Low-Level Cyclo-Sarin (GF) Vapor Exposure in Rats: Effect of Exposure Concentration and Duration on Pupil Size

The probability of cyclo-sarin (GF) vapor-induced miosis (defined as a post-exposure pupil diameter 50% or less of the pre-exposure pupil diameter) was estimated in rats exposed to various combinations of exposure concentration and duration. Groups of male and female Sprague-Dawley rats were exposed to GF vapor for a single duration (10, 60 or 240 minutes) in a whole-body dynamic chamber. Pupil diameter was measured by an infrared camem technique. For the six combinations of gender and exposure duration, the effective concentration for miosis in 50% of the exposed population (EC50) and the common probit slope were determined. Contrary to Haber's rule, ECt50 values increased with exposure duration (i.e., the Ct for 50% of the exposed population to show miosis was not constant over time). Female rats were more sensitive to GF vapor toxicity than male rats. Miosis was the only clinical sign noted following GF vapor exposure. Possible depression of blood esterase (acetylcholinesterase, butyrylcholinesterase and carboxylesterase) activities due to low-level range of GF vapor concentrations was also investigated. GF was regenerated from blood samples of vapor-exposed rats by the addition of fluoride ion at pH 4 and the samples were analyzed by GC-FPD and GC-MS. Levels of regenerated GF in the red blood cell (RBC) fraction of the samples were five to 40 times lower than in plasma. All controls were negative for regenerated GF.
See also ADM001523. Proceedings of the 2002 Joint Service Scientific Conference on Chemical & Biological Defense Research, 19-21 November 2002. The original document contains color images.