The effect of toluene on rat lung benzo[a]pyrene metabolism and microsomal membrane lipids.

Toluene (1 g/kg, i.p., 1 and 4 h) was shown to decrease total cytochrome P-450 (P450) content in rat lung. At both timepoints, reduction in pulmonary P450 content was associated with a decrease in aryl hydrocarbon hydroxylase (AHH) activity, a detoxication pathway for benzo[a]pyrene (BaP). At 4 h, toluene increased the toxication/detoxication ratios of BaP metabolites in pulmonary microsomes, primarily via inhibition of hydroxy metabolite formation. The structurally analogous solvents p- and m-xylene have been previously shown to produce a similar pattern of MFO changes in rat lung; the inhibition of BaP metabolism was found to be related to alterations in pulmonary microsomal lipids following administration of p- but not m-xylene. In the present study, toluene-induced alterations in MFO parameters were not found to be associated with changes in microsomal lipids. Toluene did not affect either total phospholipid or cholesterol content at either timepoint. Similarly, no changes in speciated phospholipids were observed. Membrane integrity, expressed as conjugated diene formation, also remained unchanged following toluene administration. Toluene did, however, decrease microsomal inner-core membrane fluidity at 4 h but had no effect on membrane leaflet fluidity at either timepoint. These data suggest that the fatty acid composition of microsomal lipids may play a role in the metabolic alterations observed in pulmonary microsomes following toluene administration.