Adenosine-A1 receptors activation restores the suppressed cardioprotective effects of ischemic preconditioning in hyperhomocysteinemic rat hearts.
ABSTRACT We have previously shown that the cardioprotective effect of ischemic preconditioning (IPC) is suppressed in hyperhomocysteinemic rat hearts. The present study investigated the effect of 2-chloro-N-cyclopentyladenosine (CCPA), a selective adenosine-A1 receptor agonist, in hyperhomocysteinemia-induced attenuation of the cardioprotective effect of IPC.
Rats were administered L-methionine (1.7 g/kg/day po) for 8 weeks to produce hyperhomocysteinemia. Isolated Langendorff perfused normal and hyperhomocysteinemic rat hearts were subjected to 30-minute global ischemia, followed by a 120-minute reperfusion. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride staining. Coronary effluent was analyzed for lactate dehydrogenase and CK-MB release to assess the extent of cardiac injury. The oxidative stress in the heart was assessed by measuring thiobarbituric acid reactive substance and reduced form of glutathione.
Ischemia and reperfusion (I/R) produced myocardial injury by increasing myocardial infarct size, elevating lactate dehydrogenase and CK-MB release in coronary effluent, decreasing coronary flow rate, and inducing oxidative stress in normal and hyperhomocysteinemic rat hearts. The hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with high oxidative stress. The IPC afforded cardioprotection against I/R-induced myocardial injury in normal rat hearts. However, IPC-mediated myocardial protection against I/R injury was abolished in hyperhomocysteinemic rat hearts. Administration of CCPA did not alter the cardioprotective effect of IPC in normal rat hearts, but its administration markedly restored the cardioprotective effect of IPC in hyperhomocysteinemic rat hearts.
It may be concluded that the activation of adenosine-A1 receptors using CCPA markedly restored the suppressed cardioprotective and infarct size-limiting effects of IPC in hyperhomocysteinemic rat hearts. Thus, the reduced availability of extracellular adenosine and impaired activation of adenosine-A1 receptors may be responsible for abolishing the cardioprotective potential of IPC against I/R-induced myocardial injury in hyperhomocysteinemic rat hearts.
- SourceAvailable from: stroke.ahajournals.orgStroke 03/2004; 35(2):345-7. · 6.16 Impact Factor
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ABSTRACT: Adenosine (Ado) accumulates in tissues under metabolic stress. On myocardial cells, the nucleoside interacts with various receptor subtypes (A(1), A(3), and probably A(2A) and A(2B)) that are coupled, via G proteins, to multiple effectors, including enzymes, channels, transporters and cytoskeletal components. Studies using Ado receptor agonists and antagonists, as well as animals overexpressing the A(1) receptor indicate that Ado exerts anti-ischemic action. Ado released during preconditioning (PC) by short periods of ischemia followed by reperfusion induces cardioprotection to a subsequent sustained ischemia. This protective action is mediated by A(1) and A(3) receptor subtypes and involves the activation and translocation of PKC to sarcolemmal and to mitochondrial membranes. PKC activation leads to an increased opening of ATP-sensitive K(+) (K(ATP)) channels. Recent studies implicate mitochondrial rather than sarcolemmal K(ATP) channels in the protective action of PC. Other effectors possibly contributing to cardioprotection by Ado or PC, and which seem particularly involved in the delayed (second window of) protection, include MAP kinases, heat shock proteins and iNOS. Because of its anti-ischemic effects, Ado has been tested as a protective agent in clinical interventions such as PTCA, CABG and tissue preservation, and was found in most cases to enhance the post-ischemic recovery of function. The mechanisms underlying the role of Ado and of mitochondrial function in PC are not completely clear, and uncertainties remain concerning the role played by newly identified potential effectors such as free radicals, the sarcoplasmic reticulum, etc. In addition, more studies are needed to clarify the signalling mechanisms by which A(3) receptor activation or overexpression may promote apoptosis and cellular injury, as reported by a few recent studies.Cardiovascular Research 11/2001; 52(1):25-39. · 5.94 Impact Factor
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ABSTRACT: Hyperhomocysteinemia is an independent risk factor for cardiovascular disease. Most previous investigations focused on the role of homocysteine as direct pathogenetic factor for these adverse vascular events. However, the exact pathophysiological mechanism is still unknown. In this review we discuss the hypothesis that a decreased extracellular concentration of adenosine could contribute to the adverse cardiovascular effects of hyperhomocysteinemia. Fundamental to this hypothesis is that, in vivo, any increase in the plasma concentration of homocysteine reflects an increased intracellular homocysteine concentration, which inevitably will result in a decrease in the adenosine concentration. In this situation, the hydrolase reaction catalysed by S-adenosylhomocysteine hydrolase will reverse and S-adenosylhomocysteine will accumulate at the expense of adenosine. Stimulation of adenosine receptors by adenosine results in various cardio- and vasoprotective actions, like modulation of vascular resistance, presynaptic inhibition of norepinephrine release, ischaemic preconditioning, inhibition of platelet aggregation, modulation of inflammation and regulation of vascular cell proliferation and death. In this respect, a decrease in the adenosine concentration could contribute significantly to the cardiovascular effects of hyperhomocysteinemia.Cardiovascular Research 09/2003; 59(2):271-6. · 5.94 Impact Factor