Abstract
Composed by a molecule of adenine and a molecule of ribose, adenosine is a paradigm of recyclable nucleoside with a multiplicity of functions that occupies a privileged position in the metabolic and regulatory contexts. Adenosine is formed continuously in intracellular and extracellular locations of all tissues. Extracellular adenosine is a signaling molecule, able to modulate a vast range of physiologic responses in many cells and organs, including digestive organs. The adenosine A1, A2A, A2B, and A3 receptors are P1 purinergic receptors, G protein-coupled proteins implicated in tissue protection. This review is focused on gastric acid secretion, a process centered on the parietal cell of the stomach, which contains large amounts of H+/K+-ATPase, the proton pump responsible for proton extrusion during acid secretion. Gastric acid secretion is regulated by an extensive collection of neural stimuli and endocrine and paracrine agents, which act either directly at membrane receptors of the parietal cell or indirectly through other regulatory cells of the gastric mucosa, as well as mechanic and chemic stimuli. In this review, after briefly introducing these points, we condense the current body of knowledge about the modulating action of adenosine on the pathophysiology of gastric acid secretion and update its significance based on recent findings in gastric mucosa and parietal cells in humans and animal models.
Highlights
Adenosine is a purine nucleoside widely found in nature
To facilitate comparisons and comprehend causes for seemingly potential discrepancies, we review here the most relevant publications clustered in five sections: studies in intact animals, isolated stomach, gastric mucosa, isolated gastric glands, and isolated gastric parietal cells
In rabbits, the gastric parietal cell is endowed with a density of A2B receptors sufficient to promote acid secretion even though the affinity constants were similar to those reported in other tissues and cell models (Klotz et al, 1998; Fredholm et al, 2001b, 2011)
Summary
Adenosine is a purine nucleoside widely found in nature. It is a component of the nucleotides ATP, ADP, AMP, of the cyclic nucleotide cAMP, of the nucleotide polymer RNA in all its forms and of the redox coenzymes NAD+, NADP+, and FAD, all of which are critic molecules for (unicellular and multicellular) life. In the neighborhood; it is possible, to speculate that the autocrine regulation described above for myenteric neurons might operate too in the cholinergic fibers of the ENS innervating both parietal and D cells, representing an additional regulatory mechanism for adenosine in gastric acid secretion. The inhibition was found to be due to a reduction in vagal efferent activity to the stomach acting at the brain level on xanthine-insensitive P1 receptors (Puurunen and Huttunen, 1988) These findings are compatible with other studies conducted in unanesthetized rats, such as those of Westerberg and Geiger who demonstrated that adenosine analogs regulate the acidity and the volume of gastric secretions; they showed that 5′N-ethylcarboxamideadenosine (NECA) and 2-chloroadenosine decreased basal acid output in a dose-dependent manner and that low doses of NECA inhibited gastric volume almost entirely (Westerberg and Geiger, 1989). The perfused stomach maintains the chemical and neural interconnections of the gastric gland cells though the extrinsic secretomotor innervation (the vegetative system) may be attenuated by the unavoidable anesthesia
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
