====== Purine ======


A purine is a [[heterocyclic aromatic compound]] that consists of a [[pyrimidine]] ring fused to an [[imidazole]] ring. Purine gives its name to the wider class of molecules, purines, which include substituted purines and their tautomers, are the most widely occurring nitrogen-containing heterocycle in nature.

Purine is water soluble.
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To preserve the disequilibrium between [[ATP]] and [[ADP]] necessary to drive cellular metabolism, enzymatic pathways rapidly convert ADP to [[adenosine]] and the downstream purines [[inosine]] and [[hypoxanthine]]. During [[ischemia]], these same pathways result in the production of purines.

Tian et al. performed a prospective observational study to test whether purine levels in arterial blood might correlate with brain ischaemia. They made real-time perioperative measurements, via microelectrode biosensors, of the purine levels in untreated arterial blood from 18 patients undergoing regional anaesthetic carotid endarterectomy. Pre-operatively, the median purine level was 2.4 μM (95% CI 1.3-4.0 μM); during the cross-clamp phase, the purines rose to 6.7 μM (95% CI 4.7-11.5 μM) and fell back to 1.9 μM (95% CI 1.4-2.7 μM) in recovery. Three patients became unconscious during carotid clamping, necessitating insertion of a temporary carotid shunt to restore cerebral blood flow. In these, the pre-operative median purine level was 5.4 μM (range 4.7-6.1 μM), on clamping, 9.6 μM (range 9.4-16.1 μM); during shunting, purines fell to below the pre-operative level (1.4 μM, range 0.4-2.9 μM) and in recovery 1.8 μM (range 1.8-2.6 μM). Our results suggest that blood purines may be a sensitive real-time and rapidly produced indicator of brain ischaemia, even when there is no accompanying neurological obtundation
((Tian F, Bibi F, Dale N, Imray CHE. Blood purine measurements as a rapid
real-time indicator of reversible brain ischaemia. Purinergic Signal. 2017 Aug
12. doi: 10.1007/s11302-017-9578-z. [Epub ahead of print] PubMed PMID: 28803399.
)).