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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.
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]
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]
A 1 receptors are implicated in sleep promotion by inhibiting wake-promoting cholinergic neurons in the basal forebrain. [6] A 1 receptors are also present in smooth muscle throughout the vascular system. [7] The adenosine A 1 receptor has been found to be ubiquitous throughout the entire body. [citation needed]
A 2A receptor antagonists may prevent hepatic cirrhosis, and pentoxifylline may inhibit phosphodiesterase and provide renal protection. [6]The A 2A receptor antagonists may be used for treatment of attention deficit hyperactivity disorder (), because of the receptors ability to regulate neurotransmission in the basal ganglia and cortex, particularly dopaminergic and glutamatergic signaling.
The alpha-2 (α 2) adrenergic receptor (or adrenoceptor) is a G protein-coupled receptor (GPCR) associated with the G i heterotrimeric G-protein. It consists of three highly homologous subtypes, including α 2A-, α 2B-, and α 2C-adrenergic. Some species other than humans express a fourth α 2D-adrenergic receptor as well. [1]
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.
alpha-1 (α 1) adrenergic receptors are G protein-coupled receptors (GPCRs) associated with the G q heterotrimeric G protein. α 1-adrenergic receptors are subdivided into three highly homologous subtypes, i.e., α 1A-, α 1B-, and α 1D-adrenergic receptor subtypes.