ADENOSINE​

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Adenosine is an endogenous purine nucleoside that plays a significant role in various physiological processes. It has vasodilatory, anti-inflammatory, and antiplatelet properties and acts on specific adenosine receptors (A1, A2A, A2B, and A3). While its primary use is in the management of supraventricular tachycardia (SVT), adenosine also has important roles in the context of anesthesia:

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1. Treatment of perioperative arrhythmias: Adenosine is primarily used for the rapid termination of paroxysmal supraventricular tachycardia (PSVT) during the perioperative period. It is administered intravenously and has a very short half-life, making it an effective and relatively safe option for treating these arrhythmias.

2. Assessment of arrhythmias: In some cases, adenosine can help differentiate between various types of arrhythmias. By transiently slowing or blocking atrioventricular (AV) nodal conduction, adenosine can help reveal the underlying atrial activity, which aids in the diagnosis and subsequent management of arrhythmias.

3. Myocardial protection: Some research suggests that adenosine may provide myocardial protection during cardiac surgery by reducing the risk of ischemia-reperfusion injury. 

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The mechanism of action of adenosine varies depending on the receptor subtype involved and the target tissue. Some of the main actions of adenosine include:

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1. A1 receptor activation: A1 receptors are found in various tissues, including the heart, brain, and kidneys. When adenosine binds to A1 receptors, it inhibits adenylate cyclase, leading to decreased cyclic adenosine monophosphate (cAMP) levels. In the heart, this results in decreased conduction through the atrioventricular (AV) node, which can slow the heart rate and help terminate certain types of supraventricular tachycardia.

2. A2A receptor activation: A2A receptors are predominantly found in the vasculature, platelets, and immune cells. Adenosine binding to A2A receptors leads to the activation of adenylate cyclase, increasing cAMP levels. This results in vasodilation, inhibition of platelet aggregation, and modulation of immune cell function.

3. A2B receptor activation: A2B receptors are expressed in various tissues, including the vasculature, lungs, and gastrointestinal tract. Activation of A2B receptors also stimulates adenylate cyclase, increasing cAMP levels. In the vasculature, this leads to vasodilation, while in the lungs, it can contribute to bronchial smooth muscle relaxation.

4. A3 receptor activation: A3 receptors are found in various tissues, such as the eyes, heart, and immune cells. Their activation can lead to various cellular responses, including modulation of immune cell function, promotion of cell survival, and inhibition of tumor cell growth.

                                                                                       

                                                                                              Key points about Adenosine

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• Endogenous nucleoside that slows the conduction of cardiac impulses through the atrioventricular node.

 

• Effective alternative for the acute treatment of paroxysmal supraventricular tachycardia.

 

• It stimulates cardiac adenosine-1 receptors to increase potassium ion currents, shorten the action potential duration, and hyperpolarize cardiac cell membranes.

 

• It has an elimination half-time of 10 seconds.

 

• Side effects include facial flushing, headache, dyspnea, chest discomfort and nausea.

 

• Bronchospasm has been observed after administration.

 

• Used with caution in patients known to have active wheezing.

 

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