Conjugation of benzoic acid in marsupials

The fate of benzoic acid was studied in 7 species of marsupials and the echidna. Radiolabelled [7-14C]-benzoic acid was administered to 3-7 animals of each marsupial species (brown bandicoot, barred bandicoot, Tasmanian devil, potoroo, pademelon, brush-tailed possum and sugar glider) and urine was collected over ice for 24 hours. Metabolites were extracted from acidified urine with ethyl acetate and separated on fluorescent silica gel TLC plates. Bands were visualised under UV, and eluted with methanol. After methylation with diazomethane, benzoic acid, hippuric acid and ˜í‚â§-hydroxyphenylpropionic acid were identified by GC/MS. The methylated benzoyl glucuronide required trimethylsilylation before GC/MS. Quantification was by liquid scintillation spectrometry. It was found that all species excreted most of the dose in 24 hr. As with eutherians, the major metabolite was hippuric acid, with smaller amounts of benzoic acid and ˜í‚â§-hydroxyphenylpropionic acid. Benzoyl glucuronide excretion varied greatly, from 2% of the dose in the pademelon to 32% in sugar gliders. Similar variability has also been reported in eutherians.