OPTIMIZATION AND APPLICATION OF THE HEAD SPACE LIVER S9 EQUILIBRATIONTECHNIQUE FOR METABOLIC STUDIES OF ORGANIC-SOLVENTS

A head space liver S9 vial equilibration technique for qualitative and quantitative metabolism of volatile organic solvents in vitro is desc ribed and investigated for optimal experimental conditions with toluen e and n-hexane as model substrates. The method was also used for study ing the metabolic interaction between acetone and styrene. NADP(+) was a critical cofactor in the system as concentrations above 2.5 mM resu lted in inhibition of metabolism. Induction of cytochrome P450 by phen obarbital did not alter the observed cofactor dependency, and addition of vehicles such as rat blood did not enhance metabolism. Acetone-ind uced liver S9 increased the primary oxidation of styrene and also the formation of styrene oxide, but not significantly that of mandelic aci d. Acetone as such had no effect on the metabolic elimination of styre ne, indicating that the interaction is mainly on the level of enzyme i nduction occurring after long-term exposure to acetone. As earlier rep orts on styrene metabolism in vivo has not been able to detect styrene oxide in toxicokinetic studies with a sufficient degree of accuracy, the head space liver S9 vial equilibration technique may offer a fast and sensitive tool for screening of metabolic interactions between org anic solvents when optimized for metabolic activity.