ISSN:1025-6016    

DOI:10.1080/10256019508036263

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019508036264

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

[15N]Taurocholate has been prepared and used as a simple urine test substrate as a substitute for14C- and13C breath test substrates. [15N]Taurocholate was administered instead of [15N] glycocholate assuming that taurine is mainly used in the cholate cycle. Differences were found between healthy and diseased subjects, although deconjugated [15N]taurine was recovered in urine much less than expected. To get additional information on the actual excess of free taurine, [15N]taurine was administered orally in parallel investigations. Apparently, large fluctuations in the whole body taurine metabolism are responsible for the unexpected results.

ISSN:1025-6016    

DOI:10.1080/10256019508036265

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

As for the unlabelled (±)-1(e)-(m-methoxyphenyl)-2(e)-(dimethylaminomethyl)cyclohexane 1(a)-ol, tramadol, (T), pronounced stereochemical effects were observed for the isotopomers with regard to the extent of formation of O- and N-demethylated metabolites. The pharmacological active O-demethylated metabolite M1 was formed from the unlabelled as well as from the labelled (+)-tramadols about 6 times less than from the corresponding (−)-T. In contrast, the N-demethylated metabolite M2 was formed from the (+)-tramadols about 1.5 times more than from the corresponding (−)-T. These steric effects were modulated by the smaller apparent isotope effects for the isotopomers. Isotope effects were expressed askH/kD(calculated from concentrations) and asDV,DV/KandHKm/DKm(from Eadie-Hofstee plots).

ISSN:1025-6016    

DOI:10.1080/10256019508036266

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The metabolism of tumor-cells differs in many ways from normal (healthy) cells. One of the major differences is the high glycolytic activity in tumor-cells with the subsequent formation of lactate from glucose, even in the presence of oxygen. The question whether this high rate of glycolysis has any effect on the13C/12C-relation of the cells is examined in experiments with a tumor-cell line (HT29) and in specimens of human breast cancer.

ISSN:1025-6016    

DOI:10.1080/10256019508036267

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Isotopic enrichment of branched-chain L-amino acids (BCAA) and branched-chain 2-oxo acids (BCOA) in standard preparations and in human plasma samples withdrawn after oral loads with 1-13C labelled BCAA were measured on a conventional GC-MS system and an on-line GC-C-IRMS employing O-TMS quinoxalinol derivatives. It was concluded that the recently introduced GC-C-IRMS, owing to its high sensitivity, is the adequate analytical tool when tracer doses of stable isotope labelled compounds of low enrichment are to be used in biomedicalin vivostudies.

ISSN:1025-6016    

DOI:10.1080/10256019508036268

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019508036269

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:1025-6016    

DOI:10.1080/10256019508036270

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

For the high precision isotope analysis of atmospheric trace gases a computer controlled concentration interface has been developed. From small air samples it collects either N2O or CO2derived from CH4at their respective concentrations (0.3 ppm for N2O, 1.7 ppm for CH4) into a small diameter cold trap (−196°C) and interfaces via GC and open split to an isotope ratio mass spectrometer (Finnigan MAT 252) for on-line isotope evaluation. External reproducibilities for repeated measurements of 100 ml air samples from the same source of < 0.2° (δ-notation) have been achieved for13C/12C from CH4and for15N/14N and18O/16O from N2O. The precision is adequate to monitor the isotopic changes in these gases during a day's course.

ISSN:1025-6016    

DOI:10.1080/10256019508036271

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Tests were made for a quantitative decomposition of N2O to N2and for the setting of a statistical equilibrium in mixtures with gaseous nitrogen of nonrandom distribution by emission spectrometric continuous-flow-measurements. Under high-frequency-discharge conditions a residence time of 0.5 seconds is enough for a quantitative decomposition. In this time the statistical balance in the mixture of N2O and N2is reached. The determination of the relative15N abundance in pure N2O or N2gases or in mixtures of N2O and N2in a continuous-flow-emissionspectrometer can directly be achieved.

ISSN:1025-6016    

DOI:10.1080/10256019508036272

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor