Acetyl- and pseudo-cholinesterase activities of plasma, erythrocytes, and whole blood in male beagle dogs using Ellman's assay

Organophosphate and carbamate ester insecticides, main causes of pesticide poisoning, inhibit cholinesterase (ChE) enzymes The aim of this study was t o measure and compare baseline values for pseudocholinesterase and acetylch olinesterase (AChE) enzyme activities of different blood fractions in the d og to aid in diagnosis of anticholinesterase poisoning. After collecting bl ood samples from 23 6-24-mo-old male beagle dogs, Ellman's colorimetric ass ay was run on plasma, red blood cells (RBC), and whole blood fractions prep ared in triplicate. The procedure described in a commercially available kit was applied to plasma and RBC. Hemolyzed whole blood fractions (final dilu tion 1:8) avoided the time-consuming and laborious separation of plasma and RBC. In addition to the kit substrate acetylthiocholine (ASCh), we used bu tyrylthiocholine (BSCh) as substrate. Whatever the substrate, ChE: activity was lower in RBC than in other blood preparations. It was higher when usin g ASCh rather than BSCh as substrate (mean IU/L+/-SD): 563 +/- 144 and 303 +/- 45 respectively, in contrast to plasma (1640 +/- 310 and 2510 +/- 450). Whole blood enzyme activity did not differ significantly according to subs trate: ASCh, 1590 +/- 190 : BSCh, 1620 +/- 250) with a 2 to 3% within-day c oefficient of variation. Enzyme activity was significantly lower in dogs <1 -y old. This study confirms the low ChE activity in dog RBC compared to oth er species and other blood fractions. It shows that using whole blood inste ad of separating RBC from plasma minimizes the variability of ChE activity in the hemoglobin-rich fraction.