Effects of intravenous injection of soman on specific binding with 3H.QNB in rat brain homogenates

Rats were injected iv soman 25-70 microg and , after 15 min, the specific binding of [3H]QNB to their whole brains (except cerebellum) homogenates was studied by radioligandreceptor assay. Soman inhibited the [3H]QNB binding in a dose-depependent manner and the ID50 was 66 microg/kg. But the inhibition was diminished when the iv dose of soman was over 70 microg/kg. Double-reciprocal plot of data revealed that the inhibition of soman on [3H]QNB binding was competitive. This inhibition took place before complete inhibition of cholinesterases(ChE)by soman. The dual actions of soman on ChE and M-AChR in vivo confirmed our previous results in vitro.