Adenosine's action in the body is primarily mediated through its binding to specific cell surface receptors, known as adenosine receptors [1]. There are four known subtypes of these receptors: A1, A2A, A2B, and A3 [1]. The effects of adenosine depend on which receptor subtype is activated and where that receptor is located [2].
How does adenosine affect heart rate?
Adenosine significantly slows down the heart rate by acting on the A1 receptor, which is abundant in the atrioventricular (AV) node of the heart [3]. When adenosine binds to A1 receptors, it increases the flow of potassium ions out of cardiac cells and reduces the flow of calcium ions into them. This leads to hyperpolarization of the AV node cells, making them less excitable and slowing the conduction of electrical signals [4]. This property is utilized in medicine to treat supraventricular tachycardias (SVT), a type of rapid heart rhythm [5].
What is adenosine used for in medicine?
In addition to its use in treating SVT, adenosine has other medical applications. It is used in cardiac stress testing to help diagnose coronary artery disease [6]. During a stress test, adenosine is infused to simulate the effects of exercise on the heart by dilating coronary arteries and increasing blood flow to the heart muscle [6]. This allows doctors to see how well the heart muscle is supplied with blood, especially during exertion [6].
What are the side effects of adenosine?
When administered medically, adenosine can cause transient side effects due to its widespread receptor interactions [7]. Common side effects include flushing, shortness of breath or dyspnea, chest discomfort, and a feeling of impending doom [7]. Nausea, dizziness, and headache can also occur [7]. These effects are typically short-lived because adenosine is very rapidly metabolized in the blood [8].
How quickly does adenosine work and how long do its effects last?
Adenosine has an extremely rapid onset and a very short duration of action when given intravenously. Its effects on the heart begin within seconds of administration, typically within 10 to 30 seconds [5]. The duration of these effects is also very brief, lasting only about one to two minutes [5][8]. This is because adenosine is quickly broken down by enzymes in the bloodstream and tissues [8].
What is the difference between adenosine and other heart rhythm medications?
Adenosine's mechanism of action is distinct from many other antiarrhythmic drugs. Unlike beta-blockers or calcium channel blockers that affect heart rate and conduction more broadly, adenosine specifically targets AV nodal conduction through A1 receptors [3][4]. Its extremely short half-life also differentiates it, allowing for precise control and rapid resolution of effects, which is particularly useful in acute situations like SVT [5][8].
Where are adenosine receptors found in the body?
Adenosine receptors are widely distributed throughout the body, influencing various physiological processes [1][2]. A1 receptors are found in the heart, brain, kidneys, and adipose tissue [2]. A2A receptors are concentrated in the striatum of the brain, immune cells, and blood vessels [2]. A2B receptors are present in the lungs, bladder, and leukocytes [2]. A3 receptors are found in various tissues, including the heart, liver, and immune cells [2].
How does adenosine interact with the immune system?
Adenosine can modulate immune responses by binding to A2A and A2B receptors on immune cells, such as lymphocytes and macrophages [9]. In general, activation of these receptors tends to suppress inflammatory processes and immune cell activity [9]. This immunosuppressive role has led to research into adenosine-targeting therapies for inflammatory and autoimmune diseases [9].