Automated procedure for estimation of blood cholinesterase activities in rabbits.

An automated procedure for estimation of blood cholinesterase activities was evaluated and used to determine baseline cholinesterase activities in rabbits. In addition, the kinetics of cholinesterase inhibition and recovery from diazinon challenge were determined by use of this procedure. The procedure developed is a modification of the colorimetric Ellman technique, adapted for use with the Instrumentation Laboratory Multistat III Plus Centrifugal Analyzer. The substrate used in this technique was acetylthiocholine. Baseline cholinesterase activities in domestic rabbits were plasma cholinesterase, 360 mU/ml; red blood cell cholinesterase, 2,658 mU/ml; and whole blood cholinesterase, 1,332 mU/ml. Rabbits were challenged with 0.3 LD50 (40 mg/kg) of diazinon, and blood samples were obtained at hourly, then daily intervals. Cholinesterase activity in these samples was determined to monitor the effect of the cholinesterase inhibitor diazinon in vivo, as estimated by the Multistat III Plus Centrifugal Analyzer procedure. Plasma cholinesterase activity decreased to 4% within 6 h, whereas red blood cell cholinesterase activity decreased to 51%. By 10 days, plasma and red blood cell cholinesterase activities had returned to 100 and 91%, respectively, of pre-challenge activities.