Comparison of oxime-initiated reactivation of organophosphorous-inhibited acetylcholinesterase in brains of avian embryos

Organophosphorous (OP) insecticide-induced inhibition and oxime reactivation of acetylcholinesterase (AChE) was determined in whole-brain homogenates prepared from 15-d-old chick embryos. Doses of chlorpyrifos, parathion, acephate, and trichlorfon that inhibited AChE >70% were administered to the embryos. Following insecticide exposure, an in vitro system compared the capability of the oximes pralidoxime (2-PAM), obidoxime, TMB-4, and HI-6 to reactivate the OF-inhibited AChE. Concentration-related increases in AChE activities were noted in embryo brains reactivated with 2-PAM, TMB, and HI-6. 2-PAM was the most effective reactivator of trichlorfon-inhibited AChE; 2-PAM and obidoxime were relatively similar in effectiveness for reactivation of AChE inhibited with the other OP insecticides used as test agents. All oximes were similarly effective against acephate, bur HI-6 was the least effective reactivator of AChE in chick embryo brain homogenates inhibited by the other OP insecticides. These results suggest that both the OF insecticide inhibiting AChE and the oxime reactivating this enzyme can contribute to the effectiveness of the avian brain AChE reactivation.