Acetylcholine in the corneal epithelium of diurnal and nocturnal mammals.

Purpose: To analyze the concentration of acetylcholine (ACh) in the corneal epithelium and aqueous humor of various diurnal and nocturnal mammals. Methods: The following species were examined: roe deer, cattle, horse, human, moose, sheep, reindeer, wild boar, polecat, lynx, cat, and rat. ACh was determined by liquid chromatography-tandem mass spectrometry. Results: ACh was present in significant amounts in the comeal epithelium of all diurnal mammals, the concentrations varying from one species to the next. By contrast, it was not detected in any of the nocturnal tissue samples. None of the species showed detectable amounts of ACh in the aqueous humor. Conclusions: The amount of ACh in the comeal epithelium varies from one species to the next, with diurnal species showing significant concentrations and nocturnal species no detectable concentrations.