Adenosine receptor (ADORA) (ADORA)

Adenosine receptors are a class of purinergic G protein-coupled receptors (GPCRs) that mediate the physiological effects of the nucleoside adenosine (StatPearls, 2023). The family consists of four distinct subtypes—A1, A2A, A2B, and A3—each with unique tissue distributions and signaling mechanisms (UniProt, 2024). Caffeine, the most widely consumed psychoactive substance, acts as a non-selective antagonist at these receptors, with its primary stimulant effects attributed to the blockade of A1 and A2A subtypes in the brain (PubMed, 2011). Under normal conditions, adenosine accumulates during wakefulness and binds to these receptors to promote sedation and inhibit arousal; caffeine competitively inhibits this binding, thereby increasing alertness and cognitive performance (NIH, 2022). Beyond the central nervous system, adenosine receptors regulate critical functions such as heart rate, vascular resistance, and inflammatory responses (Wikipedia, 2024). Due to their diverse roles, these receptors are therapeutic targets for a variety of conditions, including Parkinson's disease, where A2A antagonists like istradefylline are used to improve motor function, and cardiac imaging, where A2A agonists like regadenoson are used for stress testing (PubMed, 2015; StatPearls, 2023).

Other names

P1 receptorPurinergic receptorAdenosine A1 receptorAdenosine A2A receptorAdenosine A2B receptorAdenosine A3 receptor

Caffeine and other methylxanthines act as competitive antagonists at adenosine receptors, particularly the A1 and A2A subtypes, preventing the binding of endogenous adenosine and thereby inhibiting its sedative, vasodilatory, and anti-inflammatory effects (StatPearls, 2023; PubMed, 2011).