The Metabolism of Biphenyl. II. Phenolic Metabolites in the Rat

The metabolic conversion of biphenyl to phenolic metabolites was studied in the rat. The metabolites were identified by mass spectrometry and quantified by gas chromatography following conversion to their trimethylsilyl (TMS) ethers. The main route of excretion was via the urine, and the major part (22.3 %) of the biphenyl metabolites was excreted in the first 24 hrs. The total urinary recovery 96 hrs after administration was 29.5 % of the dose and the metabolites detected were conjugates of mono–, di– and tri–hydroxy derivatives of biphenyl as well as the meta– and para–methyl ethers of the catecholic compounds. The two main urinary metabolites were 4–hydroxybiphenyl (7.7 %) and 4,4′–dihydroxybiphenyl (11.4 %). The experiments also showed that biphenyl has to be hydroxylated and then conjugated before it appears in the rat bile. Thus, 5.2% of the dose was found in the 24 hrs bile as conjugates, mainly of 4–hydroxy–, 4,4′–dihydroxy– and 3,4,4′–trihydroxy–biphenyl. Faecal excretion of phenolic biphenyl derivatives was found to be of minor importance, but 4.7 % of the dose was detected during the first 24 hrs after dosing. The following previously undetected metabolites of biphenyl were found: 3,4′–dihydroxy–, 3,4,4′–trihydroxy–, 3,4′–dihydroxy–4–methoxy– and 4,4′–dihydroxy–3–methoxy–biphenyl.