Acadesine lowers temporal threshold for the myocardial infarct size limiting effect of preconditioning.
OBJECTIVE
The aim was to test the hypothesis that adenosine A1 receptor activation triggers the cardioprotective effects of ischaemic preconditioning, by determining whether pretreatment with acadesine (5-amino-4-imidazolecarboxamide riboside), an agent which increases cardiac adenosine level during ischaemia, could alter the threshold for preconditioning.


METHODS
A branch of the left coronary artery of rabbit hearts was occluded for 30 min and reperfused for 3 h. Infarct size and risk zone size were determined with tetrazolium and fluorescent particles, respectively. Four groups were studied: untreated controls, a group which was pretreated with acadesine (2.5 mg.kg-1.min-1 for 5 min followed by 0.5 mg.kg-1.min-1 for 30 min ending 10 min prior to ischaemia), a group which was preconditioned with 2 min coronary branch occlusion + 10 min reperfusion, and a group which received pretreatment with acadesine prior to 2 min ischaemic preconditioning.


RESULTS
Percent infarction, normalised as a percentage of the ischaemic zone, in the 2 min preconditioning group was 43.2(SEM 5.1)% which was not different from control [40.2(3.5)%]. Two minutes of preconditioning was not long enough to confer the cardioprotective effect of preconditioning. Acadesine alone had no protective effect on infarct size [38.5(4.5)%], but acadesine + 2 min preconditioning significantly limited infarction [18.1(2.7)%; p < 0.01].


CONCLUSIONS
Acadesine lowered the threshold for preconditioning in the rabbit to below 2 min of ischaemia. This observation supports the theory that endogenous adenosine which accumulates during the preconditioning ischaemia mediates the protective effects, and that this response can be augmented by acadesine.
Tsuchida
A
A
Department of Physiology, College of Medicine, University of South Alabama, Mobile 36688.
Liu
G S
GS
Mullane
K
K
Downey
J M
JM
D000241:Adenosine / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D005260:Female; D008297:Male; D009203:Myocardial Infarction / Q000517:prevention & control*; D017202:Myocardial Ischemia / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D011817:Rabbits; D011983:Receptors, Purinergic / Q000187:drug effects; D012263:Ribonucleosides / Q000494:pharmacology*; D013997:Time Factors
D011983:Receptors, Purinergic; D012263:Ribonucleosides; D000620:Aminoimidazole Carboxamide; C011651:acadesine; D000241:Adenosine