Why does caffeine prevent adenosine from working?

Question

Why do methylxanthines prevent binding of adenosine at receptor sites?

Also,
Does adenosine only dilate the blood vessels in the brain or the whole body?

Answer 1

Since caffeine and other methyxanthines act as competitive antagonists to adenosine. This means that they bond to the same receptor site but fail to activate it. As they are bound to the receptor, the true agonist is unable to bind and activate that receptor. Similar to carbon monoxide, caffeine could have a higher affinity to the receptor thus attaching to the receptor longer and/or displacing adenosine from the receptor to attach.

As for the role of adenosine in dilation of blood vessels, I have only found that it dilates coronary arteries and constricts the the afferent arterioles of the glomerulus.