In the present report, a new assay combining specific substrates and a selective BChE inhibitor (ethopropazine hydrochloride) was used to measure both AChE and BChE in canine whole blood samples. Acetylthiocholine iodide (ATCI) and butyrylthiocholine iodide (BTCI) were used as substrates, whereas 2,2’-dithiodipiridine was used as chromophore. Ethopropazine concentration inhibiting over 95% BChE with minimum AChE inhibition was fixed at 0.3mM. The results confirmed that whole blood cholinesterase activity measured with BTCI in absence of ethopropazine corresponded with serum BChE, whereas whole blood cholinesterase analysed with ATCI in presence of ethopropazine reflected mainly erythrocytes and plasma AChE activity. This procedure showed good repeatability, it was easy and fast, and can be routinely used in veterinary laboratories.

Key words: Acetylcholinesterase, Butyrylcholinesterase, Dog, Ethopropazine, Substrate, Whole blood