Effect of parathion on water intake in the rat

The effect of several subtoxic doses of parathion on water intake was studied in conscious rats with centrally induced thirst. A potent and long-lasting antidipsogenic effect was obtained when single doses ranging from 100 to 600 μg of parathion/100 g body wt were ip given to rats in which thirst was induced either by 24 hr water deprivation or sc injection of hypertonic NaCl solution. A significant thirst inhibition was also obtained when paraoxon or dichlorvos (DDVP) was given. The antidipsogenic effect was prevented by the previous administration of diacetylmonoxime (DAM), an acetylcholinesterase reactivator, but not prevented by pralidoxime (2-PAM), another reactivator that is unable to cross the blood-brain barrier (BBB). Thirst inhibition induced by parathion administration was also prevented when muscarinic cholinergic blockers were previously given, such as atropine sulfate. Acetylcholinesterase activity (AChE) was not inhibited on either blood or hypothalamic tissue with the different doses of parathion given. Locomotor activity and emotionality also remained unaltered. The results obtained indicate that the antidipsogenic effect of the organophosphorus pesticide is centrally produced by stimulation of muscarinic cholinergic pathways.