The Effect of Locally Applied Cholinesterase Inhibitors and Oximes on the Acetylcholinesterase Activity in Different Parts of the Guinea‐Pig Eye

High activities of acetylcholinesterase and choline acetyltransferase were found in the guinea‐pig retina compared to the brain, and in the cornea, iris and the external eye muscles compared to striated muscles. Instillation of diisopropyl phosphorofluoridate (DFP), sarin and paraoxon into the conjunctival sack was followed by rapid inactivation of the acetylcholinesterase in the cornea and iris, whereas the enzyme activity in the retina and the external eye muscles were much less affected. The de novo synthesis of acetylcholinesterase in the iris and cornea was studied after irreversible inhibition of the enzyme by locally applied diisopropyl phosphorofluoridate following which 50 % of the enzyme activity returned to both regions after 7–10 days. Acetylcholinesterase inhibited by diisopropyl phosphorofluoridate, sarin or paraoxon could be reactivated by locally applied toxogonin or pyridine‐2‐aldoxime methyliodide. Benzalkonium in 0.03 % solution increased the degree of reactivation probably by increasing the permeability of the cornea.