Parathion toxicity in relation to liver microsomal oxidases, lipid composition and fluidity

Rats were injected intraperitoneally with phenobarbital (PB) and 3-methylcholanthrene (MC), 80 and 20 mg/kg, respectively, for 3 consecutive days and then administered threshold lethal dose of the organophosphorus insecticide, parathion, 10 mg/kg i.p. to compare its toxicity in these, with those fed high fat, diet (HFD-50% saturated fat, and normal diet (ND-10% saturated fat) for 30 days. Hepatic microsomes of these four groups of rats without the parathion administration were also analysed to evaluate toxicity and metabolism of the insecticide in relation to some physico-chemical changes in microsomal membranes. Results showed that in comparison to ND, all three pretreatments (PB, MC and HFD) significantly decreased parathion toxicity, increased microsomal oxidase activity and elevated microsomal cholesterol/phospholipid ratio. However, microsomal cytochrome P-450 was significantly raised only in PB and MC, and microsomal fluidity was significantly raised only in MC, as measured by DPH-fluorescence polarization technique.