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Caffeine keeps you awake by blocking adenosine receptors. Each type of adenosine receptor has different functions, although with some overlap. [3] For instance, both A 1 receptors and A 2A play roles in the heart, regulating myocardial oxygen consumption and coronary blood flow, while the A 2A receptor also has broader anti-inflammatory effects throughout the body. [4]
The adenosine A2A receptor has also been shown to play a regulatory role in the adaptive immune system. In this role, it functions similarly to programmed cell death-1 (PD-1) and cytotoxic t-lymphocyte associated protein-4 ( CTLA-4 ) receptors, namely to suppress immunologic response and prevent associated tissue damage.
However, in altered cardiac function, such as hypoperfusion caused by hypotension, heart attack or cardiac arrest caused by nonperfusing bradycardias, adenosine has a negative effect on physiological functioning by preventing necessary compensatory increases in heart rate and blood pressure that attempt to maintain cerebral perfusion. [citation ...
The α 2-adrenergic receptor binds both norepinephrine released by sympathetic postganglionic fibers and epinephrine (adrenaline) released by the adrenal medulla, binding norepinephrine with slightly higher affinity. [4] It has several general functions in common with the α 1-adrenergic receptor, but also has specific effects of its own.
Regadenoson, a vasodilator which acts on the adenosine A2A receptor, was approved by the United States Food and Drug Administration in 2008 and is currently widely used in the field of cardiology. [80] [81] Both adenosine and dipyridamole, which act on the A2A receptor, are used in myocardial perfusion imaging. [82]
Adenosine A 2A receptor locations in the body could help us to understand the possible therapeutic applications in the future. They can be found in the lungs, white blood cells, sympathetic nervous system, striatum, tuberculum olfactorium, coronary, lymphatic, brain and other blood vessels, platelets and kidneys.
Alpha 2 receptors are associated with sympatholytic properties. Alpha-adrenergic agonists have the opposite function of alpha blockers . Alpha adrenoreceptor ligands mimic the action of epinephrine and norepinephrine signaling in the heart, smooth muscle and central nervous system, with norepinephrine being the highest affinity.
Blood vessels with α 1-adrenergic receptors are present in the skin, the sphincters [4] of gastrointestinal system, kidney (renal artery) [5] and brain. [6] During the fight-or-flight response vasoconstriction results in decreased blood flow to these organs. This accounts for the pale appearance of the skin of an individual when frightened.