Response of Brain Antioxidant Defense System to Acute Doses of Paraoxon in Male Rats

The toxic effects of some Organophosphates (OPs) are not limited to inhibition of cholinesterase, they are capable to produce free radicals and induce disturbance in body antioxidant systems. Paraoxon is an OP, which is the active form of parathion. The aim of this study was to investigate the effects of paraoxon on oxidant-antioxidant system in rat brain tissue. Wistar rats were randomly divided into four groups (n=7), one control group (corn oil as paraoxon solvent) and three experimental groups who received different doses of paraoxon (0.3, 0.7 and 1 mg/kg) by intraperitoneal injection. 24 hours after injection, rats were anesthetized by ether and brain tissue was removed. After brain tissue hemogenation, superoxide dismutase (SOD), catalase (CAT), lactate dehydrogenase (LDH), glutathione s-transferase (GST) activities, glutathione (GSH) and malondialdehyde (MDA) levels were determined by biochemical methods. At doses higher than 0.3 mg/kg paraoxon, activity of SOD, CAT, GST and LDH significantly increased, comparing with the control group, while GSH level significantly decreased. There were no significant changes observed in MDA level. The results suggest that paraoxon induces the production of free radicals and oxidative stress in a dose- dependent manner. The enhanced activity of antioxidant enzymes in rats’ brain is probably the result of increased detoxification capacity. Depletion of tissue GSH is a prime factor which can impair the cell’s defense against the toxic actions of free radicals.