Straus_2006_Toxicol.Mech.Methods_16_235

The present study was undertaken to investigate the significance of monooxygenases in bioactivation of DEF to a more effective anticholinesterase in fish. Channel catfish were exposed via the water column for 20 h to piperonyl butoxide (PBO) followed by a 4-h exposure to the organophosphate defolient DEF (concurrent with the PBO). Acetylcholinesterase (AChE) and aliesterases (ALiEs) activities were determined at 0 and 12 h after the exposure period. Inhibition of brain, liver, and plasma AChE activity by DEF was antagonized by PBO; muscle AChE was not inhibited by DEF. Piperonyl butoxide did not antagonize the inhibition of liver or plasma ALiEs by DEF. These results suggest that PBO retards the formation of the metabolite(s) of DEF that inhibit AChE, and that DEF is an effective inhibitor of ALiEs without metabolic activation.