ISSN:0021-1915    

DOI:10.1080/00211919408046720

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The experiment was carried out with 24 male albino rats (5 weeks old, live weight 79 ± 5.1 g) divided into 2 groups. Gr. 1 (control group) was fed the commercial breeding food Ssniff with 22.4% crude protein ad lib., Gr. 2 (test group) for the first fortnight a mixture of the breeding food/cellulose 60/40 (restriction period) and subsequently for the second fortnight (compensatory period) also the breeding food ad lib. During both of these periods an 8 day N balance trial and a 4 day15N tracer trial were included for estimation of growth rate and protein synthesis rate. Protein synthesis was ascertained by the endproduct method (oral application, single dose, mixture of 1215N-labelled amino acids); protein breakdown was calculated as the difference of protein synthesis rate and growth rate. The estimated rates were converted into fractional ones by referring to the body N content of corresponding animals. From the results of this experiment is concluded: The smaller N balance during moderate nutritional restriction can be attributed to a decrease of protein synthesis. The compensatory growth of the animals during the realimentation period is caused by an increase of protein synthesis and the enhanced protein conversion. Protein degradation is nearly unaffected.

ISSN:0021-1915    

DOI:10.1080/00211919408046721

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Tramadol (T), racemic 1(e)-(m-methoxyphenyl)-2(e)-(dimethylaminomethyl)-cyclohexane-1(a)-ol is an effective analgesic drug. Metabolites were formed by O- and N-demethylation. Six deuterated tramadol isotopomers have been synthesized; their kinetic isotope effects in oxidative demethylation reactions were investigated in vitro using human liver microsomes. In comparison to unlabelled (±)-tramadol, (±)-T-OCD3and (±)-T-D9displayed an unequivocal (< 3), (±)-T-ND6and (±)-T-ND3a noticeable, and (±)-T-cyclohexyl-D3as well as (±)-T-15ND2nomeasurable isotope effect. Metabolic switching (favoring the N-demethylation) was observed only after incubation of a tramadol with a trideuterated methoxy group. Additional N-CD3-groups prevented this metabolic switching. Metabolic switching favoring the O-demethylation was not observed. The isoenzyme responsible for the O-demethylation was always saturated under the experimental conditions required to detect the metabolites.

ISSN:0021-1915    

DOI:10.1080/00211919408046722

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nitrogen isotope ratio disproportionation (N-IRD) is the result of isotope effects of different magnitude in branched pathways of nitrogen metabolism of the liver. N-IRD is measured as the difference of natural15N abundance of urea and plasma protein and is noted in ‰ (per mill) as the difference of their δ values.

ISSN:0021-1915    

DOI:10.1080/00211919408046723

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Hippurate, synthetized from benzoate and glycine in the liver and in the kidney of several species modulates the activity of renal γ-glutamyl-transpeptidase. By this mechanism hippurate interferes with renal intra-luminal ammonia production. Besides, in the rat hippurate serves as a minor substrate for renal ammoniagenesis as well. Hippurate may yield ammonia from its glycine moiety either after cleavage by hippuricase, or after condensation with an aldehyde according to Erlenmeyer's reaction. This reaction results in producing equimolar amounts of ammonia, benzoate and an α-keto acid, thus in a net gain of an acid equivalent. -In order to evaluate variability and extent of renal ammonia production from hippurate in different species, experiments were carried out on isolated tubular segments of the rat and on cortical kidney slices of rat, cow, man and cat. The incubation medium was enriched with J0mmol/1 hippurate spiked with 5% of15N-hippurate, some of the known inhibitors of hippuricase and γGT as well as glyceraldehyde or propional-dehyde. Factors known to affect hippuricase or γGT did not interfere with renal ammonia production from hippurate, but glyceraldehyde and propionaldehyde (up to 1mmol/1) had a stimulating effect. Renal ammoniagenesis from hippurate as well as production of benzoate was lowest in the cow (∼ 0.1%), amounted to 1–2% in rat and man and reached high values in the cat (up to 15% of the total ammonia production). These results indicate that hippurate could have physiological significance in the renal metabolism of some species.

ISSN:0021-1915    

DOI:10.1080/00211919408046724

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The coronary reserve of mammalian hearts is significantly heterogeneous. From this phenomenon we conclude on a heterogeneous energy-demand, i.e., ATP-demand and therefore on a nonuniform ischemic tolerance of cardiomyocytes.

ISSN:0021-1915    

DOI:10.1080/00211919408046725

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Interindividual variability of leucine catabolism was studied in eight overnight fasted healthy volunteers by means of a controlled oral L-[1-13C]leucine loading test (5 mg/kg body weight). With the exception of total CO2expiration (CV = 5%),a considerable variation (CV generally < or ≪10%)was observed with all other metabolic parameters: increase of leucine/2-oxoisocaproate in serum,13C-enrichment in serum metabolites and13CO2in expired air, and estimated oxidation rates. The degree of variation was only partially referable to individual differences. A comparable high degree of variability was found when two probands underwent multiple loading tests (n= 4). Possible reasons and implications are discussed.

ISSN:0021-1915    

DOI:10.1080/00211919408046726

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0021-1915    

DOI:10.1080/00211919408046727

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nitrous oxide is a potential environmental hazard responsible for the green house effect and the destruction of the ozone layer in the lower stratosphere. Biological denitrification under anaerobic conditions in soils results in the formation of both N2O and N2, whereby highly nitrogen-fertilized agricultural soils contribute to a considerable extent of the N2O emission. Latest results in the literature indicate that nitrous oxide can also be formed as a byproduct of the microbial nitrification. This is of importance for soils in central Germany because of the non-existence of typical denitrification conditions in a semiaride climate.

ISSN:0021-1915    

DOI:10.1080/00211919408046728

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The precision of the15N-emission and that of the15N-balance methods was evaluated and both methods were compared in a denitrification experiment.15N-analysis was performed with an isotope ratio mass spectrometer which was coupled to an elemental analyzer. The measuring sensitivity in soil and gas analysis was tested by analyzing15N-standards. The detection limit for gas samples with two different procedures of15N-gas analysis was δ15N = (4.5 ± 1.0)‰ and (0.5 ± 0.05)‰, respectively. The error in measurement was 19% and 12% respectively.15N-analysis of a15N-labelled soil (4.15 ppm15N) resulted in a CV of 1.32%. The measurements had to be calibrated with soil standards because the15N-values showed a continuous downward fluctuation in a range of 10–20% within several days, when only acetanilid was used for calibration. Mean15N-losses which were determined with both methods during the denitrification experiment were in good agreement. The precision of the15N-emission method was adequate in all variants of the experiment. The precision of the15N-balance method however was unsatisfactory at low15N-losses (0.2–2% of added15N).

ISSN:0021-1915    

DOI:10.1080/00211919408046729

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor