Changes in the excretion of endogenous glycine conjugate as a possible artifact in toxicological experiments

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Abstract
Changes in the urinary excretion of hippuric acid (HIA) and phenaceturic acid (PUA) as well as their metabolic precursors, i.e. benzoic (BA) and phenylacetic acid (PAA), in rats housed in glass metabolic cages for 4 days were monitored using gas-liquid chromatography. The amount of HIA excreted was 128±63 μmol/kg for female and 79±43 μmol/kg for male rats in the first 24 h and decreased to 11±7 μmol/kg (p< 0.01) for female and 3.2±2.4 μmol/kg (p< 0.001) for male rats on the 2nd day. These values remained nearly at the same level until the end of the experiment. The amount of PUA decreased from 48±12 μmol/kg on the 1st day to 22±9 μmol/kg (p< 0.05) on the 2nd day by male rats, whereas by the females the decrease from 30±9 μmol/kg to 21±8 μmol/kg was not significant. The decrease in the excretion of glycine conjugates was compensated by a parallel increase in the level of unconjugated BA and PAA.