Adenosine:
 
What is adenosine?
Adenosine is a substance produced in humans that helps protect against ischemia (lack of blood flow). It's produced in blood vessels, heart and skeletal muscle, and other organs.
 
What does adenosine do?
When the demand for oxygen increases, as during exercise, adenosine is produced in the muscle and vessels. It has these effects:
  • Provides more energy to the exercising muscle.

  • Enlarges blood vessels to improve the blood and oxygen supply.

  • Helps raise blood pressure, which also increases oxygen supply.

  • Produces pain that tells us to stop exercising and rest, because our muscles aren't getting enough energy and need to recover.
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    What does adenosine do for the heart?
    Adenosine helps protect the heart muscle from damage when myocardial ischemia occurs. Myocardial ischemia happens when the heart muscle (myocardium) doesn't get as much blood and oxygen as it needs.
  • When this happens, adenosine is released in the heart vessels and myocardium and has these effects:

  • Enlarges vessels to increase blood and oxygen supply.

  • Improves energy supply for the myocardium and helps decrease energy needs.

  • Produces angina pectoris chest pain or discomfort due to coronary heart disease). This symptom of myocardial ischemia warns us to rest.

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    What are the clinical applications for adenosine?
    The sinoatrial node, located in the atrium (upper chamber) of the heart, produces the electrical impulses that cause the heart to beat. Adenosine has a depressant effect on sinoatrial node activity. This is called an arrythmogenic effect of adenosine. This makes adenosine effective in treating tachyarrhythmias(extremely fast heart rates) involving the sinoatrial node.

    Adenosine is also used in diagnosing and treating supraventricular tachycardias. These are extremely fast heart rates that originate above the ventricles (lower heart chambers). It's also used in nuclear medicine and during stress tests to detect coronary artery disease. Ongoing research suggests that adenosine will be important in protecting the heart during open-heart surgery.