Hippuric acid synthesis in the rat

Abstract

Hippuric acid formation by the rat was studied by injecting graded doses of Na benzoate and N15- and alpha- alpha-C14 -labelled glycine at different time intervals and isolating the excreted hippuric acid. With doubly labelled glycine no marked change in the N15/C14 ratio was found. With simultaneous admn. of benzoate and labelled glycine, increase of the benzoate dose diminished markedly the isotope content of the excreted hippuric acid. Injn. of varying closes of benzoate 3 hrs. after the glycine resulted in only slight variations of the isotope content of the hippuric acid; with time intervals of 6 hrs. or longer there was no variation. Within wide limits the quantity of glycine in which a given amt. of isotope was administered had little or no effect on the isotope content of the hippuric acid. It is concluded that the amt. of glycine immediately available for conjugation with small doses of benzoate is about 10 mg./100 g. body wt. This "first glycine pool" is in relatively slow equilibrium with a larger "pool" of glycine and glycine precursors, which participate in hippuric acid formation only when larger doses of benzoate are given.