Species differences in normal brain cholinesterase activities of animals and birds

The normal cholinesterase activity in brain tissue was measured in 15 mammalian and 44 avian species using the Ellman method. Enzyme activity exhibited considerable interspecies variability. In mammals, the enzyme activities ranged from approximately 2 to 10 micromole/min/g of wet tissue. With the exception of the carnivores (dog, fox, coyote), no consistency of the enzyme activity could be identified in related mammalian species. The range of interspecies differences associated with avian cholinesterase activity were approximately double when compared to the mammalian species tested. Enzyme activities in avian species ranged from approximately 10 to 30 micromole/min/g. Comparisons for uniformity of enzyme activity between closely related avian species were poor in most instances. The considerable variability of the brain cholinesterase activities in avian and mammalian species illustrates the need for reliable normal values for individual species to improve ability to monitor environmental exposure or to confirm acute poisonings associated with organophosphate or carbamate insecticides.