Comparison of different diluents and chromophores for spectrophotometric determination of livestock blood cholinesterase activity

Effects of seven different blood diluents (distilled water, Triton X-100, s aponin, isotonic saline solution, pH 7.5 and 8 phosphate buffers and bovine serum albumin) and two chromophores: 5,5'-dithiobis 2-nitrobenzoic acid (D TNB) and 2,2'-dithiodipyridine (2-PDS) on blood ccholinesterase determinati on in four domestic species (cow, sheep, goat and horse) are described and compared. Haemolytic diluents (distilled water, Triton X-100 and saponin) g ave the best precision results when fresh blood was assayed. However, Trito n X-100 induced lower ChE activity values in horses, and saponin yielded ve ry high backgrounds in all species tested; so distilled water was recommend ed as diluent for fresh blood cholinesterase determination. In frozen sampl es all diluents (except Triton X-100) gave homogeneous final ChE results an d showed good between-run precision. Use of 2-PDS as chromophore allowed to do kinetic measurements with approxi mately 1/3 less haemoglobin interference than when DTNB was employed. This fact allows the use of more concentrated whole blood samples, improving mea surements accuracy and decreasing the possible reactivation of inhibited Ch E. On the basis of these results, distilled water as diluent and 2-PDS as chro mophore are recommended for ChE determination in whole blood. (C) 1999 Harc ourt Publishers Limited.