Acetylcholinesterase and neuropathy target esterase activity in female and male rats exposed to pesticide terbufos.

An organophosphate pesticide terbufos (S-t-butylthiomethyl-O,O-diethyl phosphorodithioate; TBF) has been extensively used as an insecticide. A sexual dimorphism in TBF toxicity was not reported and remains unclear. The objective of the work was to investigate the influence of TBF on sexual dimorphism after oral administration of TBF to rats by using acetylcholinesterase (AChE) and neuropathy target esterase (NTE) as endpoints. TBF was orally administered to Sprague-Dawley rats, where female rats were received 0, 0.1, 0.4 and 0.8mg/kg TBF for 2 days and male rats 0, 0.1, 0.5 and 1.0mg/kg TBF for 3 days for dose-dependent study. Age-matched female and male rats also received equally 0.5mg/kg TBF for 2 days and sacrificed 0, 6, 12, 24 and 72h after the last dose for time-dependent study. In the dose-dependent study, mortality was 25% in 1.0mg/kg TBF group of male and 50% in 0.4 and 0.8mg/kg TBF groups of female rats, resulting in about two-fold higher in female than male. AChE was significantly decreased only in the frontal and entorhinal cortexes of female rats receiving 0.4 or 0.8mg/kg TBF. In the time-dependent study, the maximal inhibition in the brain regions or plasma was two- or three-fold higher in female, which occurred 6 or 12h after the last dose. However, effects of TBF on alteration of NTE activity were minor, compared to AChE, indicating that AChE is more sensitive marker than NTE in TBF toxicity. These results also indicate that female was more vulnerable to AChE inhibition than male rats after exposure to TBF.