Activation of the phosphorothionate insecticide parathion by rat brain in situ.

The ability of the rat brain to activate the phosphorothionate insecticide parathion to its potent anticholinesterase metabolite paraoxon in situ was observed by ligating the posterior portion of the circulatory system and thus removing the liver from the circulation. Under these conditions no acetylcholinesterase inhibition was observed in 15 min at a dosage of parathion (nominally 2.4 mg/kg) which yielded 95% inhibition when the liver was in the circulation. However, at a higher dose (nominally 48 mg/kg) there was substantial (about 70%) inhibition of brain acetylcholinesterase after 15 min, suggesting that the brain does have the ability to activate parathion in the intact situation.