Follow up studies on the respiratory pattern and total cholinesterase activities in dichlorvos-poisoned rats

A human prospective study confirmed that the severity and time-course of organophosphate poisonings depend on the compound. Our purpose was to assess the ventilation at rest and cholinesterase activities from 5min to 72h in rats poisoned with dichlorvos at 40% of the MLD (5.12mg/kg). Ventilation at rest was recorded by whole body plethysmography and core temperature by infrared telemetry (DSI system). Results are expressed as mean±SEM. Statistical analyses used two-way ANOVA. Dichlorvos induced the onset of respiratory effects within 5min and hypothermia which peaked at 15min, both reversed within 90min post-injection. Dichlorvos significantly decreased respiratory frequency, resulting from an increase in expiratory time and associated with increased tidal volume. Tissues and whole blood cholinesterase activities were significantly decreased until the end of experiment. Our study showed that an inhibition of cholinesterase was correlated with an effect on respiratory functions at 15min and 60min. However, 24h post-poisoning, the increase in cholinesterase activity was not completed while ventilatory parameters were within the normal range. Respiratory effects were both qualitatively and quantitatively similar to those induced by diethylparaoxon. However the effects strongly differed between diethylparaoxon lasting hours while dichlorvos lasted tens of minutes.