Propionyl cholinesterase

Failure to consider propionyl cholinesterases. Strictly speaking, rat plasma does not contain a BuChE it is known to favor propionyl esters more than butyryl esters and both of those esters more than acetyl esters. Sheep plasma is said to have little if any ChE activity, although it is known to have platelet AChE. 

Evans and Wroe (E22) conducted a study of the hydrolysis rates of four commonly used substrates as related to cholinesterase genotypes and suc-cinylcholine hypersensitivity. They concluded that the propionyl-thiocholine hydrolysis rate is capable of detecting over 90% of hypersensitive individuals, with no false positives. The cutoff value was the mean for the usual phenotype minus 2.5 SD. Acetylcholine and butyrylthiocholine were slightly inferior, and benzoylcholine was almost useless. If... 

The spleen in some species contains relatively large amounts of propionyl-choline . This fact, together with the presence of butyrocholinesterase in the central nervous system and the pharmacological activity of the choline esters, suggests the possibility that substances related to acetylcholine may also participate in the processes of synaptic transmission. Although choline esters other than acetylcholine, as well as other substances with acetylcholine-like activity, have been reported to occur in the brain " , pharmacological and biochemical analyses of brain extracts have failed to confirm these claims " . Similar reports of the existence of acetylcholine-like substances in peripheral nerve extracts have also proved impossible to confirm . The physiological substrate of pseudocholinesterase in the nervous system—if, indeed, it is not acetylcholine— remains unknown. Attempts to solve the problem by differential inhibition of the two cholinesterases in the brain have so far proved unsuccessful. 

Differences between the species toward the thiocholine substrates have been reported. Table 11.1 illustrates some observed differences with three species. For plasma pseudocholinesterase measurements, dog, rabbit, and man show higher substrate specificity for butyryl substrates, whereas rat, mouse, and hamster show higher specihcity for propionyl substrates all the species show less specihcity toward benzoyl substrates. Female rats have higher values compared to males with all three substrates, and the cholinesterase levels in platelets are higher in rats compared to the very low levels in human platelets. 

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