In Vivo and In Vitro Inhibitions of Red Drum (Sciaenops ocellatus) Brain Acetylcholinesterase and Liver Carboxylesterase by Monocrotophos at Sublethal Concentrations

Abstract

The toxic effects of monocrotophos at sublethal concentrations on red drum (Sciaenops ocellatus) brain acetylcholinesterase (AChE, EC 3.1.1.7) and liver carboxylesterase (CaE, EC 3.1.1.1) were examined. After monocrotophos exposure for 4 days at 0.25, 0.5, 1 and 2 mgL-1 respectively, the AChE activity goes down progressively with the increaseof monocrotophos concentration, and CaE activity reaches the lowest rapidly at the lowest monocrotophos concentration and keeps almost the lowest with the increase of monocrotophos concentration. In time-effect experiments, after exposure to 0.5 mg L-1 monocrotophos for 1, 2, 4 and 7 days, the activities of two enzymes change in similar trends as found in concentration-effect experiment. The in vivo inhibitions of brain AChE by monocrotophos depend better on concentration and time than CaE. The inhibition of brain AChE by monocrotophos are weaker significantly than that of liver CaE, revealing that CaE may protect AChE in vivo. In addition, half inhibition concentration(IC50) of CaE is significantly lower than AChE(7.2 × 10-4 mmol L-1 vs 0.21 mmol L-1), explaining the protection role of CaE on AChE.