanone, 2,5-hexanedione, 2,5-dimethyltetrahydrofuran, 2,5-dimethyl2,3-dihydrofuran and γ-valerolactone were identified by their retention times and their mass spectra. Quantitative gas chromatographic analyses were performed using an FID. Experiments on the hydrolysis of conjugated n-hexane metabolites revealed that enzymatic hydrolysis (in addition to acid hydrolysis) was not required, as treatment with HCl hydrolyzed conjugates sensitive to acid as well as conjugates sensitive to β-glucuronidase. By incorporating acid hydrolysis only and by using C18-cartridges for sample extraction, a method was developed that allowed the determination of n-hexane metabolites with a sample preparation time of only 45 min. Assay precision was assessed by repeated analyses of the same urine sample. Coefficients of variation for the individual metabolites ranged from between 1.8 and 3.3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00381383
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  • 2
    Electronic Resource
    Electronic Resource
    Pharmacokinetics of halogenated ethylenes in rats (1978)
    Springer
    Archives of toxicology 42 (1978), S. 123-136 
    Details
    ISSN: 1432-0738
    Keywords: Halogenated ethylenes ; Vinyl fluoride ; Vinylidene fluoride ; Vinyl chloride ; Vinylidene chloride ; Cis-dichloroethylene ; Trans-dichloroethylene ; Trichloroethylene ; Perchloroethylene ; Vinyl bromide ; Pharmacokinetics ; Metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Inhalation pharmacokinetics of the halogenated ethylenes vinyl fluoride (VF), vinylidene fluoride (VF2), vinyl chloride (VC1), vinylidene chloride (VC12), cis- and trans-dichloroethylene (cis-DCE and trans-DCE), trichloroethylene (Tri), perchloroethylene (Per), and vinyl bromide (VBr) have been comparatively studied in the rat. Rats were exposed in a closed inhalation system to various initial atmospheric levels of halogenated ethylenes, and the decline of atmospheric concentration was followed using gas Chromatographic analysis. From pharmacokinetic analysis of the experimental curves the following general patterns of the halogenated ethylenes were derived. Distribution of the compounds in the organism and in the gas phase is determined by physical factors. For practical purposes, a relation of the equilibrium constants with the volatilities of the compounds, expressed by the boiling points, may be used: compounds with a low boiling point are enriched in tissues much less than those of a higher boiling point, and vice versa. Compounds with high accumulation in tissues (Tri, Per) need much more time for completion of the equilibration process than more volatile compounds. Metabolic elimination of halogenated ethylenes is a saturable, dose-dependent process. If animals are exposed to atmospheric concentrations of a halogenated ethylene which exceed the “point of saturation (Sp)”, elimination is determined by a zero-order law, i.e., its rate is independent of the concentration of the compound. In contrast, below saturation normal first-order kinetics apply. If the rate of metabolic elimination is related to the concentrations of the compounds in the tissue compartment, very similar rates for first-order elimination of the different halogenated ethylenes are found. This suggests a common rate limiting factor applicable for the lower concentration range. The maximal velocities (V max) of metabolic elimination of halogenated ethylenes which are reached above the “saturation points” depend on the chemical structures of the individual compounds. In general, with the exception of Tri, further halogen substitution inhibits metabolic conversion. Of the halogenated ethylenes, VF2 and Per are extremely slowly metabolized. The present report also provides the data necessary for calculation of the rates of metabolism of halogenated ethylenes in rats at a given concentration of atmospheric exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00316492
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  • 3
    Electronic Resource
    Electronic Resource
    Inhalation pharmacokinetics based on gas uptake studies (1981)
    Springer
    Archives of toxicology 47 (1981), S. 279-292 
    Details
    ISSN: 1432-0738
    Keywords: Pharmacokinetics ; Metabolism ; Halogenated ethylenes ; Vinyl fluoride ; Vinylidene fluoride ; Vinyl chloride ; Vinylidene chloride ; cis-Dichloroethylene ; trans-Dichloroethylene ; Trichloroethylene ; Vinyl bromide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract An improved pharmacokinetic model is described for inhalation of volatile xenobiotics from a closed gas phase system. This model is based on steady-state kinetics and covers metabolic elimination processes of either first-order, zero-order, or Michaelis-Menten characteristics. It is emphasized that the distribution of a volatile compound between gas phase and organism under steady-state conditions may be much different from a static equilibrium obtained in absence of metabolism, as it is observed after application of a metabolic inhibitor. A re-analysis of previous experimental data on dose-dependent pharmacokinetics of different haloethylenes reveals that, in general, the metabolic elimination processes of the rapidly equilibrating mono-haloethylenes (and vinylidene fluoride) can be resolved with excellent accuracy into sections of first-order and zero-order kinetics. Other compounds show a more smooth transition from first-order elimination (at lower atmospheric concentrations) into conditions of saturation (dichloroethylenes, trichloroethylene). The analyses are consistent with a recent concept of Andersen (1980) that metabolic elimination of inhaled xenobiotics is limited by either the capacity of metabolic enzymes or factors of transport to the metabolic sites.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00332394
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  • 4
    Electronic Resource
    Electronic Resource
    Alkylation of RNA by vinyl bromide metabolites in vitro and in vivo (1979)
    Springer
    Archives of toxicology 41 (1979), S. 279-286 
    Details
    ISSN: 1432-0738
    Keywords: Vinyl bromide ; RNA alkylation ; 1,N6-ethenoadenosine ; 3,N4-ethenocytidine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract [1,2-14C]Vinyl bromide was incubated with rat liver microsomes, NADPH, and polyadenylic acid, polycytidylic acid, or RNA, respectively. Part of the adenosine moieties in RNA or in polyadenylic acid were alkylated and labelled 1,N6-ethenoadenosine structures were formed. Part of the cytidine moieties were converted into 3,N4-ethenocytidine. In addition, a further unidentified cytidine alkylation product was observed which was not seen in experiments using [1,2-14C]vinyl chloride. When rats were exposed to [1,2-14C]vinyl bromide, radioactive ethenoadenosine and ethenocytidine were present in hydrolysates of liver RNA. A further alkylation product was observed in the RNA hydrolysates which did not occur in experiments using [14C]vinyl chloride. The data show that vinyl bromide metabolites alkylate nucleic acids; although in general in this respect vinyl bromide and vinyl chloride behave similarly, some differences are observed in the alkylation behaviour of both compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296897
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  • 5
    Electronic Resource
    Electronic Resource
    Pharmacokinetics of the neurotoxin n-hexane in rat and man (1987)
    Springer
    Archives of toxicology 60 (1987), S. 77-80 
    Details
    ISSN: 1432-0738
    Keywords: n-Hexane ; Pharmacokinetics ; Man ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The pharmacokinetics of inhaled n-hexane in rat and man were compared. In the rat metabolism was saturable. Up to 300 ppm, the metabolic rate was directly proportional to the concentration in the atmosphere, reaching 47 μmol/(h· kg). Only 17% of n-hexane was exhaled unchanged. Above 300 ppm, the amount of n-hexane in the body rose with increasing atmospheric concentrations from 1.6 up to a limiting value of 9.6, which corresponded to the thermodynamic distribution coefficient of n-hexane between the organism and the atmosphere. Up to 3000 ppm, the rate of metabolism increased to 245 μmol/ (h· kg); only a slow further increase was found up to 7000 ppm (285μmol/(h· kg)). In man the steady-state concentrations of n-hexane were about 1 ppm. The metabolic clearance was 1321/h, and n-hexane accumulated to a factor of 2.3 in the organism. The thermodynamic distribution coefficient was calculated to be 12. Twenty per cent of n-hexane in the body was exhaled unchanged. At low concentrations the rate of metabolism of n-hexane is limited in both species by transport to the enzyme system. Under these conditions the rate of metabolism of n-hexane should not be influenced by xenobiotics which induce the n-hexane metabolizing enzyme system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296952
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  • 6
    Electronic Resource
    Electronic Resource
    The relevance of 4,5-dihydroxy-2-hexanone in the excretion kinetics ofn-hexane metabolites in rat and man (1987)
    Springer
    Archives of toxicology 61 (1987), S. 131-137 
    Details
    ISSN: 1432-0738
    Keywords: n-Hexane ; 2,5-Hexanedione ; 4,5-Dihydroxy-2-hexanone ; Biological monitoring
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Male Wistar rats were exposed ton-hexane concentrations between 50 and 3000 ppm for 8 h, and urinary excretion kinetics of then-hexane metabolites 1-hexanol, 2-hexanol, 3-hexanol, 2-hexanone, 2,5-hexanedione, and 4,5-dihydroxy-2-hexanone were assessed. The amounts of metabolites excreted were linearly dependent on then-hexane exposure concentration, up to an exposure of about 300 ppm. Above 300 ppm exposure the metabolite excretion indicated saturation kinetics in the metabolism ofn-hexane. In its quantity, the newly described 4,5-dihydroxy-2-hexanone was the second metabolite, its amount in the urine being about ten times higher than that of excreted 2,5-hexanedione. Using gas chromatography-mass spectrometry the occurrence of 4,5-dihydroxy-2-hexanone as ann-hexane metabolite in urine of man was confirmed after exposure of a male volunteer to a mean of 217 ppmn-hexane for 4 h (laboratory exposure). Twenty-six hours after starting this exposure the excretion of 4,5-dihydroxy-2-hexanone (as a result of then-hexane exposure) reached a level which was four times higher than the excretion of 2,5-hexanedione. The results in both rat and man indicate the relevance of 4,5-dihydroxy-2-hexanone as a metabolite ofn-hexane metabolism. Formation of this metabolite may be viewed as a route of detoxification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00661371
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  • 7
    Electronic Resource
    Electronic Resource
    DNA adducts of halogenated hydrocarbons (1986)
    Springer
    Journal of cancer research and clinical oncology 112 (1986), S. 92-96 
    Details
    ISSN: 1432-1335
    Keywords: Methyl chloride ; Methyl bromide ; 1,2-Dichloroethane ; 1,2-Dibromoethane ; Vinyl chloride ; Vinyl bromide ; Vinylidene chloride ; Trichloroethylene ; Perchloroethylene ; 2,2′-Dichloro-diethyl ether ; Acrylonitrile ; Vinyl acetate ; Vinyl carbamate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Although formation of DNA adducts has been postulated for several halomethanes, no chemical identification of such adducts has been performed so far. There is, however, evidence that methyl chloride does not act biologically as a DNA methylating agent. 1,2-Dichloroethane and 1,2-dibromoethane are activated through conjugation with glutathione. There is some evidence for formation on an N-7 adduct of guanine which carries an ethyl-S-cysteinyl moiety. Extensive work has been published on adducts of vinyl chloride, both in vitro and in vivo. The major DNA adduct is 7-(2-oxoethyl)guanine; a minor adduct appears to be N2,3-ethenoguanine. Other “etheno” adducts, i.e., 1,N6-ethenoadenine and 3,N4-ethenocytosine, are readily formed with DNA, vinyl chloride, and a metabolizing system in vitro and with RNA in vivo, but are usually not detected as DNA adducts in vivo. The data on DNA alkylation by vinyl chloride (and vinyl bromide) metabolites are compared with those of structurally related compounds (acrylonitrile, vinyl acetate, vinyl carbamate).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00404388
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