Modulation in acetylcholinesterase of rat brain by pyrethroids in vivo and an in vitro kinetic study.

Abstract

The modulation of acetylcholinesterase (AChE) of rat brain by two pyrethroids--permethrin (PM) and cypermethrin (CPM)--was studied both in vivo and in vitro. PM inhibited AChE activity in all regions of the rat brain (cerebral cortex, cerebellum, corpora striata, brain-stem, hippocampus, and hypothalamus) at 4, 8, and 12 h after gastric intubation, whereas CPM elevated the enzyme activity in vivo. Substrate-dependent enzyme kinetic studies have shown that PM and CPM behave as mixed-type inhibitors, as evidenced by alterations in both Michaelis-Menten constant (Km) and maximal velocity (Vmax) values. This indicates that both PM and CPM and substrate acetylcholine interact at hydrophobic subsites and may be able to bind simultaneously to the enzyme.