The Pseudocholinesterase

Definition – What is pseudocholinesterase?

Pseudocholinesterase is an enzyme that cleaves an ester bond with the help of water, this process is also called hydrolytic ester cleavage. The enzyme can be found almost everywhere, especially high concentrations can be found in the blood, liver and pancreas. The enzyme is mainly relevant in the case of a deficiency, as complications can arise under general anesthesia.

An ester is a compound of an acid and an alcohol. There are different types of acids and alcohols that can react with each other to form an ester. The products resulting from this reaction are therefore also very diverse. Pseudocholinesterase mainly cleaves choline esters. The best known and most common choline ester is acetylcholine, which is a very important messenger substance that is omnipresent in the body.

The function and effect

The pseudocholinesterase has different functions, since not only one single substance is converted by this enzyme. Besides the substance that is mainly converted, namely acetylcholine, cocaine, heroin, aspirin and various muscle relaxants are also broken down. It is assumed that the main function of pseudocholinesterase is to render acetylcholine, which is not located in the synaptic cleft, ineffective.

The synaptic cleft is the site of action of acetylcholine. This gap is the connection between nerve cells and they communicate among other things via the messenger acetylcholine. The ability to split other substances leads to their rapid breakdown in the bloodstream.

An important example are muscle relaxants, which are used in anaesthesia. These are given so that the operation can be performed without involuntary movements of the patient. These have only a very short time of action and are therefore normally easy to dose. This short time of action is caused by the breakdown of the substance in the bloodstream, by pseudocholinesterase. Also the relatively short effect of heroin and cocaine is partly caused by the degradation, by the pseudocholinesterase.

What happens in case of pseudocholinesterase deficiency?

A lack of pseudocholinesterase may not be noticed. The substances that are converted by the enzyme can also be broken down by related enzymes. For example, acetylcholine is mainly broken down by acetylcholine esterase.

Although this enzyme specifically cleaves acetylcholine, other substances that occur naturally in the body are also broken down by other enzymes. The lack of pseudocholinesterase only becomes noticeable when the person concerned is given a general anaesthetic during an operation. If certain muscle relaxants are used during this operation, they cannot be broken down as quickly as usual.

Mivacurium and suxamethonium are the agents that should be emphasized. Both act differently, but are mainly broken down by pseudocholinesterase. They are degraded more slowly due to the deficiency or also due to a defective pseudocholinesterase.

A muscle relaxant causes the respiratory muscles not to function either. It is important to recognize whether breathing starts again when the muscle relaxant is stopped. Otherwise, the patient must be ventilated longer and the anesthesia must be maintained.