[Dynamics of cholinesterase inhibition in methylparathion poisoning]

The inhibition of cholinesterase (ChEA) and acetylcholinesterase activity (AcChEA) in blood and brain of albino rats was followed up after repeated exposure to methylparathion (MP). An abrupt reduction of ChEA and AcChEA was observed by 30 th and 90 th min after the single peroral administration of 32 mg/kg MP. Furthermore, the reduction was most manifested with ChEA, where the activity was reduced with 71 per cent, AcChEA was reduced to 54 per cent. By 24 th h after the administration of the dose ChEA was significantly higher than the value in the control animals. That could be explained by a quick reactivation of enzyme activity. No clinical picture of intoxication was observed during that period. AcChEA in blood and brain remained strongly reduced, both by 24 th hour after the single MP quantity administered and during the following observation periods--till 14 th day. After the discontinuation of MP administration, a slow tendency to increase of AsChEA values was observed, being strongly decreased as compared the level of the enzyme in the control animals. The reduction of ChEA and AcChEA is associated with the appearance of non-identified metabolites of MP-inhibitors of ChEA with Rf 0. I and 0.65 during the first periods--to 90 min. On 14 th day, after 13-days administration, metabolites with Rf 0.15 and 0.4 were confirmed in chromatogram, besides the main spot with Rf--0.26 (corresponding to MP). Due to the considerable ChEA reduction, prior to the manifestation of the clinical picture of intoxication, ChEA determination in blood could be an early index for confirming the exposure to organophosphoric compound.