Low-Level Effects of VX Vapor Exposure on Pupil Size and Cholinesterase Levels in Rats

The effective concentrations (EC(sub 50)'s,) for miosis in male and female rats exposed to VX vapor for 10, 60, and 240 min were estimated using whole body vapor exposures conducted in a 750 L dynamic airflow inhalation chamber. Miosis was defined as at least a 50% reduction in pupil diameter relative to baseline measurements. Contrary to Haber's Rule, median effective dosages (ECT(sub 50)'s) increased with increasing exposure durations (i.e., the CT for 50% of the exposed population to show miosis was not constant over time). Ordinal regression was used to develop an empirical toxic load model for predicting VX vapor induced miosis by defining the relationship between C and T with a VX specific, toxic load exponent (n) in the equation: C(exp n)xT=k. Female rats were more sensitive than male rats to the miotic effects of VX vapor. Statistically significant acetylcholinesterase (AChE) inhibition was detected at the higher concentrations of each exposure time. A VX-G analog assay successfully used rat blood plasma as a biomarker for VX exposure. A general relationship between increasing dose (CT) and increasing amounts of VX-G in the plasma was found.