DIFFERENTIAL IN-VIVO INHIBITION OF THE FETAL AND MATERNAL BRAIN ACETYLCHOLINESTERASE BY BROMOPHOS IN THE RAT

Bromophos, an organophosphorus compound, is known to cross the placent al barrier. The response of the foetal brain acetylcholinesterase (ACh E) to in vivo Bromophos exposure is not known. This study measured the in vivo time-course of cholinesterase (ChE) inhibition and recovery i n rat maternal serum, brain, and foetal brain after administration of a single acute oral dose of Bromophos (500 mg/kg b.w.) on Day 18 of pr egnancy. ChE inhibition in all tissues started as early as 2 h and rea ched a maximum at 16 h post-exposure. Foetal brain AChE was inhibited least and the first to recover followed by maternal brain and serum. T he in vivo ID50 values for the ChE inhibition by Bromophos were 2.02, 205.0, 952.92 mg/kg b.w. and the in vitro IC50 values were 119.12, 115 .17, 112.14 muM for the maternal serum, brain, and foetal brain, respe ctively. The IC50 values show that maternal serum, brain, and foetal b rain are equisensitive to Bromophos. However, the ID50 values suggest that they have differential in vivo sensitivity to Bromophos. The foet al brain seems to be protected against the AChE inhibition by Bromopho s, probably by detoxication in the maternal, placental, and foetal com partments.