Use of whole blood for spectrophotometric determination of cholinesterase activity in dogs

Whole blood has been compared with erythrocytes and plasma for spectrophotometric cholinesterase determination in the dog. Cholinesterase activity was characterized using two substrates: acetylthiocholine and butyrylthiocholine. Acetylcholinesterase was the only form of cholinesterase present on erythrocytes and hydrolysed only acetylthiocholine, Butyrylcholinesterase (pseudocholinesterase) was predominant in plasma, hydrolysing mainly butyrylthiocholine. Based on these results, a method based on the use of mio substrates (acetylthiocholine for monitoring acetylcholinesterase and butyrylthiocholine for determining butyrylcholinesterase) in the same whole blood sample is recommended for canine cholinesterase analysis. This way of monitoring both enzymes can be easily automated, yielding good within (CVs < 5%) and between-run (CVs < 7%) precision. The suitability of whole blood samples for detecting exposure to cholinesterase inhibitors was assessed by comparing cholinesterase analysis in whole blood, plasma and erythrocytes after in-vivo and in-vitro exposure to the organophosphorus insecticide coumaphos. Butyrylcholinesterase was found to be more sensitive than acetylcholinesterase. Results from whole blood and plasma samples showed good correlation, supporting the stability of using whole blood for monitoring the inhibitory effects of anticholinesterase agents. (C) 2000 Harcourt Publishers Ltd.