Spectrophotometric determination of circulating cholinesterases in rats

A spectrophotometric assay was established to determine circulating levels of cholinesterase (ChE) in the whole blood of rats. A commercially available ChE reagent set was obtained and the suggested procedure modified to quantify and correct for the activity resulting from nonenzymatic hydrolysis of the substrate. The stability of ChE as well as the effect of sampling site, exercise, and carbamate administration were evaluated. The ChE activity of blood drawn from a jugular cannula (central sample) was less than that drawn from a lateral tail vein (peripheral sample), but percent change in activity between sampling times was not different between the two sites. Cholinesterase in carbamate-inhibited blood was not stable and had to be assayed soon after sampling. Therefore, if the assay is performed soon after sampling, rat whole blood ChE activity may be determined spectrophotometrically, and the blood may be sampled either peripherally or centrally.