Red cell and plasma cholinesterase activities in microsamples of human and animal blood determined simultaneously by a modified acetylthiocholine/DTNB procedure

Abstract

A modification of the acetylthiocholine/DTNB method has been developed for the simultaneous determination of red cell and plasma cholinesterases in samples of only 0.01–0.03 ml of whole human and animal blood, using a relatively short incubation period of 10 min and an incubation temperature of 30°C. In contrast to many other micromethods, these test conditions allow activity determinations of cholinesterases inhibited by insecticidal carbamates in vivo, because decarbamylation of the enzymes after dilution is comparatively low after 10 min at 30°C. Human blood cholinesterases are assayed with propionylthiocholine, whereas for blood samples of various laboratory animals acetylthiocholine was found to be the better substrate. The experimental procedure of this micromethod is based on two cholinesterase measurements, of which the first determines total activity in whole blood, and the second, plasma cholinesterase activity alone. Erythrocyte cholinesterase activity is determined by subtraction. Normal activity values of the enzymes in red cells, plasma, and brain are given for a variety of species, and a few in vivo inhibition data after organophosphate and carbamate poisoning are also presented.