The metabolism of vanillin and isovanillin in the rat

1. The metabolism of vanillin, isovanillin and the corresponding alcohols and acids in rats was investigated using t.l.c., g.l.c. and combined g.l.c.-mass spectrometry. 2. Oral dosage (100 mg/kg) of the aldehyde resulted in urinary excretion of most metabolites within 24 h, mainly as glucuronide and/or sulphate conjugates although the acids formed were also excreted free and as their glycine conjugates. In 48 h 94% of the dose of vanillin was accounted for as follows (%) : vanillin (7), vanillyl alcohol (19), vanillic acid (47), vanilloylglycine (10), catechol (8), 4-methylcatechol (2), guaiacol (0-5) and 4-methylguaiacol (0-6). Similarly, 89% of the dose of isovanillin was accounted for as follows: isovanillin (19), isovanillyl alcohol (10), isovanillic acid (22), vanillic acid (11), isovanilloylglycine (19), catechol(7) and 4-methylcatechol (1). Protocatechuic acid was also formed from both aldehydes. 3. By means of (a) investigation of biliary metabolites, (b) prevention of biliary excretion, (c) suppression of intestinal bacteria with neomycin sulphate and (d) inhibition of intestinal beta-glucuronidase with saccharo-1,4-lactone, it was found that glucuronides of the aldehydes and their respective alcohol and acid derivatives are excreted in the bile and that the conjugates are metabolized by the intestinal bacteria to toluene derivatives and decarboxylated products.