Adenosine A1 and A2 receptor agonists reduce endotoxin-induced cellular energy depletion and oedema formation in the lung

Background and objective: Tissue depletion of adenosine during endotoxaemia has previously been described in the lung. Therapeutic approaches to prevent adenosine depletion and the role of A(1) and A(2) receptor agonists, however, have not been investigated until now. Methods: In isolated and ventilated rabbit lungs, it was tested whether pretreatment with adenosine A, agonist 2-chloro-N6-cyclopentyladenosine (CCPA; 10(-7) mol, n = 6) or A(2) receptor agonist 5'-(N-cyclopropyl)-carbcxyamido adenosine (CPCA; 10-7 mol, n = 6) prior to injection of lipopolysaccharide (LPS) (500 pg mL(-1)) influenced pulmonary artery pressure (PAP), pulmonary energy content and oedema formation as compared with controls, solely infused with LPS (n = 6). Release rates of adenosine and uric acid were determined by high-performance liquid chromatography. Pulmonary tissue concentrations of high-energy phosphates were measured and the adenine nucleotide pool, adenosine 5'-triphosphate (ATP)/adenosine 5-diphosphate (ADP) ratio and adenylate energy charge of the pulmonary tissue were calculated. Results: Administration of LPS induced increases in PAP within 2 h up to 20.8 +/- 2.9 mmHg (P < 0.01). While pretreatment with the A, agonist merely decelerated pressure increase (13.8 +/- 1.1 mmHg, P < 0.05), the A(2) agonist completely suppressed the pulmonary pressure reaction (9.6 +/- 1.0 mmHg, P < 0.01). Emergence of lung oedema after exclusive injection of LPS up to 12.0 +/- 2.9 g was absent after A(1) (0.6 +/- 0.5 g) and A(2) (-0.3 +/- 0.2 g) agonists. These observations were paralleled by increased adenosine release rates compared with LPS controls (P < 0.05). Moreover, tissue concentrations of ADP, ATP, guanosine 5'-diphosphate, guanosine 5'-triphosphate, nicotinamide-adenine-dinucleotide and creatine phosphate were significantly reduced after LPS. Consequently, the calculated tissue adenine nucleotide pool and the adenylate energy charge increased after adenosine receptor stimulation (P = 0.001). Conclusions: Adenosine A(1)- and A(2)-receptor agonists reduced LPS-incluced vasoconstriction and oedema formation by maintenance of tissue energy content. Thus, adenosine receptor stimulation, in particular of the A(2) receptor, might be beneficial during acute lung injury.