Adenosine is a naturally occurring nucleoside formed in the body by the enzymatic breakdown of adenosine triphosphate (ATP). Adenosine is not a typical hormone or neurotransmitter, but is an important neuromodulator in the central and peripheral nervous systems. Adenosine is released from inflamed (infected) tissues or ischemic tissues where there is a decreased blood supply to a particular body organ or part.
Adenosine is a nucleoside formed when adenine is attached to a ribose ring (also known as a ribofuranose) via a β-N9-glycosidic bond. Adenosine plays an important role in biochemical processes, such as energy transfer - as adenosine triphosphate (ATP) and adenosine diphosphate (ADP) - as well as in signal transduction as cyclic adenosine monophosphate, cAMP. Adenosine can be very effective at slowing or ending a rapid heart rate if the problem is caused by an abnormal electrical pathway in the heart. Adenosine will not work if the fast heart rate has a different cause. Therefore, it may have limited value in diagnosing tachycardia or helping identify the location of the fast heart rate. If adenine is attached to a deoxyribose ring, it is known as a deoxyadenosine. When administered intravenously, adenosine causes transient heart block in the AV node of the heart.
In individuals suspected of suffering from a supraventricular tachycardia (SVT), adenosine is used to help identify the rhythm. Certain SVTs can be successfully terminated with adenosine. This includes any re-entrant arrhythmias that require the AV node for the re-entry (ie: AV reentrant tachycardia (AVRT), AV nodal reentrant tachycardia (AVNRT)). In addition, atrial tachycardia can sometimes be terminated with adenosine.
Fast rhythms of the heart that are confined to the atria (i.e. atrial fibrillation, atrial flutter) or ventricles (ie: monomorphic ventricular tachycardia) and do not involve the AV node as part of the re-entrant circuit are not typically effected by adenosine. Because of the effects of adenosine on AV node-dependent SVTs, adenosine is considered a class V antiarrhythmic agent. The pharmacological effects of adenosine are blunted in individuals who are taking methylxanthines (ie: caffeine (even coffee) and theophylline)
and as a signal of inflammation. Levels rise rapidly in ischaemic tissue due to adenosine kinase inhibition, and mediate ischaemic pre-conditioning, where a prior, brief episode of organ ischaemia protects against subsequent ischaemia! Inflamed tissues also release adenine nucleotides which are converted to adenosine. Cells that release these nucleotides include platelets, mast cells, nerves and the endothelium.
The four adenosine receptors which detect local changes in adenosine concentration are called A1, A2A & B, and A3. They are "seven-spanning" proteins coupled to various G-proteins. As one might expect, things are hellishly complex, as interactions occur with a vast array of other receptors. A2 receptors work on Gs, but A1 and A3 interact with Gi and Go. There may be other G-protein interactions.
Adenosine is an endogenous nucleoside occurring in all of the cells of the body. It is chemically 6-amino-9-B-D-ribofuanosyl-9-H-purine and has the chemical formula of C10H13N5O4. Adenosine naturally hydrogen bonds to thymidine by two hydrogen bonds to construct a stable structure. Adenosine is present in every cell in the human body. Adenosine is a purine, meaning that it is a single ring structure. A carbon sugar ring attaches to nitrogen in the base to form an N-glycosylic bond. The nitrogenous bases, which are primarily nonpolar, pack tightly enough to exclude water and form a stable, primarily nonpolar environment in the helix interior.
Synonyms: 9-b-d-ribofuranosyl-9H-purin-6-amine, adenine riboside
Molecular formula: C10H13N5O4
CAS No: 58-61-7