Abstract
The metabolism of clenbuterol by liver microsomal fractions and precision-cut liver slices was studied in rats and cattle using a14C-labeled molecule and radio-HPLC quantitation of the resulting metabolites. 4-N-Oxidation of clenbuterol was found to be an extensive in vitro metabolic pathway in both species. Clenbuterol hydroxylamine was by far the major metabolite characterized from microsomal and slice incubation media. Trace amounts of 4-nitro-clenbuterol were also detected. Another important microsomal biotransformation of clenbuterol, resulting in the production of 4-amino-3,5-dichlorobenzoic acid, was observed only when the drug was incubated with bovine liver microsomes. The corresponding glycine conjugate, namely 4-amino-3,5-dichlorohippuric acid, was detected when clenbuterol was incubated with bovine or rat liver slices. Structural characterization of the major metabolites was performed using electrospray ionization-mass spectrometry, either coupled to liquid chromatography or with direct infusion of collected samples. In addition to these compounds, only quantitatively minor metabolites were detected in bovine (but not rat) microsomal incubation media. Analysis of incubation media from liver slices also allowed the quantitation of a few additional metabolites, some of which were shown to be conjugated compounds.
Footnotes
-
Send reprint requests to: Jacques Tulliez, Laboratoire des Xénobiotiques INRA, 180 chemin de Tournefeuille, B.P. 3, 31931 Toulouse Cédex, France.
-
This study was supported by a grant from the Ministère de l’Enseignement Supérieur et de la Recherche, within the project “Aliment Demain” (95G0098).
- Abbreviations used are::
- CL
- clenbuterol
- N-OH-CL
- 4-hydroxyamino-3,5-dichloro-α-(tert-butylaminomethyl)benzyl alcohol
- NO-CL
- 4-nitroso-3,5-dichloro-α-(tert-butylaminomethyl)benzyl alcohol
- NO2-CL
- 4-nitro-3,5-dichloro-α-(tert-butylaminomethyl)benzyl alcohol
- ADBA
- 4-amino-3,5-dichlorobenzoic acid
- 7-EC
- 7-ethoxycoumarin
- 7-OHC
- 7-hydroxycoumarin
- LDH
- lactate dehydrogenase
- ESI
- electrospray ionization
- Received May 30, 1997.
- Accepted September 23, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|