The effect of three organophosphorus esters on brain and blood neurotoxic esterase and acetylcholinesterase

Abstract

The effects of three organophosphorus esters (OPs) on brain and blood neuropathy target esterase (NTE) and acetylcholinesterase (AChE) were evaluated in immature chicks. Enzyme inhibition by desbromoleptophos ( O-2,5-dichlorophenyl O- methyl phenylphosphonothionate), a known inducer of organophosphorus ester-induced delayed neuropathy, and by fenitrothion ( O,O-dimethyl O-3-methyl-4-nitrophenyl phosphorothionate), without delayed neurotoxic effects, was compared to inhibition by fenthion ( O,O-dimethyl O-3-methyl-4-(methylthio)phenyl phosphorothionate). Chicks were treated orally or dermally with maximum tolerated doses of the 3 OPs. The inhibition of enzymes was measured from 24 to 72 hr after dosing. Desbromoleptophos inhibited NTE and AChE in both blood and brain. Fenitrothion and fenthion inhibited AChE both in blood and brain, but did not inhibit either brain or lymphocyte NTE. Blood NTE inhibition paralleled brain enzyme inhibition. Theses data provide additional evidence that fenthion-induced functional deficits are not caused by inhibition of NTE and are not the direct result of AChE inhibition.