Continual determination of acetylcholinesterase inhibition following organophosphate poisoning using an auto analyzer

A modification for continual monitoring of the blood acetylcholinesterase activity in the rat on an auto analyzer system was described. With using this technique, inhibition of the enzyme in vitro with O-ethyl-S-(2-dimethylaminoethyl)-methylphosphonothioate was determined. Bimolecular rate constant and I50 values were 1.66-10(6) M-1-min-1 and 1.4-10(-8)M, respectively. Rats treated i.m. with 0.043 mg/kg of this compound showed fast and rapid inhibition of the blood acetylcholinesterase after intoxication. The bimolecular rate constant of inhibition in vivo, calculated analogously as that in vitro was 1.37-10(6) M-1-min-1. On the presumption that both rates of inhibition (in vitro and in vivo) are identical, the concentration of organophosphate producing inhibition effect in vivo was 82% of the dose administered.