Investigation of the metabolism of 14C/13C-practolol in rat using directly coupled radio-HPLC-NMR-MS.
1. The metabolic fate of 14C/13C-practolol was investigated using on-line HPLC-NMR-MS following oral administration to rat. The major route of elimination for the radiolabel was via the urine with the principal biotransformation products confirmed as the 2-hydroxy- and 2-hydroxyglucronide metabolites. 2. In addition, futile deacetylation, determined by the replacement of 13C-labelled acetyl groups with endogenous 12C-acetyls accounted for approximately 7-10% of the urinary metabolites, corresponding to approximately 5% of the dose undergoing N-deacetylation. 3. Evidence for chiral metabolism was sought via NMR of isolated metabolites using beta-cyclodextrin as a chiral shift agent. Practolol was excreted as a racemate. However, some enantioselective metabolism/excretion had occurred as the hydroxy- and hydroxyglucuronide were not excreted as racemic mixtures. 4. Directly coupled radio-HPLC-NMR-MS is extremely effective for the identification of the metabolites of radiolabelled xenobiotics in urine samples.
Scarfe
G B
GB
Biological Chemistry, Biomedical Sciences Division, Imperial College of Science, Technology and Medicine, South Kensington, London, UK.
Lindon
J C
JC
Nicholson
J K
JK
Martin
P
P
Wright
B
B
Taylor
S
S
Lenz
E
E
Wilson
I D
ID
D000319:Adrenergic beta-Antagonists / Q000493:pharmacokinetics*; D000818:Animals; D001711:Biotransformation; D002851:Chromatography, High Pressure Liquid; D006868:Hydrolysis; D007553:Isotope Labeling; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D013058:Mass Spectrometry; D011217:Practolol / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D013056:Spectrophotometry, Ultraviolet
D000319:Adrenergic beta-Antagonists; D011217:Practolol