Automated Instrument Analysis of Cholinesterase Activity in Tissues From Carbamate-Treated Animals: A Cautionary Note

Abstract

Summary: When using a spectrophotometric method to measure cholinesterase activity in carbamate-treated tissues, precautions must be taken to limit the reactivation of the inhibited cholinesterase. Many testing laboratories use automated instruments to measure cholinesterase activity, instruments that usually employ a spectrophotometric method. To date, there has been no systematic investigation of the validity of the cholinesterase data obtained from carbamate-treated tissues using these automated instruments. The purpose of this study was to compare the cholinesterase data obtained using an automated analyzer with those obtained using a radiometric assay (i.e., the optimal method for unstable inhibitors). Using both an automated analyzer and the radiometric method, cholinesterase activity was measured in whole blood and brain tissue taken from rats treated with various dosages of carbaryl. Reactivation occurred when using the automated instrument. In the brain tissue, cholinesterase activity of the treated tissues was as much as 16% higher with the automated method than with the radiometric method. In the whole blood, there was an 18-26% reactivation using the automated method. Further detailed analyses indicate that this reactivation is not due to the initial dilution required of the tissue sample for automated analysis. The results indicate that the length of the preincubation may be a major factor that encourages the reactivation of the cholinesterase activity; however, even when the preincubation period is minimized, reactivation still occurs.

Keywords: :

• [K]Key [K]Words: Automated Analysis, Carbamate, Cholinesterase Inhibition.