Improved functional recovery after ischemic preconditioning in the globally ischemic rabbit heart is not mediated by adenosine A1 receptor activation

Abstract

Experiments were carried out to test the hypothesis that preconditioning reduces the impairment of recovery of cardiac mechanical function and that this effect is mediated by activation of adenosine A1 receptors. Isolated hearts were Langendorff-perfused at 37 degrees C with oxygenated blood and paced at 3 Hz. They were divided into 5 groups, all subjected to 45 min global ischemia followed by one hour of reperfusion: 1) Control hearts (n = 7) which received no treatment or short ischemia before the long ischemia, 2) preconditioned hearts (n = 7), submitted to 5-min zero-flow global ischemia, followed by 5 min reperfusion before the long ischemia, 3) hearts pretreated with sulfophenyltheophylline (SPT 100 microM) before preconditioning and long ischemia (n = 6), 4) hearts in which preconditioning was substituted by administration of 10 microM phenyl-isopropyl-adenosine (PIA) over 5 min, and 5) hearts in which preconditioning was substituted by the administration of 1.5 mg adenosine over 5 min. Hemodynamic results show significant improvement of the postischemic recovery of left ventricular developed pressure (DP) by preconditioning. SPT pretreatment did not reverse the improvement of recovery, obtained by preconditioning, whereas PIA treatment could not mimic preconditioning. Adenosine treatment caused some improvement of recovery of DP, but which remained lower compared to that caused by preconditioning. The contracture developed during ischemia persisted in control hearts, whereas contracture disappeared in non-treated preconditioned hearts. SPT did not prevent the decrease in contracture by preconditioning although values remained slightly higher than in the non-treated preconditioned hearts. PIA did not substitute for preconditioning in preventing contracture. In the adenosine treated group, some decrease of contracture occurred during reperfusion, but values remained significantly higher than in preconditioning. We conclude that receptor A1 activation is not the main mechanism underlying improved functional recovery conferred by preconditioning since an A1 receptor blocker (SPT) cannot reverse the effect of preconditioning and an A1 receptor agonist (PIA) cannot mimic it. Administration of exogenous adenosine reduces functional impairment to a certain extent, but less than preconditioning.

Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion

“…In these investigations, we have used SPT, DPCPX, GR-69019X, and MRS-1191/MRS-1220 at previously reported concentrations that putatively allow for the selective antagonism of adenosine A 1 and/or A 3 receptors (1,7,8,15,24). Previous reports (1,9,10,15) have indicated that SPT is a nonselective antagonist (A 1 /A 2 /A 3 ) that blocks all adenosine receptor subtypes in the rabbit heart, whereas DPCPX is selective for A 1 receptors in the rabbit myocardium. Hill et al (10) reported that the inhibitory constants (K i values) for the inhibition of 125 I-labeled N 6 -(4-amino-3-benzyl)adenosine (ABA) to rabbit A 1 receptors are 430 Ϯ 279 for SPT compared with 1 Ϯ 0.1 for DPCPX compared with K i values of 37,797 Ϯ 4,409 for SPT and 1,120 Ϯ 145 for DPCPX for the inhibition of 125 Ilabeled ABA to rabbit A 3 receptors.…”

“…The concentration of SPT (A 1 /A 2 /A 3 ) used in these experiments was derived from the previous investigation of Hen-drikx et al (9). The concentration of DPCPX (A 1 ) used in these experiments was derived from previous investigation by others (1,14).…”

“…At present, there is no direct evidence for the existence of adenosine A 3 receptors in the rabbit heart; however, there is sufficient indirect evidence to suggest that adenosine A 3 receptors are involved in the cardioprotection afforded by preconditioning in this model (1,2,8,9,10,14,15,21,24). Armstrong and Ganote (1) have presented evidence for the role of A 3 adenosine receptors in the protection afforded by preconditioning in the isolated rabbit cardiomyocyte.…”

Adenosine Receptors and Reperfusion Injury of the Heart

“…To more directly test for a role of AR activation in triggering nonpharmacological forms of PC, AR antagonists or adenosine deaminase have been added, often in both trigger and mediation phases, to limit any contributions from ARs. A number of these studies independently provided no evidence for essential roles for ARs in PC (Liu and Downey 1992; Lasley et al 1993; Hendrikx et al 1993; Bugge and Ytrehus 1995; Lasley et al 1995b), leading to premature elimination of this class of GPCRs as contributing to PC (Cave et al 1993; Li and Kloner 1993). In the context of protective thresholds and contributions of multiple stimuli, a more accurate conclusion may be that the roles of ARs in triggering/mediating PC are redundant, with other concomitant stimuli (e.g., endogenous opioids and bradykinin) being able to compensate and surpass the signaling threshold required for protection.…”

Further evidence for the role of nitric oxide in the antiarrhythmic effect of ischaemic preconditioning: the effect of peroxynitrite and changes in NOS-dependent NO production

“…Since then the protective effects of PC have been described and confirmed in various experimental settings. It was shown that PC markedly reduces the severity of ischaemia and reperfusion-induced ventricular arrhythmias (Shiki and Hearse, 1987;Végh et al 1990Végh et al , 1992a and improves the restoration of contractile dysfunction following reperfusion (Cave and Hearse, 1992;Hendrikx et al, 1993). Somewhat later it was also turned out that not only the brief periods of I/R insults, but other stimuli, such as cardiac pacing (Végh et al, 1991a), heavy physical exercise (Babai et al, 2002), heat stress (Cumming et al, 1996), an increase in myocardial stretch (Ovize et al, 1994), as well as various pharmacological agents can induce a PC-like protection.…”