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

Organophosphorous (OP) insecticide-induced inhibition and oxime reactivatio n of acetylcholinesterase (AChE) was determined in whole-brain homogenates prepared from 15-d-old chick embryos. Doses of chlorpyrifos, parathion, ace phate, and trichlorfon that inhibited AChE >70% were administered to the em bryos. Following insecticide exposure, an in vitro system compared the capa bility of the oximes pralidoxime (2-PAM), obidoxime, TMB-4, and HI-6 to rea ctivate the OF-inhibited AChE. Concentration-related increases in AChE acti vities 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-PA M and obidoxime were relatively similar in effectiveness for reactivation o f AChE inhibited with the other OP insecticides used as test agents. All ox imes were similarly effective against acephate, bur HI-6 was the least effe ctive reactivator of AChE in chick embryo brain homogenates inhibited by th e other OP insecticides. These results suggest that both the OF insecticide inhibiting AChE and the oxime reactivating this enzyme can contribute to t he effectiveness of the avian brain AChE reactivation.