adenosini

Adenosine, in some languages adenosini, is a purine nucleoside composed of adenine linked to a ribose sugar. It is a fundamental component of the energy-carrying molecules ATP, ADP, and AMP, and it participates in intracellular energy transfer as part of the cellular energy economy. It is also a signaling molecule with extracellular effects that influence vascular tone, neurotransmission, and inflammation.

Adenosine is produced intracellularly during ATP turnover and can be released into the extracellular space, especially under metabolic stress or hypoxia. Extracellular adenosine derives from the dephosphorylation of AMP by 5'-nucleotidases (CD73) and is removed by uptake into cells via nucleoside transporters and by enzymatic metabolism.

Adenosine exerts its effects through four G protein-coupled receptors: A1, A2A, A2B, and A3. A1 and A3 typically inhibit adenylyl cyclase, lowering intracellular cAMP, while A2A and A2B stimulate adenylyl cyclase, increasing cAMP. Receptor distribution varies across tissues, with A2A prominent in the basal ganglia and immune cells, and A1 widespread in the brain and peripheral tissues. Through these receptors, adenosine promotes sleep, protects tissues during stress, causes coronary vasodilation, and modulates inflammatory responses.

In pharmacology, intravenous adenosine is used to terminate certain supraventricular tachycardias due to its rapid onset and short duration of action, reflecting its very short half-life. Adverse effects can include flushing, chest discomfort, and bronchospasm.