Total esterase measurement in saliva of pigs: Validation of an automated assay, characterization and changes in stress and disease conditions

An automated spectrophotometric method for total esterase activity (TEA) measurement in porcine saliva has been developed and validated, using 4-nitrophenyl acetate (4-NA) as substrate. The method was precise and accurate, with low limit of detection, and was able to measure samples with TEA activities up to 400 IU/L without any dilution. In addition, the different enzymes contributing to TEA were characterized, being identified carbonic anhydrase VI (CA-VI), lipase, cholinesterase (ChE) and cholesterol esterase (CEL). TEA significantly increased (1.49-fold, P < 0.01) in healthy pigs just after applying an acute stress stimulus consisting of nasal restraint, being lipase and cholinesterase the main responsible of this increase. TEA was significantly increased (1.83-fold, P < 0.001) in a group of pigs with lameness; in this case, in addition to lipase and ChE, CA-VI also increased. The results found in this report indicate that TEA can be easily measured in porcine saliva with an accurate and highly reproducible automated method. Salivary TEA is mainly due to the activity of four enzymes: CA-VI, lipase, ChE and CEL, and these enzymes can change in a different way in situations of stress or disease.