Polyacrylamide Gel Electrophoresis of Rat Brain Acetylcholinesterase: Isoenzyme Changes Following Parathion Poisoning1

Brain acetylcholinesterase (EC 3. 1. 1. 7) isoenzymes of 15‐ and 30‐day‐old rats were found to be inhibited by 2.5 mg/kg and 1.25 mg/kg dosage levels of intraperitoneally administered parathion (E‐605; O, O‐diethyl‐p‐nitrophenyl phosphorothionate). With 2.5 mg/kg dose level, the response of isoenzymes in 15‐ and 30‐day‐old rats was similar. At both ages, there was no significant sex difference in the degree of depression of the isoenzymes. There were no significant regional differences in the degree of inhibition of acetylcholinesterase isoenzymes in the rat brain. At 1.25 mg/kg dosage level, a differential isoenzyme inhibition was evident, with the major isoenzyme (isoenzyme 3) exhibiting the greatest sensitivity to the inhibitor in all brain areas examined. The course of isoenzyme depression and recovery following the administration of parathion differed in brain, serum and skeletal muscle. Whereas brain isoenzymes exhibited most marked inhibition at 2 h after injection, inhibition of serum and skeletal muscle isoenzymes was more prolonged. At 4 h after injection, these isoenzymes were still inhibited while brain isoenzymes had recovered to a substantial degree. Twenty four h following the injection of parathion, when brain and serum acetylcholinesterase isoenzymes had returned to control activity levels, isoenzymes of skeletal muscle demonstrated only minimal recovery.