THE ROLE OF ESTERASE INHIBITION IN TETRAETHYLPYROPHOSPHATE POISONING IN THE HOUSEFLY, MUSCA DOMESTICA L.

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Abstract
The effect of tetraethylpyrophosphate (TEPP) was studied on the in vivo activity of different esterases in the housefly. TEPP was found to cause inhibition of the acetylcholinesterase and of the ali-esterase which hydrolyzes ethylbutyrate. The latter esterase could be selectively inhibited in vivo by treating the flies with tri-o-cresylphosphate (TOCP). Typical symptoms of organophosphorus poisoning developed only after TEPP when acetylcholinesterase was inhibited. Inhibition of this enzyme coincided with a rise of the level of acetylcholine in the insects. Treatment with TOCP caused a lowering of the level of acetylcholine. The insects became less sensitive to subsequent treatment with TEPP and in this case showed a lesser degree of accumulation of acetylcholine. The importance of acetylcholinesterase and ali-esterase in TEPP poisoning is discussed. It is concluded that the major biochemical lesion effected was the inhibition of acetylcholinesterase. Inhibition of the ali-esterase was not directly related to the toxic action of TEPP, although possibly it led to interference with the accumulation of acetylcholine resulting from the acetylcholinesterase inhibition.