INHIBITION OF CHOLINESTERASE BY DI-ISOPROPYL FLUOROPHOSPHATE, PHYSOSTIGMINE AND HEXAETHYL TETRAPHOSPHATE IN THE ROACH

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Abstract
By means of a manometrie technique it was detd. that di-isopropyl fluorophosphate (DFP), physostigmine salicylate and hexaethyl tetraphosphate (HTP), in the concs, which are toxic to the roach, Peri-planeta americana L., inhibit the cholinesterase activity of roach nerve cord in vitro and in vivo. The approx. ranges of concs, over which these effects were observed were: for DFP, 1 X 10-6 to 1 X 10-4 M; for physostigmine, 1 X 10-9 to 1 X 10-4 M; for HTP, 1 X 10-7 to 1 X l0-6 M. With DFP, the percentage of mortality after injn. was paralleled closely by the degree of enzyme inhibition which resulted from the same dosage. The comparisons with physostigmine and HTP were less satisfactory. The following LD50''s were detd. for the compounds by injn. in aqueous soln.: DFP, 5.2 mg./kg.; physostigmine salicyclate, 15.6 mg. per kg.; HTP, 6.75 mg. per kg. Although the possibility of other toxic mechanisms for the agents is not excluded, it is concluded that their toxicity is largely a function of their anticholinester-ase activity. The significance of the findings for theories of nervous transmission is discussed.