Metabolic interaction between n-hexane and toluene in vivo and in vitro

Summary Metabolic interference between n-hexane and toluene was studied both in vivo and in vitro. In in vivo experiments the urinary excretion of n-hexane and toluene metabolites was tested in rats treated with the two solvents separately or in combination. The same experimental program was repeated in rats pretreated with phenobarbital (PB). The urinary excretion of n-hexane metabolites in rats treated with the two solvents showed a significantly decreased excretion of all n-hexane metabolites in comparison with those treated with n-hexane alone. In rats pretreated with PB the excretion of n-hexane metabolites was significantly higher compared with that of unpretreated rats; the combined administration of the two solvents showed in this case, too, that n-hexane metabolite excretion was less than that found in rats treated with n-hexane alone. The biotransformation of toluene to o-cresol and hippuric acid studied in the urine of rats treated with or without n-hexane and pretreated or not with PB did not show any difference. The in vitro metabolic interference was studied by measuring the disappearance of solvents from rat's incubated liver microsomes. The maximum velocity (Vmax) of n-hexane was 2.8 nmol/g/min when incubated alone, 1.9 and 0.9 nmol/g/min when incubated with 5 and 20 M of toluene respectively. The Vmax of toluene was 14.9 nmol/g/min when incubated alone and 13.1 and 10.5 nmol/g/min when incubated with 10.4 and 20.9 M of n-hexane respectively. The inhibition constant (Ki) of toluene on n-hexane biotransformation was 7.5 M and that of n-hexane on toluene was 30 M. The data show that a mutual non-competitive interference exists in vitro betweeen n-hexane and toluene. The interference of toluene on n-hexane biotransformation was detectable also in vivo experiments, while n-hexane did not modify the biotransformation of toluene.