A comparison of the in vitro metabolism of parathion in the lung and liver of the rabbit

Abstract

Varying concentrations of parathion were incubated with microsomes isolated from the lung and liver of untreated, phenobarbital-treated and 3-methylcholanthrene-treated rabbits, and the rates of formation of paraoxon and diethyl phosphorothioic acid determined. From these data the K m and V max values were determined. The results indicate the K m values for formation of paraoxon and diethyl phosphorothioic acid are significantly lower using microsomes isolated from lung as compared to liver. The V max values for the formation of these two metabolites using microsomes isolated from lung are about 20% the values obtained using microsomes isolated from the liver. This difference in activity is most likely due to a smaller concentration of mixed function oxidase enzymes in the lung. The mixed function oxidase activity toward parathion in rabbit liver was induced by both phenobarbital and 3-methylcholanthrene. However, the mixed function oxidase activity toward parathion in the rabbit lung could be induced only by pretreatment with phenobarbital. The implications of metabolism of parathion to paraoxon in the lungs and the liver as it pertains to the toxicity of parathion is discussed.