The role of
adenosine in ischemic preconditioning in different species remains controversial. Ischemic preconditioning was examined in perfused rat and rabbit hearts. In rat and rabbit hearts subjected to 30 min global normothermic
ischemia followed by 30 min of reperfusion, left ventricular developed pressure (LVDP) recovered to 36 +/- 8% and 44 +/- 7% of preischemia, respectively. Pre-treatment with transient (6 min) global
ischemia improved recovery of LVDP (75 +/- 7% and 82 +/- 9% pre-
ischemia, respectively), and improved recovery of coronary flow and end-diastolic pressure. Effects of preconditioning were unrelated to cytosolic [
ATP], but were associated with reduced ischemic
acidosis, and improved post-ischemic recovery of [Mg2+], [P(i)] and delta GATP. In addition to
ischemia, transient episodes of
hypoxia (5% O2),
norepinephrine stimulation (0.1 microM) or metabolic inhibition (5 mM
cyanide minus glycolytic substrate) all improved recovery from prolonged
ischemia. Microdialysis revealed that 6 min of ischemic preconditioning increased
dialysate [
adenosine] from 0.25 to 6.81 +/- 0.87 microM in rat hearts, and from 0.33 to 1.98 +/- 0.41 microM in rabbit hearts. Extracellular [
adenosine] was also enhanced during the transient periods of
hypoxia,
norepinephrine stimulation and metabolic inhibition shown to be protective. Pre-treatment with 0.5 microM Nb-cyclohexyladenosine mimicked preconditioning, and 50 microM 8-(rho-sulfophenyl)
theophylline attenuated ischemic preconditioning in rat and rabbit hearts. 8-(rho-sulfophenyl)
theophylline also abolished effects of preconditioning on ischemic
acidosis, and post-ischemic [Mg2+], [P(i)] and delta GATP. The data demonstrate that (i) preconditioning is triggered by transient periods of energy imbalance: (ii) endogenous
adenosine is of primary importance in mediating the cardioprotection following a single transient ischemic stimulus in rat and rabbit hearts; and (iii) post-receptor mechanisms of this
adenosine-mediated preconditioning appear to involve reduced ischemic
acidosis and enhanced recovery of [P(i)], [Mg2+] and delta GATP.