Effects of Echothiophate on Cholinesterases in Cat Irides

Abstract

In vivo application of echothiophate iodide to cats' eyes resulted in approximately 70% inhibition of true cholinesterases (ChE) and 15% inhibition of pseudo-ChE in treated eyes. Contralateral untreated eyes, however, showed a similar magnitude of enzymatic inhibition. In both eyes, the acetyl-β-methylcholine bromide (MeCh) dose-response curve showed a 1 log unit increase in sensitivity, whereas the carbachol dose-response curves were unaltered. The latter finding indicates that the sensitivity of cholinergic receptors in this structure is unaltered by echothiophate. Results of the current study showed excellent correlation with previous in vitro studies of cat irides treated with echothiophate. Maximum enzymatic inhibition and shift in the dose-response curves was obtained after one day of treatment with echothiophate.