Automated Cholinesterase Measurements: Canine Erythrocytes and Plasma
F. Prescott Ward, Thomas L. Hess · American Journal of Veterinary Research · 1971
SUMMARY An automated method was developed to measure red blood cell (rbc) and plasma cholinesterase (ChE) in venous blood samples from Beagles. Advantages of the procedure were simplicity, high reproducibility, speed, and direct measurement of a product of enzymatic action. Sample ChE hydrolyzed the substrate acetylthiocholine (ASCh); one of the products, thiocholine, combined with a chromogenic indicator of sulfhydryl groups. The intensity of the resulting color was automatically recorded. Routine sampling speed was 50/hour, and mean error between test results of repeated samples was ±1%. In contrast to most accepted ChE test procedures, edta was better than heparin as an anticoagulant for collected blood samples, because rbc and plasma ChE activities were lower in heparinized samples. Hemolyzing the rbc by diluting with deionized water increased apparent enzyme activity; however, in hemolyzed samples, nonenzymatic activity was even higher, yielding lower net enzyme activity. In samples hemolyzed by a nonionic detergent, apparent activity was also higher than in nonhemolyzed samples, but net activity was the same. The optimum substrate concentrations and the kinetic values Km and Vmax were defined for both rbc and plasma ChE. In 15 dogs from which blood samples were collected 8 times in 2 weeks, average variation in rbc ChE was less than ±4% and that of plasma ChE, less than ±5%. The rbc ChE values in males did not differ from those in females; males, however, had significantly less plasma ChE activity.