Phenolic metabolites of amitriptyline and nortriptyline in rat bile

Anesthetized bile fistula rats received amitriptyline (AT), its N-oxide (AT-NO), or nortriptyline (NT) at doses of 72 mumol/kg ip, and bile was collected for 6-9 hr. Isolation of metabolites was achieved by enzymic deconjugation and repeated TLC of extracted aglycones. Purified compounds were characterized by UV, NMR, and mass spectrometry, by color reactions, and by chemical interconversions. Besides the alcohols E-10-hydroxy-AT and 10,11-dihydroxy-AT, the phenol E-2-hydroxy-AT occurred as a major AT metabolite, while 2,10- and 2,11-dihydroxy-AT, 2,10,11-trihydroxy-AT, and 2-hydroxy-3-methoxy (or 3-hydroxy-2-methoxy)-AT were present in smaller quantities. Further minor metabolites were 2-hydroxy-11-oxo-AT, 3-hydroxy-AT, 3,11-dihydroxy-AT, and its dehydration product 3-hydroxy-10,11-dehydro-AT. The exact position of the functional groups was elucidated by the nuclear Overhauser effect (NOE) in NMR spectroscopy and by analyzing metabolite patterns in the bile of rats given E- or Z-10-hydroxy-AT. Administration of AT-NO led to a larger proportion of methylated catechols and a smaller one of 10-hydroxy metabolites. Besides the tertiary amines, rats given AT or AT-NO excreted the demethylated analogues of some of the hydroxylation products. The latter also occurred as metabolites of NT, the ratio of aromatic and aliphatic hydroxylation being lower than with AT or AT-NO. Urine of rabbits treated orally with AT contained mono- and dihydroxylated metabolites resulting from attack at positions 2, 3, 10, and/or 11 and the same methylated catechols as rat bile.