Review of a Practical Electrometric method for determination of Blood and Tissue Cholinesterase activities in Animals

Abstract

Measurement of cholinesterase activity is of diagnostic value in cases of poisoning with  organophosphate and carbamate insecticides. The enzyme is inhibited to various extents  with concomitant appearance of signs of cholinergic hyperstimulation. The present report  introduces and reviews a practical and simple electrometric technique to measure blood  (plasma, erythrocyte and whole blood) or tissue (brain, liver and muscle) cholinesterase  activities in animals as well as to measure blood cholinesterase activities in man.  Typically, the procedure involves the addition of 0.2 ml of blood sample or tissue  homogenate to 3 ml of distilled water followed by 3 ml of barbital-phosphate buffer  solution (pH 8.1). The pH (pH1) of the mixture is measured, and then 0.1 ml of 7.1% of  acetylcholine iodide or 7.5% acetylthiocholine iodide, as a substrate, is added. The  reaction mixture is incubated at 37º C for 20-40 minutes according to the animal species.  The pH (pH2) of the reaction mixture is measured after the end of the incubation period.  The unit of enzyme activity is expressed as Δ pH / incubation time= pH1- pH2 - (Δ pH of  the blank). The blank is without the enzyme source. Literature are cited regarding the  expected normal cholinesterase activities in man and several animal species including  mice, rats, sheep, goats, cattle, chickens, fish and wild birds. The method was found to be  efficient, simple, accurate and reproducible for possible monitoring of exposure of man  or animals to organophosphate or carbamate insecticides.