The conjugation of benzoic acid in rabbits.

A study has been made of the excretion of free benzoic acid, hippuric acid, and total combined benzoic acid in the urine of normal adult rabbits following the administration of sodium benzoate. The maximum rate of synthesis of hippuric acid occurred after the ingestion of 0.5 gm. of benzoic acid per kilo. Larger doses of benzoic acid increased the rate of excretion of combined benzoic acid but not that of hippuric acid. In the 24 hour period following the administration of 1.0 gm. of benzoic acid per kilo, the average excretion of hippuric acid in six rabbits was 82 per cent of the combined benzoic acid, the individual variations ranging from 65 to 90 per cent. These urines contained an ether-soluble, non-fermentable reducing substance which gave a positive naphtho-resorcin test. Therefore, it was concluded that 10 to 35 per cent of the combined benzoic acid excreted by the six rabbits was benzoyl glycuronic acid. It has long been known that the rabbit excreted benzoyl glycuronic acid following benzoate administration, but it has generally been assumed that this substance was present only in traces. These experiments indicated that the extent to which the rabbit detoxi-cates ingested benzoate by conjugation with glycuronic acid has been underestimated.