Preconditioning of rat hearts by adenosine A 1 or A 3 receptor activation

Abstract

Our study in rat hearts examined whether activation of adenosine A 1 or A 3 receptors improved functional recovery and reduced apoptosis resulting from low-flow ischemia. Prior to 30 min low-flow ischemia (0.6 ml/min; 6% of baseline flow), Langendorff rat hearts were preconditioned with two 5-min cycles of (a) ischemia (PC; n=7), (b) infusion of 250 nM adenosine A 1 receptor agonist 2-chloro- N 6-cyclopentyladenosine (CCPA; n=6), or (c) infusion of 50 nM adenosine A 3 receptor agonist N 6-(3-iodobenzyl)-adenosine-5′- N-methyl-uronamide (IB-MECA; n=8). Recovery of function was improved in PC (71±3%), CCPA (68±6%) and IB-MECA (68±4%) groups compared to control hearts (46±5%; P<0.05). Cumulative release of total purines during ischemia–reperfusion was approx. 50% lower in PC, CCPA and IB-MECA groups compared to controls ( P<0.05) and was significantly correlated to the percentage functional recovery ( R 2=0.55; P<0.05). The number of cytosolic histone-associated-DNA fragments, a hallmark of apoptosis and measured by Enzyme Linked ImmunoSorbent Assay (ELISA), was small and not different between groups after 30 min reperfusion. However, CCPA (0.6±0.1 absorbance units) and MECA (0.7±0.1 units; P<0.05 vs. PC) decreased apoptosis after 150 min reperfusion compared to PC (1.4±0.3 units) and control (1.2±0.1 units) hearts. This study shows that adenosine triggers protection of function in preconditioned rat hearts via both the adenosine A 1 and A 3 receptor. In clinical practice, pharmacological stimulation of adenosine A 3 receptors may be advantageous over adenosine A 1 receptor activation due to a lack of contractile side-effects. In contrast to ischemic preconditioning, pharmacological stimulation of adenosine A 1 or A 3 receptors reduced apoptosis. Furthermore, total purine release may serve as a marker of the degree of functional protection.