title: Ischaemic tolerance in aged mouse myocardium: the role of adenosine and effects of A1 adenosine receptor overexpression.
abstract: The genesis of the ischaemia intolerant phenotype in aged myocardium is poorly understood. We tested the hypothesis that impaired adenosine-mediated protection contributes to ischaemic intolerance, and examined whether this is countered by A1 adenosine receptor (A1AR) overexpression. Responses to 20 min ischaemia and 45 min reperfusion were assessed in perfused hearts from young (2-4 months) and moderately aged (16-18 months) mice. Post-ischaemic contractility was impaired by ageing with elevated ventricular diastolic (32 +/- 2 vs. 18 +/- 2 mmHg in young) and reduced developed (37 +/- 3 vs. 83 +/- 6 mmHg in young) pressures. Lactate dehydrogenase (LDH) loss was exaggerated (27 +/- 2 vs. 16 +/- 2 IU g-1 in young) whereas the incidence of tachyarrhythmias was similar in young (15 +/- 1 %) and aged hearts (16 +/- 1 %). Functional analysis confirmed equipotent effects of 50 micro M adenosine at A1 and A2 receptors in young and aged hearts. Nonetheless, while 50 micro M adenosine improved diastolic (5 +/- 1 mmHg) and developed pressures (134 +/- 7 mmHg) and LDH loss (6 +/- 2 IU g-1) in young hearts, it did not alter these variables in the aged group. Adenosine did attenuate arrhythmogenesis for both ages (to ~10 %). In contrast to adenosine, 50 micro M diazoxide reduced ischaemic damage and arrhythmogenesis for both ages. Contractile and anti-necrotic effects of adenosine were limited by 100 micro M 5-hydroxydecanoate (5-HD) and 3 micro M chelerythrine. Anti-arrhythmic effects were limited by 5-HD but not chelerythrine. Non-selective (100 micro M 8-sulfophenyltheophylline) and A1-selective (150 nM 8-cyclopentyl-1,3-dipropylxanthine) adenosine receptor antagonism impaired ischaemic tolerance in young but not aged hearts. Quantitative real-time PCR and radioligand analysis indicated that impaired protection is unrelated to changes in A1AR mRNA transcription, or receptor density (~8 fmol mg-1 protein in both age groups). However, A1AR overexpression improved tolerance for both ages, restoring adenosine-mediated protection. These data reveal impaired protection via exogenous and endogenous adenosine contributes to ischaemic intolerance with ageing. This is independent of A1AR expression, and involves ineffective activation of a 5-HD-/diazoxide-sensitive process. The effects of A1AR overexpression indicate that the age-related failure in signalling can be overcome.
authors.affiliation: Heart Foundation Research Centre, School of Health Science, Griffith University, Southport, QLD 4217, Australia. j.headrick@gu.edu.au
authors.forename: John P
authors.initials: JP
authors.lastname: Headrick
authors.forename: Laura
authors.initials: L
authors.lastname: Willems
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Ashton
authors.forename: Kirsten
authors.initials: K
authors.lastname: Holmgren
authors.forename: Jason
authors.initials: J
authors.lastname: Peart
authors.forename: G Paul
authors.initials: GP
authors.lastname: Matherne
mesh_terms: D000241:Adenosine / Q000494:pharmacology; D058916:Adenosine A1 Receptor Antagonists; D000375:Aging / Q000502:physiology*; D000470:Alkaloids; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D053119:Benzophenanthridines; D003326:Coronary Circulation / Q000502:physiology*; D017931:DNA Primers; D003652:Decanoic Acids / Q000494:pharmacology; D003981:Diazoxide / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000502:physiology; D006321:Heart / Q000502:physiology* / Q000503:physiopathology*; D006880:Hydroxy Acids / Q000494:pharmacology; D066298:In Vitro Techniques; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009200:Myocardial Contraction / Q000502:physiology; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D009206:Myocardium / Q000378:metabolism; D009929:Organ Size / Q000502:physiology; D010617:Phenanthridines / Q000494:pharmacology; D043682:Receptor, Adenosine A1 / Q000096:biosynthesis* / Q000502:physiology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D058916:Adenosine A1 Receptor Antagonists; D000470:Alkaloids; D053119:Benzophenanthridines; D017931:DNA Primers; D003652:Decanoic Acids; D006880:Hydroxy Acids; D010617:Phenanthridines; D043682:Receptor, Adenosine A1; D014665:Vasodilator Agents; C052853:5-hydroxydecanoic acid; C016299:chelerythrine; D007770:L-Lactate Dehydrogenase; D000241:Adenosine; D003981:Diazoxide